OBJECTIVE: To investigate synergistic effect of Reduning (RDN) injection plus ribavirin against severe pneumonia induced by H1N1 influenza A virus in mice.METHODS: We established a mouse model of severe pneumonia induced by influenza A virus by infecting Balb/c mice with CA07 virus.We randomly assigned the infected mice into four groups,and treated them with normal saline (NS group),RDN (injection,86.6 mg/kg),ribavirin (injection,66.6 mg/kg) or double Ribavirin plus RDN group,the same dosage as used in the single treatments) for 5 d.Lung index and lung pathology were recorded or calculated in terms of the curative effective.Cytokines,NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome related protein including caspase-associated recruitment domain (CARD) domain Apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC),caspase-1 and NOD-like receptor family,pyrin domain containing 3 (NLRP3),and reactive oxygen species were simultaneously investigated.RESULTS: RDN plus ribavirin treatment,not RDN or ribavirin alone,provided a significant survival benefit to the influenza A virus-infected mice.The combination treatment protected the mice against severe influenza infection by attenuating the severe lung injury.The combined treatment also reduced the viral titers in mouse lungs and lung index,downregulated their immunocytokine levels,including IL-1β and IL-18,and down regulated the NL-RP3,especially the transcription and translation of caspase-1.Meanwhile NS group had significantly higher reactive oxygen species (ROS) expression which could was dramatically reduced by the treatment of RDN plus ribavirin.CONCLUSION: Our study showed that RDN combined with ribavirin could protect the mice,and reduce the lung immunopathologic damage caused by severe influenza pneumonia.The mechanism could be that it reduced ROS produce and inhibited NLRP3 inflammasome activation so that mainly lower the downstream inflammatory cytokines IL-1β and IL-18.