Kinetics and localization of FoxP3+ cells in neonatal thymus organs. A: FoxP3 expression in 1–6 day old newborn or adult thymus lobes was analyzed by immunohistochemical staining with an anti-FoxP3 antibody. Rabbit IgG was used as control. No FoxP3+ cells could be detected in the 1–2 day old newborn thymus. In the 3–6 day old thymus, as in the adult thymus, the majority of FoxP3+ cells were found in the medullary region. NB: newborn, C: Cortex, M: Medulla. B: Total FoxP3+ cell numbers from each section were determined by counting 3 different medulla regions/sections and summarized. C: Immunofluorescence phenotyping of FoxP3+ cells in the thymus. a and d: Dapi (Blue), FoxP3 (Red) and CD25 (Green). b and e: FoxP3 (Red) and CD25 (Green). c and f: FoxP3 (Red) and CD4 (Blue). C: cortex; M: medulla. In d-f: 1 indicates a CD4+CD25+FoxP3- cell; 2, a CD4+CD25+FoxP3+ and 3, a CD4+CD25-FoxP3+ cell.