Characterization of T-helper epitopes of the glycoprotein of vesicular stomatitis virus.

The T-helper (Th) cell epitopes in the glycoprotein (GP) of vesicular stomatitis virus serotype Indiana (VSV-IND) were analyzed with a complete panel of overlapping synthetic peptides. Three Th-cell epitopes in C57BL/6 (H-2b) mice and two epitopes in BALB/c (H-2d) mice were defined by their ability to stimulate in vitro proliferation of virus-primed, CD8+ T-cell-depleted spleen cells in a class II-restricted manner. A series of CD4+, I-Ab-restricted T-cell hybridomas from VSV-primed C57BL/6 mice were characterized by their production of interleukin-2 and interleukin-3 upon stimulation with VSV-IND or purified VSV GP in vitro. Of nine hybridomas derived from three independent fusions, five were specific for amino acids (aa) 415 to 433 (p8) of VSV-IND GP, three recognized aa 52 to 71 (p41), and one reacted against aa 316 to 335 (p17). Fluorocytometric analysis of Th hybridomas or VSV-stimulated T-cell lines with monoclonal antibodies specific for the T-cell receptor V beta chain did not reveal obvious correlations between the T-cell receptor V beta gene segment used and the epitope recognized. All three peptides recognized by H-2b mice and both epitopes recognized by H-2d mice which were characterized in primed T-cell populations were capable of activating specific Th cells in vivo as measured by the induction of antibody class switch from immunoglobulin M (IgM) to IgG. Thus, the epitopes are relevant for VSV GP-specific Th response in vivo and are able to provide functional help for the production of anti-VSV-specific neutralizing IgG antibodies.