Abstract
Species-specificity and reacting site of antiglobulin factors, non-neutralizable by homologous γ-globulin, were studied and the following results were obtained:
1) Many of human sera showing only weak antiglobulin activity of anti-antibody nature against human red cells sensitized with human whole Rh-antibody were found to be capable of agglutinating the red cells sensitized with pepsin fragment —F(ab′)2— of the Rh-antibody.
2) In serum of a rabbit exhibiting antiglobulin activity of anti-antibody nature, there was found, in addition to a factor reacting only with rabbit antibodies, a factor capable of cross-reacting with both rabbit (homologous) and human (heterologous) antibodies.
3) Rabbit anti-antibodies were found to agglutinate sheep red cells sensitized with non-agglutinating pepsin fragment of rabbit anti-sheep erythrocyte antibody. This finding seems to indicate that reacting site against anti-antibody must be located in the Fab portion of rabbit IgG.
4) Cross-reacting antiglobulin factor of anti-antibody nature was also found in a rabbit antiserum against HB antigen, prepared by immunization with specific immune complex.
