Immunoglobulin C gene expression. IV. Alternative control of IgG 1 ‐producing cells by helper cell‐derived B cell‐specific growth or maturation factors

The influence of helper cell‐derived B cell‐specific growth or maturation factors in the membrane expression and secretion of IgG 1 and IgG 3 isotypes among lipopolysaccharide‐activated B cell blasts was studied in mass cultures and in single clones. The results demonstrate that helper cells regulate IgG 1 expression by two alternative modes: growth‐promoting factors expand membrane IgG 1 ‐bearing nonsecretory activated B cells, while maturation factors induce terminal differentiation to high‐rate secretion of IgG 1 in previously switched cells. Apart from the isotype specificity in the maturation‐inducing signals for activated B lymphocytes, the present experiments demonstrate that isotype control by helper cells is intimately connected to the control of proliferation vs . terminal maturation in proliferating B cell populations.