Genetically encoded and post-translationally modified forms of a major histocompatibility complex class I-restricted antigen bearing a glycosylation motif are independently processed and co-presented to cytotoxic T lymphocytes

The mechanisms by which antigenic peptides bearing a glycosylation site may be processed from viral glycoproteins, post-translationally modified, and presented by major histocompatibility complex class I molecules remain poor ly understood. With the aim of exploring these processes, we have dissected the structural and functional properties of the MHC-restricted peptide GP9 2-101 (CSANNSHHYI) generated from the lymphocytic choriomeningitis virus (L CMV) GP1 glycoprotein. LCMV GP92-101 bears a glycosylation motif -NXS- that is naturally N-glycosylated in the mature viral glycoprotein, displays hig h affinity for H-2D(b) molecules, and elicits a CD8(+) cytotoxic T lymphocy te response. By analyzing the functional. properties of natural and synthet ic peptides and by identifying the viral sequence(s) from the pool of natur ally occurring peptides, we demonstrated that multiple forms of LCMV GP92-1 01 were generated hom the viral glycoprotein and co-presented at the surfac e of LCMV-infected cells. They corresponded to non-glycosylated and post-tr anslationally modified sequences (conversion of Asn-95 to Asp or alteration of Cys-92). The glycosylated form, despite its potential immunogenicity, w as not detected. These data illustrate that distinct, non-mutually exclusiv e antigen presentation pathways may occur simultaneously within a cell to g enerate structurally and functionally different peptides from a single gene tically encoded sequence, thus contributing to increasing the diversity of the T cell repertoire.