The effect of a water-soluble fraction (CEF) that was prepared from an extract of Corynebacterium equi on primary reaginic antibody formation was studied in Balb/c mice. Mice were immunized with a hapten carrier (DNP-OVA) and received intra-peritoneal injections of CEF 7 and 2 days prior to, or 2 and 7 days after the immunization. PCA titers of both antihapten (DNP) and anticarrier (OVA) antibodies of IgE class were reduced significantly by the CEF treatment. Evidence was presented in adoptive transfer experiments that the number of IgE-producing cells in the CEF-treated mice was lower than that of controls. Suppression of IgG1 anti-DNP antibody formation was also achieved by the CEF treatment. Formation of IgG1 anti-OVA antibodies, however, was not suppressed significantly by the treatment. The suppressive activities of CEF were shown to be dose-dependent, but timing of CEF administration did not appear critical.

Effects of a water soluble fraction of Corynebacterium equi (CEF) on the histamine release from rat peritoneal mast cells (RPMC) were investigated. The treatment of RPMC with CEF resulted in a significant inhibition of the histamine release from RPMC which was induced by IgE antibody-antigen interaction as well as nonimmunological histamine liberators. CEF was much more effective in inhibition of IgE-mediated histamine release and compound 48/80 or polymyxin B-induced histamine release when the mast cells were treated with CEF prior to the incubation with the antigen or the liberators. In contrast, CEF was equally effective in inhibition of the histamine release by concanavalin A with phosphatidyl serine when the mast cells were treated with CEF prior to or simultaneously with the liberator. Evidence was also presented that CEF inhibits degranulation of mesenteric mast cells induced by immunological as well as nonimmunological mechanisms.

A water-soluble fraction (CEF) obtained from Corynebacterium equi was administered intradermally or intravenously into Sprague-Dawley rats. Passive cutaneous anaphylaxis (PCA) was elicited in these rats along with the controls by sensitization with mouse anti-DNP serum and challenge with the corresponding antigen. PCA reactions were markedly inhibited by the pretreatments of the rats with CEF. Similar treatments of the animals 2–4 h after the sensitization did not inhibit PCA. Inhibitory activity of CEF in the pretreated animals was shown to be dose-dependent. Incubation of rat peritoneal mast cells with CEF effectively blocked the binding of murine IgE antibodies to the cells as evidenced by the failure of the treated cells to bind the antibodies. Furthermore, antigen-induced histamine release from rat mast cells, which were sensitized with murine IgE antibodies, was reduced significantly by CEF treatment of the cells prior to the sensitization. Results of this study indicated that CEF inhibits the PCA in rats, presumably by blocking the binding of heterocytotropic antibodies to Fc receptor of mast cells.