AhR restrains primary B cell response to influenza virus. (A) Representative flow cytometry plot showing B220⁺ cells that are within germinal centers (GC; GL7⁺; top), B220⁺GL7⁺IgG1⁺ (middle), and B220⁺GL7⁺IgG1⁺ HA specific (bottom) in mock (PBS + 0.1% BSA)-infected or PR8-infected AhR mixed chimeras at day 16 after intranasal challenge. (B) Contribution of WT (CD45.1) and AhR^−/− (CD45.2) cells to the B220⁺ and B220⁺GL7⁺ pool. (C) Contribution of WT (CD45.1) and AhR^−/− (CD45.2) cells to the B220⁺GL7⁺IgG1⁺ pool. (D) Contribution of WT (CD45.1) and AhR^−/− (CD45.2) cells to the B220⁺GL7⁺IgG1⁺ HA-specific pool. (B–D) n = 7. Mean ± SD is shown. (E) Contribution of WT (CD45.1) and AhR^−/− (CD45.2) cells to the B220⁺GL7⁺IgA⁺ and B220⁺GL7⁺IgA⁺ HA-specific pool. n = 3. Mean ± SD is shown. (F) ELISA data showing endpoint titer (reciprocal of lowest serum dilution above background of day 0 sera) of PR8-specific IgG at day 10 after infection in AhR^−/− mix chimera and control mix chimera. n = 6–8. Mean ± SEM is shown. (G) Percentage of plasma cells (B220^lo CD138⁺) at day 10 after PR8 infection (or mock infected) in AhR^−/− mix chimera and control mix chimera. n = 2 for mock and n = 3–5 for PR8 infected. Mean ± SD is shown. (H) Percentage of plasma cells (left), total B220⁺ (middle), and germinal center⁺ (right) cells that come from CD45.1 versus CD45.2 in PR8-infected AhR^−/− mix chimera and control mix chimera. n = 5–6. Mean ± SD is shown. *, P < 0.05; **, P < 0.005 (Student’s t test).