Abstract:
The present invention relates to a purified and isolated merozoite protein which is a specific indicator of infection by Babesia equi (B. equi) in horses. This protein contains a conserved region found in all strains of B. equi. It has a molecular weight of approximately 28 KDa and has been successfully purified and sequenced. The isolated and purified merozoite protein is used to prepare antibodies which can then be used in a competitive inhibition enzyme linked immunosorbent assay for the diagnosis of B. equi infection in horses.

Description:
This application is a continuation of application Ser. No. 07/902,164, filed Jun. 22, 1992, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a purified and isolated merozoite protein derived by either conventional or recombinant means useful for the detection of Babesia equi in horses by means of a competitive inhibition enzyme-linked immunosorbent assay (CI ELISA). The instant invention likewise relates to antibodies to the protein as well as cell lines which produce the antibodies. 
     2. Description of the Related Art 
     Equine babesiosis, caused by Babesia equi or Babesia caballi, is a tick-borne hemoprotozoan disease of horses (Schein, E., 1988. Equine Babesiosis, pp. 197-208. In M. Ristic (Ed.), Babesiosis of Domestic Animals and Man. CRC Press, Boca Raton, Fla.). Clinical disease is characterized by fever, anemia, and icterus, most likely arising from hemolysis caused by merozoites, the intraerythrocytic stage of equine Babesia infection. Mortality rate is high during initial infection of horses introduced into enzootic regions, and horses which survive initial infection are protected from clinical disease upon subsequent challenge. It is hypothesized that this immunity acquired by horses in enzootic areas is the result of persistent infection. 
     The complement fixation test (CFT) is presently the official United States Department of Agriculture test for detecting antibody to B. equi and B. caballi. Horses with antibody to either parasite are restricted from importation into the United States. Three problems with the CFT are that (i) sera with anticomplement activity are not testable by the CFT; (it) sera which react with CFT control erythrocyte antigen cannot be evaluated by the GFT; and (iii) sera containing specific immunoglobulin G(T) [IgG(T)] antibody may yield false-negative results because IgG(T) does not fix complement by the classical pathway. 
     Merozoite surface proteins are known to be important in the pathogenesis of hemoprotozoan diseases because of their role in parasite recognition of, attachment to, and penetration of host erythrocytes. Antigens recognized by antibody from hosts demonstrating immunity to clinical disease during Plasmodium spp., B. rhodhaini, B. bovis, and B. bigemina infection include surface proteins of merozoites, the only blood stage of the parasite that is extracellular and directly accessible to serum antibody. It has previously been demonstrated that cattle immune to infection with B. bovis had high-titered antibody preferentially directed against four immunodominant merozoite surface proteins (Hines et al., Mol. Biochem. Parasitol. 37:1-9; 1989). Invasion of erythrocytes by merozoites of Plasmodium knowlesi was inhibited by immune sera, and inhibition of P. falciparum merozoite invasion of erythrocytes in vitro required high concentrations of specific antibodies. These observations suggest that antibody to merozoite surface proteins may block erythrocyte invasion in vivo and that these proteins should be tested as potential immunogens. 
     Detection of antibodies has been the method of choice for diagnosis of infection with equine Babesia spp.; however, the specificity or role of antibodies in the acquired protective immunity against clinical disease following equine Babesia infection has not thus far been determined. 
     Applicants have now developed a competitive inhibition enzyme-linked immunosorbent assay (CI ELISA) based on the use of a merozoite protein for detection of antibody to B. equi. The formatting of the CI ELISA overcomes the above three problems related to use of the CFT. Furthermore, a high concordance was found to exist between the CI ELISA and CFT in detecting antibody to B. equi. 
     SUMMARY OF THE INVENTION 
     The present invention relates to the discovery and use of a novel merozoite protein of Babesia equi which has been isolated and purified. This protein contains a conserved epitope that is diagnostically useful as a sensitive and specific indicator of infection by Babesia equi in horses. The isolated protein has a molecular weight of approximately 28 kDa, with the amino acid sequence having been determined as follows: 
     
         __________________________________________________________________________1  RPPVKMISKS       FAFVFASIAI                 SSILAEEEKP                          KASGAVVDFQ                                   LESIDHVTID51 KQSEEHIVYT       AHEGYAVEKV                 KEGDSVIKTF                          DLKEQTPKTV                                   VRHIKDNKPY101   VVIAVESALH       LVLKKDGDKW                 VELEVAEFYQ                          EVLFKGFEAV                                   SVDLAAAVSD151   KFTETTFGSG       KKHTFKAPGK                 RVLKVVDGKT                          ELIDGDNEVV                                   LDLELFVSSD201   NKVARVVYLY       KGDGRIKEIF                 LKLVEKAWKR                          VEVKDAAETL                                   HGINSTFPAD251   YKVVYDGFSV       YGALLAVAAI                 AFSTLFY 277__________________________________________________________________________ 
    
