Antigenic competition in IgE antibody production. II. Effect of cyclophosphamide.

The effects of cyclophosphamide (CY) on antigenic competition in IgE antibody production were studied in mice treated with the drug on different days and immunized with a mixture of two non-related antigens. Injection of 100 mg of CY/kg of body weight 3 days before or 6 days after immunization resulted in a partial or total recovery of the IgE, but not of the IgGl antibody response to the test antigen. In contrast, when the same dose was given together or 3 days after immunization both responses were much more suppressed than in untreated animals. This same effect was obtained when a higher concentration (200 mg/kg) of cyclophosphamide was injected on day--3. When a different antigenic system was tested, the suppressive effects of competition in IgGl antibody production were also abolished after CY treatment. These results seem to provide further evidence for an important role of suppressor T cells in the mechanism of antigenic competition.