Mechanisms of lipopolysaccharide-initiated rabbit platelet responses: alternative complement pathway dependence of the lytic response.

Experiments were performed to examine the relationship of endotoxin-initiated complement activation and rabbit platelet lysis. The results of these experiments supported the concept that activation of the alternative pathway is required for endotoxin-initiated complement-dependent rabbit platelet lysis. Our data demonstrated that preparations of endotoxin or isolated lipid A, which activate selectively the classical pathway, are incapable of initiating platelet lysis. Essentially equivalent results were obtained in citrated or heparinized plasma, although the latter anticoagulated plasma appeared to be more efficient in supporting lysis. Additional data support the concept that natural antibody to either the polysaccharide or the lipid A region of the lipopolysaccharide, which might be present in rabbit plasma, probably did not play a prominent role in the complement-mediated lytic response.