     The isolated and purified merozoite protein is used to prepare antibodies which are useful in immunoassays for the diagnosis of B. equi in horses. A molecular clone of the protein expressing the conserved epitope has been obtained and shown to likewise be useful in such immunoassays. This recombinant merozoite protein is designated SEQ ID NO:1. 
     It is an object of this invention to provide an immunological assay for B. equi in horses based upon the antigenicity of a conserved epitope of a novel merozoite protein of 
     It is also an object of this invention to provide hybridomas for the production of antibodies to the conserved epitope of the merozoite protein. 
     It is a further object of this invention to provide antibodies as immunochemical reagents for the diagnosis of B. equi in horses. 
     Other objects and advantages of this invention will become readily apparent from the ensuing description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1. Immunoprecipitation of  3  H-amino acid-labeled merozoite-associated proteins of B. equi with serum from experimentally infected horse H5. Shown are labeled protein profile (lane 1), preinoculation serum (lane 2), postinoculation serum (2 months after primary infection) (lane 3), and post-second inoculation serum (1 month after second infection; 3 months after primary infection) (lane 4). 
     FIG. 2. Immunoprecipitation of  3  H-amino acid-labeled merozoite-associated proteins of B. equi with MAb 36/133.97. Shown are postinfection serum, horse H5 (lane 1), MAb 36/133.97 (lane 2), MAb isotype control (lane 3), protein A control (lane 4), and labeled protein profile (lane 5). 
     FIG. 3A. Comparisons of immunoprecipitations of [ 35  S]methio-nine-labeled in vitro translation products with dilutions of sera from experimentally infected horse H5. 10 -2  dilution of H5 preinoculation serum (lane 1), 10 -2  dilution of H5 postinoculation serum (lane 2), 10 -3  dilution of H5 postinoculation serum (lane 3), 10 -4  dilution of H5 postinoculation serum (lane 4). 
     FIG. 3B. Comparisons of immunoprecipitations of [ 35  S]methio-nine-labeled in vitro translation products with dilutions of sera from MAb 36/133.97 (lane 1) and MAb isotype control (lane 2). Arrowheads indicate locations of 38-,28-, to 26-, and 23-kDa proteins. 
     FIG. 4. Comparisons of dilutions of sera from infected horses and MAb 36/133.97 in Western blots: H5 preinoculation serum, 10 -3  (lane 1) and 10 -4  (lane 2); H5 postinoculation serum, 10 3  (lane 3) and 10 -4  (lane 4); SN76N8401 (control serum from the National Veterinary Services Laboratory, Ames, Iowa), 10 -3  (lane 5) and 10 -4  (lane 6); naturally infected horse serum, 10 -3  (lane 7) and 10  -4  (lane 8); MAb 36/133.97 (lane 9); and MAb isotype control (lane 10). Arrowheads indicate locations of 44-, 36-, 34-, and 28-kDa proteins. 
     FIG. 5. Immunoprecipitation of [ 35  S]methionine-labeled in vitro translation products with 1:10 dilutions of sera yielding discrepant results in the CFT and CI ELISA. Lanes 1 to 5 represent sera which tested CFT(-) and CI ELISA(+), HS, 8, 17, 113, and 175, respectively. Lane 6, SN76N8401, CFT(-) control serum. Lanes 7 to 11 represent sera which tested CFT(+) and CI ELISA(-), 18, 22, 126, 167, and 171, respectively. Lane 12, serum 236, CFT(-) and CI ELISA(-). Numbers on left show size in kilodaltons. 
     FIG. 6. Immunoprecipitation of [ 35  S]methionine-labeled in vitro translation products with 1:10 dilutions of equine sera with anticomplement activity or reactivity with CFT erythrocyte control antigen. Lanes: 1, serum H5; 2, serum 2, CFT(-) CI ELISA(-); 3 to 6, sera 215, 216,140, and 146, respectively, CFT (+) CI ELISA(+); 7, serum 213, anticomplement, CI ELISA(+); 8 and 9, sera 240 and 245, respectively, anticomplement, CI ELISA(-); 10, SN76N8401, CFT(-) control serum; 11, serum 238, reactive with CFT erythrocyte control, CI ELISA(+). Numbers on left show size in kilodaltons. 
     FIG. 7. Is the plasmid pBluescript™II SK(+/-)phagemid. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the present invention a novel protein isolated and purified from the merozoite of B. equi has been discovered and proven to be a sensitive and specific indication of the presence of antibodies to B. equi in horses. The novel protein of the invention is effective for use in immunoassays such as the competitive inhibition enzyme-linked immunosorbent assay (CI ELISA). Samples used in the test may be obtained from the serum of the horse to be tested. Immunoprecipitation of B. equi merozoite proteins recovered from an infected horse were found to have apparent molecular masses of 210, 144, 108, 88, 70, 56, 44, 36, 34, 28 and 25 kDa. The descri 36/133.97 was found to react with a protein epitope on the 44-, 36-, 34-, and 28-kDa merozoite antigens. This monoclonal antibody, 36/133.97, has been deposited under the Budapest Treaty in the American Type Culture Collection (12301 Parklawn Drive, Rockville, Md., 20852, USA) on Jan. 10, 1995, and has been assigned Deposit Number ATCC HB11788. Applicants found, through a competitive binding assay, that horses infected with B. equi throughout the world consistently produce antibodies to the antigens associated with this epitope. The 28-kDa antigen was found to be of particular interest due to its immunodominance in infected horses as recognized by MAb 36/133.97 in serum dilution studies. This protein was subsequently determined to possess the amino acid sequence: 
     
         __________________________________________________________________________1  RPPVKMISKS       FAFVFASIAI                 SSILAEEEKP                          KASGAVVDFQ                                   LESIDHVTID51 KQSEEHIVYT       AHEGYAVEKV                 KEGDSVIKTF                          DLKEQTPKTV                                   VRHIKDNKPY101   VVIAVESALH       LVLKKDGDKW                 VELEVAEFYQ                          EVLFKGFEAV                                   SVDLAAAVSD151   KFTETTFGSG       KKHTFKAPGK                 RVLKVVDGKT                          ELIDGDNEVV                                   LDLELFVSSD201   NKVARVVYLY       KGDGRIKEIF                 LKLVEKAWKR                          VEVKDAAETL                                   HGINSTFPAD251   YKVVYDGFSV       YGALLAVAAI                 AFSTLFY 277__________________________________________________________________________ 
    
