Lymphoid organs

A lymphoid organ is any organ or tissue involved in the origin, maturation and proliferation of lymphocytes — the immune system's principal specialist cells. Because these organs serve different roles, immunologists sort them into two functional classes. Primary (central) lymphoid organs provide the protected environment in which lymphocyte precursors mature into fully functional, immunocompetent cells; in mammals this means the bone marrow (for B cells) and the thymus (for T cells), while birds additionally have the Bursa of Fabricius, where B lymphocytes mature to support humoral immunity. Secondary (peripheral) lymphoid organs, by contrast, do not manufacture new lymphocytes — instead they trap and concentrate antigen so that already-mature lymphocytes can encounter it efficiently and mount an effective response. This distinction between 'where lymphocyt …