MHC molecules

Definition

MHC molecules, or Major Histocompatibility Complex molecules, are proteins found on the surface of cells that play a critical role in the adaptive immune response by presenting peptide fragments derived from proteins to T cells. They are essential for the recognition of self and non-self by the immune system, enabling T cells to distinguish between healthy body cells and potentially harmful pathogens. MHC molecules come in two main classes, Class I and Class II, each with distinct functions in immune surveillance.

5 Must Know Facts For Your Next Test

1. MHC Class I molecules present endogenous peptides from proteins synthesized within the cell, allowing CD8+ cytotoxic T cells to recognize infected or abnormal cells.
2. MHC Class II molecules present exogenous peptides from extracellular sources, which are important for the activation of CD4+ helper T cells that assist in orchestrating the immune response.
3. Each individual has a unique set of MHC molecules determined by their genetic makeup, which is crucial for organ transplantation compatibility.
4. The process of antigen presentation is vital for T cell activation; without this interaction, T cells cannot effectively respond to pathogens.
5. Certain pathogens have evolved mechanisms to evade detection by interfering with MHC molecule expression or function, demonstrating the ongoing arms race between host defenses and infectious agents.

Review Questions

• How do MHC Class I and Class II molecules differ in their structure and function?
  • MHC Class I molecules are composed of a heavy chain and a beta-2 microglobulin chain, presenting endogenous peptides to CD8+ cytotoxic T cells. In contrast, MHC Class II molecules have two chains (alpha and beta) and present exogenous peptides to CD4+ helper T cells. This structural difference allows each class to interact with different types of T cells, playing unique roles in the adaptive immune response.
• Discuss the importance of MHC molecules in organ transplantation and how they affect transplant rejection.
  • MHC molecules are critical in organ transplantation because they play a key role in determining graft compatibility. The recipient's immune system can recognize foreign MHC molecules on transplanted tissue as non-self, leading to an immune response that can cause transplant rejection. This is why matching donor and recipient MHC types is essential to improve the success rates of transplants.
• Evaluate how pathogens may adapt to evade the immune response facilitated by MHC molecules and discuss potential implications for vaccine development.
  • Pathogens may adapt by downregulating MHC molecule expression or producing proteins that interfere with peptide loading onto MHC molecules, effectively hiding from T cell surveillance. This evasion can complicate vaccine development since vaccines aim to elicit a robust T cell response against specific antigens. Understanding these mechanisms allows researchers to design better vaccines that enhance immune recognition despite such evasion strategies.

Related terms

T cells:

A type of white blood cell that is crucial for the adaptive immune response, responsible for recognizing and responding to specific antigens presented by MHC molecules.

Antigens:

Substances that induce an immune response, typically recognized by antibodies or T cell receptors, which can be presented by MHC molecules.

Cytokines:

Signaling proteins released by immune cells that mediate and regulate immunity, inflammation, and hematopoiesis, playing a role in the communication between T cells and other immune cells.