Augmentation of delayed-type hypersensitivity reactions to ovalbumin by cyclophosphamide in the mouse: strain variability, antigen specificity and nature of the suppressor cell.

The use of complete Freund's adjuvant (CFA) or pretreatment with cyclophosphamide (Cy) resulted in augmented delayed-type hypersensitivity (DTH) reactions in mice immunized with ovalbumin (OVA) and challenged 8 days later with heat-aggregated antigen. In 7 different strains, the degree of enhancement of DTH ranged from 2.5 to 4.2-fold with CFA and from 1.2 to 3.6-fold with Cy. More intense 24-h reactions (increased 3.3-8.8-fold) were elicited by use of both Cy and CFA. The effect of Cy was reversed by systemic transfer (at the time of immunization) of immune spleen cells, but not by cells treated with anti-Thy-1.2 and complement. The capacity of the suppressor T cells to reverse the potentiating effect of the drug was antigen-specific.