Immunosuppressive Properties of a Peptic Fragment of BSA

Abstract

The immunogenic properties of a peptic fragment of BSA were investigated. BSA was subjected to limited proteolysis by pepsin and the resulting fragments were separated on DEAE cellulose. The fragment under consideration, Fraction Ia (m.w. 8000 to 10,000), did not precipitate with anti-BSA serum but did inhibit the binding of specific antibody to labeled BSA, indicating the presence of determinants found on the native antigen. BDF₁ mice immunized with Fraction Ia in A1(OH)₃ gel or in complete Freund's adjuvant produced no significant antibody response as measured by passive cutaneous anaphylaxis (PCA) or by a modified Farr assay. The fragment elicited a PCA reaction in mouse skin sensitized with anti-BSA serum. Treatment of mice with single doses of Fraction Ia at various time intervals before immunization with BSA resulted in significant suppression of the formation of anti-BSA antibody. The conditions of suppression of the IgE response by the peptic fragment were studied in greater detail. Evidence is presented that such suppression can be attributed to the presence of specific T suppressor cells in our system.