Immune System

Immune System - Immune System In innate immunity...

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Immune System In innate immunity, recognition and response rely on shared traits of pathogens o Innate Immunity of Invertebrates Insect defenses begin with their protective exoskeleton. Lysozyme (an enzyme that attacks microbial cell walls), low pH, and chitin lining the intestine all protect the digestive system. Hemocytes are circulating cells that can engulf and destroy bacteria by phagocytosis, trigger production of chemicals that entrap multicellular parasites, and secrete antimicrobial peptides that kill fungi and bacteria. Different classes of pathogens bind to distinct Toll receptors that activate pathways for the production of antimicrobial peptides effective against that group of pathogens. o Innate Immunity of Vertebrates In mammals, skin and mucous membranes lining the digestive, respiratory, and genitourinary tracts are physical barriers to microbes. Skin secretions maintain a low pH, which discourages colonization by microbes. Acidity of gastric juice kills most microorganisms that reach the stomach. Lysozyme present in tears, saliva, and mucus also kills bacteria. Cellular innate defenses involve specific Toll-like Receptors (TLRs) that recognize molecules that are common to a set of pathogens. Recognition by a TLR triggers phagocytosis of microbes by leukocytes (WBCs). Neutrophils are the most numerous phagocytic WBCs. Macrophages may migrate through the body or become permanently attached in various organs of the lymphatic system. Macrophages attack microbes filtered from blood in the spleen and from lymph. Eosinophils are WBCs that attack multicellular parasitic invades w/ destructive enzymes. Dendritic cells , located in tissues in contact with the environment, stimulate acquired immunity. Virus infected cells produce interferons , which stimulate neighboring cells to produce substances that inhibit viral reproduction in those cells. Another type of interferon activates macrophages. The complement system is a group of about 30 proteins in the blood plasma that may lyse cells, trigger inflammation, or assist in acquired defenses.
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Chemicals released in response to physical injury or pathogen entry can trigger an inflammatory response, characterized by redness, swelling, and heat. Damaged mast cells in connective tissue release histamine , which triggers dilation and leakiness of blood vessels; activated macrophages and other cells release signals that promote blood flow to the damaged area. Vasodilation, as well as signaling proteins, results in the congregation of phagocytic cells and the production of antimicrobial compounds. Pus is an accumulation of fluid, WBCs, and dead microbes. Fever may be triggered by toxins produced by pathogens, or by
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Immune System - Immune System In innate immunity...

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