From www.bloodjournal.org by guest on October 15, 2014. For personal use only. 1994 84: 1968-1974 Production and nucleotide sequence of an inhibitory human IgM autoantibody directed against platelet glycoprotein Ia/IIa H Deckmyn, J Zhang, E Van Houtte and J Vermylen Updated information and services can be found at: http://www.bloodjournal.org/content/84/6/1968.full.html Articles on similar topics can be found in the following Blood collections Information about reproducing this article in parts or in its entirety may be found online at: http://www.bloodjournal.org/site/misc/rights.xhtml#repub_requests Information about ordering reprints may be found online at: http://www.bloodjournal.org/site/misc/rights.xhtml#reprints Information about subscriptions and ASH membership may be found online at: http://www.bloodjournal.org/site/subscriptions/index.xhtml Blood (print ISSN 0006-4971, online ISSN 1528-0020), is published weekly by the American Society of Hematology, 2021 L St, NW, Suite 900, Washington DC 20036. Copyright 2011 by The American Society of Hematology; all rights reserved. From www.bloodjournal.org by guest on October 15, 2014. For personal use only. Production and Nucleotide Sequence of an Inhibitory Human IgM Autoantibody Directed Against Platelet Glycoprotein Ia/IIa By H. Deckmyn, J. Zhang, E. Van Houtte, and J. Vermylen Human B-cell lines were derived by limiting dilutions of Epstein-Barr virus (EBV) transformed peripheral B cells from a patient with an autoantibody against glycoprotein (GP)la/ Ila, and manifesting defective collagen-induced platelet aggregation and a bleeding problem. Antibody-producing clones were selected for their reactivity with wholeplatelets or with affinity-purified GPlallla by enzyme-linked immunosorbent assay (ELISA). One of these cell lines, selected for further evaluation, produced an IgM (E&) that interfered with plateletaggregation responses. Polymerase chain reaction (PCR) amplifications with two different sets of primers specific forhuman K-chains resulted in therescue ofa unique and identical sequence. The same was true for the p-chain, from which it was concluded that the cell line was mono- clonal. Further analysis showed that the K variable domain sequence is similar to the germline gene A30, to 2E7,an anti-GPllb human autoantibody, and to HF2-1/17, a systemic lupus erythematosus (SLE)-associated broad-specificity human autoantibody. Thus, the specificityofour antibody, E&, appears to bedetermined by the p-chain, the sequence of which is encoded by a Vnlll gene segment strongly homologous to the germline gene DP-77, by a D gene that is not homologous to any of the germline D genes reported to date, and by JH4gene segment that is germline. All four mutations versusDP-77 are in CDRs, and result in amino acid substitutions, which implies that E& may have been derived from an antigen-driven response. 0 1994 by The American Societyof Hematology. T autoantibody specificity. Furthermore, by comparing several autoantibodies of defined antigen specificity, the contribution of individual segments of the variable regions to the identified specificity of the autoantibodies may be determined. HE PLATELET glycoprotein (GP)Ia/IIa complex is a member of the integrin family, where it is known as a2PIor VLA-2. In the platelet membrane, as in other cell membranes, itplaysacrucial role in the interactionwith collagen, oneof the more thrombogenic substances in a damaged blood vessel wall. Its role as a collagen receptor was first indicated by the finding that platelets lacking GPIa fail to react properly with collagen." Later, it was shown that GPIdIIa could be adsorbed specifically onto collagen in a Mg2+-dependent whereas liposomes incorpowith rated GPIdIIa bound to collagen.' Several monoclonal antibodiesreacting with GPIa"" or with GPIIa interfere, to a variable extent, with collagen-induced platelet aggregation. We havepreviously described apatientwithanacquired bleeding disorder, whose platelets specifically failed to react with collagen." Further studyofthispatient showed the presence of an IgG autoantibody against