Nonspecific elicitation of antibody-forming cells in the mouse spleen by bacterial lipopolysaccharide

Abstract

Mechanisms of nonspecific elicitation of anti-sheep erythrocyte (SRBC) hemolytic antibody plaqueforming cells (PFC) in mouse spleens with an injection of bacterial endotoxin (lipopolysaccharide (LPS)) were studied in comparison with the genesis of naturally occurring "background" PFC in normal mouse spleens and of rapidly arising PFC in mouse spleens after immunization with SRBC. The cytokinetic pattern of anti-SRBC PFC response after an injection of LPS was quite different from that of the response elicited after immunization with SRBC. In addition, even though LPS nonspecifically elicited anti-SRBC PFC response in mice, LPS could not confer any immunological memory on mouse immunocytess for a "secondary-type" anti-SRBC PFC response to restimulation with LPS or SRBC. The administration of rabbit anti-mouse thymocyte immunoglobulin or anti-SRBC antiserum in mice markedly suppressed the PFC response after immunization with SRBC, but did not do so after stimulation with LPS. Neonatally thymectomized mice could still respond to stimulation with LPS, producing anti-SRBC PFC in their spleens. Injections of actinomycin D or cyclophosphamide into mice resulted in obvious reductions of the PFC responses elicited by either LPS or SRBC. However, injections of these immunosuppressive antisera or drugs did not affect the number of anti-SRBC PFC in normal mouse spleens. These results suggest that the genesis of anti-SRBC PFC developed under different conditions, i.e., background PFC, LPS-stimulated PFC, and antigen-stimulated PFC, are quite different from each other, and that the nonspecific elicitation of anti-SRBC PFC by LPS does not require the helper function of T lymphocytes. No obvious difference, however, was observed in the time of ontogenic maturation among these three different anti-SRBC PFC in the mouse spleens judging from when they were first manifested after birth.