Representative immunohistochemical analysis of T-cell subsets in duodenal mucosa. T_regs (arrows, bottom row), identified by double immunoenzymatic labeling for CD3 (red, membranous) and FOXP3 (brown, nuclear), showed a dramatic increase in untreated HIV-infected patients. Inset: CD8⁺ T cell (red) without expression of FOXP3 (brown). Original magnification ×200, ×400 (bottom row), and × 600 (inset). Microscope: Olympus AX70. Numerical aperture of objective lenses: ×20, 0.70 mm; ×40, 0.95; ×60, 1.40. Stains: hematoxylin and eosin (top panel only); APAAP and immunoperoxide. Camera: JVC KY-F70 (JVC). Acquisition software: DISKUS. Software used for image processing: Adobe Photoshop 7.0 (Adobe Systems, San Jose, CA).