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From www.bloodjournal.org by guest on June 15, 2017. For personal use only. Polymorphism of Human Platelet Membrane Glycoprotein IIb Associated With the Bak"/Bakb Alloantigen System By Suzanne Lyman, Richard H. Aster, Gian P. Visentin, and Peter J. Newman The human Bak"/Bakb alloantigen system has been implicated in the pathogenesis of post-transfusion purpura and neonatal alloimmune thrombocytopenic purpura. Human alloantisera specific for either the Bak' or Bakb allele have been shown t o react exclusively with the heavy chain of membrane glycoprotein (GP) Ilb. To investigate the structure of the Bak epitopes, w e used the polymerase chain reaction (PCR) t o amplify GPllb cDNA synthesized from platelet RNA samples prepared from individuals of known serologic phenotype. Subsequent DNA sequence analysis of amplified GPllb cDNAs derived from one Bak' homozygous individual and one Bakb homozygous individual revealed a single nucleotide base difference near the 3'end of the mRNA encoding the GPllb hefivy chain. Short 13 base allele-specific oligonucleotides (ASO) containing the putative phenotype-specific base in the middle were then synthesized, end-labeled with digoxigenin-1 1-dUTP using terminal transferase, and used as probes in subsequent dot-blot hybridization experiments. Platelet RNA was prepared from a panel made up of four Bak"", three BakbIb,and t w o BakaIbindividuals, and the mRNA encoding GPllb was amplified using PCR and spotted onto nylon membranes. AS0 hybridization showed that the nucleotide base difference identified above segregated with Bak phenotype in all nine individuals examined ( P = .002).The base pair substitution results in an amino acid polymorphism at residue 843 of the mature heavy chain. The Bak" form of GPllb encodes an isoleucine at this position, whereas the Bakb allele contains a serine. Identification of the polymorphism associated with this clinically important alloantigen system should permit new therapeutic and diagnostic approaches for treating and managing patients with alloimmune thrombocytopenic disorders. 0 1990by The American Society of Hematology. P systems," and these predictions appear to have been borne out by more recent physical mapping studies using pulse-field gel electrophoresisz0 Recent developments have now made it possible to examine the molecular basis of the Bak"/Bakb alloantigen system. First, the nucleotide sequence of GPIIb has been fully determined." Subsequently, it was reported that the polymerase chain reaction (PCR) could be adapted for the amplification and subsequent analysis of platelet-specific mRNA sequences from single individuals.22 We have recently used this approach to elucidate the molecular nature of the PIA' and PIA' p ~ l y m o r p h i s m .In ~ ~this report, we provide evidence that a single base difference at nucleotide position 2622 of GPIIb mRNA is associated with the Baka/Bakballoantigen system. This base change results in an isoleucine/serine polymorphism at amino acid 843 near the C-terminus of the GPIIb heavy chain. LATELET MEMBRANE glycoproteins bear serologically defined determinants that can elicit an alloimmune response leading to platelet destruction in such clinical settings as post-transfusion purpura (PTP) and neonatal alloimmune thrombocytopenia (NATP).' These well-characterized syndromes are associated with the development of platelet-reactive alloantibodies as a result of platelet incompatibility in blood transfusion recipients (PTP) and in maternal sensitization to paternal antigens on fetal platelets (NATP).' While the incidence of PTP is not precisely known, the incidence of NATP has been estimated to be as high as 1 in 2,000 live birth^,^ and delivery can result in significant morbidity and mortality to the n e ~ b o r n . ~ ~ ' Nine different platelet alloantigen systems have thus far been described. The PlA'/PlA2antigen system, located on membrane glycoprotein (GP) IIIa, is perhaps the most important clinically, accounting for a majority of reported cases of PTP and NATP. However, other antigen systems have clearly been implicated in these two immune disorders as well. These include, in order of clinical significance, the Bak"/Bakb system that has been localized to the heavy chain of GPIIb,6.7the recently described Bra/Brb alloantigen system that has been localized to the GPIa/IIa c0mplex,8.