Any discussion of the innate immune response usually begins with the physical barriers that prevent pathogens from entering the body, destroy them after they enter, or flush them out before they can establish themselves in the hospitable environment of the body’s soft tissues. This brings the phagocyte and bacterium into close proximity and enhances the phagocytosis of the bacterium by the process known as opsonization. A monocyte is a circulating precursor cell that differentiates into either a macrophage or dendritic cell, which can be rapidly attracted to areas of infection by signal molecules of inflammation. acute inflammation: inflammation occurring for a limited time period; rapidly developing, chemokine: soluble, long-range, cell-to-cell communication molecule, chronic inflammation: inflammation occurring for long periods of time, complement: enzymatic cascade of constitutive blood proteins that have antipathogen effects, including the direct killing of bacteria, cytokine: soluble, short-range, cell-to-cell communication molecule, early induced immune response: includes antimicrobial proteins stimulated during the first several days of an infection, fas ligand: molecule expressed on cytotoxic T cells and NK cells that binds to the fas molecule on a target cell and induces it do undergo apoptosis, granzyme: apoptosis-inducing substance contained in granules of NK cells and cytotoxic T cells, histamine: vasoactive mediator in granules of mast cells and is the primary cause of allergies and anaphylactic shock, inflammation: basic innate immune response characterized by heat, redness, pain, and swelling, interferons: early induced proteins made in virally infected cells that cause nearby cells to make antiviral proteins, macrophage: ameboid phagocyte found in several tissues throughout the body, mast cell: cell found in the skin and the lining of body cells that contains cytoplasmic granules with vasoactive mediators such as histamine, monocyte: precursor to macrophages and dendritic cells seen in the blood, neutrophil: phagocytic white blood cell recruited from the bloodstream to the site of infection via the bloodstream, opsonization: enhancement of phagocytosis by the binding of antibody or antimicrobial protein, pattern recognition receptor (PRR): leukocyte receptor that binds to specific cell wall components of different bacterial species, perforin: molecule in NK cell and cytotoxic T cell granules that form pores in the membrane of a target cell, phagocytosis: movement of material from the outside to the inside of the cells via vesicles made from invaginations of the plasma membrane. The previous discussions have alluded to chemical signals that can induce cells to change various physiological characteristics, such as the expression of a particular receptor. In fact, both can cooperate and one can influence the other in their responses against pathogens. Interferons. A neutrophil is a phagocytic cell that is attracted via chemotaxis from the bloodstream to infected tissues. has memory- it recognizes and mounts even stronger attacks on previously encountered pathogens. The Immune System has 3 Lines of Defense Against Foreign Pathogens: 1. Inflammation also facilitates the transport of antigen to lymph nodes by dendritic cells for the development of the adaptive immune response. A macrophage is an irregularly shaped phagocyte that is amoeboid in nature and is the most versatile of the phagocytes in the body. Whereas barrier defenses are the body’s first line of physical defense against pathogens, innate immune responses are the first line of physiological defense. Other early induced proteins specific for bacterial cell wall components are mannose-binding protein and C-reactive protein, made in the liver, which bind specifically to polysaccharide components of the bacterial cell wall. Interferons enhance the immune system in many ways so can be used to treat different conditions involving the immune system. Specific defense system recognizes and attacks specific foreign substances (lymphocytes, antibodies, and macrophages). attract phagocytes through chemotaxis- the phagocytes follow the chemical trail and dispose of pathogen and cell debris. Cytokines are secreted into the intercellular space, and the action of the cytokine induces the receiving cell to change its physiology. The earlier fragments of the cascade also have important functions. Antimicrobial proteins (such as lysozyme, which breaks down the cell walls of bacteria) are contained in saliva, tears, and other secretions found on mucous membranes. The phagocytes of the immune system engulf other particles or cells, either to clean an area of debris, old cells, or to kill pathogenic organisms such as bacteria. Considering how often you breathe compared to how often you eat or perform other activities that expose you to pathogens, it is not surprising that multiple barrier mechanisms have evolved to work in concert to protect this vital area. Consequently, an immune response initiated in the gut-associated lymphoid tissue can affect immune responses at other mucosal surfaces. Specific(Adaptive) Defense: the immune response. Interferons not only exhibit important antiviral effects but also exert a key influence on the quality of the cellular immune responses and amplify antigen presentation to specific T cells. Phagocytosis is an important and effective mechanism of destroying pathogens during innate immune responses. Another barrier is the saliva in the mouth, which is rich in lysozyme—an enzyme that destroys bacteria by digesting their cell walls. The adaptive immune system is highly specific. The alternate pathway does not require an antibody to become activated. Phagocytic cells such as macrophages and neutrophils are attracted to an infection site by chemotactic attraction to smaller complement fragments. Drugs that boost those levels could help fight off illness. Phagocyte chemotaxis is the movement of phagocytes according to the secretion of chemical messengers in the form of interleukins and other chemokines. The cell debris and damaged cells induce macrophages to begin to clean them up. In fact, both can cooperate and one can influence the other in their responses against pathogens. NK cells are not specific, their numbers do not increase when exposed to a specific antigen and they do not “remember” the antigen from a previous contact. 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