Functional heterogeneity of alloantibodies against the human platelet antigen (HPA)-1a

Summary

The integrin αIIbβ3 is the major fibrinogen receptor on the platelet membrane and plays a crucial role for platelet aggregation. The β3-subunit carries the human platelet alloantigen (HPA)-1a, which is the main target for alloantibodies (alloabs) responsible for foetal and neonatal alloimmune thrombocytopenia (FNAIT) and post-transfusion purpura (PTP).Whereas PTP is almost invariably associated with severe bleeding, the clinical presentation of FNAIT ranges from mild thrombocytopenia to severe haemorrhagic diathesis. However, this clinical heterogeneity is not fully understood as it is not explained solely by the variability of the platelet count. Here, we examined the ability of HPA-1a alloabs from mothers with FNAIT (n = 43) and PTP patients (n = 8) to inhibit cell adhesion to fibrinogen and asked if this inhibition was correlated with the heterogeneity of the clinical picture. Stably transfected cells expressing HPA-1a (β3-Leu33) and –1b (β3-Pro33) isoforms were incubated with sera containing HPA-1a alloabs and were allowed to adhere to immobilised fibrinogen. The inhibitory activity was measured as percentage of cell adhesion in the presence of patient sera versus normalAB serum. Only two FNAIT sera specifically inhibited the adhesion of HPA-1a, but not HPA-1b cells. Two other FNAIT sera blocked the adhesion of HPA-1a as well as HPA-1b cells. Interestingly, all four neonates with inhibitory HPA-1a alloabs (9% of all sera) suffered severe bleeding. In comparison, the majority of PTP sera (75%) inhibited cell binding to fibrinogen, four PTP sera selectively inhibited the adhesion of HPA-1a cells whilst 2 sera impaired the binding of both allotypes. Our observations indicate that 1) HPA-1a alloabs are heterogeneous in their ability to interfere with fibrinogen binding, and 2) inhibition of the αIIbβ3 fibrinogen receptor by HPA-1a alloabs may contribute to pronounced bleeding in patients with alloimmune thrombocytopenia.

