Secondary lymphoid tissue tonsils

Figure 31-1 (A) Locations of the primary and secondary tissues of the immune system. The primary lymphoid organs are the thymus, which makes T cells, and the hone marrow, which forms B cells. After moving from these organs into the blood circulation the cells reach one of the secondary lymphoid organs, which include lymph nodes, spleen, tonsils, and Peyer s patches on the small intestine. Immature dendritic cells are found in body tissues including skin and mucous membranes and respond to foreign proteins by inducing attack by T lyphocytes and antibody formation by B cells. (B) Schematic drawing of a lymph node. From Nossal.1 Courtesy of Gustav J. V. Nossal.

The spleen, lymph nodes, tonsils, and gut-associated lymphoid tissue comprise the secondary or peripheral system wherein T and B lymphocytes undergo terminal differentiation in response to antigen stimulation. 

Stimulation of the human immune system through the lymphoid tissue of the intestines can occur directly or indirectly. Such stimulation may involve the effect produced on the primary (bone marrow, thymus, and liver) and secondary organs (spleen, lymph nodes, tonsils, lymphoid tissue of bronchi, intestines, and skin) and... 

The lymphoid tissues include primary (or central) lymphoid organs (bone marrow, thymus and bursa of Fabricius in birds), and secondary (or peripheral) lymphoid organs (lymph nodes, spleen, tonsils, appendix, Peyer s patches). 

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