In vivo effects of lipopolysaccharide on lymphoid and non-lymphoid cells in the mouse spleen. Suppressive and adjuvant effects of LPS on the development of specific antibody forming cells in situ.

Mice were immunized i.v. with 2,4,6-trinitrophenyl (TNP)-carrier conjugates and received lipopolysaccharide (LPS) before, simultaneously with or after these antigens, in order to study the effects of LPS on the in situ development of anti-TNP antibody forming cells in the spleen. LPS given before, simultaneously with or shortly after the thymus dependent (TD) antigen TNP-keyhole limpet haemocyanin (KLH) suppressed the development of anti-TNP antibody forming cells in the spleen, but serum IgM-anti-TNP titres were not reduced, suggesting a selective inhibiting effect of LPS on the local immune response in the spleen. Splenic responses to thymus independent (TI) antigens TNP-Ficoll and TNP-LPS were not reduced when these antigens were administered one day after LPS. LPS given 4 days after TNP-KLH and 1 day before killing of the animals had induced severe alterations in splenic histology, but we found no marked influence on numbers and distribution pattern of anti-TNP forming cells. Results indicate that the LPS induced suppression of the immune response to TD antigens in the spleen is not caused by a direct effect of LPS on antigen reactive B-lymphocytes or on the anti-TNP antibody forming cells themselves. Possible explanations for the LPS-induced immunosuppression are discussed.