Regulation of human B-cell colony growth

PHA-induced B-cell enriched populations from venous blood of healthy adults developed into B-cell colonies. Analyses of individual colonies revealed that 80-85% of the cells in each colony were surface membrane immunoglobulin positive. Most colonies, 84%, contained surface IgM-bearing cells. Only a few, 16%, were found with surface IgG-bearing cells. Surface IgM- and surface IgG-bearing cells were not observed in the same colony. Thirty-nine percent of the colonies contained cells bearing surface IgD in addition to either surface IgM- or surface IgG-bearing cells. There was no evidence of cytoplasmic immunoglobulin in the colony cells. The development of B-cell colonies was T-cell dependent; it appears that at least two different T-cell subpopulations, one with low density (D = 1.05) and the other with high density (D = 1.08) are responsible for this helper effect. Monocytes were found to inhibit B-cell colony formation; the inhibition was mainly by endogenous prostaglandin E2 (PGE2) synthetized and released by monocytes. The addition of physiological concentrations of synthetic PGE2 to monocyte-depleted B-cell enriched populations inhibited B-cell colony growth, this paralleled the effect of endogenous PGE2 released by monocytes. Indomethacin (10-5 M) obviated the inhibitory effect of monocytes.