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Chapter 21 The Immune System BB Version

Organs all other lymphoid organs are secondary

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Unformatted text preview: mphocyte origin Humoral immunity Cellular immunity Primary lymphoid organs: site of development of immunocompetence as B or T cells Secondary lymphoid organs: site of antigen encounter, and activation to become effector and memory B or T cells Red bone marrow 1 Lymphocytes destined to become T cells migrate (in blood) to the thymus and develop immunocompetence there. B cells develop immunocompetence in red bone marrow. Thymus Bone marrow Lymph nodes, spleen, and other lymphoid tissues 2 Immunocompetent but still naive lymphocytes leave the thymus and bone marrow. They “seed” the lymph nodes, spleen, and other lymphoid tissues where they encounter their antigen. 3 Antigen-activated immunocompetent lymphocytes (effector cells and memory cells) circulate continuously in the bloodstream and lymph and throughout the lymphoid organs of the body. Figure 21.8 Antigen-presenting cells Antigen-presenting Engulf foreign particles and present Engulf fragments of these antigens on the surface s...
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