Final answer:
Dendritic cells uptake antigens by phagocytosis or receptor-mediated endocytosis, process them in phagolysosomes, and present the most immunodominant epitopes bound to MHC Class II molecules on their cell surface for T cell activation.
Step-by-step explanation:
Dendritic cells uptake antigens through a process known as phagocytosis. When they receive signals from the environment, such as the presence of a pathogen, dendritic cells engage in phagocytosis to engulf and digest these pathogens. Within the dendritic cells, pathogens are encased in a phagosome, which then fuses with a lysosome to form a phagolysosome where the pathogen is destroyed, and its proteins are processed.
Once processed, the most antigenic or immunodominant epitopes are selected for presentation. These epitopes are bound to Major Histocompatibility Complex (MHC) Class II molecules and transported to the cell surface of the dendritic cell. This process is referred to as antigen presentation, and it is crucial for the activation of T cells. The presented antigens on MHC Class II molecules are then recognized by T cells, which are essential for orchestrating an appropriate adaptive immune response.
It is important to note that dendritic cells can also acquire antigens from outside the cell through receptor-mediated endocytosis. Such extracellular antigens often come from bacteria, parasites, and fungi. After internalization, they follow a similar pathway involving association with MHC Class II and travel to the cell surface for T cell activation. Dendritic cells, along with macrophages and B cells, are professional antigen-presenting cells (APCs) and are key for the immune response to various pathogens.