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Scattered throughout the body, lymph nodes perform the critical function of filtering both exogenous and endogenous antigens and producing immune response through activated lymphocytes and antibodies. They can become enlarged in infections, autoimmune diseases, lymphomas, and metastatic carcinomas.[1] Histological assessment is imperative in diagnosing these entities. In the case of metastatic carcinomas, additional information like extracapsular extension and the size of the metastatic carcinoma is of prognostic significance.[2]
Lymph derives from interstitial space fluid. The lymphatic channels carry it to lymph nodes along with all kinds of exogenous and endogenous antigens and antigen-presenting cells. Antigen-presenting cells include dendritic cells, macrophages, and B lymphocytes. The antigen is processed and linked to major histocompatibility complexes (MHC) to stably export them to the cell surface for presentation to CD 4+ helper and CD 8+ killer T lymphocytes. CD 4+ helper T cells bind to and activate B cells that turn into mature plasma cells that secrete antibodies that fight infection.[9] Natural killer and cytotoxic CD8+ T-cell kill infected cells by releasing cytotoxic granules and cytokines.