Neutralization mechanisms of C7G6-IgM, C3G10-IgM, C11B10 and C10H10-IgG. MDCK cells were inoculated with B/Florida/4/2006 (Yamagata), B/California/10/2016-like (Yamagata), B/Hong Kong/330/2001 (Victoria) or B/California/11/2016-like (Victoria) virus preincubated with the indicated antibody. The expression of influenza B NP protein in MDCK cell monolayers 16-18 h after inoculation was detected by immunofluorescence using a monoclonal anti-NP primary antibody. Green, infected cells positive for NP protein; black, infected cells negative for NP protein. Scale bars = 100 μm. This experiment was repeated three times; one representative dataset is shown.