CD4-class II major histocompatibility complex interaction does not enhance killing by a class I-restricted CD4+CD8+ cytotoxic T cell clone.

As unusual tumor-specific cytotoxic T lymphocyte (CTL) clone was isolated which expressed both CD4 and CD8 molecules. The target cells for this CTL can be induced to express either class I major histocompatibility complex (MHC) alone (with dimethylsulfoxide) or both class I and class II MHC (with interferon-gamma). Lysis of the tumor target depends on expression of class I MHC molecules, but does not require expression of class II MHC molecules. Furthermore, the lysis of target cells expressing both class I and class II is inhibited only by antibodies to class I (Kd), and not by antibodies to class II, demonstrating that the T cell receptor is class I restricted. We have used this CTL to assess the role of the interaction between CD4 and class II MHC in the absence of a class II-restricted T cell receptor. Our data indicate that CD4-class II interaction does not contribute to recognition by T cells in the absence of binding of the T cell receptor to class II molecules.