Immunosuppressive effects of cyclophosphamide in pigs.

Effects of cyclophosphamide (CY) on circulating leukocytes, lymphoid tissues, and antibody response of the pig were examined. Pigs (10 weeks old) were treated with intraperitoneal injections of 30 mg of CY/kg of body weight at 2-day intervals. Three CY injections depressed total leukocyte, neutrophil, and lymphocyte counts. Circulating B-lymphocyte percentages were depleted by 80% and absolute B-lymphocyte counts by 90%. Circulating T-lymphocyte percentages were not affected by CY treatment, but absolute T-cell counts were depressed by 50%. Lymphocytes were depleted from the cortex of the thymus gland and from the spleen and lymph nodes with a preferential effect on B-dependent areas. All these variables were depressed for the duration of CY treatment and had started to return to within normal values by 4 days after the final treatment. Formation of antibodies to sheep erythrocytes was suppressed in CY-treated pigs until 10 days after inoculation (6 days after final CY treatment); the response of control pigs was detectable 4 days after inoculation. The 6 CY treatments prolonged the depression of all the previously mentioned variables.