Question

A patient with recurrent bacterial and viral infections is referred to an internist who determines that, while there are normal numbers of T cells in the circulation, the T cells are extremely unresponsive to all antigenic stimuli. Further testing determines that the T lymphocytes are severely deficient in the ability to signal following exposure to antigen. Which of the following cell surface molecules is most likely to be mutated, making these lymphocytes unable to generate and transmit activation signals upon binding of antigenic peptide by the cell?

a. Ig alpha

b. CD3

c. CD25

d. CD56

e. Beta-2-microglobulin

Answer 1

Answer- b. If CD3 mutated that makes these lymphocytes (T lymphocytes) unable to generate and transmit activation signals upon binding of antigenic peptide by the cell.
[Notes- β2 microglobulin is necessary for cell surface expression of MHC class I and stability of the peptide binding groove.
Ig-α and Ig-β to regulate B cell antigen receptor function.
CD56, is a natural killer cell, has a homophilic binding glycoprotein. It expressed on the surface of neurons, glial cell and skeletal muscle.
During activation, all T cells express CD25.
CD3 (cluster of differentiation 3) is a protein complex and T cell co-receptor that is involved in activatingboth the cytotoxic T cell (CD8+) and T helper cells (CD4+). ]