Alloimmunization against platelet antigens in renal transplant patients with acute vascular rejection

Acute vascular rejection (AVR) of a kidney graft, in which the graft vascular endothelium is main target for the injury, is considered antibody-mediated. Integrins of vascular endothelium and platelets have several alloantigenic epitopes in common, e.g. human platelet alloantigen (HPA) 1 on beta(3) integrin of glycoprotein (GP) IIbIIIa and HPA-5 on alpha(2) of GP IaIIa. The clinical significance of HPA expression by vascular endothelial cells is unknown. Platelet antibodies in serum samples from 26 renal allograft recipients with AVR and 30 patients without AVR were studied. Also the HPA-types of the patients and their respective graft donors were determined. Strong platelet alloantibodies were observed in seven of the 26 AVR patients (27%). In five of these cases the antibodies had HPA-specificity. No reference patient without AVR had strong platelet antibodies. In two AVR patients strong HPA-5b antibodies coexisted with an HPA-5b-positive graft. Despite acute rejection episodes, neither of the grafts was lost. It seems likely that, with current immunosuppressive treatment, anti-HPA-5b does not necessarily cause permanent dysfunction of a graft originating from HPA-5b-positive donor.