Blocking of the induction and expression of immunologically functional T lymphocytes by rat antiactivated T-cell serum

Abstract The preparation of a xenogeneic rat anti-mouse CTL serum, RAT ∗ , which potently inhibits CTL function in the absence of complement, has recently been described. In the present study, this serum is further characterized. The membrane antigens recognized by RAT ∗ were shown by FACS analysis to be detected most intensely on CTL, but are also present in lesser amounts on splenic T cells, thymocytes, and B cells. The T-cell proliferative response induced by Con A, PHA, TCGF, and modified self were all inhibited by RAT ∗ , but no effect was seen on LPS-induced B-cell proliferation. In addition, the in vitro induction of secondary CTL was not observed in the RAT ∗ -treated cultures. Finally, the effect of RAT ∗ pretreatment is shown to be irreversible. It is proposed that RAT ∗ serum reacts with receptors on T cells which are intimately involved in the “activation” step during the induction or expression phases of the response.