Inhibition of platelet aggregation by monoclonal antibody reactive with β₂-microglobulin chain of HLA complex

A mouse monoclonal antibody that reacts with β₂- microglobulin, the light chain of class I major histocompatibility antigens, inhibited the second wave of human platelet aggregation induced by adenosine diphosphate and epinephrine and blocked aggregation and platelet protein phosphorylation induced by sodium arachidonate. Thrombin-induced platelet aggregation was inhibited at threshold concentrations but not at higher concentrations. The antibody also inhibited aggregation and secretion in response to thromboxane A₂ or the stable endoperoxide analog, U46619. These results suggest that β₂-microglobulin in the histocompatibility complex is intimately associated with transmission of the endoperoxide-thromboxane signal at the platelet membrane.