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NBME 24 Answers

nbme24/Block 3/Question#32

A 15-year-old girl is brought to the physician ...

CD8+ T lymphocytes

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submitted by m-ice(180),

This girl has Mono caused by Epstein-Barr Virus. The symptoms are relatively vague, but lymphadenopathy like this would be common for Mono. The CBC shows elevated lymphocytes, implying this is not a bacterial illness, so viral is likely. Combined with the lymphadenopathy, this makes us worry about Mono. The Mono-Spot test for EBV is what the question is referring to when describing the sheep erythrocytes agglutinating. From there, this question requires that you know that in EBV infection, EBV infects B cells, but does not cause them to become abnormal. Instead, CD8 cells, which are actively trying to kill the B cells, become abnormal.

medskool123  NBME does trick now and then.. when they zig you zag. then when you think they are going to zag, they zig just to destroy yourself confidence. +7  
kylemax  The abnormal T-cells are known as Downey type II cells (Sketchy) +2  
haliburton  I was recognized EBV, then knew EBV infects Bc, and the atypical lymphocytes are Tc. Then I said CD8 are MHC1 for virii, and bingo bango, boom. +1  
trichotillomaniac  congrats you played yourself +2  
lilyo  Soooooooo EBV infested B- cells is not considered atypical WTFF?? +  
med4fun  They are atypical b/c usually you do not see a super high amount of CD8+ in peripheral blood. Now there are a ton to try to stop the infected cells. +  
aneurysmclip  oh and primary CNS lymphoma caused by EBV has T cells NOT B cells. I just try to remember the peripheral blood has atypical lymphocytes which are CD8+ T cells, and the CNS lymphoma is the opposite, ie; B cells +  

Lymphocytosis associated with infectious mononucleosis is caused by an increase in the number of circulating activated T and B lymphocytes.

The atypical lymphocytes are CD8+ T- cells that are activated to eliminate EBV infected B- lymphocytes.