Antibodies directed against the following human surface proteins were used: HLA-DR (L243), CD11c (B-ly6), DC-SIGN (DCN46),3CXCR1 (5A12), β7 (FIB504), α4 (9F10), cytokeratin (CAM5.2), CD45 (2D1, all from Becton Dickinson, San Jose, CA); BDCA-1/CD1c (L161), SIRP-α (SE5A5, both from Biolegend, San Diego, CA); CCL25 (rabbit polyclonal, from AbD Serotec, Raleigh, NC); and CD103 (B-Ly7, eBioscience, San Diego, CA). Our lineage cocktail contained antibodies to CD3, CD14, CD19, and CD20 (all from Becton Dickinson). A LIVE/DEAD® yellow dye (Life Technologies, Carlsbad, CA) or propidiumiodide were used to exclude dead cell populations. The capacity of live cells to convert retinaldehyde to RA was measured using the flow cytometry-based Aldefluor™ assay according to the manufacturer’s protocol (Stemcell Technologies, Vancouver, BC, Canada). The Aldefluor™ assay employs a fluorescent non-toxic aminoacetaldehyde, which freely diffuses into intact and viable cells and is converted by ALDH into an aminoacetate that is retained inside the cells. An LSRII flow cytometer (Becton Dickinson) and FlowJo 7.6.5 software (TreeStar, Ashland, OR) were used for analysis. Immunofluorescence staining of frozen gastric and intestinal sections was performed as described previously (26 (link)).