     hereby designated as SEQ ID NO:1. 
     The mRNA associated with the 28 kDa merozoite protein of B. equi, as isolated in Example II, may be used as a template in the synthesis of cDNA by conventional techniques such as those described by Maniatis (1982, Molecular Cloning: A Laboratory Manual. Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y.), herein incorporated by reference. 
     The selected vector may be cut with an appropriate restriction enzyme, ligated via conventional techniques to the ends of the fragments of B. equi cDNA, and inserted into a host microorganism resulting in the synthesis of the 28 kDa protein referred to hereinabove. Without being limited thereto, suitable techniques for the preparation of vectors and transformed microorganisms are described by Drummond et al., U.S. Pat. No. 5,041,378, issued Aug. 20, 1991; the contents of which are herein incorporated by reference. 
     The antigen may be employed for the generation of hybrid cell lines producing MAb&#39;s specific thereto. Establishing the antibody-secreting cell lines for use in the invention is a multistep procedure which includes hyperimmunizing an animal to induce a proliferation of antibody-producing cells, promoting fusion between the primed cells and cells of an immortal cell line, selecting for antibody-secreting hybridomas, screening the hybridomas for selectability in a subsequent fusion stage, and then cloning the antibody producing hybrids. The practitioner skilled in the art would recognize that hybrid cell lines could be produced by conventional techniques. Suitable techniques for the generation of hybrid cell lines include those described by Kohler and Milstein (Nature; Vol. 256; pp. 495-497; 1975); herein incorporated by reference; and Stites (Clinical Laboratory Methods for Detection of Antigens and Antibodies. In Basic and Clinical Immunology; Stites et al. (Ed.) Lang Medical Publications, Los Altos, Calif., 1984, pp. 350-351). Without being limited thereto, particularly preferred is, the hybrid cell line producing MAb 36/133.97 discussed in Example IV below. The resultant MAb produced from the cell line binds selectively with B. equi. 
     It is envisioned that the monoclonal antibody (MAb) specific for the 28 kDa merozoite protein of this invention may be employed for the detection of infection by B. equi in clinical specimens, particularly serum, by use of conventional immunoassay techniques. Such an immunoassay would comprise the steps of: A) collecting serum from a horse to be tested; B) contacting the serum with antibodies specific for a conserved epitope of a merozoite protein of B. equi; and C) detecting the presence of the antigen-antibody complex. While the skilled practitioner will recognize that suitable immunoassay techniques include IFA, immunoelectrophoresis and Western Blot; enzyme-linked immunosorbent assays (ELISA) are preferred, with competitive inhibition enzyme-linked immunosorbent assays (CI ELISA) as described in Knowles et al. (Infect. Immun. 59:2412-2417, 1991), herein incorporated by reference, being most preferred. 
     The present invention is not limited to any specific separation or identification methodology. Rather, all modifications obvious to one skilled in the art are envisioned and encompassed by the present invention. The following examples are offered to illustrate the present invention and are not intended to limit its scope. 
     EXAMPLE I 
     Babesia equi isolates 
     A B. equi isolate was obtained in 1976 from a horse in Florida and cryopreserved as a blood stabilate containing 10% dimethyl sulfoxide in liquid nitrogen. A nonsplenectomized horse (H5) was infected with 30 ml of the Florida B. equi first-passage stabilate containing 5.6×10 6  viable organisms per ml. Viability was determined by incubating merozoites with fluorescein diacetate (FDA) as described by Rotman et al. (Proc. Natl. Acad. Sci. USA 55:134-141; 1966). This horse was monitored for clinical disease and parasitemia. During ascending parasitemia, 200 ml of whole blood was passaged to a splenectomized horse. At peak parasitemia (49%), infected erythrocytes were collected and stored in liquid nitrogen as a blood stabilate containing packed erythrocytes 1:1 with a cryopreservant of 20% (wt/vol) polyvinylpyrrolidone and 2% (wt/vol) glucose in Puck&#39;s saline G (GIBCO Laboratories, Chagrin Falls, Ohio); see Palmer et al. (Parasitology 84:567-572; 1982). Aliquots (25 ml) of washed packed infected erythrocytes were frozen at -70° C. 
     The Europe isolate of B. equi was obtained from a mare from Georgia, USSR; gee Kutler et al. (Am. J. Vet. Res. 47:1668-1670; 1986). A splenectomized pony was infected with the Europe isolate, and blood smears for indirect immunofluorescence assay (IFA) were prepared. 
     EXAMPLE II 
     In vitro translation of B. equi mRNA 
     B. equi merozoite mRNA was isolated from infected erythrocytes by modification of methods previously described by Maniatis et al. (Molecular Cloning: A Laboratory Manual. Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y.; 1982). A 25 ml aliquot of washed packed infected erythrocytes was thawed in the presence of equal volumes of guanidinium isothiocyanate (4.0 M guanidinium isothiocyanate [Bethesda Research Laboratories, Gaithersburg, Md.], 0.1 M Tris-HCl [pH 7.5], 1% 2-mercaptoethanol, 2% SARKOSYL® (N-Lauroylsarcosine, sodium salt) 0.01 M EDTA [pH 7.6]). Lysates were sequentially extracted with buffered phenol, phenol-chloroform-isoamyl alcohol, and ether before nucleic acids were ethanol precipitated. Polyadenylated mRNA was isolated by POLY(U)SEPHADEX® (Bethesda Research Laboratories) chromatography. In parallel, mRNA was isolated from 25 ml of washed packed uninfected erythrocytes. Stained smears of washed infected erythrocytes revealed less than 1 leukocyte per 10 4  erythrocytes. Integrity of mRNA was evaluated by the migration of rRNA species in 1% agarose gel. Merozoite mRNA was translated in vitro (Promega, Madison, Wis.), using 2 μg of polyadenylated mRNA per reaction and a nuclease-treated rabbit reticulocyte lysate; see Jackson et al. (Methods Enzymol. 96:50-71; 1983) and Pelham et al. (Eur. J. Biochem. 67:247-256; 1976). The rabbit reticulocyte lysate was chosen because it lacks microsomal membranes necessary for processing events such as signal peptide cleavage and core glycosylation. 
     EXAMPLE III 
     Radiolabeling of B. equi proteins 
     Defibrinated blood from a splenectomized horse infected with the Florida isolate of B. equi was collected when ascending parasitemia reached 5%. Erythrocytes were washed twice in Puck&#39;s saline G to remove the majority of buffy coat cells. A final wash was made in serum- and amino acid-free medium 199 (Hazleton Laboratories, Lenexa, Kans.). Short-term cultures were established in 2.5-cm 2  flasks at a 10% erythrocyte suspension in amino acid-free medium 199 containing 40% autologous, preinoculation horse serum, 1% penicillin G, streptomycin, amphotericin B, 25 μCi (500 μCi total) each of tritiated isoleucine, lysine, tyrosine, valine, and arginine per ml (respective specific activities, 110.8, 97.4, 46.7, 64.6, and 53.3 Ci/mmol; Dupont-New England Nuclear, Boston, Mass.) and buffered with 10 mM 3-[N-tris-(hydroxymethyl)methylamino]-2-hydroxy propanesulfonic acid, pH 7.35. Metabolic labeling proceeded during an 18-h incubation period at 37° C. in 5% CO 2  and ambient air. The labeled cells were then washed and solubilized as described by McElwain et al. (J. Immunol. 138:2298-2304; 1987). In vitro translation products were labeled with [ 35  S] methionine at 0.8 mCi/ml per reaction. 
     EXAMPLE IV 
     Production of monoclonal antibody (Mab) 
     Eight-week-old BALB/c mice were immunized subcutaneously with 10 7  viable merozoites in 0.1 ml of phosphate-buffered saline (PBS) emulsified in an equal volume of Freund&#39;s complete adjuvant. Merozoites for MAb production were prepared from stabilates containing a 49% parasitemia. The stabilates were diluted with 2 volumes of PBS and centrifuged at 2,500×g for 5 min. Pellets were lysed for 30 s with an equal volume of distilled water, diluted with 3 ml of PBS, vortexed gently, and centrifuged at 400×g for 5 min. The supernatant was centrifuged at 2,500×g to pellet the merozoites. Two additional immunizations consisting of the same number of parasites in incomplete Freund&#39;s adjuvant were given subcutaneously at 10-day intervals. The mice were then immunized intravenously with 10 7  viable merozoites in 0.1 ml of PBS 72 h prior to fusion. Cell fusions and cloning by limiting dilution were performed utilizing x63-A68.653 murine myeloma cells utilizing methods described by Riggs et al. (J. Immunol. 143:1340-1345; 1989). The CI ELISA used an IgG1 MAb (36/133.97) which reacts with a protein epitope on the surface of B. equi merozoites as disclosed by Knowles et al. (Infect. Immun. 59:2412-2417; 1991). Heavy-chain isotypes were identified by enzyme-linked immunosorbent assay (ELISA), and concentrations of antibodies were determined by immunodiffusion; as described by Johnstone et al. (1982, Precipitation Techniques in Agar and Agarose, pp. 120-140. In A. Johnstone and R. Thorpe (Ed.), Immunochemistry in Practice. Blackwell Scientific Publications, Boston). Supernatants from the initial fusion and from limiting-dilution clones were screened by IFA with acetone-fixed B. equi organisms. 
     EXAMPLE V 
     Immune sera from horses experimentally and naturally infected with B. equi 
     Serum was obtained from an adult horse (H5) infected intravenously twice at a 2-month interval with a Florida isolate of B. equi. After 50 ml of serum was obtained, the initial inoculation of H5 was with 30 ml of a first-passage stabilate of a Florida isolate of B. equi. This stabilate in 10% dimethyl sulfoxide contained 5.6×10 6  viable merozoites per ml. The second inoculation was with a 2.0-ml stabilate containing a 49% parasitemia prepared as described for B. equi isolates. Equine sera that tested positive for antibodies to B. equi by the complement fixation test; see Hirato et al. (Jpn. J. Vet. Sci. 7:197-205; 1945) were obtained from the National Veterinary Services Laboratory, U.S. Department of Agriculture, Ames, Iowa. These sera were obtained from horses in 19 countries, the data regarding such are herein presented as Table 1. 
     