GPIa in her plasma, whichinhibited collagen-induced aggregation of normal platelets. To furthercharacterize thisantibody,its correspondingepitope,and itspotentialantithromboticeffects, we set off to generate a B-cell line that would produce this human anti-GPIa/IIa antibody. In addition, elucidation of its sequence was undertaken to provide better insight into the utilization of particular immunoglobulin germline genes and the contributionofindividualvariableregion segments to From the Center for Molecular and Vascular Biology, Leuven; and the Department of Immunology, DrH. Willems Institute, Diepenbeek, Belgium. Submitted October 11, 1993; accepted May 3, 1994. Supported by a grant from the Vluums Aktieprogramma Biotechnologie (VLAB/08I). J.V. is holder of the Dr J. Choay Chuir in Haemostasis Research. Address reprint requests to H. Deckmyn, PhD, Center for Molecular and Vascular Biology, University of Leuven, Campus Gasthuisberg, Herestraat 49, B-3000 Leuven, Belgium. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. section 1734 solely to indicate this jact. 0 1994 by The American Society of Hematology. 0006-4971/94/8406-0006$3.00/0 1968 MATERIALS ANDMETHODS Production of Ig-producing B-cell lines b.y Epstein-Barr virus of blood from the transformation. B-cell isolationfrom30mL patient with the anti-GPla autoantibody was performed essentially as described." The T-cell-depleted cellular fraction was incubated with Epstein-Barr virus (EBV)-containing supernatant from a culture of the marmoset cell line B95.8 for 2 hours at 37°C. The cells were then pelleted and seeded in microwells. Culture and cloning of the EBV-infected cells was performed as previously described." Briefly, cells were seeded in supplemented RPM1 1640 on a feeder cell layer ofIO4 irradiated (30 Gy) allogeneic peripheral blood mononuclear cells. Cells were incubated at 37°C in 5% CO2, with the culture medium being replaced weekly. The supernatant of each well was screened for specific antibody production by enzyme-linked immunosorbent assay (ELISA) (see below). Positive cultures were transferred to 24-well plates, and selected for further cloning at dilutions ranging from 1 to 50 cells per well. in the presence of IO4 irradiated feeder cells. Charucterizufion qf untibodies. Screening of cellsupernatants was performedwith ELISA procedures using microtiter plates coated with human platelets, purified GPIdIIa, or human plasminogen activator inhibitor-l (PAT-I) as a negative control. Human platelet-rich plasma (PRP) was prepared by differential centrifugation (10 minutes, 150g) of blood anticoagulated with 0.15 vol 25 mmolk trisodium citrate, 7 1 mmol/L citric acid, I 1 1 mmoll L dextrose, pH 4.5 (ACD). Gel-filtered platelets (GFP) were obtained from this PRP by chromatography on a 20 X 2.5 cm Sepharose 2B column (Pharmacia, Uppsala, Sweden), using5 mmol/L Hepes, 0.34 NaCI. 2.9 m m o l k Na2HP0,,12 mmollL NaHCO,,134mmol/L mmol/L KCI, and 10% ACD, pH 5.5.'' After two cycles of centrifugation (10 minutes, 800g) and resuspension, 125 X IO" platelets were disrupted by sonication. On removal of intact platelets during centrifugation at 2,OOOg for 10 minutes, membranes were collected by centrifugation at 50.0001: for I hour.Themembranepelletwasresuspended,solubilizedwith 10 mmol/L CHAPS (3-[3-~holamidopropyl) dimethylammonioJ- I-proSt Louis, MO), and first-passed pane sulfonate; Sigma Chemical CO, over a Sepharose column. The nonbound fraction was then applied to a CNBr-Sepharose column, to which the monoclonal anti-GPIa antibody CLB-IOGl I (a gift from Dr Van Mourik. Amsterdam, the Blood, Vol 84, No 6 (September 15). 