A study of the cellular immune response to enteroviruses in humans: identification of cross-reactive T cell epitopes on the structural proteins of enteroviruses.

We have attempted to extend our understanding of the enteroviral cross-reactive T cell response in humans. Peripheral blood mononuclear cells (PBMC) from healthy donors were stimulated in vitro with six different serotypes of enterovirus and 15 synthetic peptides representing conserved regions in the four structural proteins of these viruses. Upon challenge with different antigens, PBMC from donors responded specifically with proliferation and production of interferon-gamma (IFN-gamma). In contrast, synthesis of interleukin-4 (IL-4) or IL-10 was not detected. A T cell response to each enterovirus serotype was recorded in all individuals even though not all individuals had serum neutralizing antibody against each virus. These data confirmed previous findings that human T cells recognize enteroviral cross-reactive epitopes. Analysis of the peptide-induced IFN-gamma production and proliferative response showed that the cross-reactive T cell epitopes are localized mainly in capsid protein VP2 and VP3 and to a lesser extent in VP1. Surprisingly, T cell epitopes were not identified in the most conserved structural protein of enterovirus, VP4. Immune responses were mediated by CD4+ T cells in association with MHC class II molecules. The sources of IFN-gamma in response to the most immunodominant cross-reactive T cell epitopes were CD4+, CD8+ and NK cells. The two latter subsets produced IFN-gamma provided CD4+ T cells were present. Since T helper 1 (Th1) cells can mediate an in vivo protective immune response against poliovirus infection in mice, our novel findings in humans merit further detailed characterization of T cells that recognize the enteroviral cross-reactive T cell epitopes.