Lung CD103⁺ and CD24⁺ DCs but not lung Mφs induce IgA CSR. (A–E) Siglec-F⁻MHCII^hiCD11c⁺CD103⁺CD11b⁻ (LDC CD103⁺), Siglec-F⁻MHCII^hiCD11c⁺CD103-CD11b⁺CD24⁺ (LDC CD24⁺), and Siglec-F⁻MHCII^hiCD11c⁺CD103-CD11b⁺CD64⁺ (LMφ CD64⁺), all isolated from the lungs, SpDC, SkDC, and MLN DCs were cultured with CD43^negCD19⁺IgM⁺ B cells and IgA⁺ B cells were quantified. Data from three experiments is shown with 10 mice pooled per experiment. Statistical comparisons made to LMφ CD64⁺ are shown here. (A) Representative flow cytometry plots. (B) Cumulative data quantifying of the number of CD19⁺IgA⁺ B cells. (C) ELISA quantification of the 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) Flow-sorted total LDCs were cultured with CD43^negCD19⁺IgM⁺ B cells either with α-CD40 or without α-CD40 conditions and IgA⁺ B cells were quantified. Cumulative data from three experiments (seven mice per experiment) is shown. (G) Flow-sorted lung APC subsets (LDC CD103⁺, LDC CD24⁺, and LMφ CD64⁺), MLN DCs, and SpDCs were cultured with CD43^negCD19⁺IgM⁺ B cells in (–) α-CD40 conditions and IgA⁺ B cells were quantified. Cumulative data from two experiments (seven mice per experiment) is shown. Statistical comparisons are made to LMφ CD64⁺. (H) Flow cytometric quantification of IgA⁺ B cells in the lung and MedLN at steady state and after immunization with CT. Cumulative data from two experiments (three mice per experiment) is shown. **, P < 0.01; ***, P < 0.001.