Light micrograph of a section of human thymus showing medulla with Hassall's corpuscules; magnification 10X at 35mm; brightfield. The thymus is a specialized organ in the immune system, which produces T-lymphocytes (T cells), which are critical cells of the adaptive immune system; the thymus also produces and secretes thymosins, hormones which control T-lymphocyte activities and various other aspects of the immune system.