                       TABLE I______________________________________CI ELISA for assessment of antibodies to B. equi merozoiteproteins recognized by MAb 36/133.97Country of     OD at serum dilution of .sup.a :origin    10.sup.-1              10.sup.-2                     10.sup.-3                            10.sup.-4                                 CI titer.sup.b______________________________________Argentina 0.252    0.483  1.130  1.027                                 10.sup.-2Austria   0.563    0.703  0.826  0.948                                 10.sup.-2Brazil    0.126    0.236  0.641  0.824                                 10.sup.-3Chile     0.650    0.866  1.241  1.315                                 10.sup.-1Colombia  0.180    0.713  1.259  1.191                                 10.sup.-2Ecuador   0.247    0.543  1.055  1.263                                 10.sup.-2England   0.292    0.816  1.233  1.237                                 10.sup.-1France    0.238    0.608  1.110  1.229                                 10.sup.-2Italy     0.378    0.804  1.181  1.292                                 10.sup.-1Netherlands     0.148    0.266  0.740  1.093                                 10.sup.-2North Yemen     0.663    0.851  1.166  1.193                                 10.sup.-1Panama    0.240    0.484  1.066  1.139                                 10.sup.-2Peru      0.185    0.540  1.012  1.077                                 10.sup.-2Poland    0.601    1.000  1.247  1.185                                 10.sup.-1Saudi Arabia     0.420    0.771  1.218  1.266                                 10.sup.-1Spain     0.295    0.607  0.687  0.733                                 10.sup.-3Trinidad  0.269    0.594  1.143  1.227                                 10.sup.-2United States     0.202    0.377  1.012  1.264                                 10.sup.-2Venezuela 0.325    0.771  1.244  1.324                                 10.sup.-1______________________________________ .sup.a OD of MAb 36/133.97 reaction with B. equi merozoites with equine serum at the specified dilution. OD for isotype control MAb with B. equi merozoites = 0.153 ± 0.05 (n = 8). .sup.b Dilution of serum reducing OD values to less than 3 standard deviations below the mean for control horses (&lt;0.73) in CI ELISA with MAb 36/133.97. OD for control horses at a 1/2 dilution = 0.97 ± 0.08 (n = 68). Controls included preinoculation sera of H5 and SN76N8401 (control serum from the National Veterinary Services Laboratory, Ames, Iowa). 
    
