[초청강연] Microbiota-induced vitamin A transport and its role in the intestinal immunity

Vitamin A and its derivative retinol are essential for the development of intestinal adaptive
immunity. Retinoic acid (RA)-producing myeloid cells are central to this process, but how
myeloid cells acquire retinol for enzymatic conversion to RA 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, including T and B cell homing to the intestine and
immunoglobulin A production. Our findings identify a key mechanism underpinning vitamin A’s
effects on the immune system and provide molecular insight into how the microbiota promotes
intestinal immunity.