lymphoïdes

Lymphoïdes, in English often referred to as lymphoid tissues or lymphoid organs, are components of the immune system dedicated to the development, maturation, and function of lymphocytes. They provide structured environments where antigens are captured, presented, and where adaptive immune responses are initiated and regulated. Lymphoid tissues are organized into primary and secondary categories.

Primary lymphoid organs are the sites where lymphocytes mature. The bone marrow is the origin site for B cells and provides precursors for other blood cells, while the thymus is the site where T cell precursors complete their maturation. Secondary lymphoid organs and tissues are the locations where mature lymphocytes encounter antigens and mount immune responses. Key examples include lymph nodes, the spleen, and mucosa-associated lymphoid tissue (MALT) such as tonsils, Peyer's patches in the small intestine, and bronchus-associated lymphoid tissue. These structures contain defined zones and specialized cells that facilitate antigen capture, lymphocyte activation, clonal expansion, and differentiation into effector and memory cells.

Cellular composition includes B and T lymphocytes, natural killer cells, antigen-presenting cells (such as dendritic cells and macrophages), and supporting stromal cells. Antigen presentation and cytokine signaling within lymphoid tissues drive the activation and maturation of adaptive responses, while lymphoid organs also filter fluids and remove immune cells after responses.

Disorders of lymphoid tissues can involve immunodeficiency, lymphadenopathy, splenomegaly, or lymphoid neoplasms such as lymphomas and leukemias. Lymphoid tissues are essential components of the adaptive immune system across vertebrates.