APCs expressing different markers colonize distinct areas of the human axillary lymph node. Frozen lymph node sections were probed with antibodies detecting CD3 and CD21 to identify the T lymphocyte–rich paracortex and follicles, respectively, thus providing anatomical definition (A,B). Within the paracortex, T lymphocytes were densely packed in some regions and more diffuse in others (A,B). Immunohistochemistry illustrated that cells expressing CD1a were either concentrated in diffuse T-lymphocyte zones surrounding the dense T-lymphocyte regions (C) or evenly distributed throughout areas densely packed with T lymphocytes (D). Cells expressing low and high levels of CD1a were detected (D, inset). CD208⁺ cells colonized similar areas to cells expressing CD1a (E,F). Dense bodies of cells expressing CD68, CD209, CD206, and CD14 were located in the medullary cords (G-L). Less frequent cells expressing CD68, CD206, and CD209 were also detected in the diffuse T-lymphocyte regions surrounding the medullary cords and follicles (G-K). Cells expressing CD68 or CD14 were also detected in the follicles (G,L). Rare BDCA-2⁺ plasmacytoid APCs were detected in the paracortex (M). Panels A to C, E, G, H, J, and L were acquired from the same area on sequential sections as were panels D, F, I, and K. Blue represents DAPI staining of cell nuclei (A,M, inset). *Background autofluorescence. Data are representative of 5 independent experiments. BDCA-2⁺ APC data are representative of 3 independent experiments.