IMMUNODIAGNOSTIC METHODS

Abstract: The invention relates to a novel antigenic substance isolable from Mycobacterium tuberculosis, the substance consisting substantially of proteins of molecular weight in the range 5-18 K Daltons. Immunoassay methods employing this substance are described as in a skin test for the detection of mycobacterial infection or immunity to mycobacterial infection.

Description: IMMUNODIAGNOSTIC METHODS The present invention relates to immunoassay techniques çor use in the diagnosis oç mycobacterial Infections such as those caused by Mycobacterium tuberculosis. In particular, the present invention relates to a two-part immunoassay system comprising an antigen detection immunoassay and an antibody detection immunoassay, to antigen detection and antibody detection immunoassays employing a novel proteinaceous substance, preferably isolable from M.tuberculosis, antibodies to that substance, a novel proteinaceous substance per se, a skin test and agglutination tests utilising the substance and/or its antibodies, and diagnostic kits based upon the abovementioned techniques. Current methods of diagnosis of M.tuberculosis infections commonly used include the analysis of clinical symptoms, chest X-rays, staining and microscopic examinations, animal inoculation, culturing and the tuberculin skin test. These methods all suffer from the disadvantages of being either unreliable or timeconsuming or expehsive. Several workers have developed immunoassay techniques for the diagnosis of tuberculosis; immunoassays can in principle be both inexpensive and rapid. Thus Nassau et al (Tubercle, 1976, 57, 67-70) used an enzyme-linked immunosorbent assay (ELISA) for detection of antibodies to mycobacterial culture filtrate in patients with tuberculosis. However, there was considerable overlap in patient and control values. Grange et al (Tubercle, 1980, 61, 145-152) reported high ELISA Iga titres in tuberculous patients using crude sonicates of M.bovis BCG strain, M.kansasti and M.smegmatis as antigen but there was inadequate discrimination between infected and control samples, as 20 per cent of tuberculosis patients did not have significantly elevated antibody levels. Tandon et al (Tubercle, 1980, 61, 8789), using a partially purified extract of M.tuberculosis, Purified Protein Derivative (PPD) as antigen reported that 66 per cent of cases with no evidence of disease as well as 80 per cent of tuberculous patients had detectable antibodies to the antigen. A similar technique but employing radioimmunoassay as well as ELISA has been reported by -Zeiss et al (J. Clink Microbiol., 1982, 15, 93-96). PPD, althougb a partially purified preparation, nevertheless contains a considerable number of proteinaceous and glycolipidic substances. Recently, the isolation, purification and identification of individual proteins and MH/OLM/23rd July 1985 glycolipids trom crude mycobacterial extracts has been carried out by a nuitie @ of workers, see or example Kiyotani et al (Microbiol. Immunol. 1983, 27, 695) # and Kuwabara (3. Blol. Chem., 1975, 250, 2556). A few investigators have employed purified mycobacterial proteins and glycolipids in immunoassay techniques, see for example UK Patent Application 2076406. Other examples include that of Reggiardo et al. (J. Immunol. Meth, 1980, 34, 55-60) who used three highly purified glycolipids extracted 4rom M.bovls strain BCG in an ELISA assay. Daniel et al (Am. Rev. resp. Dis., 1981, 123, 517-520) used purified mycobacterial proteins and polysaccharides in an ELISA study but they did not include negative controls. Stroebel et al (J. Inf. Dis., 1982, 146, 280-283) using antigen 6 in ELISA found significantly higher antibody titres in patients with active bone tuberculosis than in patients with inactive bone disease or other forms of chronic osteomyelitis. Benjamin and Daniel (Am. Rev, rest. Dis., 1982, 126, 1013-1016), using antigen 5, reported 95.8 and 79.9% specificity in patients from low and high prevalence areas respectively. Despite the abovementioned-reports, the only commercially available test kit of which the applicants are aware is a latex agglutination kit "agglutinotest manufactured by Immunitalia s.r.l. of Pomezia (Rome). This test is designed to detect antibodies to M.tuberculosis. It has now been discovered that the combination of an assay or the detection of antibodies to a mycobacterial antigen with an assay for the detection of the mycobacterial antigen provides a clinically usotd, rapid effective means of detecting Mycobacterial infections, the sensitivity of the combined assay being significantly greater than that of each of the constituent assays when used singly. Moreover, there have also been discovered a novel antigenic proteinaceous substance, the said substance preferably being preparable from M.tuberculosis extracts, and antibodies to the antigenic substance, the proteinaceous substance and antibodies boning particularly useful in the abovementioned immunoassays and related serodiagnostic tests. According to one aspect of the present invention therefore, there is provided a method for the detection of mycobacterial infections in a patient, which method comprises the use in combination of an assay @or the detection ow a mycobacterial antigen with an assay for the detection of an antibody to the mycobacterial antigen. Assay techniques suitable for use In combination according to the present invention are those known in the art as being useable singly in the detection of mycobacterial antigens or antibodies and include, for example, enzyme immunoassays, radioimmunoassays and agglutination assays. It has been found most convenient to employ enzyme immunoassays for the purposes of the present invention; in particular an Antigen Capture Immunoassay (ACIA) for the detection of mycobacterial antigen and an Enzyme Linked Immunosorbent Assay (ELISA) for the detection of antibodies to mycobacterial antigens. Thus in a preferred aspect there is provided a method 'or the detection o' mycobacterial infections in a patient which method comprises the use in combination of an Antigen Capture Immunoassay (ACIA) òr the detection o' a mycobacterial antigen, and an Enzyme Linked Immunosorbent Assay (ELISA) ror the detection of antibodies to the mycobacterial antigen, said ACIA comprising: : bringing a biological fluid sample from a patient into contact with a solid phase to which are bound antibodies to a mycobacterial antigen, adding a conjugate comprising an enzyme bound to an antibody to the mycobacterial antigen, separating the solid phase, adding substrate 'or the enzyme, determining any enzyme activity on the solid phase and relating this to the presence of mycobacterial antigen in the lurid sample; and