     EXAMPLE VI 
     Immunoprecipitation and SDS-PAGE 
     Immunoprecipitation of radiolabeled antigen was performed as previously described by McElwain et al. (J. Immunol. 138:2298-2304; 1987). A total of 1×10 6  to 2×10 6  trichloroacetic acid-precipitable counts of antigen and 10 μg of MAb or 10 μl of equine immune serum were used in each precipitation. Immune complexes were precipitated with protein A (Pansorbin; Calbiochem, San Diego, Calif.) or protein G (Immu-Bind; Genex, Gaithersburg, Md.). Metabolically radiolabeled antigen, in vitro-translated proteins, or immunoprecipitates were boiled for 3 min in sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE) sample buffer (final concentrations of 25 mM Trio [pH 6.8], 2% [wt/vol] SDS, 15% [vol/vol] glycerol, 2.5% 2-mercaptoethanol, and a few crystals of bromophenol blue) and were electrophoresed in a 7.5 to 17.5% SDS-polyacrylamide gradient slab gel with a 5% stacking gel; (see Takacs, B. 1979. Blectrophoresis of Proteins in Polyacrylamide Slab Gels, pp. 81-105. In I. Lefkovits and B. Pernis (Ed.), Immunological Methods. Academic Press, Inc., N.Y.). SDS-polyacrylamide gels were processed for autoradiography as described previously. 14C-labeled standards used for molecular weight comparisons (Amersham, Arlington Heights, Ill.) consisted of myosin (200,000), phosphorylase b (92,500), bovine serum albumin (69,000), ovalbumin (46,000), carbonic anhydrase (30,000), and lysozyme (14,300). 
     EXAMPLE VII 
     Western immunoblotting 
     Western blotting was performed on a miniblotter 25 (Immunetics, Cambridge, Mass.) by modification of the techniques of Towbin et al. (J. Immunol. Methods 72:313-340). Merozoite antigen was prepared from stabilates containing a 49% parasitemia as described for MAb production. Control erythrocyte antigen was prepared identically to merozoite antigen and was obtained from stabilates prepared from an uninfected horse. Pelleted merozoites were added to equal volumes of SDS-PAGE sample buffer and boiled for 10 min. Merozoite proteins separated in SDS-PAGE (as previously described) were electrophoretically transferred overnight to nitrocellulose filters in 25 mM Tris-190 mM glycine buffer containing 20% (vol/vol) methanol. Filters were blocked for 2 h in 0.17 M NaCl-0.01 M Trts-0.1 mM phenylmethylsulfonyl fluoride-1.0% (wt/vol) bovine hemoglobin (buffer A). Serum (50 μl) or MAb (10 μg) was diluted in buffer A with the addition of 0.1% (wt/vol) SDS-0.1% (vol/vol) TRITON X-100®-(polyethylene glycol p-isooctylphenyl ether) 1.0 mM EDTA (buffer B). Bound antibodies were detected by incubation for 1 h each in second antibody (rabbit anti-horse or rabbit anti-murine immunoglobulin) and  125  I-protein A in buffer B. Filters were washed three times in buffer B after incubation with equine serum or MAb, second antibody, and  125  I-protein A, followed by three washes in buffer B without hemoglobin before drying and autoradiography.  14  C-labeled molecular weight standards were the same as for SDS-PAGE previously described. 
     EXAMPLE VIII 
     IFA 
     (i) Fixed B. equi 
     IFA of acetone-fixed B. equi was performed as described previously by McGuire et al. (Infect. Immun. 45:697-700; 1984). Bound murine or equine antibodies were detected with fluorescein isothiocyanate-conjugated rabbit anti-mouse immunoglobulin or goat anti-horse immunoglobulin. 
     (ii) Live B. equi 
     Merozoites for live IFA were prepared from stabilates containing a 49% parasitemia as described for MAb production. Live IFA was performed by minor modification of methodology previously described by Goff et al. (Infect. Immun. 56:2363-2368; 1988). Merozoite pellets resuspended in 100 μl of PBS were incubated with 25 μg of MAb 36/133.97. After a 30-min incubation at room temperature, the cells were washed three times with 10% normal goat serum in PBS, diluted to 975 μl with normal goat serum-PBS, and added to 12.5 μg of goat anti-mouse antibody conjugated with tetramethylrhodamine isothiocyanate (Kirkegaard &amp; Perry Laboratories, Gaithersburg, Md.). Samples were incubated for 30 min, washed three times with PBS, and mixed with 2.0 μl of a 5-mg/ml solution of FDA. Samples were incubated for 15 min, washed once with PBS, resuspended in 100 μl of PBS, and examined in a wet mount by phase and fluorescence microscopy. A total of 757 FDA-positive merozoites were examined for reactivity to MAb 36/133.97. 
     EXAMPLE IX 
     CI ELISA 
     A competitive inhibition (CI) ELISA was established to test for a direct relationship between proteins recognized by immune equine sera and MAb 36/133.97. Merozoites were prepared as described for MAb production. Merozoite preparations were diluted to 40 μg/μl in PBS containing 20 mM MgGl 2  and treated with an equal volume of lysis buffer (50 mM Tris [pH 8.0], 5 mM EDTA, 5 mM iodoacetamide, 0.1 mM N-Cα-p-tosyl-L-lysine chloromethyl ketone, and 1.0 mM phenylmethylsulfonyl fluoride in 1.0% NONDET-P-40®). (octylphenol-ethylene oxide condensate containing an average of nine moles ethylene oxide per mole of phenol) Lysates were placed on ice for 15 min and then centrifuged at 1,500×g for 15 min, and the supernatant was collected. Four microliters of supernatant adjusted to 0.20 μg of protein per μl was added to individual wells of IMMULON-2® (96 well, non-reactive plastic flat-bottom plates (Dynatech Laboratories, Chantlily, Va.) and incubated overnight at room temperature. Each well was blocked for 2-h with 350 μl of 20% milk in PBS containing 0.2% TWEEN 20® (polyoxyethylenesorbitan monolaurate) (buffer A). Equine sera were diluted in buffer A to a final volume of 290 μl and added to the wells. Samples were incubated for 30 min, 0.125 μg of MAb 36/133.97 in 10 μl of buffer A was added, and the reaction mixture was incubated for 1-h at room temperature. Wells were washed three times with PBS containing 0.2% TWEEN 20 (buffer B). Biotinylated equine anti-murine immunoglobulin G (IgG; Vector Laboratories, Burlingame, Calif.) in buffer A was added, incubation was continued for 30 min, and the wells were washed three times with buffer B. Addition of avidin-conjugated alkaline phosphatase (Vector Laboratories) in buffer B was followed by a 30-min incubation. Wells were washed three times with buffer B, and 100 μl of a 1.0-g/μl solution of p-nitrophenyl phosphate in 100 mM NaHCO 3  (pH 9.5) with 10 mM MgCl 2  (Sigma Laboratories, St. Louis, Mo. ) was added to each well. Following a 30-min incubation, reactions were stopped with 50 μl of 0.2 M EDTA and the optical density (OD) was read at 405 nm on a Dynatech MR-5000 ELISA plate reader. 
     EXAMPLE X 
     Immunoprecipitation of B. equi merozoite proteins with equine serum 
     FIG. 1 shows immunoprecipitation of B. equi merozoite proteins with pre- and postinoculation serum from horse H5 infected with a Florida isolate of B. equi. The major B. equi merozoite proteins recognized by antibodies from this horse have apparent molecular masses of 210, 144, 108, 88, 70, 56, 44, 36, 34, 28, and 25 kDa. Immunoprecipitations with sera from 10 additional experimentally infected and 2 naturally infected horses provided similar results. 
     EXAMPLE XI 
     Immunoprecipitation of B. equi antigens with MAb 36/133.97 
     An autoradiograph comparing immunoprecipitation of merozoite proteins with MAb 36/133.97 and equine immune serum is shown in FIG. 2. MAb 36/133.97, isotyped as IgGl, immunoprecipitated proteins with approximate molecular masses of 44, 36, 34, and 28 kDa which comigrated with proteins immunoprecipitated by serum from infected horse H5. 
     EXAMPLE XII 
     IFA of fixed and live merozoites with MAb 36/133,97 
     The epitope recognized by MAb 36/133.97 is conserved on at least two isolates of B. equi, as determined by reactivity in IFA. MAb 36/133.97 reacted with both the Florida and Europe; see Kutler et al. (Am. J. Vet. Res. 47:1668-1670, 1986), isolates of B. equi at a final concentration of 0.66 μg/ml. Up to 100% of merozoites from the Florida and Europe isolates of B. equi reacted with MAb 36/133.97 in fixed IFA. MAb 36/133.97 did not react with uninfected erythrocytes or B. caballi in IFA. At the same concentrations, IgG1 isotype control MAb and rabbit anti-mouse second antibody did not react with B. equi-infected erythrocytes. The surface reactivity of MAb 36/133.97 was demonstrated by its binding to viable (FDA-positive) merozoites. Approximately 80% of isolated merozoites stained with FDA and 64% (482 of 757) of FDA-positive merozoites reacted diffusely with MAb 36/133.97. 
     EXAMPLE XIII 
     Protein character of the epitope and immunodominance of the protein recognized by MAb 36/133.97 
     Equal volumes of washed packed erythrocytes from infected and uninfected horses yielded 5.7 and 0.22 μg of polyadenylated RNA. The small amounts of polyadenylated RNA isolated from uninfected erythrocytes provided insufficient incorporation of [ 35  S]methionine from in vitro translation for use in immunoprecipitations. Immunoprecipitation of in vitro-translated B. equi mRNA with serum from infected horse H5 and with MAb 36/133.97 is shown in FIG. 3A and 3B. MAb 36/133.97 immunoprecipitated proteins at 38, 28, 26, and 23 kDa (FIG. 3B, arrowheads) which comigrated with proteins immunoprecipitated by serum from horse H5 at 10 -3  to 10 -4  dilutions (FIG. 3A). In vitro translation products derived from rabbit reticulocyte lysate are not glycosylated. Therefore, immunoprecipitation of these products by MAb 36/133.97 indicates that the binding site recognized by this antibody is a protein epitope. Immunoprecipitation of in vitro-translated B. equi mRNA with sera from four naturally infected horses provided similar results. 
     In Western blot analysis, MAb 36/133.97 did not react with antigen from uninfected erythrocytes; however, it recognized proteins of 44, 36, 34, and 28 kDa prepared from stabilates of infected erythrocytes (FIG. 4, arrowheads). Evaluation of diluted horse sera demonstrated reactivity with a 28-kDa protein at a dilution of 10 -4  as also seen in FIG. 4. 
     EXAMPLE XIV 
     Relatedness of proteins recognized by sera from B. equi infected horses and MAb 36/133,97 
     Relatedness of proteins recognized by MAb 36/133.97 and sera B. equi-infected horses was investigated by a CI ELISA. Sera from 34 noninfected horses allowed MAb 36/133.97 to bind in the CI ELISA with 0D values of 0.97±0.08. Thus, inhibition of MAb binding to B. equi merozoites was considered significant at OD values of &lt;0.73, corresponding to mean OD minus 3 standard deviations. Table I shows that sera from infected horses from 19 countries significantly inhibited the binding of MAb 36/133.97 to isolated merozoites. At a 10 -1  dilution, sera from all infected horses uniformly inhibited binding in the CI ELISA. Some of these sera also inhibited the binding of MAb 36/133.97 at dilutions of 10 -2  and 10 -3 . 
     EXAMPLE XV 
     One hundred fifty-four equine serum samples from 19 countries in North America (6 samples), South America (113 samples), Europe (28 samples), and the Middle East (7 samples) were obtained from the National Veterinary Services Laboratory, USDA-APHIS, Ames, Iowa. Each serum was tested for antibody to B. equi by the CFT as described by Frerichs et al. (Am. J. Vet. Res. 30:697-702, 1337-1341; 1969). Three anticomplement serum samples and one serum sample reactive with the CFT erythrocyte antigen control were also obtained from the National Veterinary Services Laboratory. H5 serum is from a horse experimentally infected with stabilate of a Florida B. equi isolate as disclosed by Knowles et al. (Infect. Immun. 59:2412-2417; 1991) and SN76N8401 is a GFT-negative control serum obtained from the National Veterinary Services Laboratory. One hundred and four equine serum samples submitted to Washington State University for equine infections anemia testing were used as control sera. 
     A CI ELISA was performed on all samples utilizing applicants&#39; recombinant antigen preparation of Example in conjunction with the protocol set forth in Example IX. Serum samples were tested by CI ELISA in groups of 5 to 15 per day without knowledge of the CFT results. Duplicates of each serum sample were tested at dilutions of 1:2 and 1:10. Five to 10 different control serum samples were tested at a 1:2 dilution in duplicate each day. A mean and standard deviation of the OD for the control serum samples was calculated following each test day. A serum sample was considered positive for antibody to B. equi if it inhibited the binding of MAb 36/133.97 such that the mean duplicate OD value for that dilution of test serum as at least 3 standard deviations below the mean OD value of the control serum samples for that test day. Sample data from the CI ELISA and CFT for a test day are given in Table 2. 
     
