The fate of 125I-rabbit IgG anti-mouse immunoglobulin complexed to the surface-bound immunoglobulin of B lymphocytes was investigated. Each immunoglobulin-bearing B lymphocyte bound an average of 160,000 molecules of antibody to immunoglobulin under saturating conditions. These preparations of B lymphocytes had been previously depleted in their content of non-lymphoid cells. The B lymphocytes were placed in culture and the fate of the 125I-anti-Ig was determined. Early during culture a small amount of anti-Ig sedimenting heavier than IgG was released into the culture supernatants. Most of the remaining Ig was catabolized. Examinations of culture and cell supernatants identified the 125I bound to amino acids or to smaller protein fragments. This metabolism of the anti-immunoglobulin molecules was temperature-dependent and also specific for that fraction of the rabbit IgG capable of interacting with the surface immunoglobulin present on B lymphocytes. We conclude that the B lymphocyte sheds a small percentage of the immune complex and internalizes and effectively degrades the remainder.

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This investigation was supported by Grants AI-10091 and AI-09920 from the National Institutes of Health, United States Public Health Service.

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