We demonstrated that despite these 2 strains of viruses being bound by rhMBL via the CRD of MBL at the physiological level, they infected both MBL WT and MBL KO mice effectively. Our results are consistent with a recent in vitro study by Job et al [18] , in which MBL was found to bind to pdmH1N1 fairly in vitro but the virus was resistant to the antiviral activity of MBL. The number and position of potential glycosylation sites on the viral HA globular domain determine the binding affinity between MBL and the virus. Even though MBL can physically bind to the virus, the binding may be insufficient for executing any antiviral function. Arguably, Chang et al [23] recently reported that MBL deficiency increases susceptibility to infection with influenza A virus Philippine 82 H3N2 (Phil82), which is a human strain. We reconcile with the suggestion that MBL effects would differ depending on strains of influenza A virus and thus MBL causes variable antiviral activities and host responses. The degree of glycosylation on the globular head of the HA molecule is believed to be essential for MBL to exhibit its antiviral properties. For Phil82 virus, the high-mannose oligosaccharide at residue 165 of the HA molecule has already been shown to be crucial for the neutralization by MBL [31] . Although pdmH1N1 virus contains a single potential glycosylation site at the base of the HA globular head (Asn 104 ), it lacks potential glycosylation sites on the globular head region of HA (Asn 142 , Asn 144 , Asn 172 , Asn 177 , and Asn 179 ) [18] . To our knowledge, binding of MBL on H9N2/G1 virus is not well documented in the literature. Therefore, we analyzed the potential glycosylation sites on HA of H9N2/G1 virus based on an in silico approach as suggested by Job et al [18] . The HA sequence data was retrieved from GenBank (AAF00706.1) and we used NetNGlyc 1.0 server to predict the number of potential glycosylation sites. We found that there was no potential glycosylation sites near residue 165 of the HA molecule of H9N2/G1 virus. We speculate that as a result of the absence of potential glycosylation sites near the receptor-binding domain of the HA globular head of both pdmH1N1 virus and H9N2/G1 virus, MBL fails to interfere with the viral binding to target cells despite its ability to bind the virus. This can adequately explain the discrepancy between the present in vivo data and Chang's study [23] .