EXPRESSION LEVELS OF STRESS PROTEIN GP96 ARE NOT LIMITING FOR MAJOR HISTOCOMPATIBILITY COMPLEX CLASS I-RESTRICTED ANTIGEN PRESENTATION

Immunization of mice with gp96 induces CTL with specificity for protei ns that are expressed in the cells from which gp96 was isolated (Arnol d et al., J. Exp. Med. 1995. 182: 885, Udono et al., Proc. Natl. Acad. Sci. USA 1994. 91: 3077). Recently, it has been shown that gp96 from cells transfected with vesicular stomatitis virus (VSV) nucleocapsid p rotein as well as gp96 loaded in vitro with peptides containing an epi tope of this protein are taken up by phagocytic cells which obtain the reby the capacity for stimulating VSV-specific cytotoxic T lymphocytes (Suto and Srivastava, Science 1995. 269: 1585). The immunization expe riments together with the peptide transfer from gp96/peptide complexes to major histocompatibility complex (MHC) class I molecules of phagoc ytic cells are consistent with the hypothesis that the endoplasmic ret iculum-resident protein gp96 plays a crucial role in the antigen prese ntation of a cell (Srivastava et al., Immunogenetics 1994. 39: 93). To examine the involvement of gp96 in class I-restricted antigen present ation, we reduced gp96 RNA and protein levels by transfecting P13.1 ce lls with a vector containing part of gp96 cDNA in antisense orientatio n to the promotor. We found that antisense clones expressing strongly reduced levels of gp96 mRNA and gp96 protein show normal levels of MHC class I molecules on the cell surface and are recognized by T cells t o the same extent as wild-type cells. Thus, our results show that norm al levels of gp96 expression in a cell are not limiting for class I-re stricted antigen presentation.