T Cells with Defective TCR Signaling Are Discovered, and Found $\gamma$

Multiple Choice

T cells with defective TCR signaling are discovered, and found to have an inactivating mutation in a key TCR signaling protein. Using an antibody that recognizes the phosphorylated (activated) form of the Erk Map-kinase, stimulated T cells are permeabilized, stained with this antibody, and analyzed on the flow cytometer. These data are shown in Figure Q21) . Figure Q21) Additional experiments examining Ca²⁺ influx into T cells following TCR stimulation show a normal response in the mutant T cells. One likely candidate gene that could be mutated in the defective cells is:

A) PLC- $\gamma$
B) ITK
C) RasGRP
D) Calcineurin
E) WASp