Enhancing effect of low dose cyclophosphamide treatment on the in vitro antibody response.

We have studied the effect of cyclophosphamide (CY) administration on the subsequent in vitro antibody response in the mouse. Treatment with a low dose (20 mg/kg) of CY four days before culture results in an increased IgM response to the T-independent antigen trinitrophenylated polyacrylamide (TNP-PAA), without affecting the background response of unstimulated cultures. This suggests that CY treatment eliminates a short-lived suppressor cell, involved in the regulation of the in vitro B cell response. In contrast, the same regimen decreases the ability of nude mouse spleen cells to respond to TNP-PAA, showing that the target of CY-enhancing effect is a mature T cell. The increased response observed in conventional mice should be the result of a balance between the direct suppressive effect of CY on B cells and the elimination of a suppresor T cell, the latter phenomenon being of predominant significance in our conditions. The target of CY-enhancing effect is nonadherent to plastic, but adherent to Sephadex G-10 columns.