Which of the following are secondary lymphoid organs ? (a) Bone marrow (b) Tonsils (c) Spleen (d) Thymus Choose the correct answer from the options given below :

Step-by-step solution

Primary lymphoid organs are the sites where immature lymphocytes differentiate into antigen-sensitive lymphocytes. Examples include bone marrow and thymus. Secondary lymphoid organs provide the sites for interaction of lymphocytes with the antigen, which then proliferate to become effector cells. Examples include spleen, lymph nodes, tonsils, Peyer's patches of small intestine, and appendix. Therefore, tonsils and spleen are secondary lymphoid organs, while bone marrow and thymus are primary lymphoid organs."