Related to these in vitro observations presented here, recent in vivo experiments from our team indicate that a low concentration of DON in pig feed (0.9 ppm) can increase the frequency of virus-specific IFN-γ/TNF-α co-producing CD4+ T cells after a combination of vaccination and challenge infection with porcine reproductive and respiratory syndrome virus (Pierron et al., in preparation). This evidence concerns the gene CD4 and infection.