1994: pp 1968-1974 From www.bloodjournal.org by guest on October 15, 2014. For personal use only. ANTI-GPIAAIAHUMAN ANTIBODY Table 1. Oligonucleotide PrimersUsed for PCR Amplification of EIGscDNA Primer Sequence Pst242 (backward) Pst243 (forward) Pst244 (forward) Pst245 (backward) Pst246 (backward) Psl247 (forward) Psr248 (forward) GGAAAAGGGITGGGGCGGATGC TITGGGAGGCAGCTCAGCAATC GAMATYGTGWTGACNCAGTCTCC GAMATYCAGWTGACNCAGTCTCC TGAAGACAGATGGTGCAGCCAC ACACTCTCCCCTGITGAAGCTC Sequence degeneracies are given in the single letter code: N = A/G/CF, R Netherlands) had been coupled, and was recycled over the column for 16 hours at 4°C; nonbound material was washed off with 10 ~ o V HEPES, L pH 7.4,20 MgClz, and 2 m m O V L CHAPS. Specifically adsorbed material was eluted with the same buffer containing 2 m o m KSCN, dialyzed, and concentrated. Purity of the material was checked by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and silver-staining (Biorad, Richmond, CA)," and by ELISA assays using monoclonal anti-GPIIbfiIIa13or anti-GPIa/IIa14 monoclonal antibodies. Only the latter gave a significant signal (A 492-nm >0.3 v <.07). PAL1 was purified as de~cribed.'~ Two hundred microliters of 150 to 200 X 103/pLGFP, 2 to 5 pg/ mL affinity-purified GPIa/IIa, 5 pg/mL PAI-1, or 5 pg/mL affinitypurified GPIIb/IIIa" was pipetted into the wells of microtiter plates, and coated overnight at 4°C. Unbound material was washed away, and remaining binding sites were blocked with 1% bovine serum albumin in phosphate-buffered saline. After washing, plates were incubated with 170-pL serial dilutions of cell supernatants or purified antibody for 1 to 2 hours at room temperature, washed, and further incubated for 1 hour with 170 pL of a 1:1,OOO dilution of goat antihuman IgG andlor a 1: 1,000 dilution of goat antihuman IgM (Sigma Chemicals), both coupled to horseradish peroxidase (HRP). After an additional washing step, bound antibody was stained with 160 pL of a solution containing 0.4 mg/mL 1,2-ortho-phenylenediamine (Fluka Chemie, Buchs, Switzerland) in 17 mmoVL citric acid, 65 mmovL NaZHP04,and 0.003% HZ02.The reaction was stopped with 50 pLof 4 m o m &Sod. Absorption was measured at 492 nm in an ELISA reader (EAR 400 AT, SCT-Labinstmments, Grodig, Austria). Platelet aggregations were performed either in suspensions of 200 pL 200,OOO/pL GFP in 5 mmoVL HEPES, 0.34 mmoUL NazHP04, 12 mmoVL NaHCO,, 134 mmoVL NaCl, 2.9 mmoVL KCI, I mmoVL MgCI2, 1 mmoVL CaClz, and 50 pL platelet-poor Table 2. EBV-Transformed B-Cell Lines and Clones Producing Antibodies Against GPla/lla Lines and Clones 2.7 2.5 2.3 A Patient IgG0.3 0.24 C5 MC4.100 2.2 MC4.100 E 3 F2 MC4.100 D6 MC4.100 0.2 MC F31.1 1.6 0.5 2 0.04 0.43 Negatives M Hv-FR1 5' end of MuCl 5' end ofMuC2 KV-FR1 K"-FR1 5' end of & 3' end of & AGGTGCARCTGSWGSAGTCKGG B C D E 0.08 3.0 5.4 11.0 3.1 0.53.4 1.5 0.2 1.4 0.5 0.3 5.0 7.1 8.0 ? 0.01 0.59 2 7.5 4.0 4.1 5.5 0.02 0.9 0.7 A 492-nm measurement obtained when patient IgG (30 pg/mL final concentration) or cell supernatant was tested in ELlSAs on purified GPlallla (A), platelets (B), or PAI-1 (C),and developed with a mixture of both goat antihuman IgM and IgG conjugated with HRP. For better comparison, ratios D = A/C, E = B/C are given. Results on negatives were obtained in a separate experiment. = A/G, Y = Cfl, S = G/C, W = M, K = G/T, M = A/C. plasma (from trisodium citrate anticoagulated blood), or in 200 pL citrated PRP. Aggregation at 37°C was triggered with either collagen (Hormon Chemie, Munchen, Germany) or adenosine diphosphate (ADP Sigma Chemicals) after a preincubation with antibodies for the indicated times at room temperature. Purification of anti-GPldlla antibody. ELISA-positive cell supernatants were passed over a CNBr-Sepharose (1 mL) column to which 1.05 mg affinity-purifiedGPIdIa had been coupled according to the manufacturer's instructions (Pharmacia). Specifically adsorbed material was eluted with 2 m o m KSCN anddialyzed against HEPES buffer. An IgM-producing clone (E3G6) was selected for further study. Patient IgG was purified from plasma using protein A Sepharose as described." Sequence of the variable regions of fhe K and pFd-chains of E3G6IgM. Polymerase chain reaction (PCR) amplification wasusedto rescue the entire K-chain and the p-Fd fragment (heavy-chain variable and first constant region) of the E3G6IgM,I6 thus facilitating eventual production of a recombinant E3G6-derivedFab fragment. RNAwas extracted from lo4 to lo5 E3G6 cells and mRNA was selected on oligo (dT)-cellulose. First-strand cDNA, synthetized using the forward