What are examples of lymphoid organs?

• A. Kidneys, liver and spleen
• B. Tonsils, spleen and thymus
• C. Heart, thymus and brain
• D. Muscles and bones

Answer: (B)

Lymphoid organs are parts of the immune system where lymphocytes develop, mature, or mount immune responses. Primary lymphoid organs include the thymus, where T cells mature, and bone marrow, where B cells mature. Secondary lymphoid organs encompass the spleen and tonsils, which help coordinate responses to pathogens. The spleen filters blood and triggers immune reactions to blood-borne threats, while the tonsils trap and respond to pathogens entering through the mouth and nose. The other organs listed—kidneys, liver, heart, brain, muscles, and bones—are not lymphoid organs. Therefore, the examples that fit are the thymus, spleen, and tonsils.