Five cytotoxic T lymphocyte (CTL) clones, all specific for influenza virus A/JAP/57 and all H-2K(d)-restricted, were typed for expression of MHC products. All express H2K and H-2D encoded antigens, but they differ in their expression of I region products. One clone, 14-2, is positive with antisera directed against serologically detectable products apparently related to three different I regions, namely I-A, I-J, and I-E. Two clones, 11-1 and 14-1, lack I-E-associated antigens but express I-A and I-J products, and two other clones, 14-7 and 14-13, lack detectable I region products. These observations show that although discrete CTL clones may be homogeneous in their function, they differ in their expression of I region products.
