Answer:
Step-by-step explanation:
MHC class II proteins present antigenic fragments that are derived from exogenous antigens. These antigens are typically proteins or peptides that have been taken up by antigen-presenting cells (such as macrophages, dendritic cells, and B cells) through a process called antigen processing and presentation.
Exogenous antigens are captured by antigen-presenting cells in the surrounding environment. These cells engulf the antigens through endocytosis or phagocytosis. Within the antigen-presenting cells, the antigens are broken down into smaller protein fragments called epitopes. These epitopes are then loaded onto MHC class II molecules within specialized compartments called endosomes or lysosomes.
MHC class II molecules are specifically designed to bind and present these epitopes derived from exogenous antigens. Once the epitopes are loaded onto the MHC class II molecules, they are transported to the cell surface where they can be recognized by T-helper cells of the immune system. This interaction between the MHC class II-epitope complex and T-helper cells plays a critical role in initiating and regulating immune responses against extracellular pathogens.