Viral growth inhibition by human native and recombinant MBL. MDCK cells inoculated with influenza A virus A/Ibaraki/1/90 (H3N2) (50 FFU/well) were incubated for 60 min, and then incubated with influenza viral growth medium containing 0·5% tragacanth gum and diluted human native and recombinant MBL (0, 0·125, 0·25, 0·5, 1·0 μg/ml) without or with 100 mm d-mannose (Man). The infected foci were stained by using anti-human MBL antibody with the immunohistochemistry assay described in the Materials and Methods (a). The infected area is presented as a histogram of percentages of the control (mean±SD, n = 6) (b).