FcR epsilon+ lymphocytes and regulation of the IgE antibody system. II. FcR epsilon+ B lymphocytes initiate a cascade of cellular and molecular interactions that control FcR epsilon expression and IgE production.

This study additionally explores the orderly sequence of events concerning the induction of Fc receptors for IgE (FcR epsilon) that are initiated by IgE and mediated by IgE-induced regulants (EIR). Thus, lymphoid cells exposed to monomeric IgE displayed an early phase of exclusive B cell FcR epsilon expression, followed by the progressive appearance of FcR epsilon+ T cells, ultimately resulting in equal proportions of FcR epsilon+ B cells and T cells. Parallel cultures of lymphoid cells stimulated with EIR derived from unfractionated lymphoid cells (EIRT) also manifested rapid induction of FcR epsilon+ cells, but these FcR epsilon+ cells were predominantly T cells from the outset. Data presented here demonstrate that IgE-induced FcR epsilon expression by B cells ultimately results in the production of EIRT, which then induces FcR epsilon expression by T cells. The existence of EIRT that selectively induce T cell FcR epsilon expression prompted us to search for an EIRB that is selectively active in inducing FcR epsilon+ B cells. Indeed, IgE-stimulated, T cell-depleted lymphoid cells produce an EIRB that selectively induces FcR epsilon expression by B cells. This EIRB, but not EIRT, can also be generated by IgE stimulation of Lyt-2+ cell-blocked lymphoid cells, indicating that Lyt-1+ cells are not inhibitory to EIRB production and that production of EIRT is dependent upon functionally competent Lyt-2+ cells. Similar to IgE, EIRB induces rapid FcR epsilon expression, first by B cells and then by T cells, so that by 16 hr post induction equal proportions of FcR epsilon+ B and T cells were observed. Although complete T cell depletion does not affect IgE-induced FcR epsilon expression, selective blocking of Lyt-1+ cells markedly diminishes such responses, suggesting that Lyt-2+ cells are antagonistic to the induction of FcR epsilon+ B cells. Studies involving sequential T cell subset depletion clearly demonstrated that in the absence of functionally competent Lyt-1+ cells, Lyt-2+ cells exert an inhibitory influence on IgE-induced FcR epsilon expression by B cells. Stimulation of Lyt-1+ cell-blocked cultures with EIRT, and to a lesser degree with IgE, resulted in the elaboration of an EIR (EIRI), which lacks direct FcR epsilon-inductive properties, but conversely, directly inhibits IgE-induced FcR epsilon expression in fresh B cell cultures.