Anti-HPA1a antibodies induce CD62P and fibrinogen binding

Abstract

B ackground Alloantibodies to platelet antigens may affect platelet function by delivering stimulatory or inhibitory signals or by occupying platelet receptor-ligand molecules. So far, reports from the literature are controversial. M ethods We investigated CD62P and CD63 expression, as well as fibrinogen-binding on platelets that have been incubated with sera containing anti-HPA-1a (NAIT, n = 11; PTP, n = 5) by flow cytometry. HPA-1a/a platelets from HLA-matched donors were incubated with antisera and then stimulated with TRAP-6 (20 µm and 50 µm) to study stimulatory or inhibitory effects. R esults NAIT: TRAP-6 20 µm and 50 µm induced CD62P expression was enhanced by 2 and 4 sera, respectively. Fibrinogen binding was induced by 6 sera and enhanced if with TRAP-6 20 µm and 50 µm by 3 and 8 sera, respectively. PTP: 2 sera induced CD62P and all 5 augmented its TRAP-6 50 µm induced expression. Fibrinogen binding was induced by 4 sera and all 5 sera enhanced its TRAP-6 50 µm induced binding. There were no changes in the CD63 expression. C onclusions HPA-1a antibodies activate platelets to release CD62P and support fibrinogen binding. These effects are stronger in PTP than in NAIT.