Sensitivity to immunodepressant action of cyclophosphamide: analysis of interstrain differences in mice.

In one of our previous studies (Pevnitsky et al., Bull. exp. Biol. Med., 83, 438-440, 1977), we have found significant differences between various strains of mice in the sensitivity to immunodepressant action of cyclophosphamide (CP). The degree of these differences was not determined by the level of their immune response which indicates that the cause of the interstrain differences lies in a specific reaction of mice to the immunodepressant. The main parameters of CP effect which may be responsible for variable sensitivity to the immunodepressant action in vivo were studied in several murine strains (Balb/cJLacSto, CBA/CaLacSto, and DBA/2JSto): (1) rate of the preparation activation in liver microsomes; (2) pharmacokinetics of NBP-metabolites in the blood serum; (3) immunodepressant action of the in vivo activated CP; (4) sensitivity of immunocompetent target cells to activated CP effect. It was found that DBA/2 mice are the most sensitive to CP in vivo. The level of "active" CP in their blood serum is higher than in BALB/c mice. Besides, they are characterized by a higher sensitivity of immunocompetent cells compared to BALB/c and CBA mice.