Evidence of selective processing of immunodominant epitopes in virally infected cells

Recent advances in clarifying the molecular mechanisms involved in Ag processing and presentation have relied heavily on the use of somatic cell mutants deficient in proteasome subunits, TAP transporter, and cell surface expression of MHC class I molecules, Of particular interest currently are those mutants that lack specific protease activity involved in the generation of antigenic peptides, It is theoretically possible that deficiencies of this nature could selectively prevent the cleavage of certain peptide bonds and thus generate only a subset of antigenic peptides, Gro29/K-b cell line is derived from the wild-type murine Ltk(-) cell line. This cell line is one example of a mutant that lacks specific protease activities. This deficiency manifests itself in an inability to generate a subset of immunodominant peptide epitopes derived from vesicular stomatitis virus and herpes simplex virus. This in turn leads to a general inability to present these viral epitopes to cytotoxic T lymphocytes (CTL). These studies describe a unique Ag processing deficiency and provide new insight into the role of proteasome-independent proteases in MHC class I-restricted peptide generation.