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  #1  
Old 09-13-2011
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Immunology T Cells Lacking CD3!

A 2-year-old boy is evaluated for SCID (severe combined immunodeficiency disease) His bone marrow has normal cellularity. Radioactive tracer studies demonstrate a normal number of T-cell precursors entering the thymus, but no mature T lymphocytes are found in the blood or peripheral organs. Cells populating the thymus are found to lack CD3. Which of the following capabilites would these cells lack?

A) Ability to bind cell-bound peptides
B) Ability to express CD4/CD8 coreceptors
C) Ability to produce terminal deoxyribonucleotidyl transferase
D) Ability to proliferate in response to specific antigen
E) Ability to rearrange T-cell receptor gene segments
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  #2  
Old 09-13-2011
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I would go with E) Ability to rearrange T-cell receptor gene segments

I was confused with B) or E) but if i had to choose one I would go with E) since I know CD3 helps in T cell differentiation and binds to MHC.
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Old 09-13-2011
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will go with E
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Old 09-13-2011
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My guess is Bb
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Old 09-13-2011
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D) Ability to proliferate in response to specific antigen

CD3 is responsible for the transduction and tranmitting the signal into the cell after biding to the antigen.
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Old 09-13-2011
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Correct Answer

The correct answer is D.

CD3 is the signal transduction complex in T lymphocytes. When specific antigen binding has occured on the surface of the cell, this complex is responsible for transfering the message to the cytoplasm of the cell. ->Phosphorylation ->Cell activation -> Cell Proliferation.
Ability to express coreceptors (choice B) would not be affected by the abscence of CD3, although cells would not be able to complete their differentiation in the thymus and become fully commited T cells.

Abillity to change receptor gene segments (Choice E) would not be affected by the abscence of CD3. T-cell precursors rearrange their receptor gene segments in the abscence of antigenic stimulation and before signal transduction through CD3 becomes critical
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The above post was thanked by:
Abdulaziz (09-14-2011), Amenah (09-13-2011), drhnis (09-13-2011), m82_ghasemi (09-13-2011), mi.abuaisha (06-03-2012), monsalg2502 (04-16-2012), pass7 (09-13-2011), patho2012 (02-06-2012)



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