Stimulation of Immunomodulatory Factors by Bacterial Endotoxins and Nontoxic Polysaccharides

Abstract

Immune responses are the result of a complex series of cellular and molecular interactions following exposure of lymphoid cells to specific antigens. Much is now known concerning the nature and mechanisms of antibody responses and cell-mediated immunity at both the humoral and the cellular level. The magnitude and range of the immune response to a particular antigen is regulated by a wide variety of factors, including soluble factors derived from various cell types that appear to serve as additional “signals” to the immune response mechanism (Schimpl and Wecker, 1975; Meltzer and Oppenheim, 1977). In this regard, components of microorganisms, including those derived from either gram-negative or gram-positive bacteria, are known to exert marked adjuvant effects on the immune response of animals and man, both in vivo and in vitro (Friedman, 1979; Garzelli et al., 1982). Microbial products have been shown to either enhance or suppress the immune response, as well as modify the nature of the response. In this regard, many studies have been performed concerning the adjuvant effects of cell wall-derived lipopolysaccharides (LPS) from gram-negative bacteria. Various laboratories have shown that LPS can both stimulate and inhibit the immune response, possibly by modifying macrophage activity as well as activity of responding immunocytes.