Modulatory effects of Freund's adjuvant treatment on mast cell histamine release and homocytotropic antibody synthesis.

The present study examines the influence of Freund's complete adjuvant (FCA) injections on sensitized PVG rats with respect to serum levels of IgE and IgG2 alpha antibodies and total IgE (all assessed by radioimmunoassays) and the capacity of serosal mast cells to release histamine on challenge in vitro with 'immunological' secretagogues (specific antigen, anti-IgE, concanavalin A) or with compound 48/80. The rats were immunized with 10 micrograms ovalbumin (OA); alum, Bordetella pertussis vaccine, or silica gel were employed as adjuvants. Treatment with FCA was performed by single intraperitoneal injections 3, 2, or 1 week(s) before or 1 or 2 weeks after sensitization. Tests were conducted 3 weeks after sensitization. The results show that the effect of FCA treatment varied reproducibly with the adjuvant employed for sensitization and with the timing of the FCA administration. FCA treatment could either increase, fail to affect, or decrease total serum IgE and OA-IgG2 alpha antibody levels as well as serosal mast cell responsiveness, whereas OA-IgE antibody responses were decreased or not affected. Moreover, serum levels of OA-IgE and OA-IgG2 alpha antibodies and total IgE were affected by FCA treatment independently of each other. Finally, serosal mast cell responsiveness to a given secretagogue could be influenced by the FCA treatment apparently independently of that to other secretagogues. A salient finding was that effects of FCA treatment on mast cell responsiveness did not necessarily conform to effects on antibody synthesis. Collectively, these data support the opinion that the mechanisms of action of the IgE-promoting adjuvants employed differ and suggest that the expression of serosal mast cell responsiveness to each examined secretagogue can be regulated separately. They also suggest that the serosal mast cell sensitizing capacity of homocytotropic antibodies may not be adequately quantified by immunochemical methods employing reagents prepared against IgE and IgG2 alpha protein.