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The mechanism of complement-independent action of HLA-A2 antibodies (eluates) on washed platelets was investigated. HLA-specific alteration was confirmed by serological (platelet micro-complement fixation), morphological (platelet spreading) and functional parameters (platelet aggregation, inhibition of collagen-induced platelet aggregation, 14Cserotonin release). In the presence of fibrinogen and calcium ions, HLA antibodies induced instantaneous platelet aggregation and release. Although no morphological (spreading) and functional changes (collagen-induded aggregation) were seen, these platelets did not aggregate or release when fibrinogen was subsequently added. When platelets--in the presence of fibrinogen--were incubated with antibody concentrations too low to induce platelet aggregation or release, specific reduction of platelet reactivity was observed by subsequent collagen aggregation. HLA-specific action of antibodies on washed platelets was inhibited by apyrase and acetyl-salicylic acid, indicating an active participation of platelets in HLA antibody-induced platelet alteration.
Heinrich et al. (1977) studied this question.