~the Pen," alternatively known as Yuk," alloantigen system, located on GPIIIa," and the PIE antigen, which has been localized to the heavy chain of G P 1b.l3 The Bak antigen system was first described in 1980 by von dem Borne et a1 when they reported a new specificity present in a maternal alloantibody in a case of NATP.6 Subsequently, an antibody termed anti-Leka was described by Boizard and Wautier,I4 and the antigenic determinant for this antibody was localized to 76 and 60 Kd fragments of the heavy chain of GPIIb." Shortly thereafter, the Bak" antigen was also localized to GPIIb,' and the Baka and Lek" antigens were shown to be identical.l6-" The first characterization of the allele for Bak", Bakb, was published only recently," and it too was localized to the heavy chain of GPIIb. Interestingly, Letellier et a1 predicted, on the basis of family studies, a close genetic linkage between the P I A and Bak alloantigen Blood, Vol 75, No 12 (June 15). 1990: pp 2343-2348 MATERIALS AND METHODS Platelet PCR. Platelet RNA from a panel of nine unrelated normal volunteers, including four BakaIa,three BakbIb,and two Barib individuals, was prepared according to the procedure of Chomczynski and SacchiZ4except that the final RNA pellet was From The Blood Center of Southeastern Wisconsin, Milwaukee, WI. Submitted November 29,1989; accepted February 23,1990. Supported by Grants No. HL-38166 (to P.J.N.) and HL-I 3629 (to R.H.A.)from the National Institutes of Health. G.P.V. is the recipient of a Scholarship in Biomedicine from the Lynde and Harry Bradley Foundation. Address reprint requests to Peter J. Newman. PhD, The Blood Center of Southeastern Wisconsin, I701 W Wisconsin Ave. Milwaukee, WI 53233. 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 fact. 0 1990 by The American Society of Hematology. 0006-4971/90/7512-0013$3.00/0 2343 From www.bloodjournal.org by guest on June 15, 2017. For personal use only. 2344 subjected to one additional phenol/chloroform extraction and ethanol precipitation necessary to achieve reproducible gene amplification of platelet cDNA. Bak" and Bakb phenotype was assessed using well-characterized human alloantisera in a standard antigen capture a s ~ a y . ' ~The . ' ~ C-terminal end of the GPIIb heavy and light chain message from base 1988 to 2821 was selected for sequence analysis and comparison, and two 24-base oligonucleotide primers flanking 833 base pairs of this region were synthesized on a Gene Assembler (Pharmacia Fine Chemicals, Piscataway, NJ). The antisense primer (5'-CAGGAAGGCCAGCACCGTGACCATG-3')from base 2821 to 2797 was used to prime the synthesis of cDNA from platelet RNA, as previously d e ~ c r i b e d . ~The ~ , ~second , strand was generated by the sense primer (5'-GACCTGCAGATGGACGCAGCCAAC3') from base 1988 to 2011 during the first round of PCR. Amplification was carried out in a DNA Thermal Cycler (PerkinElmer Cetus, Norwalk, CT) programmed to permit denaturation at 94°C for 1l/2 minutes, annealing at 50°C for 1]/2 minutes, and chain extension at 72°C for 3 minutes. The reaction was allowed to proceed for 30 cycles, followed by a final incubation at 72°C for 7 minutes to allow completion of strand synthesis. Analysis of PCR products. PCR samples were analyzed on 1.8% Seakem GTG agarose gels (FMC BioProducts, Rockland, ME), and the appropriate bands were excised and recovered by electroelution. The plasmid vector pCEM-SZf (Promega