MHC Molecules

Definition

MHC (Major Histocompatibility Complex) molecules are a group of proteins found on the surface of cells that play a crucial role in the immune system's ability to recognize and respond to foreign or abnormal substances within the body. These molecules are essential for the presentation of antigenic peptides to T cells, initiating an immune response.

5 Must Know Facts For Your Next Test

1. MHC molecules are divided into two main classes: MHC class I and MHC class II, which differ in their structure and the types of cells they interact with.
2. MHC class I molecules present peptides derived from intracellular proteins, including those from viruses and cancer cells, to CD8+ T cells.
3. MHC class II molecules present peptides derived from extracellular proteins, such as those from invading pathogens, to CD4+ T cells.
4. The high degree of genetic diversity in the MHC gene complex allows for the recognition of a wide range of foreign antigens, enhancing the immune system's ability to respond to a variety of threats.
5. Abnormalities in MHC molecule expression or function can lead to autoimmune diseases, where the immune system mistakenly attacks the body's own cells and tissues.

Review Questions

• Explain the role of MHC molecules in the immune system's ability to recognize and respond to foreign or abnormal substances.
  • MHC molecules are essential for the presentation of antigenic peptides to T cells, which is a crucial step in initiating an immune response. MHC class I molecules present peptides derived from intracellular proteins, including those from viruses and cancer cells, to CD8+ T cells, which can then recognize and destroy infected or transformed cells. MHC class II molecules present peptides derived from extracellular proteins, such as those from invading pathogens, to CD4+ T cells, which can then coordinate the broader immune response. This ability to present a wide range of antigenic peptides to T cells is a key function of MHC molecules in the immune system's surveillance and defense against foreign or abnormal substances.
• Describe the genetic diversity of the MHC gene complex and explain how it enhances the immune system's ability to respond to a variety of threats.
  • The MHC gene complex is highly diverse, with multiple genes encoding different MHC molecules. This genetic diversity allows the immune system to recognize a wide range of foreign antigens, as each individual will have a unique set of MHC molecules capable of presenting a diverse array of peptides. This diversity is crucial for the immune system's ability to respond to a variety of pathogens and other threats, as it increases the chances that at least some of an individual's MHC molecules will be able to present the specific antigenic peptides associated with a given threat. The high degree of polymorphism in the MHC genes is believed to be the result of evolutionary pressure, as it provides a selective advantage in the ongoing arms race between the immune system and rapidly evolving pathogens.
• Analyze the potential consequences of abnormalities in MHC molecule expression or function, and explain how they can lead to autoimmune diseases.
  • Abnormalities in MHC molecule expression or function can have serious consequences for the immune system's ability to maintain self-tolerance and prevent autoimmune diseases. If MHC molecules fail to properly present self-peptides to T cells during development, it can lead to the escape of self-reactive T cells that are not eliminated. These self-reactive T cells can then recognize and attack the body's own cells and tissues, triggering an autoimmune response. Additionally, if MHC molecules present self-peptides in an abnormal way, it can also break self-tolerance and lead to the activation of autoreactive T cells. This can result in the development of various autoimmune diseases, where the immune system mistakenly targets and damages the body's own healthy cells and organs. Understanding the critical role of MHC molecules in maintaining self-tolerance is essential for identifying the underlying causes of autoimmune disorders and developing effective treatments.

Related terms

Antigen: A substance, usually a protein, that the immune system recognizes as foreign and can trigger an immune response.

T Cells:

A type of white blood cell that plays a central role in the adaptive immune response, recognizing and responding to specific antigens presented by MHC molecules.

Immune Surveillance: The process by which the immune system continuously monitors the body for the presence of foreign or abnormal substances, such as pathogens or cancer cells.