said ELISA comprising: bringing a biological fluid sample from a patient into contact with a solid phase to which is bound an antigenic substance isolable from the mycobacterial species, adding a conjugate comprising an enzyme linked to an antibody to patient immunoglobulin, separating the solid phase, adding substrate 'or the enzyme, determining any enzyme activity on the solid phase and relating this to the presence in the fluid sample of antibodies to the mycobacterial antigen. The term "patient" used in the context of the present invention revers to any animal, human or otherwise, which it is desired to test for the presence o' a mycobacterial infection. Such mycobacterial injections include those due to M.tuberculosis, M.bovis, and M.avium. Pre'erably the patient is a human. According to a further aspect of the present invention, there is provided a proteinaceous substance recognisable by human serum antibodies to M.tuberculosis and consisting substantially of proteins of molecular weight in the range 5-18 K Daltons, which proteins are immunochemically stable at BOOC and within the pH range 5Z, are free of, or substantially free of, lipid or carbohydrate residues and eontain less than 0.1% diaminopimelic acid. The proteinaceous substance will be referred to hereinafter as SDS-M. Preferably, but not exclusively, the proteinaceous substance SDS-M is obtainable from Mycobacterium tuberculosis by extraction with sodium dodecyl sulphate. The proteinaceous substance SDS-M may be further purified by gel filtration chromatography Followed by ion-exchange chromatography on DEAE cellulose. The further purified substance will be referred to hereinafter as DEAE-II. If so desired, the further purified DEAE-II may be employed as the reagent antigenic substance in any of the diagnostic methods of the present invention as defined above or hereinafter which require the use of such a substance. The present invention also provides an immunoassay method wor the detection of mycobacteria, mycobacterial antigen and antibodies to mycobacterial antigen, the said immunoassay comprising the use, as an immunoreactive component, of the proteinaceous substance as hereinbefore defined, or an antibody thereto. The term immunoassay method includes any method known in the art in which an immunoreactive component eg an antibody or an antigen is employed. In a particular aspect o' the present invention, there is provided a method for the detection of antibodies to M.tubercu1Ols in a test sample, which method comprises the steps ob a) bringing the test sample containing said antibodies into contact with a solid phase to which is bound the abovementioned proteinaceous substance, b) adding a conjugate consisting o' an enzyme linked to a substance selectively bindable to the said antibodies but not to the said proteinaceous substance, c) adding substrate to the enzyme and determining the activity of any enzyme bound to the solid phase. Preferably, the selectively bindable substance is an antibody to the said - antibodies, for example antibody to human immunoglobulin. In a still further aspect there is provided a method for the detection of antigens of M.tuberculosis in a test sample, which method comprises the steps of a) bringing the test sample into contact with a solid phase to which is bound antibody to the abovementioned protelnaceous substance, b) adding a conjugate consisting of an enzyme bound to an antibody to said proteinaceous substance and c) adding substrate for the enzyme and determining the activity of any enzyme bound to the solid phase. Preferably the antibody forming part of the antibody-enzyme conjugate is a purified antibody. In yet another aspect of the present invention there is provided a direct agglutination test for the detection of M.tuberculosis infections which test comprises bringing a sample of biological fluid ±rom a patient into contact with a suspension of particles coated with SDS-M proteins or antibodies to SDS-M proteins, and determining the presence of M.tuberculosis infection by establishing whether or not agglutination of the particles has taken place. Also within the scope of the present invention are indirect agglutination tests utilising the antigen SDS-M and antibodies to this antigen. Thus there is provided an indirect agglutination test for the detection of M.tuberculosis infections, which test comprises the mixing o' a biological fluid sample from a patient with an antibody to SDS-M, further mixing with a suspension o± particles to which are linked the antigen SDS-M and determining whether agglutination has taken place. There is also provided an indirect agglutination test utilising the same principles as the test described hereinabove except that the biological fluid sample is first mixed with the antigen SDS-M, is then further mixed with a suspension of particles to which are bound antibodies to SDS-M and then it is determined whether agglutination has taken place. In each of the abovementioned immunoassay methods forming part ot the present invention, the solid phase may be formed ±rom any material known in the art to be suitable for such a purpose. Conveniently the solid phase for use in the ACIA and ELISA tests is formed 'rom.polystyrene. The solid phase particles referred to in the description oe the agglutination tests conveniently are non-viable bacterial cells, erythrocytes, latex polymer beads or any other materials known to the skilled man, see for example UK Patent Application 2076406. Solid phases to which the abovementloned proteinaceous substance or an antibody thereto, have been bound, are within the scope of the invention. In the Antigen Capture Immunoassay, non-speciìc interactionsi which lead to a decrease in sensitivity of the method, may be eliminated or significantly reduced by coating or "blocking" the antibody coated solid phase with bovine serum albumen (BSA). Typically this is achieved by incubating the antibodycoated solid phase with a solution of BSA, for example a 1% solution, +or an appropriate time, 2-3 hours usually being sufficient although longer or shorter periods may be employed if desired. Coating or "sensitising" of the solid phase with antigen or antibody is carried out according to methods well known in the art. It has been found most convenient to attach the antigen or antibody to the solid phase by incubating the solid phase with a solution of the antigen or antibody +or an appropriate time eg 0.5-24 hours at an appropriate temperature eg 150- 370C. The sensitised solid phase may be prepared and used immediately or it may be stored and used at a later date. To preserve the activity of the immunologically active substances during storage, it has been Sound convenient to overlay the