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Immune System

Immune System . Noel Esqueda. Important vocabulary . Interferon – Proteins that protect cells from viruses Phagocytes – white blood cells that destroy pathogens by surrounding and engulfing them

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Immune System

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  1. Immune System Noel Esqueda

  2. Important vocabulary • Interferon – Proteins that protect cells from viruses • Phagocytes – white blood cells that destroy pathogens by surrounding and engulfing them • Macrophages- white blood cells that provide the first defense against pathogens that have managed to enter the tissues • Innate immunity- the body’s earliest lines of defense against any and all pathogens • Acquired immunity- defending against a specific pathogen by gradually building up a resistance to it • Antibiotic- a substance produced by a microorganism that, in small amounts, will kill or inhibit the growth and reproduction of other microorganisms, especially bacteria • Lymph node- small mass of tissue that contains lymphocytes and filters pathogens from the lymph • Lymphocytes- a type of white blood cell that defends the body against foreign substances

  3. Lymphatic system • Its main purpose is to transport lymph around the body the body to get rid of toxins and wastes • A function of the lymphatic system is to transport white blood cells to and from lymph nodes into bones as well as antigens presenting cells to the lymph node • The thymus stores immature lymphocytes and prepares them to be active T-cells

  4. NONSPECIFIC DEFENSES AGAINST INFECTION • SKIN AND MUCOUS MEMBRANES ARE THE FIRST LINE OF BARRIERS TO INFECTION • SWEAT GLANDS GIVE THE SKIN A PH OF BETWEEN 3-5 WHICH IS ACIDIC ENOUGH TO PREVENT COLONIZATION OF MANY MICROBES • LYSOSOMES IS AN ENZYME THAT HELPS DIGEST WALLS OF BACTERIA CELLS AND HELPS DESTROY BACTERIA ENTERING THE UPPER RESPIRATORY TRACT AND OPENINGS AROUND THE EYE • MUCUS TRAPS MICROBES AND OTHER PARTICLES THAT CONTACT IT • IF THE FIRST LINE OF DEFENSE IS BREACHED, THE BODY DEPENDS MAINLY ON PHAGOCYTOSIS, THE INGESTION OF CELLS BY CERTAIN TYPES OF WHITE BLOOD CELLS • NEUTROPHILS ARE PHAGOCYTIC CELLS, MAKE UP 60-70% OF ALL WHITE BLOOD CELLS, THAT ONCE IT IS ATTRACTED TO DAMAGED CELLS IT ENTERS IT AND ENGULFS AND DESTROYS MICROBES • MONOCYTES DEVELOP INTO MACROPHAGES AND THEY ARE MORE EFFECTIVE THAN NEUTROPHILS • MACROPHAGES ENGULF MICROBES IN VACUOLES THAT FUSE WITH A LYSOSOME

  5. Continued • macrophages produce either toxic forms of oxygen or lysosomal enzymes to digest microbial components • Eosinphils only make 1.5% of leukocytes, their contribution is to large parasitic invaders but have limited phagocytic activity • Natural killer cells destroy virus infected body cells by attacking its membrane causing it to lyse • inflammatory response occurs when there is damaged tissue caused by a physical injury or entry of microorganisms • histamine is released in response to tissue injury causing dilation and increased permeability of nearby capillaries • enhanced blood flow and vessel permeability aid in delivering clotting elements to the injured area, this also helped the migration of phagocytic cells travel to the injured tissue

  6. Continued • chemokimes help attract phagocytes to an infected area as well as induce the production of toxic forms of oxygen in phagocyte lysosomes and release histamine from bastophils • pyrogens are molecules that set the body's thermostat at a higher temperature • moderate fevers contribute to defense by inhibiting the growth of some microorganisms • Complement system carry out a cascade of steps that leads to the lysis of microbes • Interferons are proteins that diffuse to neighboring cells and induce them to produce chemicals that inhibit viral production limiting the cell to cell spread of viruses in the body

