A mature naive T cell receives "Signal 1" but not "Signal 2" while interacting with an antigen-presenting cell (APC). What could explain this observation?
a) The APC cannot present peptide on MHC-II.
b) The T cell does not express the correct cytokine receptors.
c) The APC has not detected the presence of a pathogen, and does not express co-stimulatory molecules.
d) The T cell does not express a TCR capable of binding to any peptide::MHC complexes on the APC.
