Introduction to Immunology: Cells and Organs of the Immune System PDF

Click to edit Master title style Edit Master text styles Introduction Second level to Immunology: Cells and Organs Third level of the immune Fourth level system Fifth level Dr. Eman Hussein Shehata Professor of Med...

Click to edit Master title style Edit Master text styles Introduction Second level to Immunology: Cells and Organs Third level of the immune Fourth level system Fifth level Dr. Eman Hussein Shehata Professor of Medical Microbiology and Immunology 1-List organs of the immune system 2-Describe the function of each organ 3-Enumerate cells of immune system and identify the site of each cell 4-Describe the function of each cell in immune system 5-Compare between the two branches of immune system Immunology is the science that studies defensive mechanisms of the host against foreign material or infectious agent distinction of self from non-self.  cells of the immune immune cells develop system meet,interact, and mature perform their functions.  Sites of B and T Primary (Central) cell development Lymphoid Organs and maturation Bone Marrow Thymus  sites of B and T cell differentiation, Secondary activation, and initiation of adaptive Lymphoid organs immune responses Spleen Lymph nodes MALT  Organs of the Immune System: 1- Central (Primary)Lymphoid organs the sites of B and T cell development and maturation (Become competent lymphocytes ready to respond to the antigen 2- Peripheral (Secondary)Lymphoid organs @ where effective immune responses begin ( Lymphocytes are further differentiated to be activated @ site where antigen is concentrated so that lymphocytes can find the antigen , respond and get rid of it.  Mature B and T lymphocytes exit the primary lymphoid organs and are transported via the bloodstream to the secondary lymphoid organs, where they become activated by contact with foreign materials called antigens. Most lymphocyte activation and proliferation occur in secondary lymphoid organs (the lymph nodes, the spleen, and diffuse lymphoid tissue found in the mucosa of the digestive system, including the tonsils, Peyer patches, and appendix).  Primary (Central) lymphoid organs 1- Bone Marrow Bone marrow contains pluripotent stem cells which differentiate into red blood cells, platelets and leukocytes (cells of the immune system) Stem cells destined to become B- lymphocytes remain in the bone marrow as they mature, while prospective T cells migrate to the thymus to undergo further growth Pluripotent stem cells differentiate into two other types of cells : myeloid stem cells and lymphoid stem cells The lymphoid stem cell gives rise to : B lymphocytes, T lymphocytes and natural killer (NK) cells. The myeloid stem cell gives rise to erythrocytes, platelets, mast cells, eosinophils, basophils, neutrophils, monocytes/macrophages and dendritic cells  2- Thymus The thymus is dedicated to maturation of T lymphocyte. During this maturation, T cells learn to differentiate between "self" (the body's own cells) and "nonself" (foreign objects, organisms, or diseased cells). If a T cell recognizes a self- cell as foreign, the cell will be destroyed  1- Spleen Secondary 2- Lymph nodes lymphoid organs 3- MALT  Secondary (peripheral) lymphoid organs 1- Spleen The spleen is the largest secondary lymphoid organ in the body It contains lymphocytes (B cells, T cells, natural killer cells), Phagocytes as macrophages, and dendritic cells. The spleen is an immunologic filter of the blood that removes any foreign material as bacteria and damaged red blood cells or aging cells  2- Lymph Nodes Lymph nodes are small, bean-shaped organs that are the size of a pea. You have nodes throughout your body including in your armpits, neck and groin. Your lymph nodes can swell or get bigger, which is a sign that your body is fighting an infection or an illness. Lymph nodes contain the same immune cells found in the spleen ( lymphocytes , macrophages and dendritic cells) These specialized cells sample the incoming lymph (fluids drained from tissues and eventually return to the blood for circulation) to remove any foreign material Lymph Node  3- Mucosa Associated Lymphoid Tissue(MALT) Approximately >50% of lymphoid tissue in the body is found associated with the mucosal system A-Diffuse collections of lymphocytes and phagocytes As the lymphoid tissue lining the intestinal tract, the respiratory tract, and the genitourinary tract. B-Clearly organized tissues with well-formed lymphoid follicles Tonsils and Peyer’s patches The Lymphatic System Thoracic duct The immune system is closely linked to the lymphatic system. The lymphatic system is the system Lymph carrying antibodies and immune cells collect in of vessels, cells, and organs that thoracic duct where the lymph empties back into the carries excess fluids to the blood circulatory system bloodstream and filters pathogens from the blood. A major function of the lymphatic system is to drain body fluids and Site of exchange between the return them to the bloodstream. blood and lymph systems Figure 1-1. The circulation of immune cells between the circulatory and lymphatic systems  1-Circulate in blood Cells of immune 2-Reside in system tissues 3-In blood and tissues  Cells of immune system circulating in blood 1- Neutrophils Neutrophils are the most abundant population of circulating white blood cells. They contain cytoplasmic granules filled with enzymes as lysozymes, collagenase, elastase and defensins that digest phagocytosed material. They are the first phagocytic cells that encounter an infection in blood and migrate from the bloodstream into tissue spaces. Increased neutrophils are detected in acute infections of bacterial origin.  