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 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 low-density lipoprotein (LDL) receptor–related protein 1 (LRP1) as an SAA receptor that endocytoses 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 B and T cell homing to the intestine and immunoglobulin A production. Our findings identify a key mechanism by which vitamin A promotes intestinal immunity.

中文翻译：

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血清淀粉样蛋白 A 将视黄醇输送到肠髓细胞以促进适应性免疫

维生素 A 及其衍生物视黄醇对肠道适应性免疫的发展至关重要。产生视黄酸 (RA) 的骨髓细胞是这一过程的核心，但骨髓细胞如何获得视黄醇以转化为 RA 尚不清楚。在这里，我们展示了血清淀粉样蛋白 A (SAA) 蛋白——微生物群在肠上皮细胞中诱导的视黄醇结合蛋白——将视黄醇输送到骨髓细胞。我们将低密度脂蛋白 (LDL) 受体相关蛋白 1 (LRP1) 鉴定为一种 SAA 受体，可内吞 SAA-视黄醇复合物并促进产生 RA 的肠髓细胞获取视黄醇。因此，SAA 和 LRP1 对维生素 A 依赖性免疫至关重要，包括 B 和 T 细胞归巢到肠道和免疫球蛋白 A 的产生。