Fig 1: Bona fide and bystander MBCs(A) Contour plots showing Fcer2a expression by the lung MBC subsets after 70 days of influenza infection, paired t test.(B) Contour plots showing the IL-4 GFP expression at day 9 of influenza infection in the mediastinal lymph node (left) and the proportion of GFP+ cells that express PD-1 and CXCR5 (right), one-way ANOVA.(C) Experimental approach for the treatment of wild-type mice with anti-IL4 antibody, PBS, or complexed IL4 during infection.(D) Histograms showing Fcer2a expression in mice treated as in (C), one-way ANOVA.(E and F) Contour plots of (E) lung and (F) lymph node CCR6+ MBCs in mice treated as in (C), one-way ANOVA.(G and H) Contour plots of (G) the lung and (H) lymph node MBCs depicting the proportions of CCR6+CXCR3- and CCR6+CXCR3+ subsets in mice treated as in (C). Quantifications in the left panels show the CXCR3+/CXCR3- MBC ratio, one-way ANOVA. Quantifications in the middle panels show the number of NP+ MBCs, one-way ANOVA. Quantifications in the right panels show the proportion of NP+ MBCs within each subset, two-way ANOVA.(I) Contour plots showing Fcmr expression by the lung MBCs at day 70 of the influenza infection, paired t test.(J) Dot plots showing the binding of lung MBCs to labeled IgM immune complexes (ICs), paired t test.(K and L) Enumeration of ASCs in the lungs of chimeric mice receiving (K) 80% µMT + 20% wild type versus 80% µMT + 20% Fcmr-/- bone marrow or (L) 50% CD45.1 + 50% wild-type CD45.2 versus 50% CD45.1 + 50% Fcmr-/- CD45.2 bone marrow. Mice were infected with influenza PR8, challenged with influenza X31 after 50 days, and sacrificed 4 days later. In (L), CD45.2 cells were sorted before ELISpot, two-way ANOVA test. In all the panels, each dot represents one mouse, mean ± SEM, *p < 0.01, *p < 0.05, ***p < 0.001, and ****p < 0.0001.See also Figure S5.