Antibody secretion and DNA synthesis induced by lipopolysaccharide in enriched human lymphocyte subpopulations

Lipopolysaccharide (LPS)-induced human lymphocyte activation was analysed with regard to DNA synthesis and antibody secretion. Antibody secretion was measured as plaque-forming cells (PFC) against fluorescein isothiocyanate (FITC)-coupled sheep erythrocytes (SRBC) or protein-A-coupled SRBC in the presence of developing antiserum against human IgG, IgA and IgM subclasses. By co-culturing lymphocytes with various concentrations of mitomycin, without impairing cell viability, inhibition of DNA synthesis and antibody secretion by LPS was correlated. Antibody secretion against FITC-SRBC or protein A-SRBC was not stimulated by LPS in B cells enriched by elimination of SRBC rosette-forming cells (E-RFC). In mixtures of enriched T and B cells the number of PFC was much lower than in unseparated lymphocytes, but the highest number of PFC was seen in the enriched E-RFC. However, DNA synthesis by LPS was induced in enriched B cells and not in enriched T cells. The highest DNA synthesis was seen for unseparated lymphocytes. Furthermore, autoradiography studies and experiments in which activated lymphocytes were separated revealed that LPS predominantly stimulated DNA synthesis in non-E-RFC, presumably B cells and only activated a small proportion of E-RFC. Finally, antibody secretion induced by LPS was unchanged following iron treatment but was inhibited by cells adherent to plastic.