primers Psr248 and Psr244 (Table l), and Moloney murine leukemia virus (MMLV) reverse transcriptase, was amplified with Taq DNA polymerase using the primer couples Psr245/246 and Psr248 (entire K-Chain, Psr245/246 is a mixture of two oligonucleotides), and Psf244 and Psr242 (p-Fd heavy-chain fragment) (Table l). The correctly sized K and p-Fd PCR products were isolated from agarose gel, and subsequently used as templates for amplification of the respective variable regions. This was done with the primer couples Pst246 + Psf247 and Psf242 + Psf243, respectively. The reamplifications were performed with 32P-labeledprimers such that the obtained radiolabeled variable regions could be sequenced with the chemical degradation method." RESULTS Following limiting dilutions of EBV-transformed peripheral B cells derived from a patient with an anti-GPIa autoantibody, five cell lines were selected, producing positive supernatants during ELISA screenings with immobilized platelets or GPIalIIa, but notwith PAI-1. The cell line, MC4100 E3, with the highest IalIIa versus PAI-1 and platelet versus PAI-1 ratio (Table 2 ) was further subcloned, resulting in six positives again subdivided in 10 subclones, which were checked for their reactivity in the ELISAs. Clones belonging to that group (G) showing the best relative reactivity versus GPIa/IIa and platelets were further expanded, and the clone that proliferated most extensively (G6) was selected for further characterization. This E3Gs cell line was kept in culture for several months, and the cell supernatant regularly tested for the presence of anti-GPIa/IIa antibody. From www.bloodjournal.org by guest on October 15, 2014. For personal use only. DECKMYN ET AL 1970 Table 3. Determination of Specificity and Subtype of E3G6-Produced Antibody lallla Sample W IgM IgG W W IgM 1 2 3 0.060 0.058 0.055 0.579 0.631 0.516 0.132 0.128 0.128 0.438 0.262 0.203 0.000 0.000 0.000 0.092 0.048 0.020 A 492 n m value when different samples of E3Gssupernatant were checked by ELISA on purified GPla/lla, platelets, or PAI-1, and developed with either goat antihuman IgG or IgM conjugated with HRP. The antibody produced by E3G6 was of the IgM subtype as substantiated from its detection by an antihuman IgM, but not by an antihuman IgG antibody, following its binding to the GPIa/IIa receptor (Table 3). Furthermore, anti-lightchain antisera identified a K light chain in the E3G6-IgM in a Western blot. The GPIa/IIa-specific antibody could be purifiedon a GPIa/IIa-Sepharose column. Flow-through and the 2-moVL KSCN elution peak were collected, dialyzed, and analyzed in an ELISA using purified GPIa/IIa or PAI-1, and goat anti-IgM-HRP for the detection (Table 4). GPIa/IIa-reactive material was specifically recovered in the KSCN fraction. Specificity of binding was checked in a direct comparison using affinity-purified GPIIb/IIIa13 versus GPIa/IIa inan ELISA setting. E3Gs binding to GPIa/IIa resulted in a 3.2fold higher signal thanthat obtained with GPIIblIIIa, the latter being comparable to the nonspecific binding that was observed when PAI-1 was used as coating material. Finally, the activity of the E3G6antibody on platelet aggregations was assessed on several occasions. A consistent inhibition of aggregations induced by collagen using GFP (Fig l), as well as PRP (Fig 2), was observed. On the contrary, aggregations induced by ADP were not influenced (Fig 1). PCR ampl$cation of the K - and p-Fd-chains of G6-IgM. PCR amplification of first-strand cDNA resulted for both Kand p-chains in fragments of the expected size. The reactions were performed with backward primers that match the 5‘ ends of the respective framework 1 regions, while the forward primers match with sequences in the constant domains. Sequence analysis yielded a unique sequence for each, implicating that the PCR products contained single distinct fragments. To ensure that the E3G6 cell line was truly monoclonal, additional PCR amplifications were performed using Table 4. Affinity Purification of E,G6 Supernatant Over a GPla/lla Column ELISA Protein Sample GPla/lla 0.032 Pre- 0.005 