Differences in the ability of T cells to suppress the induction and expression of contact sensitivity.

T cells from mice injected with picryl sulphonic acid (PSA) inhibit the expression of contact sensitivity to picryl chloride. Adult thymectomy (aTx) prevents the production of cells which inhibit the effector stage but cells from aTx mice are, however, still able to suppress the induction of contact sensitivity. These cells are antigen-specific T cells but unlike suppressor cells for the effector phase, they cannot be produced in cyclophosphamide (Cy)-treated mice. Similar properties have been reported for cells inhibiting the DNA synthesis in lymph nodes of mice painted with picryl chloride. It was also shown that cells from Cy-treated but non-thymectomized mice could not inhibit sensitivity when injected at the time of sensitization, i.e. suppressors of the effector phase, which are induced in Cy-treated mice cannot inhibit sensitivity when injected at the induction phase. These results show there are distinct mechanisms and probably distinct cells which inhibit the induction and expression of contact sensitivity.