A 4-year-old boy suffers from an immunodeficiency disease characterized by impaired T cell activation.The disease is caused by genetic deficiency of a membrane protein whose cytoplasmic tail is involved in intracellular signaling in response to T cell receptor (TCR)recognition of antigen.Which one of the following proteins does NOT fit this description?

Question

Quizplus · Accepted Answer

Although the T cell receptor (TCR)$\alpha$ and $\beta$ chains are responsible for antigen recognition,they are not directly involved in signaling.Rather,the $\alpha$$\beta$heterodimer is noncovalently associated with signaling molecules CD3$\gamma$,CD3$\delta$,CD3? nd $\zeta$,all of which have ITAMs in their cytoplasmic tails.Although CD4 is not part of the TCR complex,it does play a critical role in initiating signaling during TCR recognition of antigen by binding Lck to its cytoplasmic tail and bringing this tyrosine kinase near the ITAMs of CD3 and $\zeta$.

A 4-Year-Old Boy Suffers from an Immunodeficiency Disease Characterized by Impaired