In a transplantation experiment, thymocyte precursors engineered to overexpress bc/-2 would most likely cause which change in the thymus compared with controls?

• A. Decreased naive B-lymphocyte production by the reconstituted marrow
• B. Increased formation of lymphoid nodules in the thymic cortex
• C. Decreased number of circulating lymphocytes
• D. Decreased cell death in the thymic cortex

Answer: (D)

Overexpression of an anti-apoptotic protein in thymocyte precursors reduces programmed cell death during T cell development. In the thymus cortex, many thymocytes die as part of the selection process to ensure proper T cell receptors. By blocking this apoptosis, more thymocytes survive, so the cortex shows decreased cell death compared with controls. This change is specific to thymic tissue and thymocyte survival; it doesn’t directly alter naive B-lymphocyte production in marrow or reduce circulating lymphocytes.