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NBME 21 Answers

nbme21/Block 3/Question#36 (67.1 difficulty score)
Which of the following best explains why the ...
Myeloma cells do not have membrane-bound surface immunoglobulinπŸ”

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submitted by hello(301),
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pulMltie yemoalm = oalsempn fo lapsma cs.ell

lPsama llsce ourcped sertorecy sAb' (aka dprcoue )Abs' -- alpasm scell do nto evha rmbn-oebueamnd gI ka(a do ton vaeh R).B'C

To :ecpar embemnnr-baoud gI = RCB iwleh cotrseyer gI = .bA

wo,N -yiidoptactnii odybaint = ioatbnyd tasgnia ibytond.a

aPsalm clsle od ton nanctio ucrfesa gI -- ecsueab plsama cslel nloy be sretcee 'Ab.s

,fTrheoere yini-ctdipioat botyanid lowud nto rkwo ot graett omlamye ellcs beecsua lemmayo cslle = aalmsp lecsl aka slmpaa clles alkc uacerfs usoemclel atht tcaiidyiitpo-n bA's olwdu deen to dibn oert/tgat.

eeS gamarid: ft4m1aq00ecfs3h.4gtfr25pmncuneep2b.oseid88fha3//cf-ac9n9.1it:-qqcca5a/

submitted by readit(14),

An anti-idiotypic antibody is an antibody which binds an antibody.

As an example, an anti-idiotypic antibody be helpful for treating a naiive B cell prior to activation, which express IgM and IgD on their surfaces. This is because the anti-idiopathic antibody can bind to the IgM/IgD antibody on the surface of a naiive B cell.

Multiple Myeloma cells, however, are made up of Plasma cells, which no longer express Ig's on their surface like naiive B cells do. Thus, there is no surface antibody [aka "membrane bound surface immunoglobulin"] for an anti-idiotypic antibody to bind to.

readit  Source: First aid Pg 105, 2019 edition +  

submitted by seagull(1404),
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diiocpyIt smane --- tdinoyab tgisana .yidotabn B lslec dot'n avhe seurafc oenatidsib ubt mere iztenssyhe

hungrybox  This is wrong. PLASMA cells (mature B cells, the ones found in multiple myeloma) secrete antibodies, but IMMATURE B cells have antibodies that haven't switched classes yet (IgM and IgD). +5  
hungrybox  To clarify - immature B cells have antibodies attached to their membrane. +  
seagull  I should have clarified that I was speaking about mature B cells. Thank You +3  
sahusema  So because MM has mature B cells, exogenous antibodies can't attach to them. Am I getting that right? +  
cienfuegos  What is an Anti-Idiotypic Antibody? As shown in figure 1, an anti-idiotypic (Anti-ID) antibody binds to the idiotype of another antibody, usually an antibody drug. An idiotype can be defined as the specific combination of idiotopes present within an antibodies complement determining regions (CDRs). A single idiotope, is a specific region within an antibodies Fv region which binds to the paratope (antigenic epitope binding site) of a different antibody. Therefore, and idiotope can be considered almost synonymous with an antigenic determinant of an antibody. +1  
cienfuegos  @sahusema: almost exactly correct, but it's important to note they are talking about idiotypic antibodies specifically because by definition these bind the "idiotype" of another antibody (see definition above) +