MHC class I and II molecules present antigenic proteolysis products of proteasome and lysosome to CD8+ cytotoxic and CD4+ helper T-cells, respectively.28 For non-professional APCs, such as carcinoma cells, MHC-I present antigenic derived from proteins synthesized by endogenous ribosome – a process generally referred as direct presentation. Here, CD8A is linked to carcinoma.