 Antigen presenting cells are the sentinels of the immune system and patrol the body for pathogens.When they encounter foreign pathogens, the antigen presenting cells alert the T cells—“the soldiers of the immune system”—that there is something foreign in the body with specific cell surface molecules.aAPCs are synthetic versions of these sentinel cells and are made by attaching the specific T-cell stimulating signals to various macro and micro biocompatible surfaces.