Concanavalin A is mitogenic for resident peritoneal macrophages

Con A, a known T-cell mitogen, is also mitogenic for resident peritoneal macrophages. The stimulated cells morphologically resemble macrophages and are actively phagocytic. The concentration of con A (30 micrograms/ml) required to stimulate 3H-TdR incorporation is ten times that required for T-cell activation. Con A must be present throughout the entire culture period to produce the maximum effect, and con A-depleted supernatant fluids from con A-stimulated cells cannot replace the con A requirement. Stimulation of 3H-TdR incorporation occurs after a 48-hour lag period and is maximal on the fifth to seventh day of culture. At the peak of the response, 20-30% of the macrophages can be stimulated to incorporate 3H-TdR, but little or no increase in the total number of cells present in the culture occurs. This and pulse-chase experiments indicate that only a single cycle of replication occurs in the stimulated cells. Con A-responsive peritoneal macrophages appear to be a distinct subpopulation and might play a different role in the interaction with T cells and B cells in the immune response than the con A-non-responsive cells.