Pathogenesis and inflammatory responses of swine H1N2 influenza viruses in pigs

Swine influenza viruses are an important pathogen in pig industry. In this study, we wanted to know whether swine H1N2 influenza viruses circulating in Korean pigs would cause clinical signs in pigs when experimentally infected. When pigs were infected with swine H1N2 viruses isolated from Korean pigs, pigs suffered from severe clinical signs of coughing, nasal discharge, labored breathing, facial edema, anorexia, and diarrhea. When the level of cytokine induction was measured using lung tissues, pro-inflammatory cytokines such as TNF-alpha, IL-1, and IL-8 were induced higher in lungs of infected pigs than in lungs of uninfected pigs. However, no increased induction of the anti-inflammatory cytokines such as IL-4 and IL-10 was observed in lungs of infected pigs. These results suggest that the pathogenesis induced in pigs by H1N2 influenza viruses may be induced by pro-inflammatory cytokines instead of anti-inflammatory cytokines.