Cytolysis by cloned helper T cells: induction by specific antigen or by anti-CD3 hybrid antibodies.

Abstract

We have explored the use of hybrid antibodies--prepared by covalently linking anti-CD3 to an antibody specific for a monomorphic major histocompatibility complex (MHC) class II determinant using N-succinimidyl 3-(2-pyridyldithio)proprionate/succinimidyl 4-(N-malcimidomethyl)cyclohexane-1-carboxylate (SPDP/SMCC) as coupling reagent--in inducing cytolysis in human tuberculin (PPD)-specific T helper (TH) clones. These clones have been shown to lyse PPD-bound Epstein-Barr virus (EBV)-transformed B-cell lines (B-EBV) in an MHC class II-restricted manner. In this paper anti-CD4-induced cytolysis is compared with antigen/MHC-induced cytolysis with the same clones. Cytolysis induced by the hybrid antibodies was highly efficient, with killing of both syngeneic and allogeneic tumour cells positive for MHC class II. Conjugate-induced cytolysis was maxima within 4 h; that of antigen-positive targets at 16 h. Killing of bystander cells was seen only when cytolysis was triggered by antigen/MHC, suggesting that the mechanism of cytolysis in the two systems may be distinct. Targets treated simultaneously with hybrid antibody and with antigen, thereby providing both activation signals to the clones, are lysed less efficiently than those treated with either PPD or hybrid antibody alone. Evidence is presented showing that this inhibition is most marked against syngeneic PPD-coated cells treated with hybrid antibody, suggesting that two signals independently capable of activating cytolytic function in the clones, when presented simultaneously, interfere with the induction of the cytolytic process.