Regulation of IgE response by IgE binding factors.

T lymphocytes from rats infected with Nippostrongylus brasiliensis (Nb) release a soluble factor with affinity for IgE that selectively potentiates the IgE response to an unrelated antigen. The factor is derived from Fc omega receptors on T cells, binds to surface IgE on precursors of IgE-forming cells, and enhances their differentiation. The factor had a molecular weight between 10,000 to 20,000 and an affinity for lentil lectin. T cells from Nb-infected rats formed another IgE-binding factor upon incubation with rat IgE. The factor has the ability to suppress rather than enhance the IgE response. The IgE-specific suppressive factor is comparable to IgE-potentiating factor with respect to molecular weight and affinity for IgE but it fails to bind to lentil lectin. The IgE-specific suppressive factor is formed by lymphocytes complete Freund's adjuvant-treated rats. The results strongly suggest that IgE-binding factors are involved in the regulation of IgE response.