Positive effect of cyclophosphamide on the expression of MHC class II antigens.

Wistar rats, 6-8 weeks old, were treated intraperitoneally (i.p.) with a single dose of 20 or 200 mg/kg cyclophosphamide (CY), one day before their immunization with 50 mg/kg ovalbumin (OVA). On the third day after CY administration, cytological slides from peritoneal cells, obtained by lavaging the peritoneal cavity and cryosection from the mesenterial lymph nodes and spleen were prepared. The slides were stained by the method of peroxidase-antiperoxidase with monoclonal antibodies OX6 (Sera-Lab) against constant region determinant of rat class II antigens. The results obtained demonstrated a strong hyperexpression of MHC class II antigens in the peritoneal cells as well as in the lymph nodes and spleen from animals treated with CY and a stronger one, when after CY administration the animals were immunized with OVA. However, immunization with OVA alone did not stimulate notable augmentation of Class II antigen expression compared to healthy nontreated animals. The hyperexpression of class II antigens in animals treated with CY resulted from a pronounced lymphocytes depletion. This suggests that it is not lymphocytic gamma-interferon, as is commonly accepted, but some other factor(s), released from the accessory cells, that takes part in the mechanism of class II antigen hyperexpression.