                       TABLE II______________________________________Sample data from CI ELISA and CFT.sup.aCI ELISA, OD.sup.b       CFT titer.sup.cSerum  1:2       1:10        B. equi B. caballi______________________________________224    0.381, 0.389            0.382, 0.441                        1:5     1:40225    0.471, 0.486            0.732, 0.721                        1.5     Negative226    1.489, 1.470            1.717, 1.672                        Negative                                1:5227    1.337, 1.369            1.146. 1.619                        Negative                                1:40228    0.217, 0.156            0.229, 0.236                        1:40    1:20229    0.301, 0.298            0.336, 0.363                        1:5     1:40230    1.374, 1.362            1.560, 1.528                        Negative                                1:5231    0.356, 0.356            0.439, 0.426                        1:40    1:5232    0.219, 0.254            0.334, 0.313                        1:5     Negative233    0.246, 0.260            0.351, 0.389                        1:5     1:10234    0.521, 0.486            0.761, 0.736                        1:10    Negative235    0.189, 0.198            0.314, 0.383                        1:40    1:10236    1.380, 1.351            1.535, 1.384                        Negative                                1:40237    0.347, 0.277            0.465, 0.345                        1:5     1:40238    0.314, 0.308            0.461, 0.470                        *       *H5     0.293, 0.303            ND.sup.d    Negative                                Negative______________________________________ .sup.a CI ELISA and CFT were performed as described in the text. .sup.b Serum samples reducing mean of duplicate OD values to less than 3 SD below mean of control horses (&lt;1.17) were considered positive. OD for control horses at a 1:2 dilution on this test day = 1.47 ± 0.10 (SD) ( = 9). OD for isotype control MAb = 0.145, 0.142. .sup.c CFT titers are presented at the highest dilution yielding a positive result. *, serum sample which reacted with CFT erythrocyte control antigen. .sup.d ND, not done. 
    
     Of the 154 serum samples testable by CFT, 126 were both CFT and CI ELISA positive [CFT(+) CI ELISA(+)] for antibody to B. equi. Eighteen serum samples were negative in both tests, and CFT and CI ELISA results differed in the remaining 10 serum samples. Sixteen of the 18 serum samples negative by both the CFT and CI ELISA for antibody to B. equi were CFT(+) for B. caballi. 
     The ten serum samples in which the CI ELISA and CFT results differed were retested in both assays and analyzed by immunoprecipitation. CI ELISA, CFT,and immunoprecipitation results for the 10 discrepant serum samples are summarized in Table 3. Upon retesting, four of the CFT(+) CI ELISA(-) serum samples had decreased CFT titers. Two of these serum samples which were originally CFT(+) were negative in the repeat CFT. The decreasing CFT titers of these serum samples may reflect, at least in part, multiple freeze-thaw cycles. 
     
                       TABLE III______________________________________CI ELISA, CFT, and immunoprecipitation results ofsera differing on initial testing.sup.aCFT             CI ELISA      Immunopre-Serum Original Repeat   Original                          Repeat cipitation______________________________________8     Negative Negative Positive                          Positive                                 Positive17    Negative Negative Positive                          Positive                                 Positive113   Negative Negative Positive                          Positive                                 Positive175   Negative Negative Positive                          Positive                                 PositiveH5    Negative Negative Positive                          Positive                                 Positive18    1:10     Trace    Negative                          Negative                                 Inconclusive22    1:10     1:5      Negative                          Negative                                 Inconclusive126   1:5      Negative Negative                          Negative                                 Inconclusive167   1:40     1:40     Negative                          Negative                                 Inconclusive171   1:5      Negative Negative                          Negative                                 Inconclusive______________________________________ .sup.a CI ELISA, CFT, and immunoprecipitation results were determined as described in the text. Serum samples which differed in the CI ELISA and CFT at original testing were retested by CI ELISA, CFT, and immunoprecipitation. CFT titers are presented as the highest dilution yielding a positive result. 
    
