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The effect of a single batch of horse anti-mouse thymocyte globulin on the immune response to type III polysaccharide antigen bas been investigated in 2–3-month-old male A/HeJ, C57BI, BALB/c, DBA/I, CBA and C3H mice. In almost all cases the intraperitoneal administration of 5 mg of this material on days -4 and -2 significantly suppressed the immune response to 0·1, 1·0 and 5·0 μg of antigen injected i.v. on day 0. Further studies undertaken in BALB/c mice indicated that effective suppression of the immune response to type III polysaccharide antigen could also be achieved by injecting 5 mg of this product (i.p.) some 15–30 minutes prior to antigenic challenge. Preliminary cell re constitution studies in antilymphocytic antibody-treated CBA mice indicate that the ability to respond to type III polysaccharide can be partially restored by the injection of syngeneic thymocytes, bone marrow cells or spleen cells. [ABSTRACT FROM AUTHOR]

The effect of an horse anti-mouse thymocyte globulin (ALG) preparation on the primary and secondary immune responses to sheep erythrocytes (RBC) was studied in 2-3-month-old male A/HeJ, C57B1, BALB/c, DBA/1, CBA and C3H mice. A wide variation in the primary and secondary responses of the individual strains was noticed but in ail cases these were significantly suppressed by ALG pretreatment. The capacity of the ALG to suppress the primary immune response was not overcome by increasing the antigen dose from 3 × 107 to 3 × 109 sheep RBC. [ABSTRACT FROM AUTHOR]

The gamma 1 (fast) and gamma 2 (slow) sub-fractions of an anti-lymphocytic IgG, preparation have been isolated and their immunosuppressive properties compared with that of the original IgG. The strongly cytotoxic gamma 2 component markedly suppressed the primary immune response to sheep erythrocytes and alum precipitated bovine serum albumin in Hooded strain rats. In contrast the weakly cytotoxic, strongly agglutinating gamma 1 component, failed to suppress the primary immune response. The practical and theoretical significance of these results is discussed. [ABSTRACT FROM AUTHOR]

The antigenic and immunosuppressive properties of normal and antilymphocytic equine globulin subfractions were investigated in the rat model in an attempt to increase the efficacy of prolonged ALG therapy by limiting the immunogenic stimulus of 'inactive' subfractions. Chromatographic separation of equine IgG components yielded an electrophoretically slow gamma 2 fraction consisting of IgG2a and IgG2b and a more heterogeneous fast gamma 1 subfraction. Immunosuppression resulting from the administration of isolated subfractions was measured by the response to alum- BSA and skin allograft survival. Antigenicity was determined by a variety of immunological procedures. The immunosuppressive character of the ALG was confined to the gamma 2 fraction, however this fraction also proved antigenic in our system. The administration of normal equine IgG subfractions in combination with Freund's complete adjuvant resulted in the demonstration of antigenic differences between the fast and slow IgG components. [ABSTRACT FROM AUTHOR]