BIOL 202 Chapter 20: Chapter 20: Innate Immunity

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Biological Science
Course Code
BIOL 202
Cathie Overstreet

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Chapter 20: Resistance and the Immune System; Innate Immunity The Immune System is a Network of Cells and Molecules to Defend Against Foreign Substances • Blood cells make up the body’s innate and adaptive immunities. o Blood consists of fluid, clotting agents, and formed elements. ▪ Fluid: serum. ▪ Clotting agents: fibrinogen and prothrombin. • Serum, in the presence of clotting agents, is referred to as plasma. ▪ Formed elements: RBCs and WBCs. o All blood and immune cells begin as pluripotent stem cells in bone marrow. ▪ Pluripotent stem cells can differentiate into myeloid and lymphoid cell lines. • Myeloid cells/progenitors can themselves differentiate into two lines: o Red blood cells and platelets (megakaryocytes). ▪ Platelets: small disc-shaped cells that function in blood clotting and assisting innate immunity. o White blood cells. • Lymphoid lines differentiate into B and T lymphocytes, natural killer cells, and dendritic cells. Leukocytes: White Blood Cells • Lack pigment in cytoplasm; number about 4-12 thousand per microliter of blood; different lifespans depending on cell type. • Can be identified by size, shape of cell nucleus, and staining of cytoplasmic granules. • Granulocytes: leukocytes containing cytoplasmic granules and present in skin, lungs, GI tract, skin breaks, portals of entry. o Basophils: have cytoplasmic granules that stain blue with methylene blue. ▪ Function in assisting innate immunity. ▪ Work like mast cells; function in allergic reactions. o Eosinophils: red or pink granules when eosin is applied. ▪ Contain cytotoxic proteins to defend against parasites. ▪ Also involved in allergy development and asthma. o Neutrophils: multilobed cell nucleus (polymorphonuclear). ▪ Contain many granules that contain enzymes and other antimicrobial agents. ▪ Most numerous leukocytes. ▪ Can use phagocytosis to engulf pathigens or foreign bacteria. ▪ Last only 1-2 days. ▪ Also considered a phagocyte. • Monocytes: single, bean shaped nucleus without granules. o Monocytes mature into macrophages in infected tissues. o Macrophages are very effective in phagocytosis and drive the innate and acquired immunity in this way. o Present in the spleen, lymph nodes, thymus, and throughout the lungs, skin and nervous system. o Phagocytes and agranulocytes. • Lymphocytes: single large nucleus and no granules. o Natural Killer cells: destroy virus infected cells and tumor cells. o B-Lymphocytes/T-Lymphocytes: drive adaptive immunity. • Dendritic Cells: resemble the dendrites of neurons. o Located at skin and mucosal surfaces where they can respond rapidly to bacterial or viral pathogens. o Phagocytes; drive innate and adaptive immunity. 2 Lymphatic System is Composed of Cells and Tissues Essential to Immune Function • Lymph: part of the interstitial fluid that supplies oxygen and nutrients while collecting waste. • Lymph is oved along through lymph vessels which collect at larger lymphatic vessels; they are filtered by lymph nodes. • Lymphatic tissues: sites where lymphocytes mature and divide. o Primary lymphoid tissues: Thymus, bone marrow. ▪ Site of B and T cell maturation. o Secondary tissues: sites where mature immune cells interact with pathogens to carry out adaptive immune response. ▪ Spleen: contains immune cells and has them on standby to monitor and fight infectious agents entering the body. ▪ Lymph nodes: neck, armpits, and groin. • Contain macrophages and dendritic cells which destroy pathogens in circulation. Innate and Adaptive Immunity Compose a Fully Functional Human Immune System • Three step response to an invader in the body: o Recognition: body’s immune self-determines which cells are host-cells and which cells are not. o Activation: appropriate immune cells are mobilized. o Effector phase: effector/mobilized cells attempt to eliminate invader. • Immune system is composed of two parts: o Innate immunity: first response to pathogen; nonspecific and coded genetically. ▪ These defense are general across different pathogens. ▪ Early Warning System o Adaptive immunity: requires adaptation and is therefore slower than the innate response. 3 ▪ Effector phase (antibodies and lymphocytes) can take more than a week to generate response. • Immune system requires chemical communication between immune cells through the release of cytokines. o Cytokines: signaling proteins. ▪ Interleukins: chemical mediators that moderate reactions between leukocytes locally or systemically. ▪ Chemokines: trigger the attraction of leukocytes to sites of infection. ▪ Cytokines are produced mostly by T-cells, DCs, and macrophages. Surface Barriers Are Part of Innate Immunity • Host defensive barriers limit pathogen entry. • Many portals of entry in the body that can be advantageous for pathogens; intact skin, mucus membranes, body cavities. Physical Barriers • Skin: impenetrable barrier to infection. o Outer layer is constantly ‘shedding’; skin is poor source of nutrition; low water content makes it a desert. • Mucus membranes (mucosa): epithelial lining of digestive, urogenital, and respiratory tracts. o Mucus (glycoproteins that trap heavy particles) line these areas. Chemical Barriers • Low pH in vaginal tract. o Due to the presence of Lactobacillus; break down glycogen into acids, keeping pH down. • Stomach acid (pH=2). o However, polio, and hep A, typhoid/tubercle bacilli, and H. pylori can cause ulcers. • Bile: enters system at duodenum and serves as inhibitory substance. 4 • Defensins: cationic, antimicrobial ;eptides that damage membranes; lyse pathogenic cells. o Produced by neutrophils, NK cells, and epithelial cells of
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