Clonal deletion of T cells during maturation primarily serves which purpose?

• A. Elimination of autoimmune responses
• B. Positive selection of CD3/TCR receptors
• C. Allelic exclusion of chromosomes
• D. Elimination of cells unable to bind to MHC antigens

Answer: (A)

In T cell development, central tolerance is established in the thymus through selective processes that shape the T cell repertoire. Clonal deletion is the step where thymocytes that bind self-peptide–MHC with high affinity are induced to die by apoptosis. This removes potentially autoreactive T cells before they enter the circulation, preventing them from attacking the body's own tissues and thereby reducing autoimmune risk. Positive selection, by contrast, preserves thymocytes that can recognize self-MHC with appropriate affinity, while death by neglect occurs when thymocytes fail to recognize self-MHC at all. Allelic exclusion is a separate mechanism ensuring only one allele of a receptor gene is expressed. So the primary purpose of clonal deletion is to eliminate self-reactive T cells and prevent autoimmunity.