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University of Toronto St. George

JAN26 Innate immune system has developed strategies different from adaptive immune system to protect against infectionInnate immune system links many places with adaptive immune systemBoth systems complement work together He observedthere were cells he called phaogcytes that had capacity to physically engulf invading thingsNot passive defense mechanismcells observed to migrate to site of injury and were once there appeared to be moving physically surrounding invading particleIn context of other work doneat time when von Behring discovered antibodiesCellular immunitybased on MetchnikoffHumoral immunityacquired immunity Distinction btw self and nonselfFundamental property ofimmune system was capacity to distinguish self and nonselfAcquire tolerance to selfantigens allowing everything else to be considered foreignbasis of selfnonself discriminationInnate immune system also has capacity to distinguish between self and nonself but does so in DIFFERENT wayModern understanding of innate immunity started withex Janeway who postulated that in microbial world commonly expressed molecules Danger hypothesisargued that shouldnt necessarily be thinking of antigenic versus nonantigenicsomething inherently dangeorus about molecules that induced the best immune responsesin many cases those molecules associated with pathogens Adaptive immune systemresponsive to external environmentadapts or modifies itself to fit cirumcstancesInnateinbornSCID people only have innate immune systemthey do not have immunological memory innate immune system cannot learn from experience In most pathogenic infections initial exposure to pathogen results in relatively small numbers of pathogen entering system and overing the following days the amount of pathogen increases dramatically and really the adaptive immune system will only sense the presence of pathogen when it reaches certain pointAdaptive immune system takes a while to begininduction clonal expansion stages etcTypically four days to start adapative immune responseso response can eliminaet pathogenProblemmany pathogens if unchecked for four days fatalfundamental problem of adaptive immunity the length of time Innate immune systemalthogugh requires activation does not require inductioncells already present waiting to be activatedInnate systemvery response to initial pathogenic insultsfirst line of defense In many cases the innate immune system is probably all that is needed to clear infection before adaptive immune system takes place Different stages of pathogen infectionfirst few hoursinnate immunitynonspecific effectors nonspecificmolecules and receptors involved do not have specificity that antibodies have but still
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