Third Lecture Immuno

Third Lecture Immuno - The first cells that generally...

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The first cells that generally respond to an infection are cells of the innate immune system. They do not just use the receptors on the cell surfaces, but also soluable factors. How they respond depends on the type of pathogen the immune system encounters. You see in the figure that some of the organisms are extracellular, meaning they survive outside of your bodys cells. Others are intercellular, such as viruses. Viruses must live within the cytoplasm of a cell. Other infectious agents as well prefer to live inside of vesicles, so they will allow themselves to be phagocytosed then will be able to survive inside the paghocyte vesicles (because they have evolved with our immune systems and found a way to hide out there). Microbacteria, which causes tiberculosis does this. Within the immune system now your body uses NK cells to get at the cytoplasmic organisms such as viruses, listeria, and some protozoa’s. Whereas activated macrophages that are activated primarily by T cells will then be able to kill the organisms that would normally survive in the vesicles. Extracellular bacteria, your immune system needs to eat them/phagocytize them, by a macrophage. It has empty vesicles that will eat the organisms around it. Viruses until they get into a cell are extracellular. Antimicrobrial peptides, the defensins are a large family that can disrupt membranes of various organisms. Along with complement family of proteins that are secreted as proenzymes and once complement is activated it will cause a cascade of activation of other complement factors that lead to recruitment of more phagocytic cells (macrophages and neutrophils) but also will lead to direct lysis of organisms if the complement cascade goes to completion. But complement is also part of the inflammatory response that occurs in a tissue because of some of the other functions that complement proteins carry out in the body. Our first line of defense against infection is complement, it is present as soluble proteins in all of our body fluids. The vast majority of the proteins are produced by liver hepatocytes and secreted into the blood stream. There are a large family of molecules that have related structure and sequence. Complement proteins were first discovered when it was observed that “fresh” serum could kill bacteria if they were incubated at 37 degrees C (this is body temperature). Serum is the fluid of blood after it coagulates, if you do not add a anticoagulant factor when drawing blood it will form a clot! Eventually the clot will retract and trap all the blood cells, platelets in it. The liquid portion on top that is left will be called serum. If you take fresh serum, right after the blood clots, and don’t freeze it or anything and mix it with bacteria then the bacteria will die. It is an innate part of your immune system that can get activated in the surface of a bacteria, form a pore in the membrane of the bacteria, cause all the intercellular parts of the bacteria to ooze out, it
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This note was uploaded on 03/27/2012 for the course BLD 434 taught by Professor Hoag during the Spring '11 term at Michigan State University.

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Third Lecture Immuno - The first cells that generally...

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