T cell requirements for the expression of the lipopolysaccharide adjuvant effect in vivo: evidence for a T cell-dependent and a T cell-independent mode of action.

The in vivo adjuvant effect of lipopolysaccharide (LPS) in mice was investigated with the soluble synthetic polypeptide antigen (T, G)-A--L, the antibody response to which is determined by the Ir-1A gene. With this specific antigen it can be demonstrated that the LPS adjuvant effect has the following modes of action: a) a T cell-dependent enhancement of primary and secondary IgM antibody response; b) a T cell-dependent enhancement of IgG secondary andibody response; and c) a T cell-dependent induction of switchover from IgM to IgG andibody in some strains of Ir-1A low responders. Although T cells are necessary for some aspects of the adjuvant effect, these data do not distinguish between a mechanism involving a direct interaction between LPS and T cells or a direct interaction of LPS and B cells with a general requirement for T cells for expression of IgG antibody.