Unit-1 Immunology 2024 PDF

Immunity and Organs of the Immune System Unit -1 Outlines of Immunology  Fundamental Function of the Immune System Distinguishing SELF AND NON-SELF Infectious Non-Self (Pathogens – Virus, bacteria, fungi, parasites etc) Non-Infectious Non-Self (Food, Pollen, dus...

Immunity and Organs of the Immune System Unit -1 Outlines of Immunology  Fundamental Function of the Immune System Distinguishing SELF AND NON-SELF Infectious Non-Self (Pathogens – Virus, bacteria, fungi, parasites etc) Non-Infectious Non-Self (Food, Pollen, dust, etc) Infectious Self (Cancer) Non-Infectious Self (Cells and proteins and other molecules of the body)  Mode of operation of the Immune System IDENTIFICATION Non-infectious Self and infectious Non-self RECRUITMENT Mobilize Effectors ELIMINATION Clears Pathogen PREVENT RECCURENCE Prevention of Future infection-(Memory) DEACTIVATION Stop fighting when the war is over-Prevention of unwanted effects on host (Reducing Collateral damage)  Types of Immunity Innate vs Adaptive (Acquired) Humoral vs Cellular  Components of the immune system Innate immune system Adaptive immune system Response is non-specific Pathogen and antigen specific response Exposure leads to immediate maximal Lag time between exposure and response maximal response Cell-mediated and humoral components Cell-mediated and humoral components Exposure leads to immunological No immunological memory memory Found in nearly all forms of life Found only in jawed vertebrates  Humoral immunity Humoral immunity is the aspect of immunity that is mediated by macromolecules - including secreted antibodies, complement proteins, and certain antimicrobial peptides - located in extracellular fluids. Humoral immunity is named so because it involves substances found in the humors, or body fluids. It contrasts with cell-mediated immunity.  Cell-mediated immunity Cell-mediated immunity is an immune response that does not involve antibodies. Rather, cell-mediated immunity is the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen.  Surface Barriers Skin Skin is a barrier that protects and seals the organisms from infection that could be caused by mechanical injury, chemical injury, and biological injury.  However, as organisms cannot be completely sealed against their environments, other systems act to protect body openings such as the lungs, intestines, and the genitourinary tract. In the stomach, gastric acid and proteases serve as powerful chemical defenses against ingested pathogens.  The flushing action of tears and urine also mechanically expels pathogens. Mucus secreted by the respiratory and gastrointestinal tract serves to trap and entangle microorganisms. Enzymes such as lysozyme and phospholipase A2 in saliva, tears, and breast milk are also antibacterials. Vaginal secretions serve as a chemical barrier following menarche, (pronounced “men are Key”) when they become slightly acidic. Semen contains defensins and zinc to kill pathogens.  In the lungs, coughing and sneezing mechanically eject pathogens and other irritants from the respiratory tract. Mechanism of Breathing  Within the genitourinary and gastrointestinal tracts, commensal flora serve as biological barriers by competing with pathogenic bacteria for food and space and, in some cases, by changing the conditions in their environment, such as pH or available iron. This reduces the probability that pathogens will reach sufficient numbers to cause illness.  Commensalism In ecology, commensalism is a class of relationship between two organisms where one organism benefits without affecting the other. Commensalism is a symbiotic relationship where the symbiont benefits but the host is neither harmed nor helped. (Relationship between Humans and normal flora). Organisms colonising the human body in a commensal realationship are called commensals, or commensal flora or “normal Flora” Commensalism is harder to demonstrate than parasitism and mutualism, for it is easier to show a single instance whereby the host is affected, than it is to prove or disprove that possibility. Often, a detailed investigation will show that the host indeed has become affected by the relationship. Many of these organisms especially the ones colonising the gut and UG tract cannot be classified as pure commensalists. Many of them provide nutritional benefits such as vitaman production, the break down of non-digestible materials, and competitive exclusion of pathogens. The vagina is colonized mostly by lactobacillus. The lactobacillus produce lactic acid which lowers the pH and inhibits the colonization of other bacteria.  Components of the immune system Innate immune system Adaptive immune system Response is non-specific Pathogen and antigen specific response Exposure leads to immediate maximal Lag time between exposure and response maximal response Cell-mediated and humoral components Cell-mediated and humoral components Exposure leads to immunological No immunological memory memory Found in nearly all forms of life Found only in jawed vertebrates Organs of the Immune System Lymphoid Organs  Primary Lymphoid Organs Bone Marrow Thymus  Bone Marrow Bone marrow is the soft, spongy, gelatinous tissue found in the hollow spaces in the interior of bones. The average weight of this tissue is about 4% of the total body weight, or 2.6 kg in an adult weighing 65 kg. Two types of bone marrow medulla ossium rubra (red marrow), consists mainly of hematopoietic tissue medulla ossium flava (yellow marrow), which is mainly made up of fat cells.  Two Kinds of Bone Spongy Bone Compact Bone  Immunological function of Bone Marrow The bone marrow is the site of generation of all circulating blood cells in the adult, including immature lymphocytes It is the site of B cell maturation (Hence the name “B” cell, B stands for Bone marrow originally, Bursa of Fabricius in birds).  