The present study examines the influence of Freund’s complete adjuvant (FCA) injections on sensitized PVG rats with respect to (1) serum levels of IgE and IgG_2α antibodies and total IgE (all assessed by radioimmunoassays) and (2) 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 μg 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-IgG_2α 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-IgG_2α 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 IgG_2α protein.

PVG rats given injections of 1 microgram ovalbumin (OA) together with 10 mg Silica gel failed to provide serosal mast cells or lung tissue with the capacity to release histamine on in vitro challenge with the antigen. However, if such animals were injected i.p. with 100 mg of alum (without any further antigen addition) 3-9 weeks after the primary antigen injection, their mast cells and lung tissue showed a clear-cut capacity to respond in vitro, when examined 1 week after the alum injection. Injection of only 15 mg alum did not induce such a response capacity. The fading of the reactivity induced by an alum injection could be prevented by a repeated injection of the adjuvant alone. Pretreatment of the rats with cyclophosphamide (33 mg/kg) 2 days before the primary antigen injection did not affect the response capacity induced by a booster injection 3 weeks later. S.c. injection of alum also precipitated response capacity in animals primed by i.p. injection of antigen and Silica gel. The anaphylactic response capacity induced by injection(s) of alum was generally accompanied by increased levels of OA-IgE and especially OA-IgG2a antibody; however, a clear-cut correlation between either serosal mast cell or lung tissue response capacity and serum OA-IgE or IgG2a antibody titer could not be demonstrated. These data show that in primed animals, which do not express allergic response capacity, such a capacity can be induced by injecting adjuvant alone, even several weeks after the primary antigen injection.

Responsiveness was compared for cell populations harvested from the peritoneal and pleural cavities of rats with respect to histamine release induced by specific antigen, anti-IgE, and Con A. Cell populations were obtained from Fischer, PVG or Sprague-Dawley (SD) rats, which were either untreated or immunized with 10 micrograms ovalbumin together with 100 mg alum intraperitoneally. Mast cell histamine release was examined with crude cell populations. The results show that differences in response capacity to the various secretagogues employed do exist between pleural and peritoneal cells in Fischer and PVG strains but under the present circumstances apparently not in SD rats. These differences vary in magnitude with the secretagogue employed and (for cells from immunized animals) with the time elapsed between immunization and test. In PVG rats, neither pleural nor peritoneal mast cell histamine release induced by antigen paralleled serum OA-IgE antibody levels. Furthermore, an increase in anti-IgE induced release of histamine from serosal mast cells occurred in parallel with a decrease in total serum IgE levels. These data indicate that the functional differences observed with respect to release properties of the two cell populations are due not only to intrinsic differences in mast cell populations but also to differences in reaginic antibodies sensitizing the cells.