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NBME 21 Answers

nbme21/Block 3/Question#36

Which of the following best explains why the use of ...

Myeloma cells do not have membrane-bound surface immunoglobulin

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submitted by seagull(437),

Idiotypic means --- antibody against antibody. B cells don't have surface antibodies but mere synthesize them.

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). +2  
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 +1  
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. https://www.genscript.com/antibody-news/what-is-an-anti-Idiotypic-antibody.html +  
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) +  

 +0  upvote downvote
submitted by hello(67),

Multiple myeloma = neoplasm of plasma cells.

Plasma cells produce secretory Ab's (aka produce Ab's) -- plasma cells do not have membrane-bound Ig (aka do not have BCR').

To recap: membrane-bound Ig = BCR while secretory Ig = Ab.

Now, anti-idiotypic antibody = antibody against antibody.

Plasma cells do not contain surface Ig -- because plasma cells only be secrete Ab's.

Therefore, anti-idiotypic antibody would not work to target myeloma cells because myeloma cells = plasma cells aka plasma cells lack surface molecules that anti-idiotypic Ab's would need to bind to/target.

See diagram: https://qph.fs.quoracdn.net/main-qimg-ae42c5c9f839fc58a3ce10feaf14c02b

Multiple myeloma is an neoplastic proliferation of plasma cells, and since plasma cells don’t have surface Ig bound innately, that was the only “true” option.

seagull  Idiotypic means --- antibody against antibody. B cells don't have surface antibodies but mere synthesize them. +1