Identification of immunodominant T-cell epitopes in membrane protein of highly pathogenic porcine reproductive and respiratory syndrome virus.

The development of cell-mediated immunity has been known extremely important in clearing porcine reproductive and respiratory syndrome virus (PRRSV) in infected pigs. However, the PRRS immunology regarding the interaction of T-cells and PRRSV proteins is poorly understood. To identify the T-cell immunodominant epitopes on the membrane (M) protein of PRRSV, a series of 31 overlapping pentadecapeptides covering the entire M protein were designed and synthesized. These peptides were screened by ELIspot analysis for their capabilities to elicit interferon-gamma (IFN-γ) responses in the peripheral blood mononuclear cells (PBMCs), which were collected from pigs immunized with attenuated PRRSV HuN4-F112 strain and challenged with highly pathogenic HuN4 strain. After three rounds of screening, 4 peptides (M3, M6, M8 and M12) were shown to elicit high expression of IFN-γ. The stimulation of high IFN-γ transcription in PBMCs by these 4 peptides was further confirmed in real-time PCR. The sequence alignment revealed that the epitope represented by peptide M6 was fully conserved in all of examined 42 North American genotype II PRRSV isolates and the epitopes represented by peptides M3, M8 and M12 showed 2-4 amino acid replacements. The finding of 4 T-cell immunodominant epitopes in the M protein of PRRSV will be beneficial to the understanding of the development of cell-mediated immunity.