The antigen presenting cell (APC) shown here is a macrophage. It has ingested a microbe. Antigen from the intracellular microbe is processed in the cytoplasm with breakdown by enzymes to peptides. The peptides are linked to an MHC 1 molecule. The MHC 1 molecule with an antigenic peptide from the microbe is transported to the cell surface for presentation to other cells of the immune system, specifically CD8 lymphocytes.

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