Abstract
The T-helper (Th) cell immune response in mice to various alphaviruses and the structural envelope (E) glycoproteins E1 and E2 of Venezuelan equine encephalitis (VEE) TC-83 virus was investigated. Antigens analysed included the structural glycoproteins expressed in a recombinant vaccinia-VEE virus (TC-5A), sodium dodecyl sulfate-polyacrylamide gel electrophoresis separated E1 and E2, and synthetic peptides prepared from the extramembranal domain of the E2 and selected regions of the E1. Subunit peptides, prepared from the biologically important amino terminus (amino acids [AA] 1-25) of the E2 of VEE Trinidad donkey virus, were also analysed. Th cells from spleens of C3H, C57BL/6 or BALB/c mice immunized with virus, glycoprotein or free peptide and enriched by nylon wool chromatography were analysed for recognition of antigen in an in vitro lymphoblastogenesis test (LBT). The associated antibody response was also measured using an indirect enzyme-linked immunosorbent assay with the appropriate antigens. The predominant proliferating cell type in LBTs secreted IL-2 and was of the Th-cell phenotype Thy-1+, Lyt-1+, 2-, L3T4+. The LBT and antibody responses in C3H mice to VEE, western and eastern equine encephalitis viruses were primarily virus specific. The Th-cell response to the recombinant TC-5A virus was similar to that seen with VEE virus. VEE virus Th cells recognized both the E2 and E1 glycoproteins in LBT and the glycoproteins were able to prime mice for an anamnestic antibody response to conformationally dependent B-cell epitopes present on the challenge VEE virus. E2 and E1 synthetic peptides defined various immunodominant virus-reactive Th-cell epitopes, and genetic restriction of the immune response was seen. The subunit peptides defined multiple Th- and B-cell elements and a dominant Th-cell epitope was found in peptide S3 (AA 9-19). The results from this study indicate that both the E1 and E2 glycoproteins contain Th-cell epitopes of biological importance and that a single residue interchange can alter the expression of both Th- and B-cell epitopes.