Which statement about central tolerance and peripheral tolerance is correct?

Which statement about central tolerance and peripheral tolerance is correct?

• A. Central tolerance occurs during lymphocyte development in the thymus or bone marrow; peripheral tolerance occurs in mature lymphocytes to prevent autoimmunity.
• B. Central tolerance occurs in mature lymphocytes; peripheral occurs during development in thymus and bone marrow.
• C. Both central and peripheral tolerance occur only in the thymus.
• D. Tolerance is not essential for preventing autoimmunity.

Answer: (A)

Central tolerance is established during lymphocyte development in primary lymphoid organs—thymus for T cells and bone marrow for B cells—where self-reactive clones are deleted or inactivated through negative selection. Peripheral tolerance then acts on mature lymphocytes outside these organs to prevent autoimmunity, using mechanisms such as anergy, regulatory T cell suppression, clonal deletion in the periphery, or ignorance of sequestered antigens. This combination fits the statement: central tolerance during development in thymus or bone marrow, and peripheral tolerance in the periphery to prevent autoimmunity. The other options misstate where tolerance occurs or its necessity—central tolerance does not occur in mature lymphocytes, peripheral tolerance is not limited to the thymus, and tolerance is essential to prevent autoimmunity.

Central tolerance is established during lymphocyte development in primary lymphoid organs—thymus for T cells and bone marrow for B cells—where self-reactive clones are deleted or inactivated through negative selection. Peripheral tolerance then acts on mature lymphocytes outside these organs to prevent autoimmunity, using mechanisms such as anergy, regulatory T cell suppression, clonal deletion in the periphery, or ignorance of sequestered antigens. This combination fits the statement: central tolerance during development in thymus or bone marrow, and peripheral tolerance in the periphery to prevent autoimmunity. The other options misstate where tolerance occurs or its necessity—central tolerance does not occur in mature lymphocytes, peripheral tolerance is not limited to the thymus, and tolerance is essential to prevent autoimmunity.