Organs of Immune System - Immunology Exam Point of View

Organs of Immune System - Immunology Exam Point of View

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  Presented By Sijo A Ph.D.Research Scholar (Microbiology) School of Biosciences, MACFAST College Tiruvalla, Kerala, India ORGANS OF IMMUNE SYSTEM
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  • The manycells, organs and tissue of the immune system are found through out the body. • The organs concerned with the production of immune cells and immune reaction are called lymphoid organs. • They are functionally classified into 2 main groups: 1. Primary lymphoid organs • It provide appropriate microenvironment for the development and maturation of lymphocytes. • It includes bone marrow and thymus. 2. Secondary lymphoid organs • They trap antigen and provide site for mature lymphocytes interact with an antigen. • It includes lymph nodes, spleen and MALT. INTRODUCTION
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  PRIMARY LYMPHOID ORGANS 1.Bone Marrow • They are the soft tissue found in the cavities of bone. • It is the main site of B cell maturation and proliferation. • It has 2 parts: Hematopoietic region and Adipose region. • Hematopoietic region: it is the site of production of all different types of blood cell from hematopoietic stem cell. • Adipose region: it is the circulatory system which supplies nutrients and removes waste from the actively growing blood cells.
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  PRIMARY LYMPHOID ORGANS •Mainly there are 2 types of bone marrow: Red marrow and Yellow marrow • Red marrow is commonly called medulla ossium rubra. It is made up of hematopoietic tissue. • It is mainly found in flat bones such as pelvis, sternum, cranium, ribs etc. • Yellow marrow is commonly called Medulla ossium flava. It is made up of fat cells. With increasing age the red marrow converted into yellow marrow. • Bone marrow is not the site of B-cell development in all species. • Bursa of fabricus is a gut associated lymphoid organ in birds and it is the primary site of B-cell maturation. • It provides humoral immunity to the birds. • It is absent in mammals (primates, rodents).
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  PRIMARY LYMPHOID ORGANS 2.Thymus • Thymus is a bilobed organ situated above the heart. • It is the site of T-cell development and maturation. • The thymus is quite large at the time of birth and reduces its size with age. • Each lobe is surrounded by capsule. • Each lobe is separated from each other by a connective tissue called trabeculae. • Each lobule consists of two compartments; namely outer cortex and inner medulla. • The outer cortex is densly packed with immature T-cells are called thymocytes. • The inner cortex is sparsely populated with mature thymocytes. • Both the cortex and medulla of the thymus are crisscrossed by a three dimensional stromal network composed of epithelial cells, dendritic cells and macrophages.
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  PRIMARY LYMPHOID ORGANS •Some thymic epithelial cells found in the outer cortex is called nurse cells which forms a large multicellular complex. • A mass of epithelial cells around a central core of degenerating epithelial cell is known as Hassel’s corpuscles. Their function are not known. Functions 1. It is the site of T-cell development and maturation 2. T-cells protect body from infection 3. It brings about cell mediated immunity 4. It brings about graft rejection 5. Thymic epithelial cells produces hormones like thymosin and thymopoietin which is responsible for the formation of T-cells
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  SECONDARY LYMPHOID ORGANS 1.Lymph nodes • Lymph nodes are solid encapsulated bean shaped structure. • It is seen in armpits and mesenteries. • It is packed with lymphocytes, macrophages and dendritic cells. • Their size is 1.5 mm. • It has three concentric regions namely cortex, paracortex and medulla. 1. Cortex • It is the outermost layer (thymus independent area). • It contain lymphocytes (mostly B cells), macrophage, follicular dendritic cells that are arranged in primary follicle. • After antigenic stimulation the primary follicle develop into secondary follicle with germinal centre.
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  SECONDARY LYMPHOID ORGANS •In children with B cell deficiency, the cortex lacks primary follicle and germinal centre. 2. Paracortex • It seen beneath the cortex. • It is called thymus dependent area. • It contains T-lymphocytes and interdigitating dendritic cells. • The interdigitating cells act as antigen presenting cells (APC) and expresses Class II MHC complex. 3. Medulla • It is the innermost layer. • It consists of lymphocytes and forms a interconnecting strands are called medullary cord. • The medullary cord is separated by large sinus is called medullary sinuses which contain plasma cell and secretes antibody molecule.
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  SECONDARY LYMPHOID ORGANS 2.Spleen • Spleen is the largest secondary lymphoid organ. • It’s a bean shaped organ situated on the left side of the abdominal cavity close to the diaphragm. • It is commonly known as ‘graveyard of RBC’ , it is involved in the destruction of RBC cells and their production. • Its major immunological role is to act as a filter for the blood stream. It traps blood born antigens and produces immune response to them. Structure • Spleen is surrounded by capsule. • A number of projections are extended from the capsule and it is called trabeculae.
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  SECONDARY LYMPHOID ORGANS 1.Red pulp • Red pulp of spleen consists of a network of sinusoids with macrophages and erythrocytes. • It helps to destroy and remove old and defective red blood cells. 2. White pulp • The white pulp of spleen consists of T-lymphocytes with branches of arteries forming periarteriolar lymphoid sheath (PALS). • PALS involved in the initial activation of T and B cells. • The interdigitating dendritic cell capture the antigen and combines with class II MHC molecule and TH cells. • As a result the activated B cells migrates into the primary follicle and develops into secondary follicle with germinal centre. • After antigenic challenge it give rise to B cells and dendritic cells.
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  SECONDARY LYMPHOID ORGANS 3.MALT (Mucosal Associated Lymphoid Tissue) • The mucosal layer of alimentary canal, respiratory and urogenital tract is provided with dispersed group of lymphoid tissue is known as MALT. • It includes NALT, BALT and GALT. • NALT (Nasal Associated Lymphoid Tissue) is composed of lymphoid tissues at the back of the nose, palate and base of the tongue. It includes tonsils. • It is quite large at the time of birth and reduces its size with age. • They are involved in the handling of airborne microbes. • BALT (Bronchus Associated Lymphoid Tissue) is composed of aggregates of lymphocytes and are found in bronchi and lobes of the lung. • GALT (Gut Associated Lymphoid Tissue) is composed of lymphoid complexes and are found in digestive system. It includes payer’s patches. • Payer’s patches are found in the ileum of small intestine as round patches of lymphatic nodules. They protect the body from invading pathogens