Final answer:
Phagosomes deliver their contents to lysosomes within the cell to form phagolysosomes, where pathogens are destroyed. In APCs, phagolysosome contents are also involved in antigen presentation to T cells.
Step-by-step explanation:
When the immune system encounters pathogens such as bacteria, special cells called phagocytes activate to protect the body. The phagocyte extends its plasma membrane to engulf the bacterium, which becomes enclosed in a vesicle known as a phagosome. This phagosome then fuses with a vesicle called a lysosome to form a phagolysosome, where powerful digestive enzymes and acids work to destroy the pathogen. After the pathogen has been degraded, the soluble debris is expelled from the cell via exocytosis. In addition, in antigen-presenting cells (APCs) like dendritic cells, after the formation of the phagolysosome, pathogenic components are broken down and linked with MHC class II molecules. These are then transported to the cell surface of the dendritic cell for presentation to T cells, which is crucial for initiating an adaptive immune response.