Biotech, Madison, WI) was prepared for ligation by restriction digestion with EcoRV (New England Biolabs, Beverly, MA) to yield blunt ends, and ligated to purified amplification products, followed by transformation into Escherichia coli strain NM522 competent cells (Stratagene Cloning Systems, San Diego, CA). Two clones representing each Bak homozygous phenotype were selected for direct sequence analysis by the dideoxy sequencing method using T7 DNA polymerase (USB, Cleveland, OH). Four 24 to 25 base oligonucleotides corresponding to internal GPIIb cDNA sequences were synthesized and used as sequencing primers. Allele-specific hybridization. Amplified cDNA from four individuals with Bak"/" phenotype, three with BakbIb,and two heterozygous for Bak was subjected to hybridization with 13-base allelespecific oligonucleotides (ASO). Probe A (TGCCCATCCCCAG) corresponds to the published sequence from base 2616 to 2628, and probe B (TGCCCAGCCCCAG) differs only in the middle base, a G instead of a T, and corresponds to a single base difference observed in the region sequenced. The oligos (200 ng) were end-labeled with digoxigenin-11-dUTP (Boehringer Mannheim, Indianapolis, IN) in 25 pL 100 mmol/L potassium cacodylate, 2 mmol/L CoCl,, 0.2 mmol/L DTT, pH 7.2 containing 1 U terminal transferase (Boehringer Mannheim), and the probes were used for hybridization without purification. Amplified DNA was used directly for blotting, or, in some cases, appropriate bands were recovered from agarose gels using Gene Clean (Bio 101, La Jolla, CA). The samples were eluted in 20 pL water, diluted 1/10,000, and 10 pL was used for reamplification using the same oligos and PCR conditions. Amplified or reamplified DNA was denatured in 0.25 N NaOH, 1.5 mol/L NaCl at room temperature for 5 minutes, followed by neutralization in 2 mol/L NaCI, 1.3 mol/L Tris, pH 7.4 at room temperature for 15 minutes. Each sample was divided between two wells of a Minifold dot blot apparatus (Schleicher and Schuell, Keene, NH) and transferred to Magnagraph nylon membrane (MSI, Westboro, MA) by vacuum suction. The filter was exposed to UV irradiation (Fotodyne, New Berlin, WI) for 5 minutes, followed by baking at 8OoC for 15 minutes. The membrane was prehybridized in 5x Denhardt's, 5 x standard sodium citrate (SSC), 5 mmol/L EDTA, I O mmol/L Na2HP04,pH 7.0 at 68°C for 1 hour and then cut into two strips that were hybridized to either probe A or probe B in 4 mL l o x Denhardt's, 5 x SSC, 5 mmol/L EDTA, 7% sodium dodecyl sulfate (SDS), SOpg/mL salmon sperm DNA, 20 mmol/L Na2HP04, LYMAN ET AL pH 7.0 at 42°C overnight. The filters were washed in two changes of 6 x SSC for 30 minutes each at room temperature, followed by two changes of 3 mol/L tetramethylammoniumchloride (Aldrich Chemical, Milwaukee, WI), 2 mmol/L EDTA, 1% SDS, 50 mmol/L Tris, pH 8.0 for 20 minutes each at 42°C. Positive hybridizations were visualized using the Genius kit (Boehringer Mannheim, Indianapolis, IN), which uses an alkaline phosphatase-conjugated antidigoxigenin antibody. Flow cytometric analysis. Platelets were washed in Ringer's citrate dextrose buffer (RCD:IO8 mmol/L NaCI, 38 mmol/L KCI, 1.7 mmol/L NaHCO,, 21.2 mmol/L Na citrate, 27.8 mmol/L dextrose, 1.1 mmol/L MgCI,, 2 mmol/L EDTA, and 50 ng/mL PGE,, pH 6.5). Approximately 5 x lo7 cells were resuspended in either 200 pL anti-Bakb(provided by the Platelet Antibody Laboratory of the Blood Center of Southeastern Wisconsin, Milwaukee, WI) antisera diluted 1:lO or 1:25, or the anti-GPIIb murine monoclonal antibody PMI-1 (provided by Dr Mark Ginsberg, Research Institute of Scripps Clinic, La Jolla, CA) diluted to 1 to 5 pg/mL in RCD buffer, and incubated for 1 hour at room temperature. After three washes, Bak-labeled cells were incubated with affinity purified F(ab'), fragments of fluorescein isothiocyanate (FITC)-conjugated goat anti-human IgG (Jackson Immunoresearch, West Grove, PA), and