Influenza virus A (IAV) causes annual epidemics and intermittent pandemics that affect millions of people worldwide. Potent inflammatory responses are commonly associated with severe cases of IAV
infection. The
complement system, an important mechanism of innate and humoral immune responses to
infections, is activated during primary IAV
infection and mediates, in association with natural
IgM, viral neutralization by virion aggregation and coating of viral hemmagglutinin. Increased levels of the
anaphylatoxin C5a were found in patients fatally infected with the most recent H1N1 pandemic virus. In this study, our aim was to evaluate whether targeting C5 activation alters inflammatory
lung injury and viral load in a murine model of IAV
infection. To address this question C57Bl/6j mice were infected intranasally with 10(4) PFU of the mouse adapted Influenza A virus A/WSN/33 (H1N1) or inoculated with PBS (Mock). We demonstrated that C5a is increased in bronchoalveolar lavage fluid (BALF) upon experimental IAV
infection. To evaluate the role of C5, we used OmCI, a potent arthropod-derived inhibitor of C5 activation that binds to C5 and prevents release of C5a by
complement. OmCI was given daily by
intraperitoneal injection from the day of IAV
infection until day 5. Treatment with OmCI only partially reduced C5a levels in BALF. However, there was significant inhibition of neutrophil and macrophage infiltration in the airways, Neutrophil Extracellular Traps (NETs) formation, death of leukocytes, lung epithelial injury and overall lung damage induced by the
infection. There was no effect on viral load. Taken together, these data suggest that targeting C5 activation with OmCI during IAV
infection could be a promising approach to reduce excessive inflammatory reactions associated with the severe forms of IAV
infections.