Fig. 2 After tumor antigen is presented to dendritic cells, DC can activate CD4+ T cells and CD8+ T cells at the same time with the absence of different MHC class molecules. CD8+ cytotoxic T cells are activated by MHC class I and co-stimulatory signal while MHC class II with also a co-stimulatory signal can activate CD4+ T helper cells. Activated T helper cells eventually either activate CD8+ T cells or initiate a negative signal against immune system based on the absence of different environmental cytokines
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