Antigen Presenting Cells Must be capable of processing antigen from extracellular and intracellular pathogens Must present processed antigen on MHC class I&II molecules Must express co-stimulatory molecules (cytokines)Antigen Presenting Cells ◼ Must be capable of processing antigen from extracellular and intracellular pathogens ◼ Must present processed antigen on MHC class I & II molecules ◼ Must express co-stimulatory molecules (cytokines)