sensitised solid phase with a coating of degraded gelatin. Test sera will normally be diluted with an appropriately buffered solution before assaying. Typically a sodium phosphate buffer will be employed to maintain a pH of 7-8.0; most conveniently the immunoassay will be carried out at pH 7.4. It is preferred that the diluent solution contains substances capable o4 inactivating factors such as complement and Rheumatoid Factor (RF) which interfere with the immunochemical reaction and thereby cause a reduction In sensitivity of the method. EDTA or salts thereto4, which inactivate Complement, and dithiothreitol, which deactivates Rhaumatoid Factor are examples os such substances. The enzyme comprising part of the enzyme-antibody conjugate can be any enzyme known in the art as being useful òr the purpose in similar enzyme immunoassays. Enzymes commonly used include peroxidase, ss-galactosidase and alkaline phosphatase. It has been found most convenient òr the purposes ow the present invention to use a conjugate containing peroxidase. The enzyme antibody conjugates per Se form a further aspect of the invention. The activity of the peroxidase is determined by the addition of the substrate, hydrogen peroxide, and a separate chromogen such as 5-aminosalicylic acid, tetramethylbenzidine or o-phenylenediamine which can react with the initial products ow the enzyme reaction. A further application of the antigenic proteinaceous substance ow the present invention is its use in a skin test for the diagnosis of tuberculosis or the detection and identification of antibodies induced by mycobacterial infection. A typical skin test (Mantoux test) involves intradermal injection Or a suitable volume (eg O.lml) of an appropriate composition of the standardised proteinaceous substance into the most superficial layers of the skin (usually the skin of the forearm in humans). The average diameter of induration is measured after a suitable time (eg 72 hours in humans) and reactions less than 5 mm in diameter are recorded as doubtful. If desired, a second test may be carried out on negative or doubtful patients using a more concentrated sample of the antigen. Compositions for intradermal injection, in addition to containing the abovementioned proteinaceous substance and a carrier, usually water, may also contain other accessory ingredients, for example an isotonic agent such as sodium chloride. In another embodiment of the invention, there is provided a kit for use in an immunoassay method, the kit comprising, as an immunoreactive component, the proteinaceous substance as hereinbeore defined and/or an antibody or antibodies thereto. In particular there is provided a kit ror use in the detection of antibodies to M. tuberculosis by the ELISA method, the kit comprising: 1. a solid phase sensitised with SDS-M or DEAE-II 2. a buffered diluent containing EDTA and dithiothreitol 3. an enzyme linked to an antibody to IgG 4. substrate and chromogen system for the enzyme There is also provided a kit for the detection of M.tuberculosis antigens by the ACIA method, the kit comprising: I. a solid phase sensitised with antibodies to SDS-M or DEAE-II 2. a buffered diluent containing EDTA 3. an enzyme linked to an antibody to SDS-M or DEAE-II 4. substrate and chromogen system for the enzyme Other components which can usefully be included in the abovementioned kits include concentrated wash fluid (Tween 20 saline solution (TS)). The substrate/chromogen system typically comprises freeze dried tetramethylbenzidine as the chromogen with a separate diluent containing a buffering agent, such as sodium acetate or citrate, and the substrate hydrogen peroxide. The enzyme antibody conjugate may be provided in the freeze dried state along with a suitable diluent containing for example Tween 20, phosphate buffering agent and bovine serum albumen (BSA). The abovementioned kits may be provided for separate use or they may be provided for use in combination. There is further provided a direct agglutination test kit for the detection of M.tuberculosis antigens or antibodies comprising a suspension of latex particles coated with the protein fraction of the present invention or antibodies thereto, In particular, there is provided a direct latex agglutination test kit for the detection of mycobacterial antigens, the said kit comprising a) latex particles coated with antibodies to SDS-M or DEAE-II, a control latex and a positive control antigen. The control latex reagent contains latex particles sensitised with either the IgG fraction taken from the animal in which the antibodies to SDS-M or DEAE-II are raised prior to inoculation with the antigen, or the IgG fraction taken from another non-inoculated animal of the same species that has been rarse@ in identical conditions, or a monoclonal antibody of the same class as that used on the test latex but having a different specificity. A negative control "antigen" solution (saline) can also usefully be included in the kit. The present invention will now be illustrated by means of examples. These examples should not be construed as imposing a limitation upon the scope of the invention. EXAMPLE 1 ISOLATION AND PURIFICATION OF AN ANTIGEN FROM M.TUBERCULOSIS Culture and harvest of Mycobacterium tuberculosis Freeze dried cultures of Mycobacterium tuberculosis were reconstituted with 0.2 ml Dubos medium and transferred to Lowenstein-Jensen slopes. They were then incubated at 370C for 4-5 weeks. Lowenstein-Jensen slopes which were visually free of contamination were harvested by washing off the surface growth with 5 ml Sauton medium which was then used-to inoculate 1-litre bottles containing 500 ml Sauton medium. This was incubated in situ at 370C until the growth was visually satisfactory. The organisms were killed by adding 90% (w/v) phenol to a final concentration of 5% and incubating for a further week at 370C. The viability of the phenolised organisms was checked by transferring two 03 ml of aliquots of cell suspension to fresh Lowenstein Jensen slopes and incubating at 370C for 2 weeks. All the work was carried out in a safety cabinet (Microflow), loops and metal instruments were sterilised In a Bacticinerator (Sherwood), and pipettes, gloves and all surfaces were sterilised with 2% glutaraldehyde (Sonacide). M.tuberculosis organisms (strain H37RV) were also grown in a 15-litre fermentor (1601) (Ultroferm, LKB) containing 10 litres Sauton medium at 370C with constant supply of 5% CO2-95% air at a rate of 0.5 1/min and with continuous agitation at 300 r p.m. They were harvested by draining the culture directly into a 20-litre bottle containing phenol calculated to give a final concentration of 5%. The fermentor vessel was then re-gllled with fresh medium. There