CD4 and infection: In pigs, the significant roles of CD4+ T-cells, CTLs and γδ T-cells have been demonstrated in PRRSV infection in pigs (47); CD8+ T-cells and T-helper/memory cells following pseudorabies live attenuated vaccination (48); CD3+ CD4-CD8αhi CTLs in classical swine fever live attenuated vaccine and virulent challenge infection (49); and CD4+CD8αhi αβ T-cells during melanoma tumor regression in swine model (50).