What is the purpose of the major histocompatibility complex (MHC) in the immune system?

The major histocompatibility complex (MHC) plays a crucial role in the immune system by presenting antigens on the surface of cells. This process is essential for the recognition of foreign substances by T cells, which are pivotal in the adaptive immune response. There are two main classes of MHC molecules: Class I and Class II. Class I molecules present antigens from within the cell (typically viral proteins) to CD8+ cytotoxic T cells, while Class II molecules present extracellular antigens to CD4+ helper T cells.

When a cell presents an antigen via the MHC molecule, it allows T cells to monitor for signs of infection or abnormality, such as cancer. If T cells recognize the presented antigen as foreign, they can initiate an immune response, leading to the activation of various immune pathways to eliminate the threat.

This mechanism of antigen presentation by MHC is vital for the immune system's ability to distinguish between self and non-self, allowing it to target pathogens while maintaining the integrity of the body's own tissues. Other options, such as transporting oxygen or synthesizing antibodies, do not pertain to the specific function of MHC, and regulating blood pressure is not related to immune response functions.