One of the primary lymphoid organs is the thymus. This organ possesses two lobes: the medulla and the cortex. These collect thymocyte cells from the bone marrow, which mature into T cells, lymphocytes that help the body build immunity to viruses, bacteria, and antigens. T cells can destroy infected and cancerous cells. The thymus is at its largest and most active during childhood and begins to shrink in the early teens, though T cell maturation continues at a reduced rate.

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