The opsonic effect of normal serum on the uptake of bacteria by the reticulo-endothelial system; perfusion studies with isolated rat liver.

A technique is described for perfusing the isolated rat liver with viable bacteria and for comparing their phagocytosis by Kupffer cells when different suspending fluids are used successively. Various general factors that modify uptake of bacteria have been studied, notably the nature of the bacteria and their concentration, the flow rate through the liver, the age of the liver preparation and the effect of repeated perfusion. Normal human, rat and mouse sera were found to exert an opsonic effect on the phagocytosis of . Thus the average uptake of these bacteria suspended in Ringer-Locke solution was 11 per cent, as compared with 41 per cent in serum. A reduction in opsonic activity of human serum was produced by heat at 56° for 30 min., absorption with the homologous strain or with an antigen-antibody system. Activity was completely abolished by homologous absorption followed by heat at 56° or absorption with an antigen-antibody system or with zymosan. Full opsonic activity was shown by a mixture of heated serum and -absorbed serum. It is concluded that the serum factors that contribute to opsonic activity in this system are specific antibody, complement and another heat-labile factor. The possible identity of the latter with properdin is considered.