recombinant e2 , cell lines , vector dna , and antibodies used in the present study . the recombinant e2 used in this screening was produced in cho cells ( e2 - cho ) ( wo 97 / 09349 ). e2 - cho binds to the human t cell lymphoma cell line molt - 4 . a subline of molt - 4 ( termed a2 a6 ), was identified by expanding individual molt - 4 cell colonies and testing for the amount of e2 - cho that bound to the cell surface . the a2a6 subline was found to bind more e2 - cho molecule on its surface than its parental line and was therefore chosen for the source of rna , expecting that this subline may have a higher representation of the transcript encoding the e2 binding molecule . these cells were chosen using an assay whereby human b and t lymphoma cells and hepatocarcinoma cell lines were incubated with recombinant e2 expressed in mammalian cells ( cho ) as described by d . rosa et al ., proc . natl . acad . sci . usa 93 , 1759 ( 1996 ) and stained with biotin - labelled anti - e2 antibodies as described by rosa et al , ( 1996 ). cells with the highest e2 binding ability were sorted using a facsvantage ( becton dickinson ) and subcloned by limiting dilution . growing clones were screened for e2 binding at the facs and clones with the highest mean fluorescence intensity were further expanded . wop is a nih3t3 - derived cell which expresses polyoma t antigen ( l . dailey and c . basilico , j . virol . 54 , 739 ( 1985 ). in this cell line , plasmids containing the polyoma replication origin cari be amplified episomally . recombinant dna constructed with pcdm8 ( invitrogen ) can be recovered from selected transfectants , which contains the polyoma replication origin and is designed for the manipulation of expression libraries in eukaryotic cells . a mouse monoclonal anti - e2 antibody ( 291a2 ) was used for detection of e2 - cho bound on the cell surface of transfectants . this antibody was obtained as follows : balb - c mice were immunised three times with recombinant e2 ( 10 μg ) in complete freund &# 39 ; s adjuvant . cell fusions between spleen cells and non - producing myeloma cells were made according to standard techniques . the supernatant from fusions was then screened for binding to e2 bound to molt - 4 cells , so as to identify monoclonal antibodies that bound to an exposed site on the e2 molecule . the most suitable antibody identified in this fashion was termed 291a2 . total rna was extracted from the a2a6 cell line according to the method described by chomczinsky and sacchi ( chomczinsky , p . and sacchi , n . ( 1987 ) anal . biochem . 162 : 156 – 159 ). poly ( a )+ was enriched twice using oligo ( dt ) cellulose . starting from 2μg of this rna as a template , the double strand complementary dna was synthesized using a superscript ii cdna synthesis kit ( life technologies ) in the presence of oligo ( dt ) ( 100 ng ) and random hexamer primers ( 100 ng ). the cdna was blunt - ended with t4 dna polymerase and was ligated with a bstxi linker , which allows the insertion of the fragment into the same restriction site in the polylinker region of the expression vector pcdm8 . the linker - ligated cdna was phenol - extracted and ethanol precipitated using ammonium sulphate to remove free mononucleotides , followed by sephacryl 500 chromatography ( lifetechnologies ) to size - fractionate the cdna . the purified cdna fragment over 500 bp were pooled and ligated with bstxi digested pcdm8 at a molecular ratio of approximately 1 : 1 . this final ligation reaction was used from transformation of e . coli mc1061 / p3 by electroporation using gene - pulser ( biorad ). a total of 2 × 10 6 cfu was amplified and pooled in liquid bacterial culture as a cdna library . the screening procedure was based largely on the method described by campbell et al . ( campbell , i . g ., jones , t . a ., foulkes . w . d . and trowsdale , j . cancer res . 51 : 5329 – 5338 , 1991 ). enrichment was carried out using magnetic beads ( the first to the third round ) ( fig1 a ) and panning techniques ( the fourth round ). ( fig1 b ). a total of 375 μg of amplified dna , which represents 2 × 10 6 of independent cdna clones was prepared . in each transfection . 