Final answer:
Before exogenous antigens are presented, they must be internalized by antigen-presenting cells (APCs) and digested to create peptide antigens. The processed antigens are then presented on the cell's surface with MHC class II molecules for recognition by T cells.
Step-by-step explanation:
Before exogenous antigens are presented, they must be internalized by antigen-presenting cells (APCs) and then digested to create peptide antigens.
This process occurs when the APC engulfs and digests the pathogen, bringing it into a phagolysosome where it is degraded by enzymes and antimicrobial chemicals.
Proteases process the antigenic epitopes, which are then presented on the cell's surface in conjunction with MHC class II molecules. T cells recognize the presented antigens and are activated.
Extracellular pathogens, such as bacteria, parasites, and fungi, are brought into the endomembrane system of the cell through receptor-mediated endocytosis.
The resulting vesicle fuses with vesicles from the Golgi complex, which contain pre-formed MHC class II molecules.
After fusion and association of antigen and MHC, the vesicle is transported to the cell surface for antigen presentation.