0.025 Flow-through Peak 0.473 0.030 0.057 alternative primer couples (a number of which were provided by Dr K. Thielemans, Hematology-Immunology Unit, Free University Brussels, Belgium). In the case of theheavy chain, a set of family-specific backward primers matching with leader sequences was used; only the use of the VHlll family-specific primer resulted in a PCR product, the sequence was identical to the one mentioned above. In addition, these experiments have identified the previously uncertain N-terminal sequence of the heavy chain as E-V-Q-L-VE-S-G-G-G. In the case of the light chain, one alternative backward primer, which like Pst245/246 matches with sequences in framework 1, was tried. The PCR product was sequenced and found to be identical to the one previously obtained. Sequence of E3G6 heavy- and light-chain variable regions. The nucleotide sequence of the E3G6heavy chain is shown in Fig 3A, along with the sequence of the germline gene DP-77,I8 a member of the VHlllfamily, with a nucleotide similarity of 98.5%. In addition, within the overlapping region, DP-77 is identical to the WHG16I9 germline gene, and to two fetal liver-derived heavy chains: the hse 54 3.2 mRNAZ0and the L3AloB-cell line.” Whereas no homology was found between the D region withany of the known germline sequences, the JH region on the other hand is identical with the JH4 germline gene. The nucleotide (Fig 4A) and amino acid sequence (Fig 4B) of the E3Gh K-chain isnearly identical tothe one of 2E7, a human autoantibody against the GPIIb subunit present in the GPIIb/IIIa or cuIIbp3 complex” and HFz-l/l7, abroadspecificity human autoantibody” that cross-reacts with ssDNA, cardiolipin, and an unidentified platelet antigen, most likely gly~olipid,”,’~ that is found in patients with systemic lupus erythematosus (SLE). Both the EIGh and the 2E7 light chains are most homologous tothe A30 germline gene,” with a nucleotide similarity of 99.6%. The E3G6 and 2E7 light chains differ from A30 by a two-base insertion. DISCUSSION PAIL1 0.1314 0.257 Eight milliters of supernatant was passed over the column; through and the 2 mol/L KSCN elution peak were collected, dialyzed, and analyzed in an ELISA using purified GPla/lla or PAI-1, and goat antihuman ISM-HRP for the detection. We report here on the identification of a monoclonal human IgM autoantibody against platelet GPIa/IIa by a B-cell line obtained following EBV transformation of B cells from a previously described patient.” This patient had an acquired bleeding disorder and defective platelet aggregation towards the flowcollagen, which was due to the presence of an autoantibody against GPIa in her plasma. Following repetitive subcloning, a monoclonal cell line From www.bloodjournal.org by guest on October 15, 2014. For personal use only. ANTI-GPIMIIA HUMAN ANTIBODY 1971 collagen 1 2 3 Fig 1. Platelet aggregation tracings of 150 pL GFP with 50 p L plasma preincubatedwith 50 p L medium (A) or EaGs cdl su15 20 pernatant (B) for 5 (l), (2). (3).or 30 minutes (4). after which aggregation was induced with 1 pg/mL collagenor 60 pmol/L ADP. was obtained. PCR amplifications using two different pairs of primers for both heavy and light chains yielded identical sequences. We have no indication that the original antibody from the patient was monoclonal, eg, no evidence for a paraprotein was obtained. Therefore, it is possible that the antibody-producing cell line that was isolated produces only one of the possible multiple anti-GPIa antibodies present originally. In addition, whereas the original plasma antibody was of the IgG class, the antibody identified here is an IgM. This was obvious from ELISA data and SDS-PAGE analysis. The IgM antibody is directed against platelet GPIdIa, because it bound to affinity-purified G P I d I a both in ELISA and during affinity chromatography on immobilized SepharoseGPIa/IIa, whereas binding topurified GPIIb/IIIa wasnot higher than the nonspecific binding to PAI-1. Furthermore, the anti-GPIa/IIa antibody E3G6 was functionally active, because, when preincubated with normal platelets in buffer or in