Keywords

HPA-1a - alloimmune thrombocytopenia - integrin αIIbβ3

• References

• 1 Hynes RO. Intergrins: bidirectional, allosteric signaling machines. Cell 2002; 110: 673-87.
• 2 Shattil SJ, Newman PJ. Integrins: dynamic scaffolds for adhesion and signaling in platelets. Blood 2004; 104: 1606-15.
• 3 Bellucci S, Caen J. Molecular basis of Glanzmann's Thrombasthenia and current strategies in treatment. Blood Rev 2002; 16: 193-202.
• 4 Niessner H, Clemetson KJ, Panzer S. et al Acquired thrombasthenia due to GPIIb/IIIa-specific platelet autoantibodies. Blood 1986; 68: 571-6.
• 5 Tholouli E, Hay CR, O´Gorman P. et al Acquired Glanzmann's thrombasthenia without thrombocytopenia: a severe acquired autoimmune bleeding disorder. Br J Haematol 2004; 127: 209-13.
• 6 Deckmyn H, Vanhoorelbeke K, Peerlinck K. Inhibitory and activating human antiplatelet antibodies. Baillieres Clin Haematol 1998; 11: 343-59.
• 7 Metcalfe P, Watkins NA, Ouwehand WH. et al Nomenclature of human platelet antigens. Vox Sang 2003; 85: 240-5.
• 8 Newman PJ, Derbes RS, Aster RH. The human platelet alloantigens, Pl^A1 and Pl^A2, are associated with a leucine³³/proline³³ amino acid polymorphism in membrane glycoprotein IIIa, and are distinguishable by DNA typing. J Clin Invest 1989; 83: 1778-81.
• 9 Dreyfus M, Kaplan C, Verdy E. et al Frequency of immune thrombocytopenia in newborns: a prospective study. Blood 1997; 89: 4402-6.
• 10 Mueller-Eckhardt C, Kiefel V, Grubert A. et al 348 cases of suspected neonatal alloimmune thrombocytopenia. Lancet 1989; I: 363-6.
• 11 Birchall J, Murphy MF, Kaplan C. et al European Collaborative Study of the Antenatal Management of Feto-maternal Alloimmune Thrombocytopenia. Br J Haematol 2003; 122: 275-88.
• 12 Williamson LM, Cohen H, Love E. et al The Serious Hazards of Transfusion (SHOT) initiative: the UK approach to haemovigilance. Vox Sang 2000; 78 (Suppl. 02) 291-5.
• 13 Shulman NR, Aster RH, Leitner A. et al Immunoreactions involving platelets. V. Post-transfusion purpura due to a complement-fixing antibody against a genetically controlled platelet antigen. A proposed mechanism for thrombocytopenia and its relevance in “autoimmunity”. J Clin Invest 1961; 40: 1597-620.
• 14 Morrison FS, Mollison PL. Post-transfusion purpura. N Engl J Med 1966; 275: 243-8.
• 15 Pegels JG, Bruynes EC, Engelfriet CP. et al Posttransfusion purpura: a serological and immunochemical study. Br J Haematol 1981; 49: 521-30.
• 16 van Leeuwen EF, Leeksma OC, van Mourik JA. et al Effect of the binding of anti-Zw^a antibodies on platelet function. Vox Sang 1984; 47: 280-9.
• 17 Duncan JR, Rosse WF. Alloantibody-induced platelet serotonin release is blocked by antibody to the platelet PLA1 antigen. Br J Haematol 1986; 64: 331-8.
• 18 Beadling WV, Herman JH, Stuart MJ. et al Fetal bleeding in neonatal alloimmune thrombocytopenia mediated by anti-PlA1 is not associated with inhibition of fibrinogen binding to platelet GPIIb/IIIa. Am J Clin Pathol 1995; 103: 636-41.
• 19 Kiefel V, Santoso S, Weisheit M. et al Monoclonal antibody-specific immobilization of platelet antigens (MAIPA): a new tool for the identification of plateletreactive antibodies. Blood 1987; 70: 1722-6.
• 20 Santoso S, Kiefel V, Richter IG. et al A functional platelet fibrinogen receptor with a deletion in the cysteine-rich repeat region of the β₃ integrin: the Oe^a alloantigen in neonatal alloimmune thrombocytopenia. Blood 2002; 99: 1205-14.
• 21 Santoso S, Amrhein J, Hofmann H. et al A mutational hot spot Thr₇₉₉Met on the α₂ integrin subunit leads to the formation of the new human platelet alloantigen Sit^a and affects collagen-induced aggregation. Blood 1999; 94: 4103-11.
• 22 Wang R, Newman PJ. Adesive and signaling properties of a naturally occuring allele of glycoprotein IIIa with an amino acid substitution within the ligand binding domain-the Pen^a/Pen^b platelet alloantigenic epitopes. Blood 1998; 92: 3260-7.
• 23 Kroll H, Yates J, Santoso S. Immunization against a low-frequency human platelet alloantigen in fetal alloimmune thrombocytopenia is not a single event: characterization by the combined use of reference DNA and novel allele-specific cell lines expressing recombinant antigens. Transfusion 2005; 45: 353-8.
• 24 Michelson AD, Furman MI, Goldschmidt-Clermont PJ. et al Platelet GP IIIa Pl(A) polymorphisms display different sensitivities to agonists. Circulation 2000; 101: 1013-8.
• 25 O´Toole TE, Mandelman D, Forsyth J. et al Modulation of the affinity of integrin alpha IIb beta 3 (GPIIb-IIIa) by the cytoplasmic domain of alpha IIb. Science 1991; 254: 845-7.
• 26 Jallu V, Meunier M, Brément M. et al A new platelet polymorphism Duv^a+, localized within the RGD binding domain of glycoprotein IIIa, is associated with neonatal thrombocytopenia. Blood 2002; 99: 4449-56.
• 27 von dem Borne AEGKr, Ouwehand WH. Immunology of platelet disorders. Baillieres Clin Haematol 1989; 2: 749-81.
• 28 Stricker RB, Lewis BH, Corash L. et al Posttransfusion purpura associated with an autoantibody directed against a previously undefined platelet antigen. Blood 1987; 69: 1458-63.
• 29 Taaning E, Tonnesen F. Pan-reactive platelet antibodies in post-transfusion purpura. Vox Sang 1999; 76: 120-3.
• 30 Watkins NA, Smethurst PA, Allen D. et al Platelet αIIbβ3 recombinant autoantibodies from the B-cell repertoire of a post-transfusion purpura patient. Br J Haematol 2002; 116: 677-85.
• 31 Stadler MB, Arnold D, Frieden S. et al Single nucleotide polymorphisms as a prerequisite for autoantigens. Eur J Immunol 2005; 35: 371-8.
• 32 Williamson LM, Hackett G, Rennie J. et al The natural history of fetomaternal alloimmunization to the platelet-specific antigen HPA-1a (Pl^A1, Zw^a) as determined by antenatal screening. Blood 1998; 92: 2280-7.