Effect of gram-negative bacterial lipopolysaccharide-derived polysaccharides, glycolipids, and lipopolysaccharides on rabbit and human platelets in vitro.

The in vitro effect of gram-negative bacterial LPS-derived polysaccharide (PS), glycolipid (GL), and lipopolysaccharide (LPS) was investigated both on rabbit and human platelets. Rabbit platelets aggregated when they were treated with either GL or LPS, but no aggregation occurred when PS was used. No aggregation occurred when human platelets were treated with LPS, PS, or GL. However, when either human or rabbit platelets were treated with LPS-antibody complexes (LPS-ab), aggregation took place. Guinea-pig serum inhibited the aggregation caused by LPS-ab, but had no effect on rabbit platelet aggregation caused by LPS or GL alone. The factor(s) in guinea-pig serum that inhibited aggregation was heat-stable. These results suggest that there may be two different mechanisms involved in rabbit platelet aggregation by endotoxin in vitro. Using human platelets, only one mechanism was observed.