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Old 12-09-2013
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Question Explanation of PPD

Hello, please someone explain the PPD test..
once you inject the purified protein a macrophage phagocytoses it and processes it presenting it with mhc class 1 (im guessing cause its a cd8 involved reaction?) and then what happens? please someone explain in detail the immunologic view of this test, thanks in advance
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macrophage presents PPD on MHC2 to CD4 which activates CD4 that releases relevant cytokines
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ok, could you answer this:
1.is the memory cd4 a Th0 cell that differentiates into th1 once the APC comes with this intracellular pathogen?or the memory cd4 is directly a th1 cell?
2. if this was NOT a sensitized person in what part the process will be stuck on?
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Quote:
Originally Posted by drpisho View Post
ok, could you answer this:
1.is the memory cd4 a Th0 cell that differentiates into th1 once the APC comes with this intracellular pathogen?or the memory cd4 is directly a th1 cell?
2. if this was NOT a sensitized person in what part the process will be stuck on?
if its a primary exposure then it is a nascent CD4 which is Th0 that is activated into th1 subset by cytokines from macrophages and the response is very mild (negative PPD)
if the body has been exposed to TB proteins prior to test then already differentiated CD4 th1 subset release massive amounts of cytokines mounting type 4 hypersensitivity reaction (positive PPD)
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thank you a lot, really cleared everything up, ive been struggling with this for hours, none of the kaplan books or the first aid get a detailed immunologic explanation of this and this is high yield.
THANKS Medicalexaminer
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