25 μg of dna was mixed with 10 7 wop cells using the gene - pulser electroporator ( biorad ) under the conditions of 300v / 500 μf . fifteen sets of transfections were performed . after transfection , cells were incubated at 37 ° c . for 2 days and then the cells were detached by trypsinization and washed with pbs supplemented with 5 % fcs and 0 . 5 mm edta twice by centrifugation at 360 × g for 10 min at 4 ° c . the cell pellet was resuspended in pbs supplemented with 5 % fcs and 0 . 5 mm edta ( 10 7 cells / ml ) and then e2 - cho was added to the cell suspension at a concentration of 10 μg / ml . the cells were incubated on ice for 60 min . after washing twice with pbs supplemented with 5 % fcs and 0 . 5 mm edta , the cell suspension was incubated with 291 a2 antibody on ice for 30 min . after washing twice with pbs supplemented with 5 % fcs and 0 . 5 mm edta , 10 μl of dynabeads ( dynal ) coupled with goat anti - mouse ig was added to the cell suspension . the mixture was gently agitated using a coulter mixer ( coulter ) for 60 min at 4 ° c . bound cells were separated using magnetic particle concentrator ( dynal ) from non - binders according to the manufacturer &# 39 ; s instructions thus enriching e2 - binding transfectants . plasmid dna was recovered from the bound transfected cells using the protocol described by campbell et al . ( campbell , i . g ., jones , t . a ., foulkes , w . d . and trowsdale . j . cancer res . 51 : 5329 – 5338 . 1991 ). e . coli mc1061 / p3 was transformed with this plasmid by electroporation . this dna pool is referred to as the first enriched pool ( 1 ° ep ). a total of 150 μg of amplified dna derived from 1 ° ep was prepared and 6 sets of the transfection were performed and transfectants were enriched using the same condition as in the first screening , this dna pool is referred to as 2 ° ep . a total of 25 μg of amplified dna derived from 2 ° ep was prepared and one set of the transfection was performed . transfectants were enriched using the same condition as in the first screening . during this separation step , transfectants formed aggregates , which might be caused by expression of irrelevant adhesion molecules . this could decrease the efficiency of enrichment because these aggregates contained magnetic beads non - specifically . to circumvent this potential problem transfectants after the second separation by magnetic particle concentrator were diluted and plated on terasaki plates . approximately 100 of single cells identified under microscope were pooled and plasmid dna was extracted from them . the dna pool prepared from this step is referred to as 3 ° ep . 291a1 monoclonal antibody was incubated in a petri dish ( 90 mm ) at a concentration of 1 olg / ml overnight at 4 ° c . a total of 25 μg of amplified dna derived from 3 ° ep was prepared and one set of transfections was performed . the transfected cells were incubated with e2 - cho as described above , and placed onto the 291a2 - coated plates for 60 min at 4 ° c . after rinsing with a large excess of pbs supplemented with 5 % fcs and 0 . 5 mm edta twice , the bound cells were directly treated with the lysing solution and plasmids were extracted as described as before . this dna pool is referred to as 4 ° ep . 3 . 4 identification of cdna encoding a molecule binding to the recombinant e2 dna was isolated from single colonies derived from 4 ° ep . a single transfection was performed for each plasmid preparation using the same conditions as used for the previous screening steps . e2 - binding of the transformants was detected using a phycoerythrin - conjugated monoclonal fab fragment of goat anti - mouse ig instead of the antibody - coupled dynabeads . transfectants of 3 ° ep and 4 ° ep were also analyzed in the same way . the e2 - bound cells were detected on facscan ( becton dickinson ) and analyzed with lysis ii program ( becton dickinson ) ( fig2 ). e2 - cho binds increasingly as the purification step advances . a single clone p3 showed strong e2 - binding . p3 contains a insert of approximately 1 kb . the dna sequence of the insert of the cdna clone which confers e2 - binding to wop upon transfection was determined by an automated sequencing system using the t7 primer , whose sequence is located adjacent the cloning site of pcdm8 . the sequence was screened through the genbank databases using