Monitoring the Cascade of Monocyte-Derived Macrophages to Influenza Virus Infection in Human Alveolus Chips.

Respiratory viruses ravage the world and seriously threaten people's health. Despite intense research efforts, the immune mechanism underlying respiratory virus-induced acute lung injury (ALI) and pulmonary fibrosis (PF) has not been fully elucidated. Here, the cascade of monocyte-derived macrophages to influenza A virus infection is monitored on an optimized human alveolus chip to reveal the role of macrophages in the development of ALI and PF. We find that viral infection causes damage to the alveolar air-liquid barrier and the release of inflammatory cytokines, which induce the M0 macrophages to gather and polarize to the M1 phenotype at the damaged site through recruitment, adhesion, migration, and activation, leading to ALI. Afterward, M1 macrophages polarize into the M2 phenotype, and then transform into myofibroblasts, followed by enhanced secretion of various anti-inflammatory cytokines and profibrotic cytokines, to promote PF. Our study provides an insight into the pathogenesis of virus-induced ALI and PF, which will assist in the development of therapeutic strategies and drugs for treating influenza and other respiratory virus infections.