plasma, it markedly inhibited platelet aggregation induced by collagen, but not by ADP. The antibody did not inhibit collagen-induced platelet shape change. All of these findings are in agreement with our earlier observations with the native antiserum" and, therefore, provide good evidence that the antibody sequence selected may also be produced in the patient. However, because the EBV- transformation technique does not allow differentiation between naturally expressed and nonexpressed antibodies, further work is needed to fully prove their identity. The human monoclonal antibody obtained nevertheless is inhibiting G P I d I a function, and sequence analysis was performed to possibly identify relevant sequences. Sequence comparison of PCR-amplified fragments indicates that the nucleotide sequence of the K-variable domain of &G6 is most homologous to the A30 germline gene,26 with a nucleotide similarity of 99.6%. The E3G6light chain differs from A30 by a two-base insertion, suggesting that A30 may be a pseudogene. Further comparison showed that the &G6 K-chain is also highly homologous to the 2E7 light chain,22which has the GG insertion identical to It is likely that the E3G6light chain is encoded by a new germline VKgene, yet to be identified. &G6 differs from 2E7 in codon 95 CCG CCT and codon 108 CGA -+ CCT (T. Kunicki, personal communication, April 1993), andonly the latter results in an amino acid substitution R + P. Despite this, we can conclude from both the nucleotide and amino acid sequence of the K-chain of E3G6 and 2E7 that the antibody light chains probably do not contribute to the specificity of the antibodies, unless they would be involved in targeting the antibodies to integrins. Furthermore, the amino acid sequence of the E3G6 K-chain + 3 Fig 2. Platelet aggregation tracings of PRP incubated for 30 minutes with 50 (l), l00 (2). or 150 (3) p L of buffer (A) or GPla/ Ila affinity-purified antibody from E.G. cell supernatants (B) and stimulated with 0.8 pg/mL collagen. From www.bloodjournal.org by guest on October 15, 2014. For personal use only. DECKMYN ET AL 1972 CDRl A E3G6 10 20 * 30 * 40 * 50 * * 60 70 * * 80 -* 90 t " GAM ATYCAGWTGACNCAGTCTCCATCCTCCCTGTCTGCATCTGTAGGAGACAGAGTCACCATCACTTGCCGGGCAAGTCAGGGCATTAGAAATGAT CDR2 110 100 120 130 140 * " L * E3G6TTA GGC TGG TATCAGCAGAAACCA GGG AAA GCC C C 1A A G ." ." ". ". ". ." "ZE7 "_ _" _ _ _ "_ 150 "_ "_ - * CGC CTGATCTATGCTGCATCCAGT _ " . _ ___ _ "_ 170 160 * "_ "_ _ _ _ "_ TTG CAAAGT "_ 180 GGG GTCCCATCAAGGTTCAGC ". - _ . _ _ _ _" _ - _ "_ _""_ "- COR3 * t 230 220 210 200 240 250 * * 270 260 * t E 3 t 6A G T GGA TCT GGG ACAGAATTCACTCTCACAATCAGCAGCCTGCAGCCTGAAGATTT1GCAACTTATTACTGTCTACAGCATAATACTTACCCG ." ". _ __-. . "." ". 2E7 ~ 3 0 .-. ___ "_ "_"_ ". ... ___ ___ ." "__" "_ "_ "_ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _" "_ _" "_ ___ ___ ___ ___ ___ 280 "* _ _ _ "- _ _ - "-"- - _ - ". - - - "_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ ". "T "T JK1 JK 290 -* 300 310 320 *- 330 * 340 * 350 * 360 * Fig 3. (A) Nucleotide sequenceof EtG. K-chain variable domain. TheVKsequence of €*G. is compared with the 2E7-anti-GPllb autoantibody and VK germline gene M O . Identical bases are represented by a dash. CDR-1, CDR-2, and CDR-3 regions are indicated. The EtGa and 2E7 JK genes are most homologous to the JK, gwmline gane, as depicted. (B) Comparison b.twem the deduced amino acid sequence of EsGsVK segments with those of 2E7, of HF2-1/17 (experimentally determined), and of the deduced gwmllne JK,-sequence. is nearly identical to that of HF2-1/17. HF2-1/17 is a broadspecificity human autoantibody that reacts with, for example, platelets and ssDNA, and for which the amino acid sequence has been determined directly by protein ~ e q u e n c i n g2E7, .