the gcg programs on a unix computer . this analysis revealed that the 5 ′ part of p3 insert is identical to human cd81 ( tapa - 1 ). restriction analysis of p3 using three enzymes ( bstxi ), hincii and ncoi ) also agreed with the restriction map of human cd81 cdna . anti - cd81 antibodies were used to assess the interaction between e2 and cd81 . ebv - b cells were incubated with increasing concentrations of recombinant e2 for 1 hour at 4 ° c . and then stained with an anti - cd81 monoclonal antibody ( clone js - 81 , pharmingen ). as shown in fig3 , recombinant e2 was found to competitively inhibit the binding of anti - cd81 antibodies to ebv transformed b - cell lines ( ebv - b cells ). the data are expressed as % inhibition of mean fluorescence intensity ( rosa et al . 1996 ). in addition , e2 reacts in western blot with anti - cd81 precipitated material ( fig4 ). this figure shows e2 recognition of membrane protein fraction immunoprecipitated by anti - cd81 antibody . approximately 300 μg of membrane protein extract prepared from the a2a6 cell line were solubilised in 8 mm chaps in pbs ph 7 . 4 , incubated with 10 μg recombinant e2 ( lanes 2 and 3 ), with 20 μg of anti - cd81 mab ( clone js81 ; pharmingen ) ( lane 4 ), or as control , with 20 μg of an irrelevant monoclonal antibody ( anti - human cd9 , atcc ) ( lane 5 ) for 2 hours at 4 ° c ., and finally precipitated with chimpanzee antiserum to e2 ( lane 2 ), chimpanzee pre - immune serum ( lane 3 ), or goat anti - mouse igg ( lanes 4 and 5 ) bound to protein a sepharose ( clab , pharmacia ). the pellet was dissolved in laemmli buffer and subjected to sds - page under non - reducing conditions . after electroblotting , the pvdf membrane ( millipore ) was incubated overnight with 1 μg / ml of recombinant e2 at room temperature and for 2 hours with 291a2 anti - e2 monoclonal antibody . e2 binding to immunoprecipitated proteins was detected with an anti - mouse igg peroxidase - conjugated polyclonal antibody ( amersham ). as a positive control membrane proteins also were loaded on the gels ( lane 1 ). the mobility of molecular weight standards is indicated on the left in kilodaltons . cd81 is also expressed on fresh lymphocytes and hepatocytes as demonstrated by immunohistochemical staining with biotin - labelled - e2 or anti - cd81 ( data not shown ). to assess whether cd81 could mediate the internalisation of ligands we exploited the fact that cd81 forms a complex with cd19 and cd21 on the surface of b lymphocytes ( d . t . fearon and r . h . carter , 1995 , annu . rev . immunol . 13 , 127 ). b cells were incubated with e2 at 37 ° c . for different times , after which cd19 or cd21 levels on the cell surface were measured by immunofluorescence . incubation of b cells with e2 resulted in down - regulation of both cd19 and cd21 ( data not shown ). it thus seems as if cd81 is able to mediate the internalisation of both these ligands . the major extracellular loop of cd81 binds recombinant e2 and viral particles . to map the cd81 domain that binds e2 protein our efforts were focused on the ec2 hydrophilic extracellular loop of the protein . this fragment was expressed in e . coli as a thioredoxin - ec2 fusion protein that has an enterokinase site between thioredoxin and ec2 , and as a gst - ec2 fusion protein which has a thrombin site between gst and ec2 and a hexa - histidine tag added to the carboxyl - terminus of the protein . we show that both proteins are expressed and are able to bind hcv e2 . in competition experiments we also show that the purified fusion proteins and the ec2 - his fragment excised from gst - thrombin - ec2 -( his ) 6 are able to inhibit the binding of e2 on the surface of cd81 expressing cells . fig5 shows the nucleotide and the deduced amino acid sequences of the ec2 fragment cloned in pthio - his c and the upstream plasmid sequence coding for the carboxyl terminus of thioredoxin and for the enterokinase cleavage site . as shown , ec2 is fused in frame with : thioredoxin through the enterokinase site which can be exploited to remove thioredoxin from the fusion protein . the fragment coding for ec2 was pcr - amplified from the plasmid pcdm8 / p3 using the following oligodeoxynucleotides . 