Effect of cyclophosphamide on delayed hypersensitivity to Staphylococcus aureus in mice.

Mice given cyclophosphamide 2-3 days before a single subcutaneous infection with Staphylococcus aures on cotton dust develop much more delayed type hypersensitivity (DTH) than normal. The enhancement is due to removal of rapidly dividing cells from the spleen. Passive transfer experiments before infection or before challenge show that immune serum suppresses the induction but not the expression but do not prevent induction. There may therefore be 2 suppressor or regulating systems involved. Cell commitment to suppressor function may be self-limiting. The results explain why DTH to staphylococci is only fully established after repeated infections and support the view that the suppressor system may function as a check on the excessive and potentially harmful development of DTH.