Patent Abstract:
the present invention relates to a surface exposed protein , which can be detected in moraxella catarrhalis , having an amino acid sequence as described in seq id no 1 , an apparent molecular weight of 200 kda and a capacity of selectively binding membrane bound or soluble igd , to an immunogenic or igd - binding fragment of said surface exposed protein , and to an immunogenic and adhesive fragment of said surface exposed protein . dna segments , vaccines , plasmids and phages , non human hosts , recombinant dna molecules and plants , fusion proteins and polypeptides and fusion products are also described . a method of detecting igd , a method of separating igd , a method of isolation of a surface exposed protein of moraxella catarrhalis and a method for treatment of an autoimmune disease are also disclosed .

Detailed Description:
mid is not identical to previously well characterized outer membrane proteins of m . catarrhalis . it is not recognized by monoclonal antibodies derived against the uspa or copb outer membrane antigens . mid also has a different migration pattern in sds - page and a different composition as shown by amino acid and dna sequence analysis . mid appeares as a 200 kda band in accordance with the mw from the deduced amino acid sequence , but also as an extra band with an estimated molecular mass of more than 1 , 000 kda . the extra band indicates that native mid is an oligomeric complex in a similar fashion as uspa ( 11 ). this is further supported by the fact that mid was eluted immediately after the void volume from a sephacryl . s - 400 column with a fractionation range of up to − 8 , 000 kda . the amino acid sequences for mid shows 11 . 1 and 6 . 7 % identity , respectively , with the uspa1 and uspa2 outer membrane proteins from m . catarrhalis ( fig7 ). in a recent patent publication , an outer membrane protein of m . catarrhalis with a molecular mass of approximately 200 kda was isolated ( 12 ). a sequence encoding a protein of approximately 200 kda was also provided . however , that protein sequence is not identical to the sequence provided by us and shows only 45 . 9 to 54 . 4 % identity with mid ( fig7 ). the protein was shown to be immunogenic , but no further biological functions were presented . in addition , a 200 kda protein is associated with hemagglutinating m . catarrhalis ( 13 , 14 ). the present investigation describes the isolation , purification , characterization , cloning and expression of the novel ig - binding protein named mid of m . catarrhalis , which has affinity for human igd , of an immunogenic or igd - binding fragment of said surface exposed protein , and of an immunogenic and adhesive fragment of said surface exposed protein . m . catarrhalis , strain bc5 , was a clinical isolate from a nasopharyngeal swab culture at our department . 118 strains isolated from blood , nasopharynx , and sputum were obtained from sweden , denmark , finland , hungary , japan , and usa . sequenced strains and plasmids used for expression are shown in table i . bacteria were grown overnight in nutrient broth ( oxoid , basingstoke hampshire , england ), harvested and washed in phosphate - balanced saline ( pbs ), ph 7 . 2 by centrifugation . the ig preparations igg1 ( κ ), igg1 ( λ ), igg2 ( κ ), igg2 ( λ ), igg3 ( κ ), igg3 ( λ ), igg4 ( κ ), igg4 ( λ ), iga1 ( κ ) iga1 ( λ ), iga2 ( κ ), iga2 ( λ ), igm ( κ ), igm ( λ ), igd ( κ ), igd ( λ ) and ige ( κ ) were all of human origin and purchased from the binding site ( birmingham , england ). igd myeloma sera igd ( κ ) and igd ( λ ) were from the same company and igd - standard serum otrd 02 / b3 was from behringwerke ag ( marburg , germany ). myeloma sera igd ( λ ) a , igd ( λ ) b , igg a , igg b , igg c , igm , iga a and iga b were obtained from the department of clinical chemistry , malmö , sweden . the concentration of respective immunoglobulins was according to the suppliers . horseradish peroxidase ( hrp )- conjugated goat anti - human igd was from biosource ( camarillo , calif .). fluoresceinisothiocyanate ( fitc )- conjugated mouse anti - human igd , unlabelled rabbit anti - human igd , and hrp - labelled rabbit anti - mouse ig were purchased from dakopatts ( gentofte , denmark ). goat anti - human igd and hrp - conjugated rabbit anti - human polyvalent immunoglobulins was from sigma ( st . louis , mo .). phycoerythrin ( rpe )- conjugated mouse anti - human cd3 and cd19 were from becton dickinson ( san josé , calif .). mouse monoclonal antibodies 17c7 ( uspa ) and 10f3 ( copb ) were kindly provided by dr . eric j . hansen , department of microbiology , university of texas ( dallas , tex .). rabbits were immunized intramuscularly with 200 μg of purified mid ( forsgren et al ., 2001 ), recombinant mid fragments , or recombinant uspa1 emulsified in complete freunds adjuvans ( difco , becton dickinson , heidelberg , germany ) and boosted on days 18 and 36 with the same dose of protein in incomplete freunds adjuvans . blood was drawn 2 to 3 weeks later . the anti - uspa1 polyclonal antibodies reacted with both recombinant uspa1 and uspa2 as examined by western blots . sds - page was run using a commercial electrophoresis system consisting of 10 % bis - tris gels with running ( mes ), sample ( lds ), and transfer buffer as well as a blotting instrument ( novex , san diego , calif .). briefly , samples were boiled for 10 min followed by electrophoresis at room temperature using protein ii vertical slab electrophoresis cells ( novex ) at 150 constant voltage . gels were stained with coomassie brilliant blue r - 250 ( bio - rad , sundbyberg , sweden ). in addition , electrophoretical transfer of protein bands from the gel to an immobilon - p membrane ( millipore , bedford , mass .) was carried out at 30 v for 2 - 3 h . after transfer , the immobilon - p membrane was blocked in pbs with 0 . 