TNF and pneumonia: In pigs with experimentally induced IAV-related VAERD, it is discussed that non-neutralizing antibodies, subsequent immune complex formation with complement activation as well as excessive expression of pro-inflammatory cytokines, i.e., TNF-α, IL-1β, IL-6, IL-8, and chemokines are involved in the development of enhanced pneumonia and neutrophilic infiltration of lungs [20,62,63].