were enough organisms left In the fermentor to continue the growth without further inoculation. As many as six harvests were obtained in this way with no apparent loss of antigenicity by the organisms. For each series, the first growth required 4 weeks incubation before it could be harvested whereas subsequent growth was rapid and the organisms were harvested every 48-72 hours. During the growth period, the pH was maintained metabolically at 7.2 by titration with 50% (w/v) sterile glucose.. From each harvest 20-SOmI of packed cells were obtained. All phenolised cultures were washed three times (total 30 volumes) with 0.5% phenol in isotonic saline and stored as 10% (v/v) suspension at 40C. Staining The cultures were checked for purity by acid-fast staining (Zlehl- Neelsen's stain). Smears were heat-fixed on a microscope sllde (pre cleaned with alcohol). The slide was then flooded with hot carbol fuchsln solution (1% basic fuchsln In 10% aqueous ethanol containing 5% phenol) for 20 min. After a brief wash In running tap water It was decolourised In acid alcohol (3% hydrochloric acid In ethanol) until no more stain leaked out. It was counterstained with 0.5% methylene blue In distilled water for 5 min., washed In running tap water and dried with blotting paper. The stained organisms were examined under oil immersion in a Leitz microscope at x900 magnification. Extraction of Antiqens Extraction of whole cells with sodium dodecyl sulphate (SDS) Mycobacteria (10% v/v) were washed three times In 66 mM phosphate buffer pH 7.4 (PB) to remove phenol and were extracted with 1% SDS In PB at 800C for 1 hour. After centrifugation at 10,0009 for 1 hour the supernatant was filtered with a 0.22p- pore size membrane (Millipore) and chromatographed according to Karp and Vinogradov (Anal. Biochem., 1978, 91, 230-235) to remove excess detergent. For this 0.59 of Ion retardation resin AG IIa8 (Blo-Rad Laboratories) per ml extract was washed with 5 volumes of 1M ammonium chlorIde and then with 20 volumes distilled water. The resin was packed into a small chromatographic column (lxlOcm) and loaded with the extract. Elutlon was carried out at a flowrate of 60 mllhr (2112 Redirac fraction collector, LKB) and the fractions containing protein, as monitored using a flow cell at 280 nm, were pooled and stored at -200C. This partially purified protein containing fraction was labelled SDS-M. Separation of antigenic components by gel filtration. Extracts to be chromatographed were concentrated before filtration using a B15 macrosolute concentrator (Amicon). Alternatively the extracts were concentrated by precipitating with ammonium sulphate and then redissolving the precipitate in phosphate buffered saline containing 0.1% (w/v) SD5. Chromatagraphy was carried out In either 13x1000mm or 17x1000mm glass columns packed with Sephacryl -5300 (Pharmacia), which had been preequilibrated with 66mM sodium phosphate buffer pH 7.4. The sample applied was 3-5% (v/v) of the bed volume, which was then fractionated at a flow rate of approximately 2ml/cm2/hr (See Figure 1). The protein content of fractions was monitored at 280 nm (Uvicord S, LKB,) recorded (2210 l-channel recorder, LKB), and 1 ml or 2ml fractions were collected (2112 Redirac fraction collector, LKB). The carbohydrate content was monitored by the phenol-sulphuric acid assay method of Dubois equal, (AnaL Biochem., 1956, 28, 350-356). EMI13.1 15 20 25 30 35 40 Fractions (ml) Profile of SDS-M fractionated by gel filtration on Sephacryl 5-300(----------antigenic activity as determined by direct ELISA; ¯¯¯¯¯¯¯¯protein; ........ carbohydrate). FICURE 2 EMI14.1 Profiles of SDS-M fractionated by gel filtration on Sephadex G-75, G-100, G-200 and Sepharose 6B (---------------protein profile; --------profile of antigenic activity). Antigenic activity was checked by direct ELISA using a peroxidaselabelled rabbit anti-SDS-M conjugate, and by gel diffusion. Two main peaks were observed. The first peak was predominantly protein and had the highest antigenic activity, whilst the second peak which appeared to contain more carbohydrate was much less active. Similar profiles were obtained with Sephadex G75, G100 and Sepharose 6B (Figure 2). Further purification of the S-300 main peak by ion-exchanqe chromatography. The major peak obtained by gel filtration was purified further by ion exchange chromatography on DEAE cellulose (DE52, Whatman). Equilibration of the exchanger was adapted from the manufacturer's instructions with certain modifications. DEAE cellulose powder was hydrated by suspending in 5ml/g exchanger of 1M Tris-HCL pH 8.4 buffer to be converted to salt form. After filtration using Whatman No. 54 filter paper, it was resuspended in 1OOmM buffer at 3ml/ml exchanger, stirred gently for 15 min and then filtered. This cycle of stir-filter-resuspend was repeated twice and then three times in 1OmM buffer. Finally the exchanger was resuspended in 10mM buffer at 1.5ml/ml exchanger and used to pack a short column by running through two bed volumes o buffer. Fractions from the 5-300 filtration of SDS-M containing the antigen were pooled and dialysed overnight against the same buffer. After application of the sample, the column was washed with two bed volumes of buffer. Over 90% of the antigenic activity was retained on the column. The fraction which did not bind (DEAE I) contained mostly carbohydrate with a small amount of protein. The antigenic activity as detected by direct ELISA was low. Bound antigen (DEAE II) was eluted as a sharp peak at 0.3M sodium chloride by applying a linear 0-1 molar gradient of sodium chloride in the same buffer. (See Figure 3) Figure 3 EMI16.1 Fractions (ml) Profile of the 5-300 main peak purified by ion-exchange chromatography using DEAE-cellulose ( antigenic activity as determined by direct ELISA; protein: ¯¯¯¯¯¯¯¯¯¯¯¯carbohydrate). Arrow indicates the beginning of the sodium chloride gradient. DEAE II was highly antigenic and appeared to be a protein. No detectable carbohydrate or free fatty acids were found (less than 0.1% (w/w). The specificity of DEAE II antigen was very similar to that of SDS-M extract when compared by TB-ELISA. APPENDIX MEDIA Lowenstein-Jensen medium - Media Production Unit, Wellcome Research Laboratories Dubos medium - Media Production Unit, Wellcom e Research Laboratories Sauton synthetic medium: L-Asparagine 4.09 Citric Acid 2.09 KH2PO4 0.5g MgS04.7H20 0459 Ferric ammonium citrate 0.059 Glycerol 40ml Tween 80 (Difco)-detoxified* 0.2ml Distilled water 960ml The pH was adjusted to 7.2 with 1M KOH, and the medium was dispensed into bottles and autoclaved at 1210C for 15 mln. *DETOXIFICATION OF TWEEN 80 One part of Tween 80 was mixed with 5 parts of ext;ractlon mixture (isopropanol 40 parts: n-heptane 10 parts: 0.5M sulphuric acid 1 part), shaken vigorously for 5 main, and then allowed to stand for 5 mln. Two parts of n-heptane and 12 parts distilled water were then added, mixed thoroughly and allowed to stand until phase separation was complete. The upper phase was removed and discarded while the lower phase was transferred to a small beaker and the remaining isopropanol was evaporated by heating at 80 C. EXAMPLE 2 STUDIES ON THE PHYSICO-CHEMICAL CHARACTERISTICS OF SDS-M AND DEAE II DETERMINATION OF THE ISOELECTRC POINT. The isoelectric points (pI) of SDS-M and DEAE II were determined by isolectric focussing in polyacrylamide gel (PAG plates pH 3.5 - 9.5, LKB). Samples and markers were focussed with constent power of 30 Watts @or 1.5 hours. Both SDS-M anci DEAE II stained weakly with Coornassie blue, were P.A.S.