2- Eosinophils Eosinophils are present in blood and may migrate from the bloodstream into tissue spaces. Eosinophils have a two-lobed nucleus and granular cytoplasm. The content of the granules when released plays a role in damaging parasites and clinical manifestations of allergy.  3- Basophils Basophils have bilobed nucleus and a cytoplasm contain basophilic granules with active mediators, such as histamine, and enzymes, such as peroxidases and hydrolases. These pharmacologically active amines when released play an important role in allergic reactions. Have an important role against helminthic and parasitic infections Can be recruited out of blood into tissues when needed  4- Lymphocytes Lymphocyte are circulating in blood or residing in secondary lymphoid organs. Lymphocytes can be divided into three populations: T cells B cells NK cells B Lymphocytes Plasma cell Y Activation Y B cell Y Antibodies -toxin and virus neutralization -stimulate an efficient phagocytic response  T- Lymphocytes T-Helper T Cytotoxic -Secrete cytokines Cytotoxic killing of -help other cells of the immune malignant cells and system as B lymphocytes virally infected cells  Natural Killer cells Natural killer (NK) cells are a small population of large, granular lymphocytes. The major NK cell function is to destroy malignant cells and virally infected cells or cells infected with intracellular bacteria Increased lymphocytic count is detected in viral infections  5- Monocytes Monocytes circulate in blood They are phagocytic cells with a bean shaped nuclei and finely granular cytoplasm Monocytes when leave blood reside in tissues giving rise to macrophages Cells of immune system residing in tissue 1- Macrophages Macrophages are present in different tissues. They ingest and kill bacteria, viruses, and other foreign particles. They produce cytokines that induce inflammation They clear dead tissues and initiate tissue repair Macrophage and E. coli ©Dennis Kunkel Microscopy, Inc., www.DennisKunkel.com 30  2-Dendritic cells The word "dendritic" means "branched like a tree Dendritic cells are present in the skin and mucous membranes of the nose, lungs, and intestine where they are ready to contact invading pathogens. Like monocytes and macrophages, dendritic cells are phagocytic cells. They are migratory cells travel to lymph nodes or spleen where they activate T lymphocytes to go out and attack any similar foreign materials in the body.  3- Mast cells Mast cells are fixed in tissues especially under the skin and in the mucosa of the respiratory and gastrointestinal tracts. Mast cells are like basophils in many ways. Their cytoplasm contains basophilic granules with active mediators, which play an important role in inflammation and allergic reaction.  Branches of the immune system Innate immune Adaptive system immune system  Innate and adaptive immunity The immune system is divided into two major components: innate immune system and the adaptive immune system. Defense against microbes is mediated by early reaction of innate immunity and later response of adaptive immunity.  Characters of Innate immune system 1- First defensive mechanism of the body. It is ready to be activated upon the first signs of infection. 2- Nonspecific to the type of organism it fights. It reacts to structures common in microbes and does not distinguish fine differences between foreign substances. 3- It has no ability to remember encountered pathogens. 4- It has the same magnitude in response even in repeated infections with same microbe.  Characters of adaptive immunity: 1. It provides protection when innate immunity fails to eliminate infection. Both innate and adaptive immunity collaborate against any invading pathogen 2. Specific response (Each B and T lymphocyte is specific for a particular antigen and can distinguish between different even closely related microbes and molecules). 3. As a population, lymphocytes have extensive diversity. 4. It has the ability to distinguish between self (host cells) and non-self (pathogens) 5. It has the ability to remember encountered pathogens. A second infection by a pathogen is met with a more rapid and vigorous immune response. Characteristics Innate Adaptive Specificity Non-specific (reacts against Highly specific (reacts common structure in specifically against the microbes). microbe initiating it). Diversity Limited High Memory No Yes Anatomic and Skin, mucosa, normal flora, Lymph nodes, spleen, physiologic barriers temperature, pH, mucosal-associated lymphoid tissues Secreted proteins Lysozyme, complement, C- Immunoglobulins reactive protein (CRP), (Antibodies) and cytokines defensins and cytokines Cells Phagocytes, granulocytes B lymphocytes and T and natural killer (NK) cells lymphocytes 38  Innate immunity Adaptive immunity Time of reaction Rapid response(hours) Slow response(days to weeks) Specificity Nonspecific Specific Memory No memory Memory is present