Fig. 2
From: T cell effects and mechanisms in immunotherapy of head and neck tumors
a Tumor cells express MHC-I molecules to provide the first signal for T cell activation through the MHC-I pathway, leading to initial activation of CD8+ T cells in CTL. b The APC recognizes tumor cells using pattern recognition receptors (PRRs), and then expresses MHC-II molecules and delivers them to CD4+ T cells, activating Th cells. c DCs can cross-present MHC-II molecules to CD8+ T cells through the MHC-I pathway and induce their differentiation into CTL. d APC and Th cells can produce a variety of co-stimulatory molecules, which provide a second signal for T cell activation, which allows T cells to fully activate