PMI-1-labeled cells were incubated with affinitypurified F(ab')2 fragments of R-phycoerythrin (rPH)conjugated goat anti-mouse IgG (Tago Immunological, Burlingame, CA) for 30 minutes at room temperature. Labeled cells were washed three times and subjected to flow analysis. To assess potential competition between PMI-1 and anti-Bakbantibodies, platelets were incubated with anti-Bakbat a 1:25 dilution (95% saturation) in the presence of PMI-1 at 5 pg/mL, which was in excess of saturation. The converse experiment was also done, in which platelets were incubated with PMI-1 at 1 pg/mL (90% of saturation) in the presence of anti-Bakb diluted to l:lO, which was in excess of saturation. Preliminary studies were done to show that FITC-goatanti-human IgG did not crossreact with mouse IgG, and rPH-goatanti-mouse IgG did not crossreact with human IgG (data not shown). The samples were analyzed on a FACStarp'"' Fluorescence Activated Cell Sorter (Becton Dickinson, Mountain View, CA) using an argon laser source at 488 nm. Fluorescein and rPhycoerythrin were detected through a 530+ / - 30 nm band-pass filter, and 10,000events were acquired per sample. RESULTS Amplijcation and analysis of the C-terminal region of GPIIb platelet mRNA. T o compare the nucleotide sequence of GPIIb m R N A derived from one Bak" and one Bakb homozygous individual, four different pairs of oligonucleotide primers were designed such t h a t overlapping segments of the molecule could be sequentially amplified a n d their sequence determined. Nucleotide sequence analysis of a n 833 base pair region positioned near the 3' end of G P I I b c D N A (Fig 1) revealed a single nucleotide difference a t base 2622 of t h e GPIIb m R N A (Fig 2). T h e Bak"'" individual has a T a t this position, whereas t h e Bakb/bindividual has a G. This results in t h e substitution of a serine for a n isoleucine at amino acid residue 843 of t h e G P I I b heavy chain. Correlation of Ne,,, t--* Ser,,, polymorphism with Bak allotype. In order t o determine whether t h e T c* G polymorphism was associated with Bak phenotype, as opposed t o a Taq polymerase error or a naturally occurring polymorphism unrelated to Bak phenotype, platelet R N A was prepared from a total of nine unrelated individuals of known Bak phenotype, and then amplified using P C R to From www.bloodjournal.org by guest on June 15, 2017. For personal use only. B u ALLOANTIGEN SYSTEM 2346 Fig 1. Amplifiatkr, .nrt.gY 8nd 8M)y.k of th. Gt.nnhul r.gkn of the pbtdet OPllb mRNA md.cule. The anthomo PCR ptimer was positionedwithin the 8equmceencodingthe N-terminaI end of the l i h t chain. and the aen8e primer was positioned such that the total region nmpli6ed -8 833 bp. Thi8 interval emompun8 exons spanning more than 3.400 base8 of genomic DNA.” and thus could only repre8ent GPllb mRNA. yield the same 833 bp product. We then performed allelespecific hybridization analysis, using two 13-base probes containing the putative phenotype-specific base in the middle, toscreen the amplified cDNAs. Allele-specificoligonucleotides will hybridize to the exact complementary sequence; however. a single base mismatch will prevent annealing of the probe at a specified temperature that is dependent on the length of the probe.I6As shown in Fig 3, probe A (containing a T in the middle) was positive with the four Bak”’ homozygous individuals, and probe B (containing a G in the middle) was positive with three BakbIbindividuals, whereas both oligonucleotides hybridized with amplified cDNA derived from the two heterozygous individuals. Thus, all nine individuals examined by DNA typing. representing the three possible Bak phenotypes, yielded the genotypes expected (P = .002) Based upon these results, wc conclude that the observed base change is directly associated with the Bak’/ Bakballoantigen system. Physical relationship of the Bok and PMI-I epitopes. Comparison of the location of the Bak