Which of the following best defines regulatory T cells (Tregs)?

• A. Tregs are a type of B cell involved in humoral immunity.
• B. Tregs are a type of T cell that attacks and destroys infected cells.
• C. Tregs are cells that produce antibodies in response to pathogens.
• D. Tregs are a type of T cell that helps regulate the immune response and maintain tolerance to self-antigens.

Answer: (D)