(H.Glossman and D.M.Neville, J. Biol. Chem., 1971, 246, 6339-6346) negative, &num; counterstained with ANS (H.Clossman and D.M.Neville, J. Biol. 1971, 246, 6339-6346) strongly. The pl of SDS-M was 3.5 and at DEAE II 3.4, both of which were very close to the limit of the pH @ange of the ampholytes. POL YACRYLAMIDE GEL ELECTROPHORESIS STUDIES IN THE PRESENCE OF SDS (SDS-PAGE) Experiments witti SDS-M conducted in gel rods using the SDS-phosphate continuous buffer system (Weber and Osborn, J. Biol. Chem., 1969, 244, 4406 4412) showed that the antigenic activity as determined by ELISA from gel section extracts, was confined to two bands. The more specific band, which stained with Coomassie blue and was PjA.S positive, had an Rf value of 0.93 (i0.3) and an estimated molecular weight of 12.4 (*0.52) K daltons. In a two dimensional polyacrylamide to asaros immunoelectrophoresls experiment two immunoprecipitin lines were obtained. These lines corresponded to the active bands. Using a 4 to 30% polyacrylamlde gradient gel (Pharmacia) In 40 mM Tris acetate-SDS buffer pH 7.4 the smaller component could be separated to two further components. The slower of these was P.A.S. positive only and corresponded to DEAE I, whereas the faster component was a P.A.S. negative polypeptide which corresponded to DEAE-II. Determination of molecular weights. Molecular weights were determined by subjecting SDS-M and DEAE II to electrophoresis in parallel with standard proteins on 10% gels in tris-glycine discontinuous buffer system (Laemmli, Nature, 1970, 227, 680-685). Over the range 30-60 K daltons four weak proteins were identified in SDS-M which were absent in DEAE II. The resolution of proteins and peptides of molecular mass less than 20 K daltons was, however, poor because they remained stacked at the moving boundary. The molecular weights of the peptides of molecular weight less than 20K Daltons were resolved using 12.5% gels in a urea-tris-phosphate buffer system (Swank and Munkres, Analyt. Biochem., 1971, 39, 462-477). Fraction DEAE-II consisted of a family of ive peptides ranging between 5.5 and 17 K daltons. O these the main one had a molecular weight of 12 K daltons whereas the other four were only weakly stained with Coomassie blue. The estimated molecular weights of the protein and peptide components of SDS-M and DEAE II as determined by the two methods are summarised in table 1. TABLE 1 Buffer system Acrylamide ANTIGEN Molecular weight (K daltons) SDS-M DEAE II Laemmll (1970) 10%(0.6%C) 66 58 II " 46 34 Swank be Munkres - 12.5%(6.8%C) 15 17 " " 12 12 9 8.4 6.7 6.4 5.8 5.8 Determination of the amino acid comeosition of DEAE II The amino acid composition of DEAE II was determined according to standard methods. The results are shown In table 2. TABLE 2 Amino acid composition of purified DEAE II from Mycobacterium tuberculosis H37RV. Amino acid Concentration No. of residues nMol/ml Per molecule** Lysine 3.16 5 Histidine 2.65 4 Arginine 4.79 7 Aspartic acid 7.67 11 Threonine 5.39* 8 Serine 4.68* 7 Glutamic acid 8.80 16 Proline 5.92 8 Glycine 8.98 13 Alanine 11.41 16 Saline 7.77 11 Methionine 2.87 4 Isoleucine 3.43 5 Leuclne 7.06 10 Tyrosine 1.39* 2 Phenylalanlne 2.13 3 Tryptophan N.D. Diaminopimelic acid 0 0 ** the values were calculated and adjusted to the best whole number by assuming that the molecular weight of DEAE II was 12, K daltons. Except for threonine, serine and tyrosine, each value was the average obtained by hydrolysis for 24, 40 and 72 hours. * values extrapolated to zero time of hydrolysis N.D. not determined Analysis of the Physical Properties of DEAE II The antigen DEAE II was treated under a variety of conditions with a variety of reagents and the level of antigenic activity remaining after treatment was determined by direct ELISA. The results are listed in Table 3. TABLE 3 Physical properties of DEAE II Treatment* % Residual activity Trypsin O Pronase O DNAase 100 RNAase 100 Phosphorylase A 100 Lipase 100 Dextranase 100 Neuraminidase 100 0 C 100 25 0C 100 370C 100 800C 100 1000C 60 pH 5-8 100 pH < 3 0 pH > 10 0 * DEAE fl was incubated for 1 hour with each treatment. EXAMPLE 3 Production of antisera (i) Antibodies to SDS-M or DEAE-II for use in the ACIA and direct ELISA assys were prepared as follows: New Zealand white rabbits weighing approximately 2.5kg were immunised with 1-5mg/ml antigen emulsified with an equal volume of Freunds incomplete adjuvant. O.lml was injected into the hind limb muscles at several sites. The rabbits were challenged 7 and 14 days later with a similar dose. 40ml blood samples were taken 4, 6 and 8 weeks after the final challenge and the resultant serum was stored at -200C. (ii) Antihuman immunoglobulins for use in the antibody detection indirect ELISA were raised in sheep according to standard procedures. Preparation o coniuqate Immunoglobulins required @or enzyme labelling and tor certain immunoprecipitation studies were purified from whole serum substantially according to the method of Axelsen, (Infect. Immun., 1971, 4, 525-527). Conjugation of horseradish peroxidase to the immunoglobulins was per'ormed using dimaleimides as described by Duncan, et al., ( Analyt. Biochem., 1983, , 68-73). For long-term storage the conjugates were lyophilised in lOmg/ml mannitol and 10mg/ml bovine serum albumin. For short-term storage, they were kept in 50% glycerol at 4 C. EXAMPLE 4 ENZYME IMMUNOASSAYS indirect enzyme Immunoassay (TB-ELISA) Volumes of 200p1 per well were used throughout the assay. Microtitre plates (Titertek Flow Laboratories) were sensitised with 30-501lg/ml antigen (SDS-M or DEAE II) in 0.06M phosphate buffer pH 7.4 (PB) at 37 0C for 30 min. Excess antigen was washed off with 0.05% Tween 20 (Koch-Light Laboratories) in saline (TS) for 10 minutes. Test sera were diluted in PB containing lmM dithiothreitol, llmM EDTA, and 0.05% Tween 20 and added to the sensitised wells. They