LDC-mediated IgA CSR is MyD88 and TRIF dependent. (A–E) LDCs from WT or TRIF^−/−MyD88^−/− mice were cultured with CD43^negCD19⁺IgM⁺ B cells and IgA⁺ B cells were quantified. Data from three individual experiments with 10 mice pooled per experiment is shown. Statistical comparisons to WT mice are shown. (A) Representative flow cytometry plots. (B) Cumulative data. (C) ELISA to quantify the levels of IgA secreted by B cells in culture. (D and E) qRT-PCR of mRNA isolated from B cells stimulated for 2 d with the respective DC populations for AICDA (D) and GLT-α (E). Data are normalized to GAPDH and expressed in relative units. (F and G) LDCs from WT, TRIF^−/−, and MyD88^−/−-deficient mice were cultured with CD43^negCD19⁺IgM⁺ B cells and IgA⁺ B cells were quantified. Data from two independent experiments with five mice pooled per experiment are shown. Statistical comparisons were made to WT mice. (F) Representative flow cytometry plots. (G) Cumulative data. (H) ELISA to quantify TGF-β1 produced by LDCs from SPF, GF, and TRIF^−/−MyD88^−/− mice after 5 d of culture. Statistical comparisons to SPF mice are shown. (I and J) Flow-sorted TRIF^−/−MyD88^−/− LDC and SpDC were cultured with CD43^negCD19⁺IgM⁺ B cells in the indicated conditions and IgA⁺ B cells were quantified. Statistical comparisons to TRIF^−/−MyD88^−/− mice are shown. (I) Representative flow cytometry plots. (J) Cumulative data from three different experiments with five mice pooled per experiment. **, P < 0.01; ***, P < 0.001.