Thymus – Location – behind the sternum in the mediastinum – The capsule divides it into 2 lobes – Development Infant – conspicuous Puberty – maximum size Maturity – decreases in size – Function Differentiation and maturation of T cells (Hence the name “T” cells, T- stands for Thymus) Thymus  2. Cells in thymus and thymus microenviroment (1)Thymus stroma cells (TSC) Thymus epithelial cells (TEC), Fibrocyte,Macrophages, Dendritic cells (2)Thymocytes The cells migrate from the bone marrow to the thymus and then become thymocytes Thymic Nurse Cells  Thymus microenviroment TSC- Thymus stroma cells Thymus epithelial TEC: Secret thymus hormones and cytokines. Interaction between cells by direct contact.  T-Ce l man l Surviv y e (Un copies s and d expa ergoes are ma nsio Clon de n) a l Poo r Bind ing T- Ce Dendritic Cell ll T-Cell Tight Binding (recognition of self antigens) T-Cell Killed -Apoptosis  Function of Thymus (1) Development and differentiation of T lymphocytes in thymus TSC interact with thymocytes directly by adhesion molecules. TSC secrete various cytokines and thymus hormones (thymosin and thymopoietin). Thymocytes secrete various cytokines (2)Immune regulation of the thymus (3)Barrier function of the thymus The blood–thymus barrier regulates exchange of substances between the circulatory system and thymus, providing a sequestered environment for immature T cells to develop. The barrier also prevents the immature T cells from contacting foreign antigens (since contact with antigens at this stage will cause the T cells to die by apoptosis). The barrier is formed by the continuous blood capillaries in the thymic cortex, reinforced by epithelial reticular cells and macrophages.  Secondary Lymphoid Organs  Lymph Node Spleen MALT (Mucosa Associated Lymphoid Tissue)  Lymph Tissue – 3 types Diffuse lymphatic tissue – No capsule present – Found in connective tissue of almost all organs Lymphatic nodules – No capsule present – Oval-shaped masses – Found singly or in clusters Lymphatic organs – Capsule present – Lymph nodes, spleen, thymus  Lymph Nodes – Oval structures located along lymphatics – Enclosed by a fibrous capsule – Cortex = outer portion Germinal centers produce lymphocytes – Medulla = inner portion Medullary cords – Lymph enters nodes through afferent lymphatics, flows through sinuses, exits through efferent lymhpatic  1. An oval structure, 1 to 25mm in diameter. 2. Enclosed by a capsule with an internal framework of trabeculae consisting of collagenous and reticular fibers. 3. Found primarily in the proximal area of the limbs, i.e., axilla, inguinal and cervical nodes, as well as, the retroperitoneal area of the pelvis and abdomen and the surface of thoracic and abdominal organs. 4. Contains two inner regions: A) a cortex consisting of densely packed nodules of lymphocytes found just below the subcapsular sinus. The nodules are called primary nodules. Each one contains lymphocytes, plasma cells and macrophages. During periods of infection or inflammation, the lymphocytes in the nodules divide forming the very active "germinal centers“ B) a medulla containing cords or rows of lymphocytes separated from one another by sinuses. There are no germinal centers here. Lymph Node  Spleen – Largest lymphatic organ – Located between the stomach & diaphragm – Structure is similar to a node Capsule present But no afferent Lymph vessels or sinuses – Histology Red pulp contains all the components of circulating blood White pulp is similar to lymphatic nodules – Functions Filters blood Stores blood Spleen Mouse Spleen PALS -Peri-Arteriolar Lymphoid Sheath –Rich in loosely packed T-cells T -Trabeculae C -Capsule Folicle  Spleen physically filters Blood Aged erythrocytes are inflexible and find hard to pass through the spaces between endothelial cells RBC specific macrophages phagocytose and digest the stuck RBCs and recycle their constituents. Area Function Composition "sinuses" (or "sinusoids"), which are filled Mechanical filtration of with blood Red pulp red blood cells. In mice: Reserve of monocytes "splenic cords" of reticular fibers "marginal zone" bordering on white pulp Composed of nodules, called Malpighian corpuscles. These are composed of: Active immune "lymphoid follicles" (or "follicles"), rich in response through White pulp humoral and B-lymphocytes cell-mediated pathways. "periarteriolar lymphoid sheaths" (PALS), rich in T-lymphocytes Lymph Nodules  Tonsils – Multiple groups of large lymphatic nodules – Location – mucous membrane of the oral and pharyngeal cavities – Palatine tonsils Posterior-lateral walls of the oropharynx – Pharyngeal tonsil Posterior wall of nasopharynx – Lingual tonsils Base of tongue Tonsils  Function of the Lymphatic System – Defense against harmful organisms and chemicals – 2 types of defense Nonspecific Specific – Specific defense = immunity Humoral immunity involves B cells that become plasma cells which produce antibodies that bind with specific antigens. Cell-mediated immunity involves T cells that directly destroy infected cells  References Lymphoid System http://faculty.ucc.edu/biology-potter/lymphoid_system.htm http://www.lymphnotes.com/article.php/id/151/ http://www.immune-system-expert.com/immune-organs.html Spleen Structure function Review http://www.uniroma2.it/didattica/IstologiaEmbriologia/deposito/spleen.pdf http://tpx.sagepub.com/content/34/5/455.full For Beautiful Photos on Lymphoid Histology and description of Lymphatic System: Spleen and Other Organs http://www.vetmed.vt.edu/education/curriculum/vm8054/labs/lab13/lab13.htm http://www.lab.anhb.uwa.edu.au/mb140/corepages/lymphoid1/lymph1.htm On Commensal/ Normal Flora http://textbookofbacteriology.net/normalflora_3.html http://mpicel.myweb.uga.edu/ Thymic Nurse cells (This site is a popular Science journal-Browse it now and then for recent advances in science -made simple) http://www.sciencedaily.com/releases/2007/05/070523073305.htm