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PATHOGENS AND INNATE IMMUNITY (LEC 2).docx

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Department
Physiology
Course
PSL301H1
Professor
Shaun Burns
Semester
Winter

Description
PATHOGENS AND INNATE IMMUNITY (802-814) • Main features of immune system are specificity and memory o Allow body to distinguish between self from non-self during immune response o 3 major functions  Recognize and remove abnormal self cells • Cancer cells form regularly but are usually detected and destroyed by immune system before they get out of control  Remove old, dead or damaged cells • Scavengers cells such as macrophages patrol extracellular compartments  Protects body from pathogens • Almost any foreign molecule can induce an immune response o Known as immunogens o Immunogens that react with antibodies are antigens • Viruses can replicate only inside host cells o Virus binds to membrane receptors of cell, triggering endocytosis of virus  Free of capsid shell, virus RNA/DNA hijacks the cell’s transcription and translation machinery to make new viral nucleic acid and proteins  Can be released in 2 ways • Virus causes host to lyse and release viral particles into ECF • Virus particles embed themselves into a vesicle then bud off • Immune response o 2 lines of defence  Physical and chemical barriers  Internal immune response • 4 basic steps PSL301H1|Lecture 2 o Detection and identification of foreign substances o Communication with other immune cells to organize response o Recruitment and coordination of response among cells o Destruction of invader • Extensive use of chemical signalling through signal molecules such as cytokines and antibodies o Cytokines are protein messengers released by one cell that affect the activity of another o Antibodies are proteins secreted by immune cells, bind antigens, markers for immune system • Immune response is divided into 2 categories o Innate immunity is present from birth and is the nonspecific immune response  Membrane receptors have broad specificity, allowing them to respond to molecular signals to various pathogenic microorganism  Responds quickly, such as inflammation o Acquired immunity is a specific immune response  Membrane receptors that mediate with specific immune responses are very specific and can differentiate between different pathogens • Specific immune response following first exposure may take days • Repeated exposure allows immune system to react more rapidly • Anatomy of immune system o Lymphoid tissues  2 primary tissues are thymus gland and bone marrow • Where cells involved in immune response develop PSL301H1|Lecture 2 • Encapsulated lymphoid tissues o Spleen contains immune cells positioned so that they monitor blood for pathogens  Also has phagocytic cells which remove old RBC o Lymph nodes are part of lymphatic circulation  Closely associated with cardiovascular system  Interstitial fluid, filtered from capillaries into interstitial space due to BP, is picked up by lymph capillaries and passes through lymph nodes  Inside lymph nodes, clusters of immune cells intercept pathogen which have invaded interstitial fluid via cuts or mucous membrane • Prevent spread throughout body • Anatomically, immune cells are positioned where pathogens are most likely to enter body • Leukocytes mediate immunity o Leukocytes (WBC) are the primary cells responsible for the immune responses of the body  Eosinophils (phagocyte w/antibody coating) • Associated with allergic reactions and parasitic diseases o Concentrated in areas most likely to be attacked by parasites  GI tract, lungs, urinary and genital epithelial o Attracted to large antibody-coated parasites  Neutrophils (phagocyte) • 50-70% of WBC • Formed in marrow, released into circulation, attracted to sites of infection • Release pyrogens (cause fever) PSL301H1|Lecture 2  Monocyte & macrophage (phag
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