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NBME 21 Answers

nbme21/Block 1/Question#3 (55.0 difficulty score)
An investigator is studying the efficacy of ...

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submitted by cantaloupe5(69),
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parslauC elroaipycdcsah cseiacvn rae tfnoe jotdnauceg ot etsnopri ot mveprio oiycinmmie.utng Flglienla is eht oyln enrswa cehcio aht'st a irpeotn.

mambaforstep  both MHC 1 and 2 are present antigens that are PROTEINS (FA 2019 pg 100). so in order to elicit a T cell response, you need a protein (CANT BE A POLYSACC). that is why vaccines for polysaccaride antigens are often conjugated to PROTEINs--> so that we can elicit a T-cell response (FA 2019 pg 127). +3  
lovebug  Flagellum = Protein, (FA19, pg.124) +  

submitted by enbeemee(13),
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i tge hyw it's iaefllgl,n but is eth csfpiice anesro ttha SLP is rwgon is eubecsa t'si tjus nto how het vecanci is ad?em PLS wlduo aols ciilte an miumne tcenorai, hgtir?

nor16  Lipid A of LPS can be sensed by CD14 of macrophages causing shock, its not a protein, so no immune reaction as in vaccination (humoral, IgG class switch via Th2 and B Cells). +2  
eclipse  actually they do use LPS as adjuvant in vaccines +1  
eclipse  actually they do use LPS as adjuvant in vaccines +1  
hyperfukus  TLRs recognize common motifs called pathogen-associated molecular pattern (PAMP) in bacteria, fungi, viruses, and other pathogens. TLR signaling in the modulation of innate immunity + adaptive immunity against pathogens, TLR agonists: CpG-DNA, flagellin, and lipid became essential candidates of effective+safe vaccine adjuvants. TLR agonists improve the efficacy of vaccine, reducing TCR-based selection thresholds and enhancing the magnitude and quality of memory T-cell response. +2  
hyperfukus  some extra info in case they ask another annoying q +3  
aturner713  Not sure if this matters for this or not, but Neisseria spp. have lipoOLIGOsaccharide (LOS) and not lipoPOLYsaccharide (LPS) +1  
schep  I don't understand why LPS couldn't be the answer also. UWorld question ID 45 specifically says that they are using LPS as a conjugate +  

submitted by wasabilateral(39),
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I khnit hyet atnw you ot kinht uatbo hwo anugecjto navccie is edma: aahicocerpdlys + eotnpir eftrmnga ot( unicde T ndetepend mneumi )sreos.nep yOln ilgnealfl is a onietrp o(r at ealst sdsoun ilke )noe ni het toniop t.sli

vi_capsule  Flagellum is protein. Pilli/Fimbriae - GLycoprotein +2