Prokaryotic 16S rRNA / Stool microbial communities of LRP1fl/fl and LRP1xdCd11c mice

Vitamin A and its derivative retinol are essential for the development of intestinal adaptive immunity. Retinoic acid-producing myeloid cells are central to this process, but how myeloid cells acquire retinol for enzymatic conversion to retinoic acid is unknown. Here, we show that serum amyloid A, SAA, proteins, retinol binding proteins induced in intestinal epithelial cells by the microbiota, deliver retinol to myeloid cells. We identify LDL receptor-related protein 1, LRP1, as an SAA receptor that facilitates endocytosis of SAA-retinol complexes and promotes retinol acquisition by RA-producing intestinal myeloid cells. Consequently, SAA and LRP1 are essential for vitamin A-dependent immunity.