Major histocompatibility complex (MHC)

Definition

The major histocompatibility complex (MHC) is a set of cell surface proteins essential for the immune system to recognize foreign molecules. MHC molecules play a critical role in antigen presentation, allowing T cells to identify and respond to pathogens. They also determine compatibility between donors and recipients in organ transplantation, highlighting their significance in both immune recognition and graft rejection.

5 Must Know Facts For Your Next Test

1. MHC molecules are divided into two main classes: Class I MHC, found on nearly all nucleated cells, and Class II MHC, primarily found on professional antigen-presenting cells.
2. Class I MHC presents endogenous antigens (from proteins synthesized within the cell), while Class II MHC presents exogenous antigens (from external sources taken up by the cell).
3. The genes that encode MHC molecules are highly polymorphic, meaning there are many different alleles within the population, which enhances the diversity of immune responses.
4. MHC compatibility is crucial in organ transplantation; mismatched MHC can lead to acute or chronic graft rejection due to the recipient's immune response against foreign antigens.
5. The process of selecting compatible donors for transplantation often involves matching MHC types to minimize the risk of rejection and improve transplant success.

Review Questions

• How does the major histocompatibility complex (MHC) facilitate the immune response?
  • The major histocompatibility complex (MHC) is essential for presenting antigens to T cells, allowing them to recognize and respond to pathogens. Class I MHC molecules display endogenous peptides to CD8+ cytotoxic T cells, while Class II MHC presents exogenous peptides to CD4+ helper T cells. This interaction is crucial for initiating an adaptive immune response, as T cells become activated upon recognizing their specific antigen presented by MHC.
• Discuss the implications of MHC polymorphism in organ transplantation and how it relates to graft rejection.
  • MHC polymorphism means there is a high variability in MHC genes among individuals, which is significant for organ transplantation. When a donor organ has an MHC profile that is not closely matched to that of the recipient, the recipient's immune system may recognize the donor MHC as foreign and initiate an immune response leading to graft rejection. Understanding this relationship helps clinicians select appropriate donors to reduce rejection risks and improve transplant outcomes.
• Evaluate the role of MHC in both disease resistance and susceptibility within populations.
  • MHC plays a dual role in influencing disease resistance and susceptibility in populations due to its critical function in immune recognition. Different MHC alleles can confer varying levels of protection against specific pathogens; however, this diversity can also lead to increased vulnerability if certain alleles fail to recognize emerging pathogens. The balance between these roles highlights the evolutionary pressure on populations to maintain a diverse array of MHC types, ensuring better survival against infectious diseases while also complicating issues like transplant compatibility.

Related terms

Antigen Presentation:

The process by which MHC molecules display peptide fragments derived from proteins within the cell on their surface for recognition by T cells.

T Cells: A type of white blood cell that plays a central role in the adaptive immune response, recognizing antigens presented by MHC molecules.

Graft Rejection: The immune response against transplanted tissue or organs that occurs when the recipient's immune system recognizes the donor's MHC as foreign.