PROCESSING OF A VIRAL GLYCOPROTEIN IN THE ENDOPLASMIC-RETICULUM FOR CLASS-II PRESENTATION

Endogenous processing of viral glycoproteins for presentation to CD4() T cells is a poorly investigated aspect of antigen processing and pr esentation. This pathway may involve not only pathogens, but also self proteins, and may thus be involved in self-tolerance. We have charact erized the processing of the endoplasmic reticulum-restricted glycopro tein (G) of vesicular stomatitis virus, termed poison tail (Gpt), bioc hemically and enzymatically, and by T cell recognition assays. Express ed with a vaccinia vector, Gpt remains endoglycosidase H-sensitive and does not mature to endoglycosidase D sensitivity. The protein is degr aded in the ER with a T1/2 of 4 h. Gpt peptides are not secreted since Gpt-infected cells are unable to sensitize uninfected antigen-present ing cells in an innocent bystander assay. Using flow cytometry, Gpt is undetectable on the plasma membrane; in contrast, wild-type G is read ily found on the surface or secreted into the milieu as soluble G foll owing infection of A20 cells with a vaccinia recombinant expressing G. The degradation of Gpt is sensitive to the thiol reagent diamide and occurs optimally at physiological pH. A series of proteolytic inhibito rs were tested: 3,4-dichloroisocoumarin and 1-chloro-3-tosylamido-7-am ino-2-heptanone inhibited degradation, which suggests the involvement of a serine protease. The degradation does not require transport to th e Golgi complex, and is not sensitive to a variety of lysosomotropic a gents. We show that the degradation products include the immunogenic e pitopes recognized by a panel of T cell clones and hybridomas.