05 % tween 20 ( pbs - tween ) containing 5 % milk powder . after several washings in pbs - tween , the membrane was incubated for 1 h in room temperature with purified igd myeloma protein ( 0 . 5 μg / ml , hu igd ( κ ) myeloma ; the bindingsite , birmingham , uk ) in pbs - tween including 2 % milk powder . hrp - conjugated goat anti - human igd diluted 1 / 1000 in the same buffer was added after several washings in pbs - tween . in some experiments , igd myeloma protein was replaced by myeloma protein of other immunoglobulin classes and hrp - labeled anti - human polyvalent immunoglobulins ( sigma ) was used as secondary layer . mouse mabs 17c7 and 10f3 were used to detect moraxella outer membrane proteins uspa1 , 2 and cop b , respectively ( 7 , 8 ). in these experiments , hrp - labeled rabbit anti - mouse immunoglobulins were used as a secondary layer . after incubation for 40 min at room temperature and several additional washings in pbs - tween , developement was performed with ecl western blotting detection reagents ( amersham pharmacia biotech , uppsala , sweden ). western blots were analysed by a personal molecular imager fx ( bio - rad ). elisa was used to quantitate the immunoglobulin d - binding protein . extracts of m . catarrhalis diluted in five - fold steps in 0 . 1 m tris - hcl , ph 9 . 0 were added in 100 μl volumes to microtiter plates ( f96 maxisorb , nunc - immuno module , roskilde , denmark ), which were sealed and incubated at 4 ° c . overnight . after washing the plate four times in pbs - tween , blocking buffer pbs - tween containing 1 . 5 % ovalbumin , was added . the plate was incubated for 1 h at room temperature and further washed four times with pbs - tween . igd ( κ ) myeloma protein , 0 . 05 μg in 100 μl pbs - tween containing 1 . 5 % ovalbumin was added to each well and after incubation for 1 h at room temperature the plate was washed four times with pes - tween . after 1 h incubation with hrp - conjugated goat anti - human igd diluted 1 / 1000 in the same buffer and subsequent washing with pbs - tween , tetramethylbenzidine ( 20 mm ) in 0 . 1 m potassium citrate solution , ph 4 . 25 , mixed with hydrogen peroxide ( final concentration 0 . 002 %) was added . after 30 min , the enzymatic reaction was stopped by adding 2 m sulphuric acid . the optical density ( od ) was then measured at 450 nm in an automated elisa reader ( multiskan plus , labsystems , finland ) purified mid ( 0 . 0005 - 0 . 2 μg ) in a volume of 100 μl in 0 . 1 m tris - hcl , ph 9 . 0 were manually applied to nitrocellulose membranes ( schleicher & amp ; schuell , dessel , germany ) by using a dot blot apparatus ( schleicher & amp ; schuell ). after saturation , the membranes were incubated for 2 h at room temperature in pbs - tween containing 1 % ovalbumin and 5 % milk powder and washed four times with pbs - tween . human myeloma protein 0 . 5 μg in 100 μl pbs - tween was added and after 2 h of incubation , followed by several washings in pbs - tween , hrp - labelled anti - human light chains ( κ and λ ) ( dakopatts ) in dilution 1 / 200 was used as a secondary antibody . development was performed as described above for the western blots . in another set of experiments , dilutions of human myeloma sera in a volume of 100 μl in 0 . 1 m tris - hcl , ph 9 . 0 was first applied to the membranes . after saturation , incubations , blocking , and washing steps were performed as described above . thereafter , [ 125 i ]- labeled protein mid probe ( 5 to 10 × 10 5 cpm / ml ) in pbs - tween was added . after overnight incubation , the membrane was washed four times with pbs - tween , air dried , and exposed to kodak cea . c x - ray films at − 70 ° c . using kodak x - omat regular intensifying screen ( eastman kodak , rochester , n . y .). m . catarrhalis bacteria ( 1 - 5 × 1011 colony forming units ( cfu )/ ml ) were suspended in 0 . 05 m tris - hcl - buffer ( ph 8 . 8 ) containing 0 . 1 - 5 % empigen ( calbiochem novabiochem , bedford , mass .). in some experiments empigen was replaced by chaps ( sigma ), n - octyl - p - d - glucoside ( bachem , budendorf , switzerland ) or triton x - 100 ( sigma ). all these detergents at a concentration of 0 . 1 - 5 % were tested with or without 0 . 01 m edta . the bacterial suspensions were mixed by magnetic stirring for 2 h at 37 ° c . after centrifugation at 8000 × g for 20 min at 4 ° c ., the supernatants were filtrated with sterile filters ( 0 . 45 μm ; sterivex - hv , millipore ). m . catarrhalis extract in 3 % empigen ® was applied to a q - sepharose column ( amersham pharmacia biotech ) equilibrated with 0 . 05 m tris - hcl ( ph 8 . 8 ) containing 0 . 1 % empigen ®. the column was eluted using a 0 to 1 m nacl linear gradient in the same buffer . fractions showing most igd - binding activity as detected by elisa and western blot were pooled , dialyzed in spectraphor membrane tubes ( molecular weight cut off 25 , 000 ; spectrum , laguna hills , ca ) against 0 . 05 m tris - hcl , ph 8 . 8 , concentrated on ym100 disc membranes ( molecular weight cut off 100 , 000 ; amicon , beverly , mass .) and then applied to gel - chromatography . the gel - filtration of igd - binding protein was done on a sephacryl s - 400 high resolution column ( 20 by 900 mm ; amersham pharmacia biotech ), equilibrated with 0 . 