Lipopolysaccharide can substitute for helper cells in the antibody response in vitro

Abstract

The effect of lipopolysaccharide (LPS) from E. coli on the primary and the secondary antibody response against sheep red blood cells (SRC) by spleen cells in vitro was studied. LPS, which is a non‐specific mitogen for B cells, often caused an increased antibody response. Stimulation was obtained on day 4 of the culture if the spleen cells gave a low response to SRC without LPS, whereas no stimulation was obtained if the antibody response was high. However, kinetic studies showed that cultures treated with LPS always exhibited increased numbers of plaque‐forming cells (PFC) to SRC if the response was studied earlier than the 4th day.LPS could substitute for certain cell types otherwise necessary for the immune response. Thus, LPS reconstituted the immune response of spleen cells depleted of adherent cells as well as of thymus‐derived lymphocytes. It was also possible to enhance the immune response of spleen cells from nude mice by addition of LPS.The results suggest that LPS increases the immune response by direct stimulation of bone marrow‐derived precursor cells for antibody production. LPS makes these cells competent to differentiate and proliferate in the absence of helper cells, such as adherent cells and thymus‐derived cells. This implies that cooperation with helper cells is not an obligatory event in the antibody response, but can be substituted by other means of stimulating the precursor cells.