Cells and Organs of The Immune System

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Cells and Organs of The Immune System by Mind Map: Cells and Organs of The Immune System

1. **Cells of Immune System**

1.1. Antigen-presenting cells (APCs)

1.1.1. capture and display antigens to lymphocytes follicular dendritic cells display antigens to B lymphocytes APC usually refers to cells that displays antigens to T cells. macrophages present antigens to T cells during cell-mediated immune response. B lymphocytes functions as APC for helper T cells during humoral response. major type that involved in initiating T cell responses is dendritic cells.

1.2. effector cells

1.2.1. Cells that cause the final effect (lysis/ killing) Eosinophils -motile phagocytic cells, can migrate from blood into tissue spaces Mast Cells -can be found in many type of tissues Macrophages -when cells active, can secrete hydrolytic enzymes in the lysosomes of the macrphages Neutrophils -produced by hematopoiesis in the bone marrow NK Cells -involve in immune defenses against viruses and tumors

1.3. **Lymphocytes**

1.3.1. B Lymphocytes arise and maturation in bone marrow produce antibody generating a population of plasma cells and memory cells

1.3.2. T Lymphocytes arise in bone marrow and mature in thymus **Helper T lymphocytes**: a) Stimuli for B cell growth and differentiation (humeral immunity) b) Macrophage activation by secreted cytokines (cell mediated immunity) c) There is two types: Th1 and Th2 activated by recognition of an antigen–class II MHC complex on an antigen-presenting cell. **Cytolytic T lymphocytes**: Killing of virus-infected cells, tumor cells; rejection of allografts (cell-mediated immunity) activated when they interact with an antigen–class I MHC complex on the surface of an altered self-cell

1.3.3. Naïve (small) lymphocyte

1.3.4. Large lymphocyte (lymphoblast)

2. Primary Lymphoid Organs (Provide appropriate microenvironments for **development & maturation** of lymphocytes)

2.1. **Thymus** : Site of T-cell development and maturation

2.1.1. **Cortex** : Densely packed with immature T cells (thymocytes) **Medulla** : sparsely populated with thymoctes

2.2. **Bone Marrow** : site of B cells origin and development

2.2.1. sites where immature B cells proliferate & differentiate, stromal cells within bone marrow interact with B cells & secretes **cytokines**

3. Secondary Lymphoid organs (**Trap antigen** from tissue or vascular spaces & sites where mature lymphocyte **interact with antigens**)

3.1. spleen

3.1.1. Specialized in filtering blood, trapping blood-borne antigens, respond to systemic infections **Red Pulp** : sites where defective red blood cells are destroyed by macrophage **White Pulp** : populated mainly by T lymphocytes

3.2. **Lymph Node**

3.2.1. -Follicles are the B cells zone of lymph nodes,

3.2.2. -Primary follicles contain mature & naive B lymphocytes,

3.2.3. -Germinal centers develop in response to antigenic stimulation

3.2.4. -sites of remarkable B cell proliferation, generation of memory B cells

3.2.5. -most of CD4+ helper T cells located in the cortex

3.2.6. -Dendritic cells concentrated in T cells zone

3.3. **Mucosal-Associated Lymphoid Tissue**

3.3.1. **Lamina Propia** : contain large number of B cells, plasma cells, activated Th cells and macrophages

3.3.2. **Peyer's Patches** : contained in the submucosal layer beneath lamina propia

3.3.3. Peyer's patches can develop into secondary follicles with germinal centers