05 m tris - hcl , ph 8 . 8 containing 0 . 1 % empigen ®. fractions containing the strongest igd - binding activity were concentrated and re - chromatographed as described above . purified mid in 0 . 05 m tris - hcl ( ph 8 . 8 ) containing 0 . 1 % empigen ® was treated with trypsin or chymotrypsin in an enzyme - protein - ratio of 1 : 10 at 37 ° c . overnight . the cleavage mixtures were subjected to sds - page and peptide bands transferred to immobilon membranes were automatically sequenced or exposed to western blot analysis as described above . in order to get an n - terminal sequence of the protein , deblocking of intact mid from a possible pyroglutamate group was attempted . two different protocols were used to deblock both soluble and membrane - bound protein . automated amino acid sequence analysis was performed with an applied biosystems ( foster city , calif .) 470a gas - liquid solid phase sequenator with on - line detection of the released aminoacid phenylthiohydantoin derivatives by applied biosystems model 120a pth analyser . purified mid was radioiodinated ([ 125 i ]; amersham , buckinghamshire , england ) to high specific activity with lactoperoxidase . the preparations contained approximately 0 . 05 mol iodine per mol protein . fitc ( sigma ) was conjugated to purified mid using a standard protocol . briefly , mid ( 2 mg / ml ) in 0 . 1 m carbonate buffer , ph 9 . 5 , was incubated with 0 . 15 μg / ml fitc solubilized in dmso . after 45 min at room temperature and constant stirring , the sample was diluted and subjected to a pd10 column ( pharmacia biotech ) pre - equilibrated with pbs , ph 7 . 4 . the resulting mid - fitc was used for binding studies . genomic dna was extracted from five m . catarrhalis strains ( see table i ) using a genomic dna preparation kit ( qiagen , hilden , germany ) and was subsequently used as template for amplification of the mid gene by pcr . degenerate primers were synthesized according to the amino terminal sequences of the four peptide fragments ( table ii ). in some of the pcr reactions ( high fidelity pcr system ; roche , bromma , sweden ), specific primers were used in combination with the degenerate ones . dna sequences flanking the central region of the gene , where the peptide fragments originated from , were isolated using inverse pcr ( ipcr ). briefly , genomic dna was cleaved with the following restriction enzymes used separately ; ecorv , sphi and psti for the isolation of the start codon , and acci , asui and finally hincii for the isolation of the stop codon sequences . the resulting fragments were religated upon themselves ( rapid dna ligation kit ; roche ) and the dna was used in ipcr . to amplify the start and stop codon areas of the gene , specific primers were designed and used in a long template pcr ( ltpcr ) ( expand long template pcr system ; roche ). all pcr products were cloned into ppcr - script - amp ( stratagene , la jolla , calif .) and sequenced using the big dye cycle sequencing ready reaction kit ( applied biosystems , warrington , england ). primers for amplification of genomic dna were designed using the oligo primer analysis software ( molecular biology insights , cascade , co ). the signal peptide was deduced using the signalp v1 . 1 world wide web prediction server center for biological sequence analysis ( http :// www . cbs . dtu . dk / services / signalp /) the complete 6 . 4 kb open reading frame of the mid gene was amplified by pcr using m . catarrhalis bcs strain genomic dna as template . the oligonucleotide primers containing bamhi restriction enzyme recognition sequences were 5 ′- cgggatccgatggccgtggcggaatatgcc - 3 ′ ( primer a , seq id no 3 ) and 5 ′- cgcggatccgaaaagtgaaaacctgcaccaactgctgc - 3 ′ ( primer b , seq id no 4 ) generating a pcr product of 6391 base pairs . bamhi - digested insert was ligated into pet16 ( b ) and the resulting plasmid pet16 - mid was transformed into dh5α . both strands of the cloned pcr product were sequenced . to examine the full length mid gene in other m . catarrhalis strains , the primers a and b were used . in addition , primers used for narrowing down the sequence encoding the signal peptide were either primer a or 5 ′- tgtcagcatgtatcatttttttaaggtaaaccaccatg - 3 ′ ( primer c ; detecting the upper start codon , seq id no 5 ) in combination with 5 ′- catcaattgcgatatgtctgggatcttg - 31 ( primer d ; located at a conserved region just outside the signal peptide , seq id no 6 ) generating 192 - and 266 - base pair long pcr products ( using bc5 genomic dna as template ), respectively . furthermore , primer a or c in combination with 5 ′- cttcaccccatcagtgccatagacc - 3 ′ ( primer e , seq id no 7 ) were used for confirming the existence of the mid gene resulting in 1355 - and 1429 - base pair long fragments , respectively . the expand long template pcr system was used in all reactions and conditions were as recommended by the manufacturer ( roche , bromma , sweden ). expression of the mid gene product in e . coli and cell fraction to express the mid gene product , pet16 - mid was transformed into the expression host bl21de3 , containing a chromosomal copy of the t7 rna polymerase gene under lacuv5 control . the recombinant bacteria were grown in lb medium supplemented with 2 % of glucose and ampicillin . overexpression was achived by growing cells to logarithmic - growth phase at od 600 of 0 . 