Overview: The Lymphoid Immune System
- The lymphoid system consists of encapsulated lymphoid tissues, diffuse lymphoid tissue, and lymphoid cells, especially T lymphocytes, B lymphocytes, and macrophages.
- Lymphoid tissue is immune tissue containing lymphocytes, antigen-presenting cells, macrophages, supporting cells, and lymph-carrying structures.
- Lymphoid immune system is the body defense network that uses lymphoid organs, diffuse lymphoid tissue, and immune cells to recognize and remove threats.
- Encapsulated lymphoid tissues are lymphoid organs surrounded by a connective-tissue capsule.
- Thymus, spleen, tonsils, and lymph nodes are encapsulated lymphoid tissues.
- Diffuse lymphoid tissue is lymphoid tissue spread through mucosal or connective-tissue regions without a complete capsule.
- Lymphoid cells include T lymphocytes, B lymphocytes, and macrophages.
- T lymphocytes are lymphocytes that mature in the thymus and help coordinate or execute cell-mediated immune responses.
- B lymphocytes are lymphocytes that mature in bone marrow and can become antibody-producing plasma cells.
- Macrophages are phagocytic immune cells that remove material and present antigens to lymphocytes.
- Primary lymphoid organs educate lymphocytes so they become immunocompetent.
- Immunocompetent means able to recognize antigen and participate in an immune response.
- Bone marrow and thymus are primary lymphoid organs.
- Secondary lymphoid organs bring antigens, antigen-presenting cells, and immunocompetent lymphocytes together.
- Immunogens are antigens that trigger immune responses.
- Antigen-presenting cells (APCs) process or display antigens so lymphocytes can respond.
- Secondary lymphoid organs help initiate immune responses that eliminate antigenic attacks.
- Antigenic attack means exposure to a recognized foreign or harmful antigen.
- Secondary lymphoid organs include diffuse lymphoid tissue, lymph nodes, spleen, and tonsils.
- Innate immunity is the rapid nonspecific defense component.
- Adaptive immunity is the specific defense component that can generate memory.
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