Most of the lymphocytes that migrate to the thymus gland from the red bone marrow are destroyed by apoptosis before they even reach maturity.

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The thymus gland plays a crucial role in the development of T-lymphocytes (T cells), a type of white blood cell that is vital for the immune response. The process involves a rigorous selection mechanism where the majority of these immature T cells (thymocytes) undergo apoptosis (programmed cell death) before they reach maturity. This is because the thymus gland tests thymocytes for their ability to correctly recognize antigens presented by the major histocompatibility complex (MHC) without reacting against self-antigens. Those that fail this selection process are eliminated, ensuring that only T cells capable of effective immune responses while tolerating the body's own cells are released into the bloodstream. This process results in the destruction of about 95% of the thymocytes that enter the thymus, leaving only a small fraction that successfully matures and exits the thymus to perform immune functions.

Most of the Lymphocytes That Migrate to the Thymus Gland