MHC class II proteins, also known as major histocompatibility complex class II proteins, are a group of transmembrane proteins that play a vital role in the immune system's response to foreign antigens. They are found on the surface of various immune cells, including B cells, dendritic cells, macrophages, and certain activated T cells.
The MHC class II protein family consists of two main chains, an alpha and a beta chain, each encoded by different genes. These chains form a complex that spans the membrane of the immune cell. Inside the cell, the MHC class II proteins bind to small peptides derived from antigens that have been internalized through phagocytosis or endocytosis.
Once bound to the antigen peptides, the MHC class II proteins migrate to the cell surface and present the peptides to CD4+ T lymphocytes, also known as helper T cells. This presentation is a critical step in the recognition of foreign antigens by the immune system. It enables the helper T cells to recognize and initiate an immune response against the specific antigen.
In addition to their role in antigen presentation, MHC class II proteins also play a crucial role in immune tolerance by presenting self-peptides to T cells during development and preventing the activation of autoreactive T cells.
Overall, MHC class II proteins are essential components of the immune system, allowing the body to recognize and respond to foreign antigens while maintaining tolerance to self-peptides.
