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NBME 1

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jean robert
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05/05/08 - 11:46 AM

After a full course of immunization with a new vaccine consisting of a recombinant polypeptide. 10% of adults fail to make antibody to the polypeptide. The nonresponders have an increased frequency of one HLA type. What is the most likely explanation for the failure of this group to respond to immunization?

A. B cell can't recognize this peptide
B. T cell can't recognize this peptide
C. Lack of class I MHC presentation of this peptide
D. Lack of class II MHC presentation of this peptide

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exams2008
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05/05/08 - 11:58 AM

1.ammara
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05/07/08 - 06:41 AM

i guess D

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Tiff
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05/07/08 - 04:17 PM

jean robert
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05/08/08 - 01:26 PM

My answer was D in NBME.

Guys,is this a case of Bare Lymphocyte syndrome?

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Tiff
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05/08/08 - 02:33 PM

Bare lymphocyte syndrome is a form of SCIDS and SCIDS is relatively rare. In this case the problem is happening in 10% of people tested. That's not rare.

Guys can you please explain why you all think it's D? I don't think we have enough clues to draw such a radical conclusion. All we have is that it's HLA related, and that they are not responding to immunization. This means to me that they can't mount an IgG immune response. Therefore the problem should be B cell related. They haven't mentioned anything else unless I'm missing something. I rationalized that it must be a Common Variable Immunodeficiency which is why I chose option A.

Would like it if you can explain why you think it's D so that maybe I can understand. smiling face

lakshya_0_7
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05/08/08 - 02:49 PM

i dont think it can be A because B-cells dont produce antibodies after directly recognising the peptide.....B cells recognise only polysacchrides directly (t cell independent response)..and Ig-M is the usual response in that case....Bcells wont produce Ig-G without the clas switching whihc needs T cell participation...

i picked D too....becoz it is the APCs having MHC-2 that usually present the peptides to the Tcells....and which then activate Bcells to produce antibodies ......

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Tiff
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05/08/08 - 03:13 PM

lakshya_0_7 wrote:
i dont think it can be A because B-cells dont produce antibodies after directly recognising the peptide.....B cells recognise only polysacchrides directly (t cell independent response)..and Ig-M is the usual response in that case....Bcells wont produce Ig-G without the clas switching whihc needs T cell participation...

i picked D too....becoz it is the APCs having MHC-2 that usually present the peptides to the Tcells....and which then activate Bcells to produce antibodies ......

Well, if the vaccine worked the B cell is supposed to recognize this via IgG after class-switching. Isn't that the whole point to a vaccine, memory? Initially it would be IgM but for memory, class switching for IgG is necessary. There's nothing in the question indicating a T cell problem. They're only talking about not responding to a vaccination, not whether there is an immune response.

Tiff
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05/08/08 - 03:18 PM

Common variable has memory B-cell defects. Any other thoughts? raised eyebrow

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