Understanding the Endocytic Pathway: Degradation of Extracellular Antigens and Loading of Antigenic Peptides onto Class II MHC Molecules

In the ________ pathway, extracellular antigens are degraded in the phagolysosomes and antigenic peptides are loaded on class ___ MHC molecules

In the endocytic pathway, extracellular antigens are degraded in the phagolysosomes and antigenic peptides are loaded on class II MHC molecules

In the endocytic pathway, extracellular antigens are degraded in the phagolysosomes and antigenic peptides are loaded on class II MHC molecules.

The endocytic pathway is a series of intracellular compartments involved in the internalization of extracellular materials, such as antigens. This pathway begins when antigens are engulfed by specialized immune cells called phagocytes through a process called phagocytosis. Once inside the phagocyte, the antigens are contained within a specialized compartment called a phagosome.

The phagosome then fuses with a lysosome to form a phagolysosome. Lysosomes contain enzymes that break down proteins, lipids, and other molecules through hydrolysis. Within the phagolysosome, extracellular antigens are degraded by these enzymes. This degradation process generates small antigenic peptides.

Class II MHC molecules are a type of major histocompatibility complex (MHC) protein found on the surface of antigen-presenting cells (APCs). These include macrophages, dendritic cells, and B cells. Class II MHC molecules are responsible for presenting antigenic peptides to helper T cells, which play a crucial role in the immune response.

In the endocytic pathway, the antigenic peptides generated within the phagolysosome are loaded onto class II MHC molecules. This occurs within a specialized compartment called the MHC class II loading compartment, also known as the antigen-processing compartment. Inside this compartment, the class II MHC molecules bind to the antigenic peptides that are derived from the degradation of extracellular antigens.

Once the antigenic peptides are loaded onto the class II MHC molecules, the MHC-peptide complex is transported to the cell surface, where it can interact with specific receptors on helper T cells. This interaction triggers an immune response, leading to the activation of the helper T cell and the subsequent initiation of the adaptive immune response.

In conclusion, in the endocytic pathway, extracellular antigens are degraded in the phagolysosomes, and the resulting antigenic peptides are loaded onto class II MHC molecules. This process enables the presentation of antigens to helper T cells and subsequent activation of the immune response.

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