The antibody response of guinea pigs to purified encephalitogenic myelin basic protein (BP) has been examined by passive cutaneous anaphylaxis (PCA) in the guinea pig. This technique is known to be a sensitive measure of 7S-γ1 antibody. Serum from animals developing experimental allergic encephalomyelitis (EAE) following a single injection of guinea pig BP in Freund's complete adjuvant contained no PCA activity. Animals protected by multiple injections of guinea pig BP in Freund's incomplete adjuvant developed variable antibody titers. Two protected animals produced no detectable antibody. 7S-γ1 antibody is thus not required for either induction or prevention of EAE with BP. PCA activity in guinea pigs was confined to the serum fraction containing γ1 but not γ2-globulin, as previously reported in other antigen-antibody systems.Experiments were also performed with bovine BP in a study of antigenic cross-reactivity. Serum from guinea pigs hyperimmunized with guinea pig BP had identical titers to guinea pig BP and bovine BP. Serum from guinea pigs hyperimmunized with bovine BP, however, had significantly higher titers against bovine BP than against guinea pig BP, indicating the presence of both shared and species-specific antigenic determinants in the bovine encephalitogen. Bovine BP showed cross-reactivity with pooled bovine serum, but not with bovine serum albumin, α-, β- and γ-globulins, hemoglobin, or fibrinogen.
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