We previously showed that murine lymphoid cells exposed to elevated levels of IgE exhibit the de novo expression of Fc receptors for IgE (FcR epsilon), and the production of soluble mediators, which we have termed IgE-induced regulants (EIR). Described herein is the preliminary physicochemical characterization of one such regulant, that being the EIR responsible for the Lyt-2+ T cell-dependent expression of FcR epsilon and secretion of an IgE-binding factor (IgE-BF) which can potentiate IgE synthesis; the former activity has been denoted EIRT for its selectivity of action on T cells, and the latter activity has been termed enhancing effector molecule (EEM) for its presumed potentiating influence on IgE antibody synthesis. Characterized in parallel was the conventional lymphoid cell-derived cEIRT and a murine monoclonal T cell hybridoma-(MBI-2)-derived mcEIRT. EIRT from either source was shown to exhibit the characteristics of a protein with a molecular mass of 45 to 60 kd. Once enriched by gel filtration, neither cEIRT nor mcEIRT preparations displayed any other EIR-like activity except that of EIRT, as evidenced by the ability of these preparations to act selectively to induce the Lyt-2 T cell-dependent expression of FcR epsilon and the production of EEM, the lack of detectable SFA activity that could induce Lyt-1+ T cells to produce the IgE-BF denoted suppressive effector molecule (SEM), and the lack of detectable levels of the B cell-selective EIRB, as indicated by the incapacity of either preparation to induce B cell FcR epsilon expression. Neither cEIRT nor mcEIRT displayed IgE-binding affinity, in contrast to the EEM produced in response to stimulation with these regulants. The only EIR-like activity detected in the unfractionated supernatant fluid from cultures of the monoclonal T cell hybridoma MBI-2 was that of EIRT. Careful in vitro analysis established that such preparations did not contain enhancing factor of allergy (EFA), SFA, EIRB, or IgE-BF. Thus, the enhancement of IgE synthesis observed in animals given this mcEIRT preparation was most likely due to the activity of EIRT known to be present. During the course of these studies, clues as to the physicochemical nature of other EIR activities was obtained. Thus, upon molecular sieve analysis, two distinct molecular mass species of EIRB (one 15 to 20 kd and the other 30 to 35 kd) were demonstrated to be present in conventional lymphocyte-derived cEIR.(ABSTRACT TRUNCATED AT 400 WORDS)

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