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NBME 24 Answers

nbme24/Block 2/Question#45 (38.4 difficulty score)
A 2-year-old boy is brought to the physician ...
Peptide transporter (TAP)πŸ”

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submitted by lsmarshall(396),
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MCH ascsl 1 tpedipe netaign spsngoreci ;tg& entAgi"n sdieetpp loadde noot CHM I ni RRE aetrf deiyvrle iav PTA nrtorrstaep( stsdacaoie iwht ainetng cgeson)isrp" - tFisr diA 20.91

arBe yhelpomyct drnmeyso yetp 2 (LBS II; ntieffcag MHC II) is due ot amotntsui in enegs hatt eodc orf raoiinsntctpr csrfota tath aolynmrl uegaletr het sxepseiorn (geen rctoitnir)pans of eth HMC II e.sneg Baer yhmltopeyc mneodsyr pyte 1 (SLB I; tnigeaffc CMH )I, si mchu remo ar,er dan si ossaactdie htiw TPA inefieicesdc.

tyrionwill  in the question, it says absence of MHC-I presenting cells. I guess the meaning is lack of MHC-I. IF TAP is missing or dysfunction (bare lym syn type-1), MHC-I should be there, however Ag cannot be loaded to the MHC-I. Can anyone help me to understand more. +  
peridot  @tyrionwill From wiki: "The TAP proteins are involved in pumping degraded cytosolic peptides across the endoplasmic reticulum membrane so they can bind HLA class I. Once the peptide:HLA class I complex forms, it is transported to the membrane of the cell. However, a defect in the TAP proteins prevents pumping of peptides into the endoplasmic reticulum so no peptide:HLA class I complexes form, and therefore, no HLA class I is expressed on the membrane. Just like BLS II, the defect isn't in the MHC protein, but rather another accessory protein." +  
j44n  i hate this question because MHCI is on all nucleated cells. So this person is literally a bag of RBC's +1  
soccerfan23  @j44n Not quite. It's true that MHC I is on all nucleated cells. Because of the TAP mutation, these cells don't express MHC I on their membranes. But these cells still exist. That is what is meant when the vignette says "flow cytometry shows absence of class I MHC-expressing cells. +  

submitted by sunshinesweetheart(69),
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AAD mtntauoi = umaotsloa seescirve SCID

RL--I2 amgma ihnac mattoniu = XRL ICDS

-ILR2- haalp nicha 2C5)(D = Tr-ge yu;fdnsntcio sacos ithw tnmuaoyituim es.p ,T1DM MS

Fas idlgan 5)(DC9 nutitaom = no T clle soptopsia in aegenvit sitceoeln ni tihmyc umlelad = rnci lanturociic of -cntsfarlegie yytmphecol = imuomautne ymiprvlfiortpoleeha rmsyeond

submitted by niboonsh(338),
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omer ionf oubta reaB hocLytypme oemrydnS i-npcm-thtmnyneihv-.dornp.iht//cglnt-iasygehy/c:olyser.oep/ob#mdiernanetiohtr

submitted by beltorres23(0),

Important uworld image

submitted by yotsubato(978),
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lCoo renahto qinoetsu enkat rmof eth itls fo hingst ton in FA

charcot_bouchard  Actually it is in FA. FA 19 Page 100 - Antigen loaded onto MHC1 in RER after delivery via TAP transporter.... Remember FA is that friend who always say I told you so. +20  
yotsubato  But not in this context +5