Bacterial lipopolysaccharide activates suppressor B lymphocytes.

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Abstract
Lipolysaccharide (LPS) extracted from the outer cell wall of Gram-negative bacteria modulates the immune response in vivo and in vitro. Depending on the experimental conditions, it may enhance or inhibit the production of humoral antibody [Ab]. The pathway by which [Salmonella] LPS suppresses Ab production is examined in this study. C57BL/6 [mouse] spleen cells incubated with LPS (> 10 .mu.g/ml) fail to produce Ab to sheep erythrocytes in vitro and, when transferred 24 h after stimulation with LPS, inhibit Ab production in spleen cells that were not treated with LPS. LPS may activate suppressor cells. A suppressor B [bone marrow-derived] cell was identified as mediator of LPS-induced immune suppression and its cell surface antigen phenotype was determined as Ig+ [immunoglobulin-positive], Ia+, CR+ [complement component 3 receptor-positive], Ly-B-2+, PCl-. LPS does not induce suppressor macrophages or suppressor T [thymus-derived] cells. Macrophages or T cells are not required for the generation of suppressor B cells by LPS.