Antigen Processing

Antigen processing: What happens when a B cell, macrophage, or dendritic cell engulfs an antigenic particle—in this case, a bacterium.


1. A phagocytic cell engulfs a bacterium.
2. An endocytic vesicle forms around the bacterium.
3. The vesicle fuses with a lysosome, which contains enzymes and MHC molecules.
4. Lysosomal enzymes digest the bacterium to molecular bits.
5. Inside the vesicle, bits of bacterium bind to MHC molecules.
6. The vesicle fuses with the cell membrane by exocytosis. When it does,the bacterial antigen–MHC complex becomes part of the plasma membrane.
7. The antigen–MHC complex displayed on the surface of the phagocyteis a signal that provokes an adaptive immune response targeting the antigen.