Antigenic specificity of porcine T cell response against foot-and-mouth disease virus structural proteins: identification of T helper epitopes in VP1.

The contribution of each of the viral capsid proteins of foot-and-mouth disease virus (FMDV) in the T cell response of vaccinated pigs has been studied. Viral polypeptides, VP1 to VP4, were expressed as fusion proteins in Escherichia coli, and were used to stimulate peripheral blood mononuclear cells of vaccinated animals. Significant, dose-dependent responses to whole virion were detected in the seven animals analyzed and, in five of them, responses to recombinant polypeptides VP1, VP2, and VP3 were noticed, VP4 was recognized only by one of the pigs. Among the responder animals, VP1 and VP3 induced the higher proliferative responses. The patterns of recognition of a nested set of VP3 fragments expressed as fusions in E. coli were different among the animals studied and were consistent with the presence of different T cell epitopes on the protein. Likewise, three of the four VP1 fragments induced significant responses and were differentially recognized by each of the animals tested. Partially overlapping synthetic peptides spanning VP1 amino acids 41 to 209 were used to identify T cell epitopes in this protein. The significant responses obtained in three of seven additional FMDV vaccinated outbred pigs analyzed revealed the existence of at least 11 different T cell epitopes distributed throughout the sequence studied, which were distinctly recognized by each of the responder animals. A peptide corresponding to a relevant B cell antigenic site, around amino acids 140-160, was shown to stimulate lymphocytes from two of the responder animals. Thus, the results obtained indicate that different T cell epitopes of capsid proteins VP1 and VP3 are recognized by pig populations. The different patterns of recognition of recombinant polypeptides and synthetic peptides observed among outbred animals support an important contribution of genetic restriction, probably mediated by MHC genes, to the individual T cell response in swine.