were incubated at room temperature for 1 hour and the wells were washed for 10 min with TS. The appropriate. conjugate was diluted to its optimum working strength with PB containing 0.5% bovine serum albumin and 0.05% Tween 20 (conjugate diluent) and added to the wells. This was incubated at room temperature for 60 min and washed with 8 changes of TS over 15 min. The substrate-chromogen solution was prepared just before use by dissolving 0.8mg/ml 5'-aminosallcylic acid (Cambrian Chemicals) purified and recrystallised according to the method of Ellens and Gielkens ( J. Immunol. Meth., 1980, ç 325-332) In 0.05M citrate buffer pH 6.5 containing 0.2p1 8.8M hydrogen peroxide per ml. The substratechromogen was added to the wells and incubated for 30 min at room temperature. The reaction was stopped by adding 25 l 1M NaOH per well and the absorbance was measured at 450nm (Titertek multiscan, Flow Laboratories). A diagrammatic representation of the assay is shown in Fig. 4. Direct ELISA Microtitre plates were sensited with 200 1ll of antigen as above and washed with TS for 10 minutes. The appropriate conjugate diluted to its working strength with conjugate diluent was added in 200 l aliquots per well. It was incubated at room temperature for 60 min and washed with TS for 15 min. Substrate-chromogen was added to the wells and incubated for 30 mins at room temperature. The reaction was stopped with sodium hydroxide and the absorbance of each well was measured at 450nm. A diagrammatic representation of the assay is shown In Fig. 5. Antigen Capture Immunoassay (ACIA) Volumes o' 200it1 per well were used throughout the assay unless stated otherwise. Purified anti-mycobacterial immunoglobulins were diluted with 50mM carbonate-bicarbonate buffer pH 9.5 to 150pg/ml and added to the wells of a microtitre plate. The plates were sensitised at 37 C for 3 hr and then stored at 4 C until used. Test samples were diluted 1:5 with 100mM EDTA bH 7.4) in PB and heated at 800 for 10 min. The denatured material was centrifuged at 3,0009 for 15 min and the resultant supernatant was dialysed tor 2 hr in a large volume of PB. A sensitised plate was washed with TS for 10 min to remove unbound antibody. Sample supernatants and dilutions of a standard antigen solution were placed into appropriate wells. The plate was incubated at 370C for 3 hour and washed with TS @or 10 min. Peroxidase-labelled rabbit anti-mycobacterial IgG was diluted to working strength (approximately 20pg/ml) with conjugate diluent and added to each well. The plate was incubated at room temperature for 1 hr and washed with 8 changes of TS over 15 mln. The substrate-chromogen solution (as above) was added to the wells and incubated for 30 min at room temperature. The reaction was stopped with 251Jl sodium hydroxide and the absorbance of reçerence antigen dilutions, and the antigen content of positive samples was estimated. A diagrammatic representation of the assay is shown in Fig.6. EMI25.1 Fig 4. Diagrammatic representation of the indirect enzyme immunoassay (TB ELISA) for measuring antibody activity in human sera. EMI26.1 Fig 5 Diagrammatic representation of the direct enzyme Immunoassay (direct ELISA) for measuring antigen activity. EMI27.1 Fig 6 Diagrammatic representation of the antigen capture immunoassay (ACIA) for detecting antigen In human sera. EXAMPLE 5 Evaluation of the TB-ELISA using sera from London Hospital. Serum samples were collected from patients who were either hospitalised or attending the out-patients clinic of the Chest Department at the London Hospital. Diagnosis was made by expert hospital clinicians according to standard criteria before a sample was taken. The sera were tested for hepatitis B virus using "Hepatube" (Wellcome Diagnostics), randomised, coded and stored -200C until use. They were tested blind. The patients studied were classified into six tuberculosis groups and six control groups, 'our of which being associated with other lung diseases would make it desirable for the assay to discriminate them +rom pulmonary tuberculosis. The results obtained rom the tuberculosis patients are summarised in figure 7, from which It can be seen that if activity of 50 was taken as the cut-o.fP point, then the assay was 76.5 per cent sensitive with new pulmonary tuberculosis cases and 84.5 per cent with extra-pulmonary cases. All relapsed patients and also the three cases with non-tuberculosis mycobacterial infections were also positive. Half of the cases with quiescent tuberculosis were negative whereas the others were marginally positive. The controls were all sera from patients with other diseases. These were divided into three main groups. The first group comprised patients suspected of pulmonary tuberculosis because of abnormalities in their chest X-ray but which were proven to be otherwise. All samples gave reactions less than 50 (Fig 8). The second group contained patients with other lung associated diseases. Reactions from the sera of patients with lung carcinoma, sarcoidosis and chronic bronchitis were below 50, and only one case in the pneumonia group gave a reaction of more than 50. The efficiency of the TB-ELISA relative to other techniques used in clinical laboratories to diagnose TB is shown in table 4. Fiqure 7 EMI29.1 ELISA Determination of Antibody Activities of Patients with Mycobacterial Infections Fig 8 EMI30.1 ELISA Determination of Antibody Activities in Control Patients Exhibiting Abnormal Chest X-rays or having Lung Associated Diseases PREDICTIVE VALUE EFFICIENCY POSITIVE VALUE NEGATIVE VALUE Chest X-ray 0.44 0.85 0.60 Chest X-ray and clinical status 0.67 0.79 0.71 Microscopical examination of sample 0.88* 0.60 0.725 Enzyme immunoassay (TB-ELISA) 0.85 0.85 0.86 Culturing of sample 1.00 0.85 0.89 *including the non-tuberculosis mycobacteria Table 4. Performance characteristics of the criteria used to diagnose tuberculosis infections at the London Hospital as compared with the clinical ability of the TB-ELISA test. EXAMPLE 6 The detection of TB antigen In sera from patients with natural inection using the ACIA Method. Serum samples were obtained from 70 London Hospital patients, 30 of whom were pre-treated TB cases and the other 40 of whom were non-TB control patients. The sera from each of these patients were treated according to the method of Smith et al (Abstracts of the annual meeting of Am. Soc. Microbiol., 1981, c140) In order to dissociate the antigen from its immune complex. Thus test serum was diluted 1:4 with sodium EDTA tO.1M) at pH 7.4, heated at 800C for 10 minutes, centrifuged to sediment denatured material and the resulting supematant was then dialysed for 1-2 hours against sodium phosphate buYer (pH 7.4). The dialysate was used immediately in