The Effect of Endotoxin on Circulating Lymphocytes in Normal Man

Summary. The effect of endotoxin administration on peripheral blood lymphocytes was studied in normal man. A partially purified bacterial endotoxin from Pseudomonas aeruginosa was given intravenously to 10 healthy volunteers. Endotoxin administration resulted in a substantial lymphocytopenia with reduction of both thymus‐dependent T and bone marrow‐derived B lymphocytes. Absolute numbers of circulating B lymphocytes decreased to a greater extent than T lymphocytes. T‐lymphocyte functional characteristics, including mitogenic response to phyto‐haernagglutinin and responder cell activity in mixed lymphocyte culture, were unaffected by endotoxin administration. Response to concanavalin A was consistently reduced. Stimulation of allogeneic lymphocytes in mixed lymphocyte culture, a function of B lymphocytes and monocytes, was also decreased. When endotoxin was used as an in vitro mitogen, a significant increase in DNA synthesis was observed only in lymphocytes from individuals previously given endotoxin and not in normal control lymphocytes. These studies indicate that experimental endotoxaemia is associated with a reduction in absolute numbers of circulating T and B lymphocytes, a decrease in B‐lymphocyte bur not T‐lymphocyte functional activity, and redistribution of a concanavalin A‐responsive subpopulation of T lymphocytes. The data suggest that endotoxin has important effects on lymphocyte distribution and function in man.