5 ′ cccc aagctt tca cag ctt ccc gga gaa gag gtc atc g3 ′ using standard cloning techniques ( sambrook et al ., 1989 ) the pcr product was double - digested with xhoi and hindiii , ligated to pthio - his c ( invitrogen ) digested with the same restriction enzymes , and transformed into top10 e . coli cells . after selection of the transformants by restriction enzyme analysis and dna sequencing of the plasmids , a correct construct coding for the expected thioredoxinenterokinase site - ec2 fusion protein was identified . glycerol batches of selected clones were stored to − 80 ° c . total protein extracts of the thioredoxin - ec2 expressing clone before and after iptg addition were subjected to sds - page to analyse protein expression . fig6 clearly shows the appearance of a protein band of the expected molecular mass ( 23 . 4 kda ) in the extract from the induced sample . the figure also shows the reactivity of the fusion protein with e2 . the top10 e . coli clone containing the pthio - his c - ec2 plasmid and a top10 clone containing the pthio - h is c plasmid devoid of insert were induced , soluble protein extracts were prepared from both clones and subjected to far western blot with e2 protein . for this blot , protein samples were brought to 1 × loading sample buffer ( lsb ) ( 5 % w / v sds , 10 % v / v glycerol , 62 . 5 mm tris - hcl , 0 . 05 % bromophenol blue ) using a 3 × lsb solution . the samples were run onto a 15 % polyacrylamide gel and transferred to a pvdf membrane ( immobilon - p , millipore ). the membrane was incubated for 30 min in blocking solution ( pbs , 10 % w / v non - fat dried milk , 0 . 05 % v / v tween 20 ). following an incubation of 15 hours at 4 ° c . with blocking solution containing 1 μg / ml of cho - e2 , the membranes were incubated for 2 hours with the 291a2 anti - e2 monoclonal antibody diluted 1 : 250 , and for 1 hour with a peroxidated goat antimouse ig antibody ( sigma ) diluted 1 : 2000 . three washing steps between all incubation steps were performed using blocking solution , which was also used to dilute the antibodies . after a final wash with pbs the membranes were incubated for 1 min with luminol ( ecl , amersham ) and exposed on hyper - film ( amersham ). as can be seen from these figures , a band corresponding to the molecular weight of thioredoxin - ec2 was visible in the lane where the soluble proteins from the pthio - h his c - ec2 were loaded . such a band was absent in the lane where the soluble proteins of the pthio - h is c clone were loaded . 1 ) osmotic shock of the cells , 2 ) protein precipitation with 30 % saturation ammonium sulphate , and 3 ) imac . after osmotic shock about 50 % of the fusion protein was released from the cells together with contaminant proteins . the ammonium sulphate precipitation resulted in a pellet which contained thioredoxin - ec2 devoid of the bulk of contaminant proteins . imac of the resuspended precipitate resulted in a fusion protein which was about 85 % pure as assessed by sds - page . with this procedure we purified 5 mg thioredoxin - ec2 from a liter of culture . this procedure is set out in detail below . the e . coli clone expressing thioredoxin - ec2 was inoculated in 500 ml lb medium containing 100 μg / ml ampicillin . at od 600 = 0 . 5 , 0 . 5 mm iptg was added to the culture and growth was continued at 37 ° c . for additional 3 . 5 hours . the culture was then centrifuged at 4000 × g for 10 min at 4 ° c ., the cell pellet was resuspended with 50 ml ice cold hypertonic solution ( 20 mm tris - hcl , 2 . 5 mm edta , 20 % sucrose , ph 8 ) and left on ice for 10 min . the resuspended cells were centrifuged again as above and the pellet was resuspended in hypotonic buffer ( 20 mm tris - hcl , 2 . 5 mm edta , ph 8 ) to osmotically shock the cells . after 20 min at 0 ° c . the suspension was centrifuged at 12 . 000 × g for 10 min at 4 ° c ., the supernatant was brought to 30 % nh 2 ( so 4 ) 2 using a room temperature saturated solution of the salt . the suspension was incubated overnight at 4 ° c . and then centrifuged at 10 . 000 × g for 10 min . the pellet was resuspended using 15 ml of 20 mm phosphate buffer , 500 mm nacl , ph 6 , clarified by centrifugation , and loaded on a 2 ml column of nickel activated chelating sepharose fast flow ( pharmacia ) equilibrated in the same buffer . after adsorption , the column was washed with 10 ml of the equilibrium buffer ( flow rate 0 . 