Effect of Adjuvants on Response to Pneumococcal Polysaccharide Injected Intraperitoneally. Platelet-Derived Immunoregulatory Activity.

The PFC response of SJL and BALB/c mice to sheep erythrocytes as well as to a polysaccharide antigen is enhanced by intravenous injection of 0.05 ml normal mouse or human serum but not by plasma. This is particularly evident in mice which have had an injection of an immunosuppressive agent along with the antigen. The factor responsible for this effect is readily absorbed by spleen cells from normal but not from athymic mice. The presence of proteolytic enzyme inhibitors during clotting prevents the appearance of this factor in serum. On the other hand, addition of thrombin to isolated platelets causes the secretion of this factor into the supernatant. Thus, a connection between platelets and the immune system is revealed by these findings.