How relevant are growth and maturation factors to the B lymphocyte response induced by LPS?

For the purpose of arriving at a unifying concept concerning the mechanisms in control of B lymphocyte responses, LPS or anti-lg receptor antibodies have conveniently served as substitutes for antigen. We report that the proliferative B cell responses in serum protein free medium to each of these polyclonal activators differ in the requirement for B cell growth factors (BCGF). Murine B lymphocytes which were prestimulated with anti-lg (Fab')2 antibody could readily be induced by semipurified BCGF (containing some IL2 activity) to incorporate thymidine. In contrast, B lymphocytes which were prestimulated with LPS failed to respond to BCGF, but could be restimulated by LPS. We have also shown that the dependence on B cell maturation factors of antigen affinity enriched B lymphocytes to develop into antibody forming cells (AFC) in response to LPS, depends on the antigen for which they were selected. B cells that have been affinity enriched with chicken red blood cells (CRBC) and stimulated by LPS to proliferate require maturation factors in order to generate a CRBC specific IgM response. In contrast, B cells that have been affinity enriched for TNP may be induced by LPS alone to generate TNP specific AFC independent of maturation factors. The results question the general validity of theoretical concepts concerning the role of lymphokines in B cell triggering, where such concepts are derived from experiments with LPS-activated B cells.