Ontogenical studies on kinetics of lipopolysaccharide-induced response to bromelain-treated mouse erythrocytes in mouse spleen cells. II. Response of spleen cells with or without Fc receptors, C3 receptors, or Ia antigens.

Lipopolysaccharide (LPS)-induced plaque-forming cells secreting IgM (IgM-PFC) and antibodies against bromelain-treated mouse erythrocytes (anti-BrMRBC PFC) on Days 1 and 2 of cultures were quantitatively estimated in spleen cells from mice of various ages. The concentrations of the four groups of PFC changed independently with age. The LPS dose dependency of the PFC response was markedly different between PFC on Days 1 and 2, but not different between anti-BrMRBC PFC and IgM-PFC or between 2- and 10-week-old mice. In a second experiment, spleen cells from 2- and 10-week-old mice were separated into subpopulations with or without Fc receptors, C3 receptors, or Ia antigens, and the LPS-induced PFC responses were quantitatively assessed in each subpopulation. Both the receptor-bearing and -lacking populations included LPS-reactive B cells, and the percentages of the LPS-reactive B cells recovered in the receptor-bearing population increased with age. However, the percentages of anti-BrMRBC PFC recovered in each receptor-bearing or -lacking population were different from those of IgM-PFC. In Ia- populations, the percentages of IgM-PFC on Day 2 were obviously higher than those on Day 1, and both of the percentages increased with age. These results suggest that the four groups of LPS-reactive B cells can be discriminated from each other by their LPS dose dependency and their cell surface markers, and that they develop differently during ontogeny.