What is the role of regulatory T cells (CD4+ CD25+ FOXP3+) in the immune system?

• A. They suppress autoreactive immune responses and maintain peripheral tolerance.
• B. They promote cytotoxic T cell responses.
• C. They secrete antibodies to neutralize pathogens.
• D. They activate macrophages to enhance phagocytosis.

Answer: (A)

Regulatory T cells enforce peripheral tolerance by dampening immune responses to prevent autoimmunity. They express FOXP3 and high levels of CD25, and they suppress autoreactive T cells through multiple mechanisms: dampening effector T cell activation and proliferation, producing anti-inflammatory cytokines like IL-10 and TGF-β, and modulating antigen-presenting cells via CTLA-4–mediated interactions. This keeps self-reactive responses in check in the periphery, and deficiencies in these cells or FOXP3 lead to autoimmune phenomena. Therefore, their primary role is to suppress autoreactive immune responses and maintain peripheral tolerance.

They do not serve to promote cytotoxic T cell responses, secrete antibodies, or activate macrophages—that would be roles of other immune cells and pathways.