6 followed by addition of 1 mm iptg . after 4 h of induction , bacteria were sonicated according to a standard protocol and the resulting proteins were analysed by sds - page . localisation of recombinant protein from pet16 - mid was carried out by osmotic shock as described . briefly , broth cultures of induced and uninduced cells were harvested and resuspended in 30 mm tris - hcl , ph 8 , containing 20 % sucrose . edta was added to a final concentration of 1 mm and the solution was slowly stired at room temperature for 10 min . after centrifugation at 10 , 000 g for 10 min at 4 ° c ., cells were resuspended in ice - cold 5 mm mgso 4 and stired for 10 min on ice . during this step , the periplasmic proteins were released into the buffer . the supernatant containing the periplasmic fraction was collected by centrifugation . bacteria were completely lysed by lysozyme at a final concentration of 100 mg / ml followed by sonication . finally , the soluble cytoplasmic and insoluble membrane fractions were collected . the different truncated mid fragments designated a to i with their specific sizes and primers for generating the proteins are shown in fig1 . the open reading frame of the mid gene from m . catarrhalis bc5 ( in pet26 - mid ) ( forsgren et al ., 2001 ) was used as template . all mid constructs , except for mid367 - 590 ( c ), were amplified by pcr using specific primers introducing bamhi and hindiii restriction enzyme sites . due to an internal hindiii restriction enzyme site in fragment c , an xhoi site was used instead of hindiii at the 3 ′ end . all pcr products , except for mid1616 - 2139 ( i ), were cloned into pet26 ( novagen , madison , wis .). the pcr product encoding for the i fragment was cloned into pmal - c2 ( new england biolabs , beverly , mass .). to avoid presumptive toxicity , the resulting plasmids were first transformed into the non - expressing host e . coli dh5α . thereafter , plasmids encoding for fragments a to d , g and h were transformed into e . coli bl21 ( de3 ), whereas the host bl21 ( de3 )- plyss was used for vectors containing fragments e and f . both e . coli strains were incubated in the presence of kanamycin , whereas chloramphenicol also was supplemented when bl21 ( de3 )- plyss transformants were used . fragment i was expressed in dh5α . bacteria were grown to mid - log phase followed by induction with 1 mm isopropyl - 1 - thio - β - d - galactoside ( iptg ). after 3 . 5 h , transformants were sonicated and the overexpressed proteins were purified according to the manufacturers instructions . resulting recombinant proteins having a histidine tag or fused to maltose binding protein were purified on resins containing nickel amylose , respectively . the concentrations of the eluted proteins were determined using the bca protein assay kit ( pierce ). thereafter , recombinant proteins were analysed by sds - page and western blots . human erythrocytes were obtained from freshly drawn heparinized human blood . the erythrocytes were washed twice in pbs ( ph 7 . 2 ) and suspended in pbs at a final concentration of 1 %. bacteria cultured in nutrient broth were harvested by centrifugation , washed and suspended to 1 - 2 × 109 / ml in pbs . bacteria and erythrocyte suspension ( 50 μl of each ) were mixed in round bottom microtiter plates ( sarstedt , newton , n . c .). in some experiments , erythrocytes were mixed with mid - sepharose or bsa - sepharose in 150 μl pbs . agglutination was read by the naked eye . the lung carcinoma cell line a549 ( type ii alveolar epithelial cells ; ccl - 185 ) was obtained from atcc . the cells were cultured in rpmi 1640 medium ( gibco brl , life technologies , paisley , scotland ) supplemented with 10 % fetal calf serum , 2 mm l - glutamine , and 12 μg / ml gentamicin ( referred to as culture medium ). on the day before adherence experiments , cells were harvested , washed twice in gentamicin - free rpmi 1640 and added to 12 - well tissue culture plates ( nunc , roskilde , denmark ) at a concentration of 1 × 104 cells / well in 2 . 0 ml gentamicin free culture medium . cells were thereafter incubated overnight at 37 ° c . in 5 % co2 . on the day of experiments , m . catarrhalis (− 2 × 108 ) in pbs , 0 . 15 % gelatin ( sigma ) was inoculated onto the monolayers . in neutralization experiments with specific antisera , bacteria were preincubated with polyclonal antibodies ( dilution 1 / 250 ). after 1 h at 4 ° c ., bacteria were added to the epithelial cells . in all experiments , tissue culture plates were centrifuged at 3 , 000 g for 5 min and incubated at 37 ° c ., 5 % co2 . after 30 min , the infected monolayers were rinsed twice with pbs , 0 . 15 % gelatin with gentle rocking to remove nonadherant bacteria and then treated with trypsin - edta ( 0 . 05 % trypsin , 0 . 5 mm edta ) to release them from the plastic support . thereafter , the resulting cell / bacteria suspension was seeded to agar plates containing 1 . 1 % isovitalex , 7 . 8 % human blood , and finally 0 . 9 % proteose peptone . data was calculated from duplicate cultures . human peripheral blood lymphocytes ( pbls ) were isolated from heparinized blood from healthy donors by centrifugation on a step gradient of ficoll - isopaque ( lymphoprep ; pharmacia , uppsala , sweden ). for flow cytometry analyses , a standard staining protocol was used with 0 . 5 % bsa ( w / v ) in pbs as buffer . pbls ( 2 . 