Fatty acids and their metabolites regulate immune cell function. The present study was undertaken to examine the detailed distribution of fatty acid binding proteins (FABPs), the cytosolic chaperones of fatty acids, in mouse peripheral immune organs. Using immunohistochemistry, FABP7 was localized to the alpha-smooth muscle actin (SMA)(+) fibroblastic reticular cells, which construct the stromal reticula in the T cell areas of the peripheral lymph nodes and spleen. Immunoelectron microscopy showed that FABP7(+) cells enclosed the collagen fibers, forming a conduit system, which transport lymph and associated low-molecular-mass proteins. In contrast, FABP5(+) cells were distributed throughout the lymph node and contained well-developed lysosome and phagocytic materials within the cytoplasm. The mesenteric lymph nodes of FABP7 knockout mice showed normal histological features, but the percentage of CD4(+) cells was significantly increased compared with that in wild-type mice. These data indicate that FABP7 may be involved in T cell homeostasis, possibly by modulating lipid metabolism in fibroblastic reticular cells within the peripheral lymph nodes.