5 ml / min ), and then the thioredoxin - ec2 was eluted using a 30 ml gradient 0 – 50 mm imidazole in 20 mm phosphate buffer , 500 mm nacl , ph 6 followed by an isocratic elution with 10 ml of 400 mm imidazole . 2 . 4 ml fractions were collected . the fractions containing the recombinant protein were pooled , dialysed against pbs , and stored to − 20 ° c . proteins were analysed by means of sds - page and protein content was assayed by the bradford method using bsa as a protein standard . fig8 represents the nucleotide and deduced amino acid sequence of the ec2 -( his ) 6 fragment cloned in pgex - kg as well as the upstream plasmid sequence coding for the carboxyl terminus of gst , the thrombin cleavage site , and a small glycine spacer . as shown , ec2 is fused in frame with gst through the thrombin site , which can be exploited to remove gst from the fusion protein . the glycine - rich spacer , located between thrombin site and ec2 , facilitates the cleavage of the fusion protein by thrombin ( guan , k . l . and dixon , j . e . ( 1991 ) anal . biochem . 192 , 262 – 267 ). the fragment coding for ec2 was pcr - amplified from the plasmid pcdm8 / p3 using the following oligodeoxynucleotides . 5 ′ caaaag gaattc ta ttt gtc aac aag gac cag atc gcc aag3 ′ the pcr product was digested with xhoi and hindiii , ligated to pgex - kg ( guan , k . l ., and dixon , j . e . ( 1991 ) anal . biochem . 192 , 262 – 267 ) digested with the same restriction enzymes , and transformed into top10 e . coli cells . after selection of the transformants by restriction enzyme analysis and nucleotide sequencing of the plasmids , a plasmid having the expected size of the insert was found to have also the correct ec2 -( his ) 6 sequence in frame with the upstream thrombin and gst coding sequence . the plasmid prepared from the selected top10 clone was then transformed into bl21 cells . glycerol batches of selected clones were stored to − 80 ° c . fig9 represents an sds - page of total proteins of the top10 e . coli clone which expresses gst - ec2 -( his ) 6 . this analysis clearly shows that in the extract of the induced sample a protein band with the expected molecular mass ( 39 kda ) was present . the corresponding far western blot clearly shows the e2 specifically reacts with the fusion protein . the gst - ec2 -( his ) 6 fusion protein was purified on a glutathione sepharose column and digested with thrombin ( fig1 ). after digestion , the ec2 -( his ) 6 moiety was further purified by two additional chromatographic steps consisting of a glutathione sepharose column to remove the gst fragment and imac chromatography . this procedure is detailed below . a single colony of an e . coli clone expressing the gst - ec2 fusion protein was inoculated in 10 ml lb , 100 μg / ml amp and cells were grown overnight at 37 ° c . the culture was then inoculated in 500 ml of medium and when od 600 = 0 . 5 was reached 0 . 5 mm iptg was added . after 3 . 5 hours the cells were harvested by centrifugation , resuspended with 9 ml pbs and disrupted with two passages at 18 . 000 psi using a french press ( slm aminco ). the lysate was centrifuged at 30 . 000 × g and the supernatant was loaded on a column of 1 ml of glutathione sepharose 4b ( pharmacia ) equilibrated in pbs . the column was washed with 10 ml pbs , and eluted with 4 ml of 50 mm tris - hcl , 10 mm reduced glutathione , ph 8 . the eluted proteins were dialysed against pbs and stored to − 20 ° c . 6 . 5 digestion of gst - ec2 -( his ) t with thrombin and purification of ec2 -( his ) 6 9 . 6 mg of protein recovered from the glutathione sepharose column were digested with 22 units of thrombin ( pharmacia ) for 8 hours at room temperature , then the enzyme was inactivated using 0 . 13 mm pmsf ( sigma ). the reaction mixture was then dialysed against pbs and loaded into 0 . 5 ml of gst - sepharose column equilibrated in pbs . the column was washed with 1 ml of pbs . the flow - through and the wash were pooled and loaded into 0 . 250 ml of nickel - activated chelating sepharose column . ec24 ( his ) 6 was recovered from the column eluting with 1 ml of 20 mm phosphate buffer , 500 mm nacl , 400 mm imidazole , ph 7 . 