polymorphism to the amino acid sequence of GPllb (Fig 4) revealed that this B A K ~ T G C A T amino acid is just outside of a 17-residue sequence that contains the epitope for the anti-GPllb murine monoclonal antibody, PMI-I.” To explore the physical relationship between these two epitopes, a series of competitive binding studies were done. In one set of experiments, PMI-I was present in limiting concentrations (approximately 904% of saturation). while anti-Bakb was in excess. The converse experiments. in which anti-Bakb was present in limiting amounts (95% saturation) and PMI-Iwas present in excess. were also done. Platelets containing one or both sets of antibodies in various ratios were analyzed by flow cytometry, and the results are shown in Fig 5. As can be seen, no competition between the two antibodies was observed, despite their apparent physical proximity. DISCUSSION The purpose of the present study was to determine the molecular basis for the Bak’/Bakb polymorphism of platelet membrane GPllb. Based on the reported nucleotide sequence of GPllb derived from HEL cells, we designed oligonucleotide primers and used the PCR to amplify an 833 base pair C-terminal region of GPllb from both a Bak’ homozygous and a Bakb homozygous individual. The sequence of the Bak’ individual proved to be identical with the published sequence of GPllb, except for a single nucleotide difference at base 2622 in the sequence from the Bakb individual. The substitution of a G for a T at this position resulted in an isoleucine * serine polymorphism at amino acid 843 of the GPllb heavy chain. GPllb is composed of a 125 Kd heavy chain that is disulfide-linked to a 23 Kd light chain.B Earlier studies of the biosynthesis and processing of GPIlbn”’ provide evidence that a single mRNA transcript is used to synthesize a precursor of GPllb that is cleaved post-translationally to yield the two disulfide-linked chains, and these studies were substantiated by the recent molecular cloning of GPllb BAK M> T G C A T GJ - - c ‘ El CJ “PI propM Fig 2. DNA seqwnw aruly.h of nmplHwd OPNb @NA from Bok.” individual and a Bok”’ individual. The 833 bp PCR prodwt.wore 8ubekmdinto +EM-621 and sequenced usingnn antismso digonucl.otidethat extended 6‘ to 3‘ from base 2779 to 2766. The ..gnnntof the a u t o r d i r a p h shown here includes the sequence from be808 2616 to 2626. The sequ(~~c. from the Bok’ indMdual is Mentical to the previowly publi8hed sequence for GPllb. having a G at base 2622. This base h chenged to a T in the Bokb individual. rowking in an i8olwcine serine polymorphism. ++ From www.bloodjournal.org by guest on June 15, 2017. For personal use only. LYMAN ET AL 2346 PHENOTYPE Bak* Bakm Bak* of Bok phenotype by eIl.k-.p.ci(ic hybridimtion. Platelet RNA war isolated from nino IndMdwh with known Bok Fig 3. AMphenotype. The C-terminal region of aPllb from base 1988 to 2821 war reverse transcribed and emplitied by PCR. Aliquot. of each PCR reaction (4pL)were blottedonto e nylon fikor in duplicate, end the fikor was cut into two parellel strips and hybridized with &her probe A (top) or probe B (bottom). The serdogically determined Bak phenotypes of the individwlr screened are indkated above the strips. cDNA.*' Hydropathicity analysis of the cDNA sequence indicates that GPllb is anchored to the platelet through a single transmembrane domain located within 20 amino acids of the C-terminus of the light chain. The studies reported here localize the amino acid difference associated with the Bak polymorphism near the C-terminus of the heavy chain within a proline-rich region. Further studies are needed to elucidate the exact nature of the epitope recognized by Bak alloantisera. Although it is most likely that these two polymorphic amino acids are responsible for directing the formation of the Bak antigenic determinants, differences in carbohydrate moieties could also play a role in antigenicity. Since