Regulatory T cells (Tregs) play a key role in maintaining immune tolerance. Which phenotype best describes them?

• A. CD8+ CD56+
• B. CD4+ CD25+ FOXP3+
• C. CD4+ CD28+
• D. CD4+ CD8+

Answer: (B)

Regulatory T cells are identified by the CD4+CD25+FOXP3+ phenotype. CD4 marks helper T cells, while CD25 is the high-affinity IL-2 receptor that is abundantly expressed on Tregs and supports their survival and function. FOXP3 is the master transcription factor governing the development and suppressive activity of these cells; it drives the expression of molecules that dampen immune responses and promote tolerance. Together, these markers define the Treg lineage and their role in preventing autoimmunity and controlling excessive immune activation. The other options either lack FOXP3, include cytotoxic/NK-like markers (CD8+CD56+), or represent conventional helper T cells (CD4+CD28+) or thymic double positives (CD4+CD8+), which are not the regulatory subset.