Lymphoid tissue

Lymphoid tissue is tissue rich in lymphocytes and other immune cells, where immune cells develop, gather, or respond to antigens.

Lymphocyte: A white blood cell that recognizes specific antigens or helps coordinate immune responses. Lymphocytes are the defining immune cells found throughout lymphoid tissue.
Lymphocyte recirculation: The continual movement of lymphocytes between blood, lymph, and lymphoid organs. Recirculation lets lymphocytes sample multiple tissues for their matching antigens.
Lymph node: A small lymphoid organ that filters lymph and supports immune responses to tissue-derived antigens. Lymph nodes are encapsulated sites where lymphoid tissue samples lymph.
Primary lymphoid organ: An organ where lymphocytes develop and mature before encountering their specific antigens. This category includes lymphoid tissue devoted chiefly to immune-cell development.
B cell: A lymphocyte that can produce antibodies and present antigens to other immune cells. B cells gather in follicles and can mature into antibody-secreting cells.
High endothelial venule: A specialized blood vessel that allows lymphocytes to enter many lymph nodes from the bloodstream. These vessels provide a major entry route for circulating lymphocytes into lymph nodes.
Spleen: An organ that filters blood and mounts immune responses to blood-borne antigens. Its white pulp is lymphoid tissue specialized for responses to blood-borne material.
Secondary lymphoid organ: An organ where mature lymphocytes encounter antigens and initiate adaptive immune responses. This category distinguishes antigen-response sites from primary development sites.
T cell: A lymphocyte that recognizes antigen fragments and coordinates or carries out cellular immune responses. T cells occupy dedicated zones and respond to antigens within lymphoid tissue.
Antigen presentation: The display of antigen fragments by cells to lymphocytes, enabling specific immune recognition. Antigen presentation turns encounters in lymphoid tissue into targeted lymphocyte activation.

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