the amino acid substitution in Bak involves a serine, it is possible that an 0-linked carbohydrate could be added to the Bakb molecule. Another possibility that must be considered is that the Ile Ser amino acid difference causes a conformational change on some other portion of the molecule that forms the actual epitope. Finally, our findings do not preclude the possibility of other polymorphisms in the GPllb gene that may be associated with Bak phenotype. It is of considerable interest that the Bak polymorphism is immediately adjacent to the 17-amino acid residue region containing the epitope recognized by the monoclonal antibody PMI-I." Functional studies using the PMI-I antibody - - Fig4. Amino.dd8sqwncopdymorphbma..odmdwiththo Bok./Bok' p l o t o h alhntigen system. Note that the i.d.ucino m i n o pdymorphism is located nmr the C-terminua of the GPllb heevv chain in an extremely prolino-rkh region. The peptide containing the .pitope for PMCl is immeddi.tely adjacent to the Bok polymorphk residue. The precise clmvaga site between the heavy and light chain has not beon experimentally determined, and the one indicated reprewnts a best estimate besed upon date obtained using anti-peptide entibody binding analysism and by compariaon with homologwr requences within the rat GPllb gena.n of antWm3 end M . 1 by Fig 6. Compotitko blndlq OMtwocdor fluoreaceme tiow qtomotry. Slmukar" Mnding of both antibodies war auossod by uring second antibodies conjugeted to red (anti-mouse) or green (anti-human) fluorophores. Top quadrent Binding of anti-BakbIgG in the presence of excess PMI-1. Note that the reletive mean fluor..c.me of neither antibody (number above the peak) is effected by the binding of the other. Bottom quadrant: Binding of PMI-1 in the prewncs of e x c e u anti-BakbIgG. From www.bloodjournal.org by guest on June 15, 2017. For personal use only. 2347 BAK ALLOANTIGEN SYSTEM have previously shown that this region may be involved in platelet adhesion to collagen.32The effect of anti-Bak alloantisera on platelet/collagen interactions has not been examined to date, nor have the possible consequences of anti-Bak antibodies on in vivo platelet function in alloimmunized patients been considered. In order to explore the possible relationship of these two epitopes, we did cross-blocking studies using PMI- 1 and anti-Bakb. Somewhat surprisingly, our data indicate that there is no competition for binding of these two antibodies. Secondary structure analysis of GPIIb33 indicates that the sequence KRDRRQ, located a t the C-terminal third of the peptide to which PMI-1 binds, is the second most likely antigenic site on this molecule. If this sequence serves as the epitope for PMI-1, then there would be 11 amino acid residues between this epitope and the likely Bak antigenic determinant. The proline-rich nature of this region and its predicted highly convoluted secondary structure may explain the co-occupation of adjacent sites by these two antibodies. In addition to its inhibition of platelet-collagen interactions, PMI- 1 has also been shown to bind preferentially to the GPIIb-IIIa complex after its occupation with either fibrinogen or the Arg-Gly- Asp tripeptide sequence; consequently, the PMI- 1 epitope has been referred to as a ligand-induced binding site, or LIBS.34Given the close association between the BAK and PMI-1 epitopes, it is interesting to note that anti-Bak" antibodies were found to bind to only 20,000 sites per platelet at ~aturation,'~ even though 40,000 GPIIb-IIIa complexes are surface exposed.36 It is tempting to speculate that the Bak alloantigen may represent another example of an occupancy-modulated region of the platelet fibrinogen receptor. Increasingly, molecular techniques are being used to define sequence variations responsible for inherited genetic disorders and naturally occurring polymorphisms. While two human platelet alloantigen systems, Bak and