Regulatory role of IgE-binding factors from rat T lymphocytes. I. Mechanisms of enhancement of IgE response by IgE-potentiating factor

T lymphocytes in the mesenteric lymph nodes of rats infected with Nippostrongylus brasiliensis spontaneously released a soluble factor that selectively potentiated the IgE-forming cell response of antigen-primed cells to homologous antigen. The factors could enhance the IgE response of DNP-OA-primed cells to DNP-HSA and T cell-replacing factor. In contrast, the treatment of OA-primed T cells with the factor failed to enhance either the IgE or IgG response of the mixture of DNP-KLH primed cells and OA-primed T cells to DNP-OA. The results collectively suggested that the target cells of the IgE-potentiating factor are B cells. Indeed, IgE potentiating factor was absorbed by B cells rather than T cells or thymocytes. Evidence was obtained that IgE-potentiating factor could be absorbed by IgE-bearing B cells or IgE-coupled Sepharose, indicating that the factor had affinity for IgE. It appeared that the potentiating factor bound to IgE-bearing B cells and selectively enhanced the differentiation of IgE-B cells to IgE-forming cells. It was also found that the major source of the factor was Fc(ε)R-bearing T cells.