Which type of cells undergoes positive selection in the thymus?

Which type of cells undergoes positive selection in the thymus?

• A. B cells
• B. Helper T cells
• C. Cytotoxic T cells
• D. All T cells

Answer: (D)

In the thymus, T cells—which include both helper T cells and cytotoxic T cells—undergo a critical process known as positive selection. This selection is essential for ensuring that developing T cells are capable of recognizing self-MHC (Major Histocompatibility Complex) molecules, which is crucial for their ability to effectively respond to pathogens while avoiding autoimmune reactions.

During positive selection, immature T cells that can adequately recognize and bind to self-MHC molecules receive survival signals and are allowed to mature further, eventually becoming functional T cells. Those that cannot appropriately engage with self-MHC are eliminated through apoptosis.

Since both helper T cells and cytotoxic T cells develop from common precursors and undergo this selection process, it encompasses all T cells that are positively selected in the thymus. Thus, the correct answer reflects the collective process that applies to all T cells rather than being limited to a specific subset.