Suppressor cell activation by anti-Thy 1.2 in NZB/WC₁ mice

A single injection of anti-Thy 1.2 serum was used to study the spontaneous loss of suppressor cells in NZB/WF₁ mice. When given 1 day before primary allografting with C57BL/6 skin, anti-Thy 1.2 significantly prolonged mean graft survival (MGS) in 5-week-old NZB/NZWF₁ graft recipients. However, four times the dose of anti-Thy 1.2 was required to cause graft prolongation when compared with BALB/c recipients. In contrast to its graft-prolonging effect in 5-week NZB/WF₁ mice, anti-Thy 1.2 failed to prolong MGS in either 17- or 34-week-old NZB/WF₁ animals. Spleen cells from anti-Thy 1.2-treated 5-week-old NZB/WF₁ mice could transfer suppression of graft rejection to otherwise untreated 5-week-old syngeneic recipients. This transfer required viable, radioresistant T cells. Although spleen cells from anti-Thy 1.2-treated 5-week-old mice transferred the suppression to 5-week-old recipients, the same cells were not effective if given to 17-week-old recipients. However, spleen cells from 17-week-old-pretreated donor mice were able to prolong MGS when given to the younger 5-week-old syngeneic recipients. The transfer studies of skin allograft prolongation by anti-Thy 1.2-treated spleen cells suggest that the ability to initiate suppressor cell activation is present in both young and older NZB/WF₁ mice, whereas suppressor effector mechanisms are deficient in the older mice. In addition to its usefulness in studying the details of suppressor cell action, the studies suggest that anti-Thy 1.2 treatment may be a valuable probe for the presence of suppressor cells and/or their precursors.