Models for assessing the effect of toxicants on immunocompetence in mice. II. Effect of cyclophosphamide on the antibody responses to type III pneumococcal polysaccharide and tetanus toxoid in BALB/c female mice.

A mixture of antigens was used to detect alterations in immunocompetence. Type III pneumococcal polysaccharide (S3) and tetanus toxoid (TT) stimulate different cellular components, and can therefore be used to assess different compartments of the immune mechanism. Cyclophosphamide (CP), a known immunosuppressant, had a potent effect upon the antibody responses to both S3 and tetanus toxoid. All doses of CP administered within 2 days of priming with S3 resulted in a dose-related immunosuppressive action which persisted even after reinjection of S3. 300 mg/kg of CP given up to 14 days prior to or following primary immunization resulted in a marked suppression of antibodies to S3. Doses of S3 which were partially tolerogenic were made even more so by injections of CP. The effect persisted over a 96 day experimental period. CP also suppressed the formation a memory cells necessary for induction of a secondary-type IgG response to TT. The time of injection for maximum suppression was days 10 to 14 after priming. Therefore, the suppression must involve cellular mechanisms different from those responsible for S3 antibody suppression. In addition, there was a difference in the degree and persistence of the suppressive effect, since the suppressed animals were able to mount an immune response to subsequent injections of TT. Double injections of a high dose (300 mg/kg) of CP 4 weeks after priming completely suppressed the acquired immunity to both S3 and TT. Low and moderate doses of CP appeared to induce a mild augmentation of S3 antibody response when given 4 weeks after priming. However, an immunosuppressive effect occurred if the primed animals were reinjected with S3 or challenged with TT within a period of 2 days prior to or after receiving the CP treatment. Doses of CP, injected prior to challenge and resulting in suppressed tetanus antitoxin production, elevated the titers of specific IgE antibody. This class of antibody is associated with adverse hypersensitivity reactions. These data provided background for the development of models to assess immunocompetence in mice, based on a study of immune profiles following exposure to selected T-dependent and T-independent antigens. Such models may be used to detect potentially hazardous chemicals found in the environment of incorporated into foods, drugs, or cosmetics.