Regulation of contact sensitivity to DNFB in the mouse: effects of adult thymectomy and thymic factor.

The contact sensitivity response to DNFB is decreased after adult thymectomy (ATX). This response decreases to 50% of the control response of normal age-matched mice as soon as 3 weeks after ATX and is not further depressed 9 to 16 weeks after ATX. These results suggest that two T cell subsets of different lifespan are involved in the anti-DNFB response. A circulating thymic factor (FTS) is able to restore the contact sensitivity response to DNFB when injected 3 to 9 weeks after ATX but not 16 weeks later. By contrast, FTS has a depressive effect on the contact sensitivity response to DNFB of normal mice through a cyclophosphamide-sensitive T cell subset. These results suggest that FTS regulates DNFB contact sensitivity by acting on a cyclophosphamide-sensitive T cell subset, still present 9 weeks after ATX but absent after 16 weeks. Thus although the T cell defect, causing a depression of the contact sensitivity reaction to DNFB is quantitatively similar 3 and 16 weeks after ATX, its nature is probably different.