IDENTIFICATION OF A CD4-CELL-STIMULATING ANTIGEN OF PATHOGENIC BACTERIA BY EXPRESSION CLONING( T)

Identifying the immunogenic proteins that elicit pathogen-specific T c ell responses is key to rational vaccine design. While several approac hes have succeeded in identifying major histocompatibility complex (MH C) class I bound peptides that stimulate CD8(+) T cells, these approac hes have been difficult to extend to peptides presented by MHC class I I molecules that stimulate CD4(+) T cells. We describe here a novel st rategy for identifying CD4(+) T cell-stimulating antigen genes. Using Listeria monocytogenes-specific, lacZ-inducible T cells as single-cell probes, we screened a Listeria monocytogenes genomic library as recom binant Escherichia roll that were fed to macrophages. The antigen gene was isolated from the E, coli clone that, when ingested by the macrop hages, allowed generation of the appropriate peptide/MHC class II comp lex and T cell activation. We show that the antigenic peptide is deriv ed from a previously unknown listeria gene product with characteristic s of a membrane-bound protein.