the ACIA test. ACIA tests were carried out blind according to the method'described In Example 4 using anti-SDS M as coating antibody and conjugate. Serial concentrations of antigen SDS-M were added to a negative serum and were extracted and assayed in order to determine a standard curve. The frequency distribution of ACIA values tor the control group (Fig 9) had a sample median of 0.14 and a range of 0.08 to 0.20. It was assumed that this group consisted of individuals totally lacking In tuberculosis antigen. Optical density of .0.22 was chosen as the baseline for positivity. This value was the mean (0.147) plus three standard deviations (D.0.027) of the ACIA values of the control group. Thirteen (43%) of the tuberculosis samples were ACIA positive (Fig 10), four of which contained antigen concentrations of 10l1g/mP or higher. When the results of ACIA were combined with those of the TB-ELISA (Fig 11) 28 samples (93%) were positive in either or both tests. Only two sera, one from a pulmonary and one from a genitourinary case were negative in both assays. The combined results of TB-ELISA and ACIA assays gave an improved predictive value (Table 5) and consequently improved efficiency over the single assay for antibody detection. EMI33.1 Optical Density (450 nm) Fig 9. Frequency distribution of ACIA readings for 40 control patient sera. EMI34.1 Optical Density (450nm) Fig 10. Distribution and concentration of detected antigen activity by ACIA in thirty tuberculosis and forty control patients sera after heat treatment. EMI35.1 Fig 11. Comparison of ACIA positive and negative sera in relation to their respective antibody activity as detected by TB-ELISA. Assay Sensitivity Specificity Predictive value Efficiency Positive Negative ACIA 0.43 1.00 1.00 0.30 0.76 TB ELISA 0.73 0.87 0.81 0.81 0.81 ACIA + TB ELISA 0.93 0.87 0.85 0.94 0.90 Table 5 Performance characteristics of the antigen detection (ACIA) and antibody detection (TB-ELISA) tests. EXAMPLE 8 Rapid Detection of TB antigen by Latex Agglutination Sensitisation of latex and test procedure Polystyrene latex particles were non-covalently coupled to anti-SDSZM purified immunoglobulins for use in the detection of TB antigen in body fluids. Latex suspension with polystyrene particle size of 0.173 in diameter (Dow laboratories) was diluted to 1% (w/v) with 0.1M glycine buffered saline pH- 8.2. This was passively sensitised by adding an equal volume of antibody solution and incubating the latex-antibody mixture at 560C for 25 min. Optimum sensitivity was obtained when 10mg ow immunoglobulin were offered per gram latex (dry weight). A control latex suspension was prepared by the same method using immunoglobulins from rabbits not exposed to TB antigens. The test procedure comprised mixing 50 l of body fluid sample breviously heated to 560C for one hour to remove non-specific Interference) with 25 l of test latex or control latex on a black plate followed by rocking the plate for 2 min. A positive reaction was indicated by the development of an agglutination pattern. The speed of the appearance and quality of latex agglutination seemed to depend on the strength of the antigen present in the sample and varied wrom large clumps which appeared within a few seconds of mixing, to smaller dumps which developed rather slowly. Clear agglutination of the test latex accompanied by a lack of agglutination of the control latex was interpreted as an indication of the presence of TB antigens In the body fluid. Visible agglutination of the control latex indicated that the reaction was non-specific. Latex agglutination studies with cerebrospinal fluids (CSF) Detection of mycobacterial antigens by the latex reagent was evaluated In two studies, (i) testing CSF samples from children and (li) testing CSF samples from adults. (i) Tuberculous meningitis (TBM) in children. A collaborative study was undertaken with Great Ormond Street Hospital for Sick Children. InvestIgations were carried out on samples of CSF obtained form eighteen children with tuberculous meningitis (TBM). Seven of these children were recent patients from whom fresh samples were available. The. remaining eleven patients were those identified as cases of TBM by a search of medical records from a ten year period and in whom stored cerebrospinal (CSF) was available. TBM was diagnosed on the basis of findings in the CSF. In fifteen cases this was by the demonstration of acid-alcohol fast bacilli (AAFB) in films made from centrifuged CSF deposit, and where these were not observed, by cytological and biochemical findings compatible with the diagnosis of TBM, supported by clinical and epidemiological evidence. Control data were obtained by the examination of 134 fresh CSF samples sent to the Department of Microbiology with diagnoses other than TBM (table 6). Thirty eight samples were from children with acute pyogenic meningitis; the remaining ninety six were from patients with a variety of invective and non-infective conditions in whom the diagnosis of TBM was not considered to be appropriate and subsequent clinical and laboratory findings supported this differentiation. TB antigen was detected in 17 of 18 cases on Initial testing. In the remaIning case the initial sample was negative but subsequent samples, including one taken at post mortem, gave positive results. Tests carried out on samples from the control group gave negative results with 133 of 134 investigated (table 6). A positive result was obtained with a sample from a child with H.influenzae type b meningitis and subdural abscess formation. Na pathogens were isolated from this CSF which gave a strong reaction with H.infiuenzae type b latex (Wellcogen H.influenzae b, Wellcome Diagnostics) as well as the TB latex reagent. Both of these reactions were inhibited specifically by addition of homologous antiserum to the CSF prior to test (table 7). All of the CSF samples were retested In a blind trial by another operator and in all cases, test as well as control, the same results were obtained. The findings of this study illustrate the usefulness of the latex particle agglutination assay of the present invention in the diagnosis of tuberculosis meningitis. TABLE 6 Control Patients tested for TB antigen in CSF Control Group No.Tested No.Positive Bacterial meningitis 38 1 (Haemophilus influenzae 6) (18) (1) (Streptococcus pneumoniae) (12) (0) (Neisseria meninqitidis) (6) (0) (Streptococcus Group B) (2) (0) Acute leukaemia 28 0 Febrile illness 19 0 Neurodegenerative disease 14 O Hydrocephalus 11 0 Encephalitis 8 0 Myelogram 5 0 Febrile convulsion 5 0 Glioma 3 0 Head Injury 2 0 Near miss cot death 1 0 TOTALS 134 1 TABLE 7 Cross-inhibition studies on a false-positive control CSF sample Blocking Antibodies Result