The effect of HLA antibodies on platelet aggregation.

Twelve different HLA antisera, detecting antigens of both A and B series and the superspecificities w4 and w6, were tested for platelet-aggregating activity in 75 antiserum-platelet combinations. The correlation between the HLA specificities of the antisera and the aggregating effect on platelets carrying the corresponding antigens was significant (P = 0.011). Because the platelet aggregation test is being used for screening of circulating immune complexes, falsely positive reactions caused by HLA antibodies must be eliminated by adequate control experiments.