PIA,have now been examined at the molecular level, it will be important to delineate the molecular basis of additional platelet membrane polymorphisms in order to achieve a better understanding of platelet membrane glycoprotein fine structure responsible for generating an alloimmune response. Knowledge of the amino acids responsible for directing the formation of these polymorphic determinants may lead to the development of more refined immunodiagnostic assays, for example, allotype-specific monoclonal antisera. Our findings also provide an alternative to immunologic-based assays, as DNA typing using allele-specific oligonucleotide hybridization is able to discriminate between Bak"', and Bakb/b individuals with a high degree of precision and reliability. DNA-based techniques can readily be adapted to establish diagnostic tests in the transplant or transfusion setting, as well as cases requiring in utero diagnosis, and may offer several important advantages over present serologic methods of phenotyping that rely on a limited supply of alloantisera. REFERENCES 1. Kunicki TJ, Beardsley DS: The alloimmune thrombocytopenias: Neonatal alloimmune thrombocytopenic purpura and post-transfusion purpura. Prog Hemost Thromb 9:203, 1989 2. Aster RH: The immunologic thrombocytopenias, in Kunicki TJ, George JN (eds): Platelet Immunobiology, Philadelphia,PA, JB Lippincott, 1989, p 387 3. Blanchette NR, Aster RH, Pearson HA, Hiller MC: Alloimmune thrombocytopenia.Review from a neonatal intensive care unit. Curr Stud Hematol Blood Transfus 52:87, 1986 4. Okada N, Oda M, Sano T, Ito J, Shibata Y , Yamanaka M: Intracranial hemorrhagein utero due to fetomaternal Bak" incompatibility. Acta Haematol Japonica 51:1086, 1988 5. Miller DT, Etzel RA, McFarland JG, Aster RH, White GC: Prolonged neonatal alloimmune thrombocytopenic purpura associated with anti-Bak(a): Two cases in siblings. Am J Perinatol4( 1):55, 1987 6. von dem Borne AEG Kr, von Riesz E, Verheught FWA, ten Cate JW, Koppe JG, Engelfriet CP, Nijenhuis LE: Baka, a new platelet-specificantigen involved in neonatal allo-immune thrombocytopenia. Vox Sang 39:113, 1980 7. van der Schoot CE, Wester M, von dem Borne AEG Kr, Huisman HG: Characterization of platelet-specificalloantigens by immunoblotting:Localization of Zw and Bak antigens. Br J Haemato1 64:715, 1986 8. Kiefel V, Santoso S, Katzmann B, Mueller-Eckhardt C: A new platelet-specific alloantigen Br(a): Report of four cases with neonatal alloimmune thrombocytopenia.Vox Sang 54:101, 1988 9. Kiefel V, Santoso S, Katzmann B, Mueller-Eckhardt C: The Br"/Brballoantigen system on human platelets. Blood 73:2219, 1989 10. Friedman JM, Aster RH: Neonatal alloimmune thrombocytopenic purpura and congenital porencephaly in two siblings associated with a "new" maternal antiplatelet antibody. Blood 65:1412, 1985 1 1 . Shibata Y , Matsuda I, Miyaji T, Ichikawa Y: Yuk", a new platelet antigen involved in two cases of neonatal alloimmune thrombocytopenia. Vox Sang 50:177, 1986 12. Furihata K, Nugent DJ, Bissonette A, Aster RH, Kunicki TJ: On the association of the platelet-specific alloantigen, Pen" with glycoprotein IIIa. Evidence for heterogeneity of the glycoprotein IIIa. J Clin Invest 80:1624, 1987 13. Furihata K, Hunter J, Aster RH, Koewing GR, Shullman NR, Kunicki TJ: Human anti-PIE' antibody recognizes epitopes associated with the alpha subunit of platelet glycoprotein Ib. Br J Haematol68:103, 1988 14. Boizard B, Wautier J-L: Leka,a new platelet antigen absent in Glanzmann's thrombasthenia. Vox Sang 46:47, 1984 15. Kieffer N, Boizard B, Didry D, Wautier J-L, Nurden AT: Immunochemical characterization of the platelet-specific alloantigen Lek": A comparative study with the PIA' alloantigen. Blood 64:1212, 1984 16. Keimowitz RM, Collins J, Davis K, Aster RH: Post- transfusion purpura associated with alloimmunization against the platelet-specific antigen, Bak". Am J Hematol21:79, 1986 