     Serum samples at a 1:10 dilution were evaluated for their ability to immunoprecipitate  35  S-labeled in vitro translation products of B. equi merozoite mRNA as described by Knowles et al. (Infect. Immun. 59:2412-2417; 1991). FIG. 5 displays immunoprecipitation data from the five serum samples which were CFT(-) CI ELISA(+), the five serum samples which were CFT(+) CI ELISA(-), and two serum samples which were negative in both tests. Five serum samples which were CI ELISA(+) CFT(-) clearly immunoprecipitated multiple B. equi proteins that comigrated with proteins immunoprecipitated by positive control serum H5 (FIG. 5, lanes 1 to 5). Interestingly, serum H5, from a horse experimentally infected with B. equi and used as positive reference serum in the CI ELISA and immunoprecipitations, was one of the serum samples consistently negative by the CFT. 
     While B. equi-specific IgG(T) antibody was not measured in the five CI ELISA(+) CFT(-) serum samples, IgG(T) remains a likely explanation for the false-negative CFT results. It has been previously shown that IgG(T) specific for equine infectious anemia virus inhibits the CFT for detecting antibody to equine infectious anemia virus because IgG(T) does not fix complement by the classical pathway disclosed by McGuire et al. (J. Immunol. 107:1738-1744; 1971). 
     Immunoprecipitation results with the five serum samples which were GI ELISA(-) CFT(+) were inconclusive (FIG. 5, lanes 7 to 11). Fewer proteins were immunoprecipitated by these serum samples than by H5 serum. However, proteins not present in the negative control serum samples (FIG. 5, lanes 6 and 12) were immunoprecipitated by the CI ELISA(-) CFT(+) serum samples. The results obtained from the five CI ELISA(-) CFT(+) serum samples may represent false-positive GFT results; however, the immunoprecipitation results show reactivity with B. equi merozoite proteins (FIG. 5, lanes 7 to 11). Three of these serum samples (22, 126, 171) also had CFT titers to B. caballi, and t immunoprecipitation results with these serum samples may reflect serological cross-reactivity between B. equi and B. caballi merozoite proteins as previously recognized by Frerichs et al. (Am. J. Vet. Res. 30:697-702; 1969). 
     If the five CI ELISA(-) CFT(+) serum samples are true positives, there are at least three possible explanations: (i) a genetic inability of those horses to produce antibody to the epitope defined by MAb 36/133.97; (ii) absence of the epitope on B. equi isolates which infected those horses; and (iii) insufficient CI ELISA sensitivity. The third explanation does not seem likely since 32 of the CFT(+) CI ELISA(-) serum samples had CFT titers of only 1:5. 
     Three anticomplement serum samples and one serum sample which reacted with the CFT erythrocyte control antigen were tested by the CI ELISA and immunoprecipitation are shown in FIG. 6. Immunoprecipitations with these serum samples were compared with immunoprecipitations with H5 serum, four randomly selected CI ELISA(+) CFT(+) serum samples, and two serum samples negative by both tests (FIG. 2). One of three anticomplement serum samples and the serum sample reactive with CFT erythrocyte control antigen were positive by both CI ELISA and immunoprecipitation (FIG. 6, lanes 7 and 11). Two anticomplement serum samples were CI ELISA(-), and one of these serum samples was clearly negative by immunoprecipitation (FIG. 6, lane 9). Lane 8 of FIG. 6 represents immunoprecipitation with the additional anticomplement serum which was CI ELISA(-). Data obtained from this immunoprecipitation were inconclusive. The proteins in lane 8 not found in the control serum samples (lanes 2 and 10) may signify cross-reactivity between antigens of B. equi and B. caballi. Also, this serum may represent a false CI ELISA(-). 
     The collective data of this report indicate a high (94%) concordance between the CI ELISA and CFT for detecting antibody to B. equi. Since 16 of 18 serum samples in this study which were CI ELISA(-) CFT(-) for antibody to B. equi were CFT(+) for antibody to B. caballi, the CI ELISA is clearly specific for B. equi. Furthermore, the formatting of the CI ELISA overcomes the aforementioned limitations associated with the CFT, and as the data clearly indicate, the geographic conservation of the epitope recognized by MAb 36/133.97 allows reliable use of the CI ELISA to detect B. equi antibody in sera from horses worldwide. 
     EXAMPLE XVI 
     Construction and expression of cDNA library 
     B. equi merozoite mRNA was isolated from infected erythrocytes as previously described in Example II. cDNA library construction was performed utilizing the methods of Maniatis et al. (1982. Molecular Cloning: A Laboratory Manual. Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y.). In this process 2 μg of merozoite mRNA were copied by reverse transcriptase followed by T4 polymerase (pharmacia). The resultant DNA was blunted, EcoRl linkers were applied and ligation into the EcoRl-site of LAMBDA ZAPII® (Stratagene Cloning Systems) was carried out. The lambda library in E. coli XL-blue was screened with MAb 36/133.97 by immunoblot assay. Transfer of bacteria to nitrocellulose was done by standard procedures and recombinant protein was detected using MAb 36/133.97 (2 μg/ml), rabbit anti-mouse second antibody and  125  I protein A. Positive plaques were isolated, replated and rescreened to achieve purity. Recombinant plasmids were excised from the bacteriophages and following induction with 5 mM isopropyl-1-B-D-thiogalactopyranoside (IPTG), tested for expression by immunoblot assay. 
     EXAMPLE XVII 
     Plasmid purification via cesium chloride 
     The bacterial suspension containing pBluescript/10E3; which has been deposited under the Budapest Treaty in the American Type Culture Collection (12301 Parklawn Drive, Rockville, Md., 20852, USA) on Jan. 10, 1995, and has been assigned Deposit Number ATCC 97016; was transferred to 250 ml proplyene bottles and pelletized by centrifugation in a Beckman at 7000 rpm for 20 min at 4° C. As a separate step 37.5 mg of lysozyme was dissolved in 7.5 ml of an aqueous reagent solution comprising 50 mM glucose, 25 mMTris and an HCl adjusted pH of 8.0 (Solution A). The pelleted bacteria are then suspended in the lysozyme-containing Solution A and transferred to a 50 ml polypropylene centrifuge tube. The suspension was allowed to stand at room temperature for 5 min, at which point 15 ml of an aqueous reagent solution comprising 0.2 N NaOH and 1% SDS (Solution B) was added and thoroughly mixed. The tube was then incubated on ice for 10 min before adding 11 ml of an aqueous reagent solution composed of 60 ml of 5 M potassium acetate, 11.5 ml of glacial acetic acid and 22.5 ml of distilled water (Solution C), and thoroughly mixed. The contents of the tube were then centrifuged at 17,000 rpm for 40 min at 4° C. in a polyallomer SW28 centrifuge tube. The resultant liquid phase of 32 ml was then distributed evenly between two SW28 tubes. The plasmid DNA present in the tubes was then precipitated by the addition of 9.6 ml of isopropanol to each tube and being allowed to stand at room temperature for 20 min. The plasmid DNA was then pelleted by centrifugation at 12,000 rpm for 30 min at 4° C. The pellets were then lyophilized, combined and suspended in precisely 4.3 ml of TE Buffer (pH 8.0) in a SW28 tube. 4.63 grams of CsCl was added to the sample. After equilibration at room temperature 80 μl of Ethictrium Bromide (10 mg/ml) was added and mixed thoroughly. The sample was then placed in a Ti65 polyallomer tube and heat-sealed. The tube was then centrifuged with a Vti65 rotor at 48,000 rpm for 16 hours at 20° C. After centrifugation, the plasmid band was then extracted by syringe as part of a 1.2 ml sample and expelled into a polyallomer SW41 centrifuge tube. The DNA was then precipitated by the addition of 2.4 ml of water and 7.2 ml of 95% ethanol to the 1.2 ml sample. The sample was then stored at -20° C. for one hour and then centrifuged with a SW41 rotor at 15,000 rpm for 30 min at 4° C. The pellet was then lyophilized and transferred to a 1.5 ml microcentrifuge tube where it was solubilized in approximately 300 μl of TE Buffer (pH 7.2). Approximately 30 μl of RNAse A Solution was added to the sample which was then incubated at 37° C. for 30 min. Approximately 2 μg of Proteinase K was then added to the sample which was then incubated again at 37° C. for 30 min. The sample was then extracted with phenol/chloroform. A reextraction with phenol/chloroform was then performed using 200 μl of TE Buffer (pH 7.2). The sample was then extracted with water-saturated ether. After removal of the ether phase the sample was precipitated by adding 1/10 th volume of 5 M NaCl and 3 volumes of the combined sample plus salt of 95% ethanol. The sample was then stored at -20° C. 
     EXAMPLE XVIII 
     Banahan Std. high frequency transformation 
     A sample of DH5 bacteria (from BRL Product Profile-see Hanahan, D., 1983, J. Mol. Biol. 166:557-580) was streaked onto SOB(Mg++) +   agar and incubated at 37° C. for about 18 hours. The colonies were transferred into 1 ml SOB broth per colony. Each 1 ml cell suspension was used to inoculate a flask containing 10 ml of SOB broth. The flasks were incubated at 37° C. and 250 rpm until a cell density of at least 4×10 7  viable cells/ml was reached. The cell suspension was then cooled on ice for 10-15 min. The suspension was then centrifuged at 2000 rpm for 12 min at 4° C. to pelletize the cells. The cells were then resuspended in 3.3 ml of TFB and incubated on ice for 10 min. The cells were then repelletized by centrifugation at 2000 rpm, for 12 min at 4° C. The cells were then resuspended in 0.8 ml of SOB with TFB, adding 28 μl of DMSO and DTT to make a 3.5% concentration. The sample was then incubated on ice for 10 min and a second 28 μl portion of DMSO and DTT was added to make a final concentration of 7%. The sample was then incubated on ice for 10 min. 210 μl of the cell suspension was then combined with less than 20 μl of the DNA solution (plasmid) resulting from Example XVII and incubated on ice for 20 min. The reaction was then heat shocked in a 42° C. water bath for 90 seconds and immediately chilled on ice for 2 min. 800 μl of SOC broth was then added to the sample and allowed to incubate at 37° C. for 30 min. 500 μl of the reactant was then spread on a YT/Amp ++   plate and allowed to dry before incubation at 37° C. 
     
