Characterization of murine colony-forming B cells. II. Limits to <i>in vitro</i> maturation, Lyb-2 expression, resolution of IgD+ subsets, and further population analysis.

Abstract

Abstract Murine colony-forming B cells were further studied to determine the extent of their heterogeneity and to investigate events that take place within the cultures. Immature, surface Ig-negative (sIg−) precursors of B cells were found to have little, if any, ability to proliferate in semisolid agar cultures. However, such cells from adult bone marrow acquired this capability within 24 hr of conventional liquid culture. Bone marrow B cells that were IgM+, IgD− did not become sensitive to anti-δ antibodies during cloning. These results suggest that two known B cell maturation events do not occur efficiently in semisolid cultures. Most clonable B cells in fetal, neonatal, and adult tissues expressed detectable amounts of Lyb-2 alloantigen. A majority adhered to nylon wool but nonadherent B cells were enriched in colony-forming and mitogen-responding cells. Azathioprine sensitivity was similar to that of B cells that respond to mitogenic, T-independent antigens. Three categories of colony-forming B cells were distinguishable on the basis of expression and function of sIgD receptors. One type lacked sufficient IgD to adhere to anti-δ antibody-coated plastic dishes. A second category was sIgD+ but proliferated in the presence of anti-δ antibodies, whereas a third, IgD+ subset, was inhibited by very small concentrations of anti-δ. The relative frequencies of these populations in various tissues were calculated. All IgD positive cells in neonates and in adult bone marrow appeared to be sensitive to anti-δ antibody added to the cultures, whereas approximately one-third of the B cells in adult spleen were anti-δ resistant.