MHC Class I

Definition

MHC Class I molecules are proteins found on the surface of nearly all nucleated cells, responsible for presenting endogenous antigens to CD8+ cytotoxic T cells. This interaction is crucial for the immune system to recognize and eliminate infected or malignant cells, making MHC Class I a key player in viral immune evasion strategies.

5 Must Know Facts For Your Next Test

1. MHC Class I molecules present peptides derived from proteins synthesized within the cell, allowing the immune system to monitor the internal state of cells.
2. Certain viruses, like HIV and cytomegalovirus, have evolved mechanisms to downregulate MHC Class I expression, helping them avoid detection by CD8+ T cells.
3. The binding of viral peptides to MHC Class I is essential for the activation of cytotoxic T cells, which play a critical role in controlling viral infections.
4. MHC Class I molecules are encoded by a set of genes known as the major histocompatibility complex (MHC), which is highly polymorphic and important for transplant compatibility.
5. Alterations in MHC Class I expression can lead to immune evasion, allowing tumors or virally-infected cells to escape destruction by the immune system.

Review Questions

• How do MHC Class I molecules contribute to the recognition of virus-infected cells by the immune system?
  • MHC Class I molecules present viral peptides from within infected cells to CD8+ cytotoxic T cells. When these T cells recognize a foreign peptide displayed on an MHC Class I molecule, they become activated and initiate an immune response aimed at killing the infected cell. This process is essential for controlling viral infections and preventing spread.
• Discuss how some viruses employ strategies to downregulate MHC Class I expression and the implications of this for viral infection outcomes.
  • Some viruses, such as HIV and cytomegalovirus, can downregulate MHC Class I molecules on infected cells to evade recognition by CD8+ T cells. This downregulation impairs the immune response, allowing the virus to persist longer within the host. As a result, this evasion can lead to chronic infections and increased difficulty for the immune system in eliminating the virus.
• Evaluate the role of MHC Class I in transplant rejection and its relevance in understanding viral immune evasion.
  • MHC Class I plays a crucial role in transplant rejection because recipient immune cells recognize foreign MHC Class I molecules as non-self, leading to an attack on transplanted tissues. Understanding this concept highlights how viruses may manipulate MHC Class I expression not only for evasion but also how similar strategies impact therapeutic settings like transplants, where matching MHC is vital for reducing rejection risks.

Related terms

Antigen Presentation: The process by which proteins (antigens) are displayed on cell surfaces by MHC molecules, enabling T cells to recognize and respond to pathogens or abnormal cells.

CD8+ T Cells: A subset of T lymphocytes that are crucial for killing infected or cancerous cells and are activated by recognizing antigens presented by MHC Class I.

Viral Evasion Mechanisms: Strategies employed by viruses to evade detection and elimination by the host's immune system, often targeting components like MHC Class I molecules.