Thymus and the Immune System

The thymus is a specialized organ of the immune system. The thymus produces T-lymphocytes (T-cells), a critical part of the adaptive immune system. T-cells attack foreign substances. T-cells have receptors that are generated by randomly shuffling gene segments. Each T-cell attacks a different substance. T-cells that attack the body's own proteins are eliminated in the thymus.

Thymus image captured with a biological microscope using a Jenoptik microscope camera.

The thymus is composed of two identical lobes and is located in front of the heart and behind the sternum. The thymus is largest and most active during the neonatal and pre-adolescent periods.  By the early teens, the thymus begins to atrophy and thymic stroma is replaced by fat tissue.  Nevertheless, residual T lymphopoiesis continues throughout adult life.