Immunoregulatory signal FoxP3, cytokine gene expression and IFN-γ cell responsiveness upon porcine reproductive and respiratory syndrome virus (PRRSV) natural infection

The study aims at evaluating gene expression of pro-inflammatory (IL-1β, IL-8, TNF-α), pro-immune (IFN-γ), anti-inflammatory (IL-10) cytokines and of the immunoregulatory signal FoxP3 in association with PRRSV-specific IFN-γ secreting cell (SC) responsiveness upon PRRSV natural infection. Forty PRRSV-negative pigs were assigned to two groups: 20 pigs were vaccinated at 3 weeks of age (weaning) against PRRSV (V-PRRSV) with a modified live virus vaccine (MLV) and 20 pigs were kept non-vaccinated (NV) as controls. Blood samples were collected at 3 (vaccination), 6, 8, 10, 12, 14, and 16 weeks of age. Natural infection occurred from 8 weeks of age onward in both groups and viremia lasted 8 weeks. In the early phase of infection, pro-inflammatory cytokines (IL-1β, IL-8, TNF-α) showed a delayed increase concomitant with the peak of viremia in both groups. In both groups, IL-10 peaked at 12 weeks in association with the increase of pro-inflammatory cytokines. Conversely, in vaccinated pigs (V-PRRSV), IFN-γ showed higher gene expression during the early phase of infection and a more intense secreting cell (SC) response in the late phase. Differently, gene expression of the transcription factor FoxP3, expressed by T regulatory lymphocytes (Tregs), increased significantly in controls only and was associated with the rise of the viral load. Moreover, FoxP3 levels remained significantly higher during the late phase of infection and paralleled with lower levels of IFN-γ SC detected by ELISPOT. The expression/production of immunoregulatory signals involved in Treg activation could be a promising marker to study the immunobiology of PRRSV infection.