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NBME 20 Answers

nbme20/Block 1/Question#23 (46.1 difficulty score)
A 34-year-old man who is HIV positive is ...
CD4+ T lymphocytes🔍
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 +5 
submitted by sympathetikey(1360),
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4CD+ sclle iaeactvt Bellc-s wchih ormf fsoelicll nad ecsua algtnnmeeer of lhmpy oedns. eerTeo,fhr in an ISDA nttapie, ot elngaer het yphml ,nesod hte 4CD+ uytnocisdnf stum be lsdroee.v

breis  Yea i get that, but if the patients CD4 was ~35, how in the world did the CD4 count rise enough to stimulate B cell proliferation...? I don't get it +9  
namira  The only thing i can think of is that: the cd4 count that is given was taken prior to having started the antiretroviral therapy. Since the question asks about "improved function", maybe its referring to the therapy actually being effective and its managed to increase cd4 count and function so as to be able to contribute to lymph node enlargement due to myco. avium +12  
kamilia20  I though it transfer to a lymphoma,OMG +  
bgreen27  This answer explanation implies that dysfunction means scarcity, right? But are the CD4 cells actually dysfunctional in HIV? or just scarce? I don't like this question because clearly both CD4 and B cells are involved in lymph node enlargement AND if improved function = increased number, then both B cells and CD4 cells would meet that criteria. +  
drdoom  @bgreen27 “depletion” is the more precise term here (although I would not be surprised if CD4s of HIV+ individuals were also somehow dysfunctional). +  
drdoom  @bgreen27 also, remember that a single CD4 can drive the proliferation of ~many~ B cells. So, yes, lymph node enlargement is driven by CD4s, but virtually all of the mass is attributable to B cell expansion. (That is, if you snipped out an activated lymph node and then weighed all the T cells and than weighed all the B cells, you’d find the lymph node is mostly “B cell weight”.) +1  
bgreen27  so I think I understand, depletion~dysfunction and repletion~"increase in function" but proliferation is neither here nor there because it's really just Bcell "function" +  



 +1 
submitted by andremosq(3),

Question asks about the cause of the enlargement of Lymph nodes .. Lymph node Paracortex enlarges in an extreme cellular immune response (paracortical hyperplasia) against virus infected cells (FA20.Pag 96.) T cells regulate cell- mediate immunity ... CD4 T cells specifically is the DIRECT Cell Immunne response. CD8 T cell is cytotoxic.




 -7 
submitted by hayayah(1079),
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toMeybucacimr imvau poecmlx notsfencii ear a mnocmo poicnropttius onfncieti ni aienptst whti anvcddea ISDA CD(4 ucont l;&)5.t0

realfakedreams  @hayayah you were being lazy.. smh.. Homie started anti-retroviral therapy. HIV infects CD4 T-Cells through either CCR5 or more commonly CXCR4. Because of anti-retrovirals start working, HIV isnt able to infect anymore CD4 T cells. Thus CD4 t lymphocytes levels start to rise and are able to active B cells. +13  
myf1991  Why can't it be monocyte? macrophage eat MAC and interact with CD4 +1  
weenathon  @myf1991 I also incorrectly chose monocytes, but if you look at the question carefully, it is specifically asking what cell is required for the lymph nodes to enlarge, not which cell is handling the mycobacterium avium infection. Since CD4 cells stimulate B cells to proliferate in lymph node follicles, which would make them bigger, CD4+ T cells is the answer. +3  
j44n  macrophages dont enlarge nodes in fact they make them smaller, tingle body macs eat all the bad B cells in a node so improved mac fxn would decrease the node size +  
mpel14  To add to @namira, an infectious disease doc described this concept in an HIV lecture where he said that prior to the Tx with antiretroviral therapy, the pt has such low CD4 count that their immune system cannot form a response to the infection, and after their immune system is given a slight boost with the drugs, their immune system can finally "see" the infection -> mount response -> causes S/S +