While our understanding of the kinetics of T-cell activation has changed over time, we now believe that:
A. antigen availability does not affect T-cell APC interactions.
B. antigen quantity does not affect T-cell APC interactions.
C. optimal proliferation of helper T cells requires only relatively brief APC exposure.
D. optimal proliferation of helper T cells requires several hours of APC exposure.
E. dendritic cell activation does not affect T cell activation.
Answer: D