Where does central tolerance of B cells primarily occur?

• A. Bone marrow
• B. Thymus
• C. Spleen
• D. Lymph node

Answer: (A)

Central tolerance for B cells is established during development in the bone marrow. Immature B cells rearrange their receptors and, if the BCR strongly recognizes self-antigen there, the cell is deleted or undergoes receptor editing (often by rearranging the light chain) to change specificity. Some become anergic instead of deleted. This removes self-reactive clones before they enter the circulating pool. The thymus handles T-cell central tolerance, while the spleen and lymph nodes are sites of maturation, activation, and peripheral tolerance for mature B cells that escaped central tolerance. So the primary site of B-cell central tolerance is the bone marrow.