Papain Fragments of Rabbit Anti-Leukocyte Antibodies: Effects in Relation to Some Serologic and Biologic Activities of the Antiserum

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Abstract
Summary: Serologically detectable antibodies in rabbit anti-rabbit leukocyte sera were digested with papain to the point of loss of the serologic activity. The papain fragments could inhibit the agglutination by anti-leukocyte sera of RBC coated with soluble rabbit histocompatibility antigens. Digestion was also demonstrated of the antibody in such sera which causes reduction in the number of hemolytic antibody plaques produced by stimulated rabbit lymph node cells. Papain fragments of the antibodies in antileukocyte sera were not effective in suppressing transferred lymph node cells in contrast to the native antibodies. The requirement for complement demonstrated in the plaque-reduction system could explain this failure. Competition between papain fragments and the native antibody for antigenic sites on the lymph node cell was shown in the agglutination of lymph node cells by RBC coated with specifically purified antibody from the anti-leukocyte sera, and in plaque-reduction and cytotoxicity. In the case of the latter two reactions, with increasing concentrations of the antibody disproportionately greater concentrations of the papain fragments were required to reduce the effect of the antibody to a given endpoint.