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Effect of Anti-Mouse IgG₁ on Some Complement-Requiring Alloantibodies of the Mouse¹

From The Children's Hospital of Philadelphia and the Department of Pediatrics, School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19146

Abstract

Ascitic fluid globulins of CBA mice previously injected with BALB/c spleen cells, containing alloantibodies which suppress hemolytic antibody plaque formation by BALB/c spleen cells, were treated by the addition of rabbit antimouse IgG₁ serum and removal by high speed centrifugation of the resulting precipitate. The titer of suppressive antibody was found to be higher in the supernatants than in the original globulin. With increasing amounts of anti-IgG₁ added, the suppressive titer rose progressively to a plateau level, at which it remained through further increases in the amount of anti-IgG₁ added. The amounts of anti-IgG₁ serum required to reach this plateau level varied between 0.1 and 0.3 ml/0.1 ml of the anti-BALB/c globulin pools. The supernatants were also examined by immunodiffusion to determine the endpoint for removal of all IgG₁ from the globulin pools; this was found to coincide with that which brought the anti-BALB/c globulin pool to its maximal (plateau) level of suppressive titer. The extent of the increase in suppressive titer to its plateau level showed an association with the amount of anti-IgG₁ required, but some overlapping was found.

Cytotoxic titers of these globulin pools also increased on addition of anti-IgG₁, to a plateau level, and each globulin pool required the same amount of anti-IgG₁ for attainment of plateau level as did the suppressive titer. The extent of the increase of the suppressive and cytotoxic titers, however, showed no relationship to each other. Titers of complement fixation against BALB/c spleen cell membrane fragments also showed such increases, again with the same relative amount of anti-IgG₁ required to attain the plateau titer. Hemagglutination titers for BALB/c red blood cells (RBC) showed no change or a slight decrease on addition of anti-IgG₁ and centrifugation.

These results indicate the presence in the anti-BALB/c globulin pools of complement-fixing antibodies, probably of IgG₂ class, and noncomplement-fixing IgG₁ antibodies of the same specificity which can compete with the IgG₂ antibodies, as indicated by the increased titers after removing IgG₁. The presence of such competing antibodies suggests that complement-requiring antibodies, in naturally occurring mixtures of IgG, could show titers substantially lower than their true level, or be entirely masked.

Footnotes

¹ This study was supported by Grants AI 09657 and T01 AI 154 of the National Institutes of Health, United States Public Health Service, and Grant T526 C of the American Cancer Society.