Induction of IgG2a secretion from mIgG2a+ B-lymphoid tumor cells by BCDF present in several antigen-specific T-helper clones.

In order to study the soluble factor(s) that play an important role for the differentiation of IgG2-secreting B cells, we examined whether membrane IgG2a (mIgG2a)-bearing BALB/c B-lymphoid tumor cells, A20, could be induced to secrete IgG2a after treatment with soluble factors. We detected a potent B-cell differentiation activity inducing the Ig secretion of A20 tumor cells (BCDF-A20) in supernatants of several soluble antigens as well as alloantigen-specific T-cell clones of various genetic backgrounds. Thus, this BCDF-A20 activity was working in an antigen-nonspecific and MHC-nonspecific manner and abundant in many T-cell clones. It was shown that neither interleukin 1, interleukin 2, interferon, T-cell replacing factor, B-cell maturation factor, nor B-cell stimulatory factor-1 alone had any significant effect on the induction of Ig secretion of A20 tumor cells. Using isotype-specific rabbit anti-mouse Ig developers, we showed that mIgG2a+ A20 tumor cells secreted IgG2a after the treatment with soluble factors. The peak of the response of A20 tumor cells to BCDF-A20 was obtained 3 days after the treatment with culture supernatants of T-cell clones. In this study, we have clearly shown that mIgG2a+ A20 tumor cells were able to secrete IgG2a after treatment with T-cell soluble factors.