5 × 105 in 100 μl ) were labeled with anti - cd3 or anti - cd19 mabs with or without fitc - conjugated anti - igd mab on ice for 30 min according to the manufacturer &# 39 ; s instructions . in blocking experiments , lymphocytes were also pre - incubated with anti - igd immunoglobulins for 30 min . after two washes , 10 μg / ml of purified fitc - conjugated mid was supplemented to the cells followed by incubation for 45 min on ice . after 4 final washes with excess pbs 0 . 5 % bsa , 105 cells for each sample were analysed in an epics ® xl - mcl flow cytometer ( coulter , hialeah , fla .). where appropriate , rabbit and goat pre - immune sera and mouse igg1 and igg2a were included as negative controls ( dakopatts ) solubilization of mid was a major obstacle in the process of purification . amongst several detergents tested , only empigen ® and n - octyl - b - d glucoside alone at a final concentration of 3 % solubilized mid from a suspension of m . catarrhalis efficiently as estimated by elisa and western blot . the two detergents were equally efficient . triton x - 100 alone did not solubilize mid , but triton x - 100 plus 0 . 01 m edta solubilized mid efficiently . c haps alone or chaps with edta or edta alone did not solubilize mid . in the following experiments , empigen ® extraction was used for solubilization and subsequent purification of mid . when the empigen ® extract of m . catarrhalis was applied to a q - sepharose column , all igd - binding material was eluted from the column with 0 . 1 % empigen ® in 0 . 05 m tris hcl , ph 8 . 8 . no additional igd - binding material could be eluted when a nacl - gradient up to 1 m was applied to the same column . after concentration of the igd - binding material obtained after separation on q - sepharose , fractionation of the extract was achieved by gel filtration in the presence of 0 . 1 % empigen ® on a sephacryl s - 400 column ( fig1 ). most igd - binding material was eluted in this first peak immediately after the void volume . mid was further purified by rechromatography of the first peak under the same conditions . fig2 shows that after purification mid appeared as two bands , one 200 kda - band and a second band with an apparent molecular mass of more than 1 , 000 kda . western blot experiments were performed to confirm that mid was not identical to the previously described outer membrane proteins uspa1 and 2 with an apparent molecular mass varying from 350 to 720 kd ( 8 - 10 ) or copb with a molecular weight of 80 kda . the crude empigen ® extract of m . catarrhalis or partly purified preparations of mid were subjected to sds - page , transferred to immobilon filters and blotted with antibodies to those moraxella proteins and also with human igd . as can be seen in fig2 , mid ( as revealed by igd - binding ) is not identical with the outer membrane proteins uspa and cop b . three attempts were made to determine the amino - terminal amino acid sequence of purified mid . approximately 1000 pmol of mid was applied each time in an automated amino acid sequencer . inasmuch as no amino acid phenylthiohydantoin derivatives were obtained , the amino - terminal end of the singel mid polypeptide chain was probably blocked . it was recently determined that the moraxella uspa1 and uspa2 proteins , which are also resistant to edman degradation , contained a pyroglutamyl residue that was removed by the treatment with pyroglutamate aminopeptidase . however , when mid purified from m . catarrhalis or recombinant mid was treated with this enzyme according to two different protocols ( twice for each method ) and then subjected to edman degradation , no n - terminal amino acid sequence was obtained . crude empigen ® extracts of m . catarrhalis and highly purified mid subjected to sds - page and transferred to filters were exposed to highly purified commercially available ig - preparations representing all human ig - classes and subclasses ( table iii ). only the two igd preparations interacted with the mid - band in the 200 kda - position in a similar fashion as shown for igd in fig2 . when dot blot experiments were performed and purified mid in dilutions was first added to membranes and purified human myeloma proteins and secondary antibodies were subsequently applied , only the two igd myelomas interacted with mid . one of the two myelomas detected as little as 0 . 001 μg of mid on the membrane . the specificity of the interaction between mid and igd was further verified by using radiolabeled mid in other dot blot experiments in fig3 , it is demonstrated that mid effectively bound four igd myeloma sera . a distinct reaction could be detected in the range 0 . 03 - 4 μg of igd . for the igd standard serum ( b . w .) reactivity was seen at even lower concentrations ( not shown ). in contrast , 6 different ig myeloma sera representing igg , iga and igm showed no visible reaction with mid at 4 μg . purified mid specifically attracted human soluble igd as revealed in dot and western blots ( fig2 and 3 , table iii ). to test whether mid bound to the surface - expressed b cell receptor ( bcr ) igd , human peripheral blood lymphocytes ( pbls ) were isolated . fitc was conjugated to mid followed by incubation with pbls for 45 min on ice . in parallel , pbls were labeled with rpe - conjugated mabs directed against the t cell marker cd3 or the b cell specific surface antigen cd19 and subsequently analysed by flow cytometry ( fig4 ). interestingly , a large fraction of cd19 + lymphocytes bound significant amounts of mid - fitc ( fig4 a ), whereas t cells ( cd3 + lymphocytes ) only displayed a non - specific background binding ( fig4 d ). the mid - fitc signal corresponded well with cd19 + cells incubated with anti - igd mabs revealing igd - postive b cells ( fig4 b ). to further elucidate the specificity of mid - fitc binding to igd bearing cd19 + lymphocytes , pbls were preincubated with a rabbit anti - human igd immunoglobulin fraction . after incubation and washings , mid - fitc binding was analysed by flow cytometry according to the standard procedure . the antiserum almost completely inhibited specific mid - fitc binding to the igd bcr when compared to cells incubated with the pre - immune serum . mean fluorescence intensity decreased from 79 . 