Lymphoid

Lymphoid is an anatomical and cellular descriptor referring to components of the lymphatic system that are associated with lymphocytes and adaptive immunity. Lymphoid tissues and organs participate in the development, activation, and regulation of immune responses.

Primary lymphoid organs include bone marrow, where B cells mature, and the thymus, where T cells mature. Secondary lymphoid organs, such as lymph nodes, spleen, tonsils, and mucosa-associated lymphoid tissue (MALT) including Peyer's patches, gather antigens and support antigen presentation, lymphocyte activation, and clonal expansion.

Lymphoid cells originate from hematopoietic stem cells and include B cells, T cells, and natural killer cells. B cells mature in the bone marrow, T cells in the thymus, and NK cells arise from common lymphoid progenitors. Lymphoid tissue contains distinct microenvironments for B cell–rich follicles and T cell–rich zones, facilitating organized adaptive responses.

Functions include antigen recognition, antibody production by plasma cells, cytotoxic and helper functions of T cells, and regulation of immune responses. Lymphoid organs and tissues filter lymph and blood, present antigens, and coordinate interactions among immune cells through dendritic cells and other antigen-presenting cells.

Lymphoid pathology includes lymphoid leukemias and lymphomas, disorders of lymphocytes, and reactive lymphadenopathy in response to infection. Abnormalities of the lymphoid compartment can affect immunity and surveillance against malignancy.