High molecular weight (19S) γ-globulin produces passive cutaneous anaphylaxis (PCA) reactions with its specific antiserum only when it is used as intravenous antigen. Reversed PCA reactions cannot be produced when the 19S protein is injected intradermally in contradistinction to the results with 7S γ-globulin.

Antibodies of the high molecular weight class, when injected intradermally, also failed to give PCA reactions following antigen injection. Heterophile antibodies from the sera of patients with infectious mononucleosis, demonstrated to be entirely of the 19S type, gave negative reactions, while 7S heterophile antibodies from guinea pig did give reactions following intravenous injection of sheep cells. Anti-B isoagglutinins of the 19S class failed to react, while those of the 7S class of similar titer gave clear reactions following the injection of B substance.

Evidence was obtained that 19S antibodies were capable of inhibiting the PCA reactions obtained with the 7S type, indicating that interaction with antigen occurred. The failure to elicit PCA reactions appeared to be due to an inability to fix to guinea pig tissues in a manner similar to that known for 7S antibodies and γ-globulin.

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