TNF and infection: In another bovine outbreak investigation and study, it was shown that BVDV-induced immunosuppression predisposes animals to secondary infection with BHV-1 [45] and enhances the pathogenic effects of BHV-1 in cattle [36], which may be related to increased secretion of pro-inflammatory cytokines (TNF-α) and decreased production of anti-inflammatory cytokines (IL-10) following secondary infection [40], resulting in the promotion of inflammation in the lungs and the establishment of a pro-coagulant environment, further disrupting lung homeostasis.