2 to 14 . 6 arbitrary units . similar results were obtained with goat immunoglobulins raised against igd ( not shown ). thus , igd - expressing b cells promoted specific mid - fitc binding to the surface - expressed bcr igd . degenerate primers were designed according to the obtained amino terminal sequences of four peptide fragments originating from mid ( table ii ) and were used in pcrs in all possible combinations . the specific primers 2982 + and 3692 − ( fig5 ) were synthesized using the deduced sequence of a distinctive pcr product generated with the degenerate primer pair 2629 +/ 3693 −. a pcr reaction using the specific primers in combination with the degenerate ones ( 718 + and 5772 −) resulted in totally 5054 bp of the gene coding for mid . flanking sequences surrounding the core of the mid gene were obtained by inverse pcr ( ipcr ). ipcr on ecorv - and asui / acci - digested m . catarrhalis genomic dna with the primer - pairs 2982 +/ 945 - and 3668 +/ 120 -, respectively , provided the sequence for the start - codon area . in addition , ipcr on hincii - digested moraxella genomic dna with the primer - pair 5898 +/ 5511 − generated the 3 ′ sequence including the stop - codon . the complete nucleotide sequence of the gene encoding mid in m . catarrhalis bc5 is shown in seq id no 2 and the resulting amino acid sequence is shown in seq id no 1 . two alternative open reading frames were revealed and are 20 ′ indicated at amino acid positions 1 and 17 , see fig6 ). consequently , the length of the mid gene product was either 2123 or 2139 amino acids . in addition to a putative ribosome - binding site ( aagg ), − 10 ( taatta ) and − 35 ( ttgaat ) consensus sequence boxes were identified . furthermore , 62 bases downstream of the taa stop - codon an inverted repeat was found with the potential of stem - loop formation that is necessary for transcriptional termination . to get an overview of the similarity and identity between diferent mid genes , the sequences of the five orf mid proteins were analysed . for 4 strains , the degree of identity and similarity was ≧ 75 . 8 % and ≧ 78 . 3 %, respectively ( fig7 ). in contrast , slightly lower values , ≧ 65 . 3 % and ≧ 71 . 2 %, respectively , were obtained for the fifth isolate ( rh4 ). identity and similarity with uspa1 was 5 . 5 - 11 . 1 % and 8 . 3 - 17 . 9 %, respectively , and with uspa2 6 . 5 - 7 . 5 % respectively 11 . 1 - 12 . 4 %. the mid gene can be detected in all m . catarrhalis strains by pcr analyses , the mid - i gene was detected in all 118 m . catarrhalis strains , whereas the moraxella ( nesseria )- related controls were negative . in addition , the size of the mid - 1 gene was confirmed using primers spanning the whole gene including the start and stop codons . analysis of the deduced amino acid sequence of mid differs from uspa1 , uspa2 and the protein described in u . s . pat . no . 5 , 808 , 024 the open reading frame defined a protein with a calculated molecular mass of just below 220 kda that readily corresponded to the empirical value of approximately 200 kda found by sds - page . the n - terminal amino acid sequence showed the typical characteristics of a signal peptide with a potential cleavage site between amino acids 66 and 67 . despite that the first amino acid after the signal peptidase cleavage site most likely was a glutamine residue , any sequence could not be determined by edman degradation . furthermore , no amino acid sequence was obtained after pyroglutamate aminopeptidase treatment . the predicted amino acid sequence was also subjected to a hydrophobicity profile analysis by the method of kyte and doolittle and showed mainly hydrophilic properties except for the putative signal peptide that was strongly hydrophobic . the deduced amino acid sequence for mid differs significantly from those for the protein described in u . s . pat . no . 5 , 808 , 024 and also from the uspa - proteins ( fig7 and 8 ). the mid gene is distributed in all m . catarrhalis strains to investigate whether or not the mid gene existed in all m . catarrhalis strains , primers were chosen based upon a conserved area upstream of the open reading frame ( orf ) and a conserved area downstream including the stop codon sequence ( forsgren et al ., 2001 ). the mid gene was detected in all 86 clinical isolates and 7 type strains analysed , and the length of the genomic mid dna was approximately 6 , 000 base pairs . the existance was further verified by southern blots using a probe containing a sequence selected from the 3 ′- end of the gene . southern blot experiments revealed that the moraxella strains contained only one mid gene . to confirm that the cloned mid gene corresponded to the purified igd - binding protein , the gene including the predicted signal sequence and start codon was subcloned into the expression vector pet16 ( b ) and thereby under the control of a t7 