8 . a dialysis was then performed against pbs . the proteins containing the human , but not the mouse ec2 loop of cd81 , bound to e2 in western blot ( data not shown ) and inhibited binding of e2 to human cells ( fig1 ). the chimeric proteins were coated on polystyrene beads and incubated with an infectious plasma containing known amounts of viral rna molecules . after washing , the bead - associated virus was assessed by quantitative rt - pcr for the amount of bound hcv rna . this experiment was performed as set out below . polystyrene beads ( ¼ inch diameter ) ( pierce ) were coated overnight with purified ec2 recombinant protein in citrate buffer ph4 at room temperature . after saturation for one hour with 2 % bsa in 50 mm triscl ph 8 , 1 mm edta . 100 mm nacl ( ten ) buffer , each bead was incubated at 37 ° c . for 2 hours in 200 μl ten - diluted infectious chimp plasma containing 5 × 10 5 hcv rna molecules . for inhibition experiments , the ec2 - coated polystyrene beads were incubated with 10μg / ml of purified monoclonal antibodies for one hour at room temperature before incubation with the virus . each bead was washed 5 times with 15ml ten buffer in an automated washer ( abbot ) and viral rna was extracted using the viral extraction kit ( qiagen ). rna ( 8 ml ) was reverse - transcribed at 42 ° c . for 90 minutes in 20 ml buffer a ( perkin elmer taq man ) containing 100pmol of the hcv antisense primer cggttccgcagaccactatg ( seq id no : 9 ), 40 u rnasin ( promega ), 5 nmol dntps , 110 nmol mgc12 , iou m - murt ( bohennger ). cdna ( 20 ml ) was amplified using a perkinlelmer abi 7700 sequence detection system ( 45 cycles ) in 50 ml buffer a containing 100 pmol of the hcv sense primer tcttcacgcagaaagcgtcta ( seq id no : 10 ), 5 pmol of the fluorescent detection probe 5 ′( fam ) tgagtgtcgtgcagcctccagga ( tamra ) ( seq id no : 11 ) ( kindly provided by david slade , pharmacia and upjohn ), 15 nmol dntps . mgc1 2 and 1 . 25u taq gold ( perkin - elmer , foster city , ca ). all reactions were quantified using hcv ( genotype la ) infected plasma ( bdna titer of 30 meq / ml ) to generate a standard curve . sequence detector software from perkin - elmer has been previously described ( u . e . gibson , c . a . heid and p . m . williams , genome res . 6 . 995 ( 1996 )). as shown in fig1 , the molecules containing the human cd81 extracellular loop bound hcv in a concentration - dependent fashion , and pre - incubation of the chimeric proteins with anti - cd81 antibodies inhibited virus binding . furthermore , serum from chimpanzees which were protected from homologous challenge by vaccination with recombinant e1 / e2 envelope heterodimer ( q .- l . choo et al . proc . natl . acad . sci . usa 91 . 1294 ( 1994 )) completely inhibited hcv binding to bead - coated - cd81 , while serum from vaccinated and non - protected animals did not ( data not shown ). these data demonstrate that expression of human cd81 , and in particular its major extracellular loop are sufficient for binding not only e2 but also hcv particles . given the wide distribution of cd81 ( s . levy , s . c . todd and h . t . maecker , annu . rev . immunol . 16 , 89 ( 1998 ), these results imply that hcv binds and may be internalised by a variety of cells other than hepatocytes . indeed , hcv rna has been found in t and b lymphocytes and monocytes ( k . blight , r . r lesniewski , j . t . labrooy and e . j . gowans , hepatology 20 , 553 ( 1994 ); p . bouffard et al ., j . infect . dis . 166 , 1276 ( 1992 ); zignego et al ., j . hepatol . 15 , 382 ( 1992 )). whether virus binding is followed by entry and infection in all cell types is not clear because of the lack of an efficient hcv culture system in vitro . it may well be that cd81 is an hcv attachment receptor and that additional factors are required for viral fusion or infectivity . cd81 participates in different molecular complexes on different cell types , a fact that may influence its capacity to serve as a receptor for hcv infection or to deliver regulatory signals to target cells . for instance , it associates with integrins on epithelial and hematopoietic cells ( f . berditchevski , m . zutter and m . e . hemler , mol . biol . cell 7 , 193 ( 1996 ); b . a . mannion , f . berditchevski , s .