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University of Toronto St. George

01Julius Adaptive immune system can respond to virtually infinite variety of antigens specificallyrandom recombinationsolved moreorlessTolerance Pathogens can overcome host defenses Primary lymphoid organs are sites of lymphopoiesis where lymphocytes are bornthus called primary T cells called such because first described based on antigen called thy1first isolated from brainAll precursorssource from marrow Secondary lympohid organsLeave thymus go to periphery In the marrow become B cell complete maturation within the bone marrow1012 lymphocytes in humans Unsure how many leave the marrow daily Precursors enter thymus start developing into T cells Thymus btw one and two hundred million cells largethymus starts to shrink involutes ultimately reduced in size to 10 at neonatal micesexual maturationnumber of cells leaving thymus also reducedT cell production wanes to fraction to what it was at birth but the number of cells remains constant T cells do not live longer than B cell sCapacity to ward off pathogen depend on specific lymphocytes undergoing clonal expansionso specific T cells to specific insult will expand hugelyyetnumber of T cells in secondary lymphoid organs remains constantLargest organ of bodyintestinegut is site of T lymphopoiesismore T cells in gut than all other places of body including thymus together But they never leave the gutinside of the gut is the surface where vast majority of interactios with antigens occurThat process that maintains this balanced number of cells in body is called lymphocyte homeostasisLymphocytes produced dailyso must be dying to make biological space for the newborn onesEXCEPT for memory cells a part of adaptive immune system Thymus source as T cellused asbone marrow as source of B cells BMBone marrow Syngenicidentical genetically A living test tube
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