~~ a human autoantibody directed against GPIIb, a member of another platelet glycoprotein complex GPIIblIIa, does not react with S S D N A .Furthermore, ~~ it is unlikely that 2E7, produced by a human-mouse heterohybridoma cell line generated from the fusion of splenocytes derived from a patient with immune thrombocytopenia, would cross-react with GPIa/IIa, because both complexes are on platelets and, therefore, characterization of the antigen would have yielded a double signal. Likewise, we did not obtain evidence for cross-reactivity of our antibody with GPIIbnIIa in an ELISA setting. Hence, despite the extremely high homology of their light chains, these antibodies have well-defined and different antigen specificities, which consequently are determined by their heavy-chain sequence. The heavy variable region of E3Gs is a member of the VHllrfamily, as evidenced by the sequence and by the finding that PCR amplification only was successful with aVHIIlfamily-specific primer. The E3G6 heavy chain has a 98.5% nucleotide similarity to the DP-77 germline gene.18 All four mutations are in CDRs, and all cause amino acid substitutions, resulting in a replacement to silent ratio of infinity, which implies that E3G6 may be derived from an antigen-driven re~ponse.~' The J H segment, on the other hand, is identical to the germline J,. The present findings seem to confirm earlier observations22,28,29 that autoantibody sequences are barely differentiated from the germline, potentially explaining why these rather immature antibodies are less able to differentiate between self- and nonself-antigens. Recently, Denomme et a130 reported on the production of human monoclonal antiplatelet autoantibodies derived from tonsillar lymphocytes from a nonthrombocytopenic donor fused to a lymphoblastoid cell. It is interesting to note that the antiplatelet antibodies obtained could be classified into two different and mutually exclusive groups. One group shows reactivity to a variety of platelet proteins, and the other to ssDNA and anionic phospholipids. Unfortunately, no sequence data on these an- From www.bloodjournal.org by guest on October 15, 2014. For personal use only. ANTI-GPWIIA HUMAN ANTIBODY 1973 COR1 10 A 40 * E3G6 GAG GTG CAG CTGGTC Dp-77 ___ _ __ __ _ _ 20 30 * 70 * ___ ___ ___ ___ 90 80 60 t- t _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ GCA ___ _ _ _ _ _ _ _ _ _ _ _ - SAG TCT GGC GGA CCC CTCGTCAACCCT ___ ___ 50 ___ CCC CCG TCCCTC ACA CTCTCC TCT CCCTCT CCA T T C ACC TTCACT ACC TAT --- - _ _ _-- -C- - - - COR2 110 100 -*- 120 130 * * 140 150 160 -* E3Gg AGC ATG AAC TGG GTC CGC CAG GCT CCA CGC AAC GGG CTC GAG TGG GTCTCATCCATTAGTCCTACTACTAGTTACATATACTAC DP-77 AC- -G- ___ ___ ___ ___ ___ ___ ___ ___ ___ __ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ 200 210 E3G6 AAG GGC CGA TTC ACC ATCTCC Dp-77 _ _ _ _____ 220 * - t ___ ___ 230 240 AGA GAC AACGCCAACAACTCACTCTATCTGCAAATGAAC ___ ___ ___ ___ _____ _______ 250 * t ___ ___ 310290 * E3Gg DP-77 - GCG AGA GAT ___ _._ 190 *- CCA GAC TCACTG 270 * 280 * _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ___ _ _ _ _ _ _ _ _ _ ___ _ _ _ _ _ _ ___ _ _ _ ___ AGC CTG AGA GCC GAG CACACCCCTCTC TAT TACTCT JH 300 GGG GCG TTTTTT 180 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ______ _ _ _ _ _ _ _ _ _ 260 * D 320 170 360 *- AGC ACT GGC TGC GGC CTT GAC TACTCG ___ ___ JHL ___ CGC CAG GGA ACCCTCCTCACCCTCTCCTCA ___ --A ___ ___ ___ _____ ___ ___ ___ Fig4. (A) Nucleotide sequence comparison of the E,Gs-VH chainand the germline VH gene of DP-77,and the germline JH-4. (---l Base (B)Deduced amino acid sequence of the EsGsand 2E7 VHgene identity with the EIGs sequence. CDR-1, CDR-P, D, and JH regions are indicated. segments comparedwith the experimentally determined protein sequence of HF2-1/17, the deduced sequence of the DP-77 V, segment, and the Jw germline segment. tibodies are available at present, excluding a further comparison. In conclusion, by transforming B cells from a patient with an acquired autoimmune bleeding disorder due to an inhibitory autoantibody against GPIa, a monoclonal cell line was selected that produced an inhibitory IgM reacting with the G P I d I a complex. This antibody shares a K-chain with at least two other human autoantibodies, and therefore the pchain must be responsible for antigen-recognition specificity. ACKNOWLEDGMENT The authors thank P. Stanssens and Y. 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