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NBME 21 Answers

nbme21/Block 3/Question#36 (62.9 difficulty score)
Which of the following best explains why the ...
Myeloma cells do not have membrane-bound surface immunoglobulin🔍

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submitted by hello(257),
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lMetipul myleoma = npmoesal of lpmaas

masaPl eclls rdpceuo scrtreeyo bAs' aka( urcpoed sA)b' -- smapla lsecl do tno vhae nuam-nedoerbbm gI (aak do tno evha 'R.)BC

To rpc:ea ne-emrbduoabmn gI = BCR hilew coretrsye gI = .bA

,Nwo dnaipocit-itiy ynobadit = ytabindo iagastn btnaioy.d

aalmsP slcle do otn tcnaoin uesafrc Ig -- cbeseau maspla lelcs nyol eb tesrece s.bA'

eerroTef,h itpyadciotiin- aonitdby udwol not okrw to etartg aymmelo lscle cbesaeu mmeayol lecsl = paalsm lslce kaa psaalm lcesl lkac sucarfe soucleelm htta itnpoitciyida- A'bs olduw eden ot dnbi at/

eSe ima:agdr eteatn9c/qpcu59f0.825.1qb3dnc1imftamf/0opi.racsg8ne:a4cf42-fshqc3e/h-a

submitted by seagull(1171),
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oIicyidpt menas --- idbntyao tasgain nbi.aodyt B lecls 'otnd eahv furscea nsdoitaebi ubt emer nezisseyth emht.

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 +2  
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) +  

submitted by readit(11),

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 +