CXCL1 and acute respiratory distress syndrome: The robust pro-inflammation could advance Pneumocystis or primary influenza viral pneumonia (PIVP) into acute respiratory distress syndrome (ARDS), a condition that is very difficult to treat with a high morbidity and mortality, through CARD9-dependent signaling pathway (38). During influenza virus or Pneumocystis infection, activation of macrophages and DCs induces an uncontrolled production of inflammatory cytokines/chemokines, such as IL-6, TNF and CXCL1, leading to the development of ARDS.