n :  the bodily system that protects the body from foreign substances, cells, and tissues by producing the immune response and that includes esp. the thymus, spleen, lymph nodes, special deposits of lymphoid tissue (as in the gastrointestinal tract and bone marrow), lymphocytes including the B cells and T cells, and antibodies .
 
 
 
Published under license with Merriam-Webster, Incorporated.  © 1997-2024.