Regulatory effects of human IgE-binding factors on the IgE response of rat lymphocytes.

Normal human peripheral blood T cells were propagated in the presence of human interleukin 2, and activated cells were incubated with human IgE-dimer to induce IgE binding factor formation. The cells were then fused with a mutant of the human T cell line CEM. Five of the T cell hybridomas formed IgE binding factors upon incubation with human IgE-dimer. Because IgE binding factors formed by the human T cell hybridomas had affinity not only for human IgE but also for rat IgE, the biologic activities of the factors were evaluated by using antigen-primed rat mesenteric lymph node (MLN) cells. When parent T cells were propagated with crude IL 2, which contained glycosylation enhancing factor (GEF), IgE binding factors formed by all of the five hybridomas had affinity for Con A, but only a fraction of the factors bound to lentil lectin. The 60,000 and 15,000 IgE binding factors formed by two representative hybridomas, i.e., 166A2 and 166G11, selectively potentiated the IgE-forming cell response of rat MLN cells. When parent T cells were obtained by propagation with purified IL 2, which did not contain GEF, and the cells were incubated with IgE-dimer in the presence of glycosylation inhibiting factor (GIF), T cell hybridomas constructed from the cells formed IgE binding factors that lacked affinity for Con A but bound to peanut agglutinin (PNA). The 30,000 IgE binding factors formed by two of such hybridomas, 398A3 and 400G2, selectively suppressed the IgE response of rat MLN cells. It was also found that the biologic activities and carbohydrate moieties of human IgE binding factors could be switched by changing the culture conditions of the hybridomas. When the 166A2 hybridoma was cultured with human IgE in the presence of bradykinin, essentially all of the IgE binding factors that were formed by the cells bound to lentil lectin, and the factors that were formed in the presence of bradykinin exerted higher potentiating activity than those obtained in the absence of bradykinin. On the other hand, IgE binding factors formed by the same cells in the presence of GIF had affinity for PNA, and selectively suppressed the IgE response of rat MLN cells.