CD8B and coinfection: High frequencies of PRRSV-2-specific CD8β+ T cells expressing TNF were observed in PRRSV-2 single-infected and PRRSV-2/H3N2 co-infection groups (64.50% vs. 45.05%, respectively), followed by double TNF/IL-2 (6.39% vs. 29.05%, respectively) and TNF/IFN-γ (28.96% vs. 25.63%, respectively) producers.