- k . kraeft , l . b . chen and m . e . hemler , j . immunol . 157 , 2039 ( 1996 )), whereas it is part of a signaling complex containing cd21 , cd19 and leu13 on b cells ( l . e . bradbury , g . s . kansas , s . levy , r . l . evans and t . f . tedder . j . immunol . 149 , 2841 ( 1991 )). this complex has been shown to facilitate antigen specific stimulation by lowering the activation threshold of b cells ( d . t . fearon and r . h . carter , annu . rev . immunol . 13 , 127 ( 1995 )). it is worth noting that hcv appears to use a molecule that is part of the same complex containing the ebv receptor ( cd21 ) ( n . r . cooper , m . d . moore and g . r . nemerow , annu . rev . immunol . 6 , 85 ( 1988 )), and the ability of ebv to activate and immortalise b lymphocytes is well documented . the following constructs were designed and made in order to generate mice transgenic for human cd81 . 1 . addition of splicing and polyadenylation signals of rabbit beta - globin gene to the human cd81 cdna fragment the human cd81 cdna fragment from the pcdm8 / p3 clone was transferred into a pbluescript ks ii (+) vector ( stratagene ) and was then inserted into the pspp plasmid ( derived from bmgsc expression vector , a kind gift from dr . karasuyama , basel institute for immunology ) between two fragments , one containing the second intron and the other containing the polyadenylation signal of the rabbit beta - globin gene ( position 902 – 1547 and 1543 – 2081 , respectively , genbank accession no . m12603 ) ( psr1p in fig1 ). the resulting recombinant dna fragment was excised from the pbluescript ksii (+) vector ( stratagene ) by sali ( at 5 ′ end ) and bamhi ( at 3 ′ end ). the sali - bamhi fragment of the psrip insert was inserted into the compatible restriction sites of pcagmcs , a modified plasmid of pcaggs ( a kind gift from dr . j . miyazaki at osaka university , japan , under restricted permission ), which contains chicken beta - actin promoter and human cytomegalovirus enhancer ( niwa , h . et al ., gene 108 , p193 ( 1991 ). ( pcagsr1pp in fig1 ). the 3 . 8 kb ecori - bamhi fragment was submitted to zygote injection . the sali site of psr1p was converted to a bamhi site by bamhi linker ligation after blunt - end formation with klenow fragment of e . coli dna polymerase 1 . this bamhi fragment was inserted into the bamhi site of the alb e / p plasmid , carrying the mouse albumin promoter and enhancer ( pinkert , c . a . et al ., genes dev . 1 , p268 ( 1987 ) ( received from dr . f . chisari , scripps research institute . la jolla , san diego ). ( paibsrip in fig1 ) the 4 . 5 kb noti - ecorv fragment was submitted to zygote injection . 4 . creation of a transgene for b lymphocyte - specific expression of human cd81 700 bp bamhi fragment of the mouse immunoglobulin heavy chain enhancer ( a kind gift from dr . a . kudo , basel institute for immunology ) and 2 . 3 kb xbai - saci fragment of the mouse kappa light chain promoter was subcloned into a pbluescript ksii (+) vector . the saci site was converted to a hindiii site by hindiii linker ligation described above . the bamhi site of pcagsr1p was first converted to noti site . then the promoter region of the modified pcagsr1p construct was removed by ecori - hindiii restriction digestion and replaced with the immunoglobulin promoter - enhancer fragment . ( pehkpsr1p in fig1 ) the 5 . 2 kb ecori - bamhi fragment was submitted to zygote injection . together , our data indicate that cd81 is an attachment receptor for hcv and may provide new insight into the mechanisms of hcv infection pathogenesis . since cd81 associates with an activation complex on the surface of b cells the present finding may explain the pathogenesis of hcv associated cryoglobulinemia even if there is no viral replication in b cells . moreover , the identification of the interaction between hcv and cd81 may help in mapping conserved neutralising epitopes on the virus envelope which should be important to develop effective vaccines and to provide a decoy receptor for viral neutralisation .
the present invention relates to the use of cd81 protein and polynucleic acid in the therapy and diagnosis of hepatitis c and pharmaceutical compositions , animal models and diagnostic kits for such purposes .