with Result with H.influenzae b TB reagent reagent Anti-M.tuberculosis + plasma membrane Anti-H.influenzae type b capsular antigen No Antibodies added + + Anti-H.influenzae type b capsular antigen and anti -M.tuberculosis plasma membrane + = Agglutination obtained - = No agglutination (ii) Latex tests with adult CSF's Twenty fresh CSF's from meningitis patients were obtained from Lewisham Hospital, and tested blind. Nineteen of these were negative with the latex test. One sample was positive. This sample originated from a TBM suspected patient, and a second sample a week later also confirmed the earlier positive result. Presence of acid fast bacilli was reported in the second CSF but not the first. The case was confirmed as TB two weeks later, by positive culture. EXAMPLE 9 8.4 Guinea piq skin test reactivity of DEAE II The skin test reactivity of DEAE II was studied and compared with that of purified protein derivative (PPD) in guinea pigs. Groups of two guinea pigs were sensitised by a single intramuscular injection o+ 0.05mg phenol-killed mycobacteria in Freund's incomplete adjuvant (Wellcome Research Laboratories). Each group of animals was injected with (1) M.tuberculosis strain H37RV, (2) M.tuberculosis strain H37RA, and (3) M.xenopi. The guinea pigs were skin tested four weeks aster sensitisation. DEAE II and PPD were dissolved and diluted in physiological saline without addition of Tween 80. Graded doses of antigen (0.1 ml) were injected intradermally on the shaved flanks. The mean diameter of induration was measured 24 hr after injection. PPD used In the experiments was prepared from M.tuberculosis strain H37RV. It was obtained from the National Institute of Allergy and Infectious Diseases (Bethesda, USA) and the stated potency was 30,000 International Units per mg. The results, which are summarised in Table 8, show that DEAE II reacted only in guinea pigs sensitised with M.tuberculosis. There were no skin reactions with M.xenopi except at the highest dose which occurred also with PPD. The potency of DEAE II in the skin reaction was about 10 times stronger than that oç PPD. The time course oS the reaction appeared within 3 hours after Injection. Diameter of induction (mm) 24 hr after injection in guinea pigs sensitised with phenol killed cells of Antigen Protein concentration M.tuberculosis M.tuberculosis M.xenopl Control H37RV H37RA DEAE II 100 18.3 # 1.9 19.7 # 1.9 3.5 # 0.6 50 16.4 # 1.9 17.2 # 1.9 - 25 15.4 # 1.8 14.3 # 1.8 - 12.5 14.8 # 1.4 12.9 # 1.5 - 6.2 13.5 # 1.0 8.4 # 1.0 - 3.1 9.1 # 1.0 3.1 # 0.5 - 1.6 7.6 # 0.6 - PPD 100 8.9 # 1.2 12.0 # 1.2 3.1 # 0.3 50 7.6 # 0.8 8.3 # 1.0 2.1 # 0.3 25 4.1 # 0.3 7.1 # 0.8 - 12.5 2.2 # 0.3 4.3 # 0.6 - -

Claims: CLAIMS 1. A proteinaceous substance recognisable by human serum antibodies to Mycobacterium tuberculosis, said proteinaceous substance consisting substantially of proteins of molecular weight in the range 5-18 K Daltons, which proteins are immunochemically stable at 8OC and within the pH range 5-8, are substantially free of liquid and carbohydrate residues and contain less than 0.1% diaminopimelic acid. 2. An immunoassay method for the detection of mycobacteria, mycobacterial antigens or antibodies to mycobacterial antigens, the immunoassay comprising the use, as an immunoreactive component, o' the proteinaceous substance of claim 1 and/or an antibody or antibodies thereto. 3. An immunoassay method according to claim 2 for the detection of antibodies to M. tuberculosis in a test sample, which method comprises steps of a) bringing the test sample into contact with a solid phase to which is bound the proteinaceous substance; b) adding a conjugate comprising an enzyme linked to a substance selectively bindable to the said antibodies and not bindable to the said proteinaceous substance; c) adding substrate to the enzyme, and determining the activity of any enzyme bound to the solid phase. 4. An immunoassay method according to claim 2 for the detection of antigens of M.tuberculosis in a test sample, which method comprises the steps of a) bringing the test sample into contact with a solid phase to which Is bound antibody to the proteinaceous substance; b) adding a conjugate comprising àn enzyme bound to an antibody to the protelnaceous substance; c) adding substrate for the enzyme and determining the activity o± any enzyme bound to the solid phase. 5. A kit for use in an immunoassay method according to claim 2, the kit comprising, as an immunoreactive component, the proteinaceous substance of claim 1 and/or an antibody or antibodies thereto. 6. A kit for use in an immunoassay method according to claim 3, the kit comprising the proteinaceous substance and a comjugate, the conjugate comprising an enzyme linked to a substance bindable to the antibody. 7. A kit for use in an immunoassay method according to claim 4, the kit comprising an antibody to the proteinaceous substance and a conjugate, the conjugate comprising an enzyme bound to an antibody to the purified proteinaceous substance. 8. An agglutination test method for the detection of M. tuberculosis antigens, or antibodies thereto, In a test sample, which method comprises bringing the test sample into contact with a suspension of particles coated either with the proteinaceous substance of claim 1, or with antibodies thereto, and establishing whether agglutination of the particles has taken place. 9. An agglutination test method according to claim 8 wherein the particles of the suspension are coated with antibodies to the proteinaceous substance. 10. An agglutination test kit for use in the method of claim 8, the kit comprising a suspension of particles coated with the proteinaceous substance. 11. An agglutination test kit for use In the method P claim 9, the kit comprising a suspension of particles costed with antibodies to the proteinaceous substance. 12. A solid phase to which is bound a proteinaceous substance according to claim 1 or an antibody thereto. 13. A conjugate comprising an enzyme linked to an antibody to the proteinaceous substance of claim 1. 14. A composition for use in a skin reactivity test for mycobacterial Infection in a patient, the composition comprising the proteinaceous substance of claim 1, a carrier therefor and optionally any other accessory Ingredients4 15. A method for the preparation ow a proteinaceous substance- according to claim 1, which process comprises extraction of mycobacteria with sodium dodecyl sulphate followed by chromatographic removal of excess detergent, and optional further purification by ion-exchange chromatography.

Inventors: KRAMBOVITIS, ELIAS
Applicants: THE WELLCOME FOUNDATION LIMITED
Application year: 1985
Main classification: G01N33
IPC codes: A61K39, C07K19, G01N33, C07K14