17. von dem Borne AEG Kr, van der Plas-van Dalen CM: Baka and Lek" are identical antigens. Br J Haematol62:404, 1986 18. Kickler TS, Herman JH, Furihata K, Kunicki TJ, Aster RH: Identificationof Bakb,a new platelet-specific antigen associated with post-transfusionpurpura. Blood 71:894, 1988 19. Letellier SJ, Hunter JB, Aster RH: Probable genetic linkage between genes coding for platelet-specific antigens of the PIA and Bak systems. Am J Hematol29:139, 1988 20. Bray PF, Rosa J-P, Luo XY, Magenis E, Shuman MA: Physical linkage of the genes for platelet membrane glycoproteins IIb and IIIa. Proc Natl Acad Sci USA 85:8683, 1988 21. Poncz M, Eisman R, Heidenreich R, Silver SM, Vilaire G, Surrey S, Schwartz E, Bennet JS: Structure of the platelet mem- From www.bloodjournal.org by guest on June 15, 2017. For personal use only. 2348 brane glycoprotein I I b Homology to the a-subunits of the vitronectin and fibronectin membrane receptors. J Biol Chem 262:8476, 1987 22. Newman PJ, Gorski J, White GC 11, Gidwitz S, Cretney CJ, Aster RH: Enzymatic amplification of platelet-specific messenger RNA using the polymerase chain reaction. J Clin Invest 82:739, 1988 23. Newman PJ, Derbes RS, Aster RH: The human platelet alloantigens, PIA’and PIAZ, are associated with a leucine3’/proline3’ amino acid polymorphism in membrane glycoprotein IIIa, and are distinguishable by DNA typing. J Clin Invest 83:1778, 1989 24. Chomczynski P, Sacchi N: Single-step method of RNA isolation by acid guanidinium thiocyanate-phenol-chloroform extraction. Anal Biochem 162:156, 1987 25. Woods VL, Oh EH, Mason D, McMillan R: Autoantibodies against the platelet glycoprotein IIb/IIIa complex in patients with chronic ITP. Blood 63:368, 1984 26. Wallace RB, Shaffer J, Murphy RF, Bonner J, Hirose T, Itakura K Hybridization of synthetic oligodeoxyribonucleotidesto PhiX174 DNA: The effect of single base pair mismatch. Nucleic Acids Res 6:3543, 1979 27. Lotfus JC, Plow EF, Frelinger AL 111, Souza SE, Dixon D, Lacy J, Sorge J, Ginsberg MH: Molecular cloning and chemical synthesis of a region of platelet glycoprotein IIb involved in adhesive function. Proc Natl Acad Sci USA 84:7114, 1987 28. Phillips DR, Agin PP: Platelet plasma membrane glycoproteins. Evidence for the presence of nonequivalent disulfide bonds using nonreduced-reduced two-dimensional gel electrophoresis. J Biol Chem 252:2121,1977 29. Bray PF, Rosa J-P, Lingappa VR, Kan YW, McEver RP, Shuman MA: Biogenesis of the platelet receptor for fibrinogen: Evidence for separate precursors for glycoproteins Ilb and IIIa. 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Pereira J, Cretney C, Aster RH: Variation of Class I HLA antigen expression among platelet density cohorts: A possible index of platelet age? Blood 71516, 1988 36. Newman PJ, McEver RP, Doers MP, Kunicki TJ: Synergystic action of two murine monoclonal antibodies that inhibit ADPinduced platelet aggregation without blocking fibrinogen binding. Blood 69:668, 1987 37. Heidenreich R, Eisman R, Surrey S, Pelgrosso K, Bennett JS, Schwartz E, Poncz M: The organization of the gene for platelet glycoprotein IIb. Biochemistry 29:1232, 1990 38. Loftus JC, Plow EF, Jennings LK, Ginsberg MH: Alternative proteolytic processing of platelet membrane glycoprotein IIb. J Biol Chem 263:11025,1988 39. Poncz M, Newman PJ: Analysis of rodent platelet glycoprotein IIb: Evidence for evolutionarily conserved domains and alternative proteolytic processing. Blood 75:1282, 1990 From www.bloodjournal.org by guest on June 15, 2017. For personal use only. 1990 75: 2343-2348 Polymorphism of human platelet membrane glycoprotein IIb associated with the Baka/Bakb alloantigen system S Lyman, RH Aster, GP Visentin and PJ Newman Updated information and services can be found at: http://www.bloodjournal.org/content/75/12/2343.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. 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