promoter . the resulting pet16 - mid was subsequently transformed into e . coli bl21de3 followed by induction with iptg . bacterial cells were lysed and subfractionated , and recombinant mid was localized by western blots using human igd as a probe . important verifying characteristics of mid were provided from the expression experiments ( fig9 ). firstly , following induction , cells containing pet16 - mid were able to produce recombinant mid confirming the correct reading frame of the gene . secondly , recombinant mid ( as shown by sds - page ) displayed a molecular mass of approximately 200 kda , corresponding to the 217 kda calculated value from the amino acid sequence . thirdly , the recombinant protein was indeed the mid gene product in e . coli as its igd - binding phenotype was confirmed by western blot analysis . total protein from e . coli containing induced pet16 ( b ) vector without insert did not display any igd - binding capacity ( data not shown ). fourthly , the subcellular localization of the recombinant protein showed that mid was equally located in the cytoplasmic and the membrane fractions , but not in the periplasmic space . the localization of mid &# 39 ; s in the membrane fraction correlated very well with the known outer membrane localization in m . catarrhalis . igd - binding is preserved in 238 amino acids of mid to in detail determine the mid igd - binding region , 9 sequences derived from the full length mid were cloned into pet26b (+) and expressed in e . coli . the recombinant proteins covered the entire mid sequence and their individual lengths and positions were as demonstrated in fig1 . the recombinant proteins comprising amino acid residues 69 - 1111 or 1011 - 2139 of mid did not bind igd as revealed in western and dot blots . in contrast , the protein mid902 - 1200 ( protein fragment f1 ) attracted igd -, strongly suggesting that the single igd - binding region of mid was within that particular sequence . to pinpoint the sequence responsible for the igd - binding , the truncated mid902 - 1200 was systematically shortened at the n - and c - terminal ends ( fig1 ). equimolar concentrations of the various recombinant proteins were compared to native full length mid1 - 2139 isolated from m . catarrhalis . the different recombinant proteins were diluted in four - fold steps , added to membranes and incubated with human igd . on a molar basis , an essentially preserved igd - binding capacity was detected for the truncated mid protein stretching from amino acid residue 962 to 1200 . the shortest truncated protein still interacting with igd - was localized between mid985 and mid1142 ( fragment f6 ). the igd - binding property was lost when the n - terminus was reduced to the mid1000 residue ( fragment f4 ) or when the c - terminal was shortened to mid1130 ( fragment f7 ). finally , a fragment ( mid902 - 1130 ; f8 ) with a longer n - terminal and a shorter c - terminal ( compared to mid985 - 1200 ; f3 ) was also manufactured and analysed . however , this truncated mid did not interact with igd , suggesting that the binding capacity was depending on a longer - c - terminal . to further characterize the specific mid - dependent igd - binding , an igd elisa was constructed using human igd as bate . all the recombinant truncated mid fragments were subjected to elisa followed by incubation with a specific rabbit anti - serum directed against mid902 - 1200 . the elisa was developed using hrp - conjugated goat anti - rabbit polyclonal antibodies . the same pattern as with the dot blot ( fig1 ) was observed , i . e . fragments f4 , f7 , and f8 was not attracted to the solid phase igd , whereas the other fragments bound to a variable degree compared to full length mid ( not shown ). to shed light upon the need for a tetramer structure in order to obtain an optimal igd - binding , mid962 - 1200 ( f2 , seq id no 10 ) was incubated at 60 or 100 ° c . followed by analysis on sds - page and western blots . mid962 - 1200 formed both a monomer and a tetramer after pre - treatment at 60 ° c . ( fig1 a ). the tetrameric structure was , however , disrupted at 100 ° c . and resulted in a monomeric form , which displayed a considerably weaker binding to igd when examined in western blots ( fig1 a and b ). to investigate the capability of the tetramer to bind igd in comparison with the monomeric form , the mid962 - 1200 fragment , seq id no 10 , was subjected to analysis at 60 ° c . in 6 different experiments . the heat treated protein was subjected to sds - page and the igd - binding activity was analysed by western blots . resulting gels and filters were analysed by densitometry and the protein concentration ( density ) of the monomer was divided with the corresponding tetramer concentration . the obtained value (%) was related to the concentration ( μg ) of total protein loaded on the gels . interestingly , when igd - binding to the tetrameric respectively monomeric forms were compared , a 23 - fold more efficient binding to igd was found with the tetrameric mid962 - 1200 ( fig1 c ). m . catarrhalis igd - binding protein ( mid ) hemagglutinates human erythrocytes to investigate a putative involvement of mid in hemagglutination , a series of clinical isolates that either expressed mid or by phase variation had shut off the mid gene was selected . interestingly , all out of 21 isolates expressing mid hemagglutinated human erythrocytes , whereas only four out of the mid - negative strains ( n = 21 ) hemagglutinated the red blood cells . an