  7. How specific immunity arises • An antigen is a foreign molecule that elicits a specific response by lymphocytes • T-cells are lymphocytes that are produced in bone marrow and are processed in the thymus gland • B-cells are lymphocytes that when activated by T-cells, become a plasma cell and produce antibodies • one way antigens elicit immune responses is by activating b cells to secrete antibodies • b cells and t cells recognize specific antigens by their plasma membrane bound antigen receptors, transmembrane versions of antibody molecules • clonal selection is when a lymphocyte makes two types of cells, effector cells that are short lived and fight the same antigen and memory cells which are long lived cells bearing receptors specific for the same antigen

  8. continued • primary immune response- the selective and differentiation of lymphocytes that occurs the first time the body is exposed to an antigen • plasma cells are created during the period in which selected lymphocytes generate the maximum effector cell response ( 10-17 days after primary response) • When an individual is exposed to same antigen again the response time is faster (2-7 days) this is the secondary immune response • b cells are located in bone marrow and t cells are located in the thymus, but at one point they were the same cell until it differentiates • lymphocytes bearing receptors specific for molecules already present in the body are either rendered nonfunctional or destroyed by apoptosis, leaving lymphocytes that only react to foreign molecules

  9. Continued • antigen presentation- an MHC molecule cradles a fragment of an intercellular protein antigen in its hammock like groove, carries it to the cell surface, and presents it to an antigen receptor on a nearby t cell, this alerts them of infectious agents • cytotoxic t cells have antigen receptors that bind to protein fragments on class one MHC molecules, Helper t cells have receptors that bind to peptides on class two MHC molecules • humans make two different MHC polypeptides per gene and that is why it is very unlikely that two people have the same set of MHC molecules • Antigen presenting cells ingest bacteria as well as viruses and destroy them, Class two MHC molecules in these cells collect peptide reminants of this degradation and present them to helper t cells, t cell signal other cell types to fight the pathogen

  10. Immune responses • Humoral immunity- involves b cell activation and results from the production of antibodies that circulate in the blood plasma and lymph, antibodies made by this defend mainly against free bacteria,toxins, and viruses present in body fluids • Cell mediated immunity- depends on the actions of T cells, the t cells of this fight against viruses and bacteria within infested body cells and fungi, protozoa, and parasitic worms • CD4- t cell surface protein that greatly enhances the interaction between an APC and a helper T cell • The interaction between CD4 and a class two MHC molecule helps keep the helper t cell and the APC joined while activation of the Th cell occurs • activated helper t cells secrete several different cytokine, proteins or peptides that stimulate other lymphocytes

  11. Continued • interleukin 2- cytokine that helps b cells that have contacted antigen differentiate into antibody secreting plasma cells and helps t cells become active killers • as a macrophage phagocytoses and presents antigens, the macrophage is stimulated to secrete interleukin 1 • Antigen activated cytotoxic t lymphocytes kill cancer cells and cells infected by viruses or other intracellular pathogens • class 1 MHC molecules expose foreign proteins that are synthesized in infected or abnormal cells to cytotoxic t cells • CD8- binds to a class 1 MHC molecule, this interaction helps keep the two cells in contact while the Tc cell is occurring • perforin- a protein that forms pores in the target's cell's membrane, this causes cells to lyse

  12. Continued • T dependent antigens- antigens that evoke clonal selection because they can stimulate antibody production only with the help from Thcells • For some people, proteins of foreign substances such as pollen or bee venom act as antigens that induce an allergic reaction or hypersensitive humoral response • Epitope- localized region on the surface of an antigen that is chemically recognized by antibodies, it also known an antigenic determinant • A single antigen such as a bacterial surface protein usually has several effective epitopes, each capable of inducing the production of specific antibody • A typical antibody molecule has two identical antigen binding sites specific for the epitope that provoked its production • The tail of the Y shaped antibody is responsible for the antibody’s distribution in the body and for the mechanisms by which it mediates antigen disposal

  13. Continued • The binding of antibodies to antigens to form antigen-antibody complexes is the basis of several antigen disposal mechanisms • Neutralization- an antigen disposal mechanism in which the antibody binds to and blocks the activity of the antigen • Opsonization- bound antibodies enhance macrophage attachment to and, thus phagocytosis of, the microbes • Complement fixation- the activation of the complement system by antigen-antibody complexes • Completion of the complement cascade results in the lysis of many types of viruses and pathogenic cells

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