Characterization of the alloreactive helper T-cell response to the platelet membrane glycoprotein IIIa (integrin-beta3) in human platelet antigen-1a alloimmunized human platelet antigen-1b1b women.
BACKGROUND
The aims were to characterize the helper T-cell response to platelet (PLT) glycoprotein (GP) IIIa, which stimulates the alloimmune antibody response to human PLT antigen (HPA)-1a, to identify immunodominant epitopes and to examine the HLA Class II associations.


METHODS
Peripheral blood mononuclear cells (PBMNCs) were obtained from 21 HPA-1b1b women who had an HPA-1a-mismatched pregnancy, 14 of whom developed anti-HPA-1a, and 11 control donors. PBMNCs were stimulated with two panels of 15-mer peptides corresponding to the HPA-1a/1b polymorphic region, with either Leu33 (-1a) or Pro33 (-1b) at each possible position, and the proliferative responses were measured. HLA Class II and HPA genotyping was by conventional polymerase chain reaction-sequence-specific priming.


RESULTS
Peptides with Leu33 at, or near, the C-terminus contained an immunodominant epitope, stimulating proliferation by helper T cells from all nine women who had anti-HPA-1a at the time of testing; peptide L1 (Val19-Leu33) stimulated a response in 50 percent of these women. Their T cells did not respond to the corresponding HPA-1b Pro33 peptides, and responses to either peptide panel were rare in unimmunized women and controls. HLA-DRB3*01+ was significantly overrepresented (p = 0.014) in alloimmunized women whose T cells responded to the major HPA-1a Leu33-containing epitope. Conversely, HLA-DRB1*15 was negatively associated (p = 0.014) with this response.


CONCLUSIONS
The HPA-1a polymorphic region of GPIIIa contains both the linear T-cell and the conformational B-cell epitopes. The immunodominant T-cell epitope is constrained by HLA-DRB3*01+, and if presented by a tolerogenic route, a peptide containing this epitope may form the basis for the prevention or reversal of the alloimmune response to HPA-1a.
Academic Transfusion Medicine Unit and the Institute of Medical Sciences, Department of Medicine and Therapeutics, University of Aberdeen, Aberdeen, United Kingdom.
Hosea
H
Sukati
Hagop
H
Bessos
Robert N
RN
Barker
Stanislaw J
SJ
Urbaniak
D016824:Antigens, Human Platelet / Q000235:genetics* / Q000276:immunology*; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes; D005260:Female; D005434:Flow Cytometry; D006680:HLA Antigens / Q000276:immunology; D006684:HLA-DR Antigens / Q000276:immunology; D059826:HLA-DRB3 Chains; D006801:Humans; D039661:Integrin beta3 / Q000235:genetics*; D007963:Leukocytes, Mononuclear / Q000187:drug effects; D010446:Peptide Fragments / Q000494:pharmacology; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000276:immunology*; D011110:Polymorphism, Genetic / Q000276:immunology; D011247:Pregnancy; D006377:T-Lymphocytes, Helper-Inducer / Q000276:immunology*
D016824:Antigens, Human Platelet; D000939:Epitopes; D006680:HLA Antigens; D006684:HLA-DR Antigens; D059826:HLA-DRB3 Chains; C061248:ITGB3 protein, human; D039661:Integrin beta3; D010446:Peptide Fragments; D019039:Platelet Glycoprotein GPIIb-IIIa Complex