         ______________________________________.sup.+ S.O.C./S.O.B. Preparation               Amt./           485H.sub.2 O/Reagent    Conc.    100 ml          500 ml______________________________________BactoTryptone      2.0%     2.0    gm         10   gmYeast Extract      0.5%     0.5    gm         2.5  gmNaCl       10    mM     1.0  ml 1M NaCl 5.0  mlKCl        2.5   mM     0.25 ml 1M KCl  1.25 m.MgCl2.MgSO.sub.4      20    mM     1.0  ml 2M Mg Stock                                   5.0  ml                        (10 mM each)Glucose    20    mM     1.0  ml 2M Glucose                                   5.0  mlDistilled H.sub.2 O      qs to 100 ml total volume______________________________________ 
    
     S.O. Broth 
     Bactotryptone, yeast extract, NaCl and KCl were added to 97 ml of distilled water, dissolved and then autoclaved. MgCl 2  and MgSO 4  were then added at a rate of 1/100 to the solution. 
     S.O.B. Plates 
     Same procedure for S.O. broth but with the additional inclusion of agar to the solution at a rate of 15 g/l prior to autoclaving. 
     S.O.C. Broth 
     Same procedure for S.O. broth but with the additional inclusion of 2M glucose at a rate of 1/100 after autoclaving. 
     
         ______________________________________.sup.++ YT/Amp Plate AgarReagent        1 liter       500 ml   250 ml______________________________________NaCl           5.0   gm      2.5 gm   1.25 gmBacto Yeast Extract          5.0   gm      2.5 gm   1.25 gmBacto Tryptone 8.0   gm      4.0 gm   3.0  gmBacto Agar     15    gm      7.5 gm   3.75 gm______________________________________ 
    
     The first three ingredients are dissolved in the desired volume of distilled water. The agar is then suspended and autoclaved for 20-30 min. 
     After the agar has cooled to about 50° C., 50 mg/L of ampicillin are added to the agar Just before it is poured into the plates. 
     EXAMPLE XIX 
     Production of recombinant antigen 
     The purified and isolated plasmid pBluescrtpt/lOE3 resulting from the cesium chloride purification process of Example XVI (see Maniatis et al., 1982. Molecular Cloning: A Laboratory Manual. Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y.; herein incorporated by reference) was used in an amount of 1 μg to transform E. coli strain DH 5 (Bethesda Research Laboratories) using the Hanahan Standard High Frequency Transformation of Example XVIII (see Hanahan, D., 1983, J. Mol. Biol. 166:557-580; herein incorporated by reference). The entire transformation reaction was added to 250 ml of YT broth containing 12.5 mg ampicillin and 59.5 mg IPTG. The culture was incubated overnight at 37° C. and 250 rpm. The cells from the culture were then pelletized by centrifugation at 1000×g for 10 min at 4° C. The resultant pellet was then resuspended in 40 ml of Proteinase Inhibition Buffer +   and recentrifuged at 1000×g for 10 min at 4° C. The resultant pellet was then resuspended in 20 ml of Proteinase Inhibition Buffer containing 1 mg/ml lysozyme and incubated on ice for 20 min. NP40 (Sigma Chemicals, #N3516) was added to 1% (200 μl) was added, and the solution was incubated on ice for 10 min. The solution was then sonicated twice at 100 watts with the probe in the solution; with each event lasting 20 min and pausing 15 min on ice between the two events. The solution was then centrifuged at 12,000×g for 10 min at 4° C. The supernatant, representing the recombinant antigen, was then recovered and stored at 4° C. 
     
         ______________________________________.sup.+ Proteinase Inhibitor Buffer           100 ml       500 ml______________________________________50    mM Tris ph 8.0  606    mg    3.03 gm5     mM EDTA         186    mg    0.93 gm5     mM lodcacetamide                 92.5   mg    0.46 gm0.1   Mm TLCK         3.69   mg    18.45                                   gm1     mM PMSF         2.27   ml    11.35                                   ml______________________________________ 
    
     EXAMPLE XX 
     Coating a plate with recombinant antigen 
     The recombinant antigen of Example XIX was slowly vortexed then made into a 1:10 dilution by addition of 50 μl of antigen to 450 μl of coating buffer + . Two tubes of 1:100 dilution were then prepared by adding 50 μl of the 1:10 dilution to 450 μl of the coating buffer. The coating buffer was then added to the wells of a Dynatech Immulon 2 plate, skipping columns 1 and 12--the total volume of the coating buffer being added equaling 100 ml less the volume of the diluted antigen. The appropriate amount of the 1:100 dilution was then added to the coating buffer in each well. The plate was sealed and stored at room temperature overnight. 
     
         ______________________________________.sup.+ Coating Buffer______________________________________To make 100 ml:        Add to 75 ml d H.sub.2 O:      0.88    gm       NaCl      0.02    gm       KCl      0.158   gm       Na.sub.2 HPO.sub.4      0.02    gm       KH.sub.2 PO.sub.4      Mix and adjust pH to 7.4 with 1M HCl      0.446   gm       MgCl.sub.2.6H.sub.2 O      Add H.sub.2 O to bring volume to 100 ml______________________________________ 
    
     
         __________________________________________________________________________SEQUENCE LISTING(1) GENERAL INFORMATION:(iii) NUMBER OF SEQUENCES: 1(2) INFORMATION FOR SEQ ID NO:1:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 277 amino acids(B) TYPE: amino acid(C) STRANDEDNESS: double(D) TOPOLOGY: unknown(ii) MOLECULE TYPE: cDNA(iii) HYPOTHETICAL: NO(iv) ANTI-SENSE: NO(vi) ORIGINAL SOURCE:(A) ORGANISM: Babesia equi(B) STRAIN: Florida(D) DEVELOPMENTAL STAGE: merozoite(vii) IMMEDIATE SOURCE:(B) CLONE: pEma1(xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:ArgProProValLysMetIleSerLysSerPheAlaPheValPheAla151015SerIleAlaIleSerSerIleLeuAlaGluGluGluLysProLysAla202530SerGlyAlaValValAspPheGlnLeuGluSerIleAspHisValThr354045IleAspLysGlnSerGluGluHisIleValTyrThrAlaHisGluGly505560TyrAlaValGluLysValLysGluGlyAspSerValIleLysThrPhe65707580AspLeuLysGluGlnThrProLysThrValValArgHisIleLysAsp859095AsnLysProTyrValValIleAlaValGluSerAlaLeuHisLeuVal100105110LeuLysLysAspGlyAspLysTrpValGluLeuGluValAlaGluPhe115120125TyrGlnGluValLeuPheLysGlyPheGluAlaValSerValAspLeu130135140AlaAlaAlaValSerAspLysPheThrGluThrThrPheGlySerGly145150155160LysLysHisThrPheLysAlaProGlyLysArgValLeuLysValVal165170175AspGlyLysThrGluLeuIleAspGlyAspAsnGluValValLeuAsp180185190LeuGluLeuPheValSerSerAspAsnLysValAlaArgValValTyr195200205LeuTyrLysGlyAspGlyArgIleLysGluIlePheLeuLysLeuVal210215220GluLysAlaTrpLysArgValGluValLysAspAlaAlaGluThrLeu225230235240HisGlyIleAsnSerThrPheProAlaAspTyrLysValValTyrAsp245250255GlyPheSerValTyrGlyAlaLeuLeuAlaValAlaAlaIleAlaPhe260265270SerThrLeuPheTyr275__________________________________________________________________________