almost full correlation between hemagglutinating capacity and mid expression was observed . uspa1 / 2 expression was similar and irrespective of the mid expression . these initial experiments prompted us to examine whether or not purified mid protein from the model strain m . catarrhalis bc5 ( forsgren et al ., 2001 ) hemagglutinates erythrocytes . to mimic the bacterial surface , mid was conjugated to sepharose beads and incubated with the human erythrocytes . bovine serum albumin ( bsa ) linked to sepharose was included as a negative control . interestingly , the human erythrocytes were hemagglutinated in the presence of mid - sepharose , whereas bsa - sepharose did not interfere with the erythrocytes ( data not shown ). the hemagglutinating domain of mid is located between amino acid residues alanine764 and serine913 to dissect the molecule and pin - point the specific site of the molecule that was responsible for the hemagglutination , a series of truncated dna fragments of the mid gene was cloned and recombinantly expressed in e . coli ( fig1 ). polyclonal antibodies against the truncated mid proteins were raised in rabbits and used in an elisa . in preparatory experiments , antibodies to mid and the mid - derived proteins were titrated to give similar values when tested in elisa against respective antigens . the capacity of the truncated mid proteins to bind to lysed erythrocytes was then measured in elisa using the specific antibodies at appropriate concentrations . mid or mid764 - 913 ( fragment e ) gave higher elisa values ( 4 to 16 times ) as compared to the other truncated mid proteins . thus , the hemagglutinating structure of mid seemed to be located within amino acid residues 764 - 913 of mid ( seq id no 8 ). mid764 - 913 ( fragment e , seq id no 8 ) binds directly to both eryhtrocytes and type ii alveolar epithelial cells to further confirm the importance of mid764 - 913 as an adhesin , mid and a selection of the truncated mid - derived proteins were radiolabelled and tested in direct binding experiments with human erythrocytes and alveolar epithelial cells ( fig1 ). both [ 125i ]- mid and [ 125i ]- mid764 - 913 strongly bound to erythrocytes , whereas the truncated mid fragments mid367 - 590 ( fragment c ), mid902 - 1200 ( f ), mid1011 - 1446 ( g ), and mid1616 - 2139 ( i ) did not bind above background levels ( fig1 a ). in parallel , the alveolar epithelial cell line a549 also attracted both the full length [ 125 i ]- labelled mid and the truncated mid764 - 913 ( fig1 b ). all the other fragments did not bind to the epithelial cells . taken together , the fragment mid764 - 913 ( seq id no 8 ) was the crucial part of the adhesin mid that mediated the attachment to mammalian cells . antibodies to full length mid1 - 2139 and m1d764 - 913 inhibit adherence of m . catarrhalis to type ii alveolar epithelial cells to further analyse the influence of full length mid and mid764 - 963 on m . catarrhalis adherence to type ii alveolar epithelial cells , a mid - expressing and a mid - deficient m . catarrhalis strain were preincubated with antibodies to mid and subsequently added to alveolar epithelial cells for adherence . as demonstrated in fig1 , polyclonal antibodies directed against full length mid1 - 2139 and mid763 - 913 ( fragment e , seq id no 8 ) effectively inhibited adherence for the mid - expressing isolate . in contrast , pre - immune serum and a pab directed against mid1011 - 1466 ( fragment g ) did not significantly interfere with adhesion . 1 . forsgren , a . and grubb , a . 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( 1997 ) a protective epitope of moraxella catarrhalis is encoded by two different genes . infect . immun . 65 , 4367 - 4377 . 9 . cope , l . d ., lafontaine , e . r ., slaughter , c . a ., hasemann , c . a . jr ., aebi , c ., henderson , f . w ., mccracken , g . h . jr and hansen , e . j . ( 1999 ) characterization of moraxella catarrhalis uspa1 and uspa2 genes and their encoded products . j bacteriol 181 , 4026 - 4034 . 10 . klingman , k . l . and murphy , t . f . ( 1994 ) purification and characterization of a high - molecular - weight outer membrane protein of moraxella ( branhamella ) catarrhalis . infect . immun . 62 , 1150 - 1155 . 12 . sasaki , k ., harkness , r . e ., loosmoore , s . m . and klein , m . h . ( 1998 ) u . s . pat . no . 5 , 808 , 024 . 13 . fitzgerald , m ., mulcahy , r ., murphy , s ., keane , c ., coakley , d . and scott , t . ( 1997 ) a 200 kda protein is associated with haemagglutinating isolates of moraxella ( branhamella ) catarrhalis . fems immun . med . microbiol . 18 , 209 - 216 . 14 . tucker , k ., plosila , l ., and samuel , j . ( 1994 ) correlation between hemagglutination and globotetraosyl - ceramide binding by branhamella catarrhalis . abstract 117 of the 94th general meeting of the american society for microbiology . 15 . lunde e , munthe l a , vabo a , sandlie i , bogen b . ( 1999 ) antibodies engineered with igd specificity efficiently deliver integrated , t - cell epitopes for antigen presentation by b cells . nat biotechnol . 17 , 670 - 675 . 16 . lycke n . ( 2001 ) the b - cell targeted cta1 - dd vaccine adjuvant is highly effective at enhancing anti - body as well as ctl responses . curr . opin . mol . ther . 3 , 37 - 44 . 17 . ito o , harada m , takenoyama m , tamada k , li t , abe k , fujie h , nomoto k . 1998 vaccination with activated b cells pulsed with tumor - lysates can induce tumor - specific cd4 + t cells in vivo . immunobiol . 199 , 133 - 147 .