In addition, we also found that most chemokines, including KC, MIP-1a, MIP-1b, MCP-1, and MCP-3, were elevated in MBL WT mice compared with the MBL KO mice in both pdmH1N1 and G1/97 virus infection. Influenza virus-infected macrophages produced large amounts of these chemokines in vitro [25, 47, 48] . Functionally, these chemokines are important mediators for immune cell activation and chemotactic factors, which recruit leukocytes to the infected sites [49] . This may help account for our histological observation that more inflammatory cell infiltration was observed in MBL WT mice than in MBL KO mice.