Human Foxp3⁺ nTreg cells colocalize with CD123⁺ pDCs within the human thymic medulla. (A) Pan-cytokeratin (Cytok, green) immunostaining of human TECs, and nuclei staining with TOPRO-3 (blue) showing differential expression of Cytok in thymic medulla (M) and cortex (C). (Top panels) Original magnification 10×. Bar represents 100 μm. Double staining of Cytok (green) and Foxp3 (red) showing the localization of Foxp3⁺ nTregs in the thymic medulla (bottom panels). Original magnification 25×. Bar represents 50 μm. (B-C) Double immunostaining of CD123 (green) and Foxp3 (red) showing colocalization of pDCs and nTregs within the thymic medulla (B). Original magnification 10×. Bar represents 100 μm and highlighting close interactions among them (C arrows and upper left inset). Original magnification 40×. Bar represents 50 μm. (D) Quantification of Foxp3⁺ nTregs interacting with CD123⁺ pDCs, and vice versa, in the human thymus. Data are mean ± SEM (percent) of interacting cells within 1465 Foxp3⁺ and 518 CD123⁺ cells in 7 fields from 3 independent tissue sections.