In which part of the thymus does negative selection primarily occur?

• A. Cortex
• B. Medulla
• C. Cortex/Medulla junction
• D. Thymic stroma

Answer: (C)

Negative selection primarily occurs in the medulla of the thymus, where developing T cells that recognize self-antigens are eliminated. This process is crucial for preventing autoimmunity, ensuring that the T cells that mature and enter the circulation do not attack the body's own tissues.

While both the cortex and medulla are involved in the development of T cells, the cortex is primarily where immature thymocytes undergo positive selection, ensuring that T cells can recognize self-MHC molecules. In contrast, the medulla is where the important process of negative selection ensures that T cells that bind too strongly to self-antigens are induced to undergo apoptosis.

The thymic stroma, which provides structural support and facilitates T cell development, does not specifically denote the location of negative selection. Consequently, the location of negative selection is correctly identified as the medulla rather than the cortex/medulla junction or cortex.