The thymus gland is a small organ located in the upper chest, just behind the sternum. It plays a crucial role in the immune system, particularly during childhood and adolescence. The thymus is responsible for the development and maturation of T cells, a type of white blood cell that helps the body fight infections and diseases. As a person ages, the thymus gradually shrinks and becomes less active, a process known as thymic involution. Despite this decline, the T cells produced during the thymus's active years continue to circulate in the body, providing long-term immunity against various pathogens.