MHC Class I

Definition

MHC Class I molecules are essential proteins found on the surface of nearly all nucleated cells in the body, playing a crucial role in the immune system by presenting endogenous peptides to CD8+ T cells. These molecules help the immune system distinguish between healthy cells and infected or malignant ones by displaying fragments of proteins from within the cell, including those from pathogens. This presentation is vital for the activation of cytotoxic T cells, which are responsible for eliminating infected or cancerous cells.

5 Must Know Facts For Your Next Test

1. MHC Class I molecules are composed of a heavy chain and a beta-2 microglobulin, which work together to present peptide fragments to CD8+ T cells.
2. The binding groove of MHC Class I can accommodate peptides that are 8-10 amino acids long, ensuring that these short sequences can effectively be presented to T cells.
3. MHC Class I molecules are encoded by genes located in the major histocompatibility complex region on chromosome 6 in humans.
4. The interaction between MHC Class I molecules and CD8+ T cells is critical for immune surveillance, allowing the immune system to detect and respond to infections and tumors.
5. Variations in MHC Class I genes among individuals contribute to differences in immune responses and susceptibility to diseases, highlighting the importance of genetic diversity in the population.

Review Questions

• How do MHC Class I molecules contribute to the activation of CD8+ T cells?
  • MHC Class I molecules present endogenous peptides derived from proteins synthesized within the cell to CD8+ T cells. This interaction is crucial for activating CD8+ T cells, as it allows them to recognize and bind to infected or abnormal cells displaying foreign antigens. Once activated, CD8+ T cells can proliferate and differentiate into cytotoxic T lymphocytes that effectively eliminate infected or malignant cells.
• Compare the roles of MHC Class I and MHC Class II molecules in the immune response.
  • MHC Class I molecules primarily present endogenous peptides to CD8+ T cells, facilitating the recognition and destruction of infected or cancerous cells. In contrast, MHC Class II molecules present exogenous peptides to CD4+ T helper cells, which help coordinate and enhance the overall immune response by activating other immune cells such as B cells and macrophages. Together, these two classes of MHC molecules create a comprehensive immune response that targets a wide range of pathogens.
• Evaluate how genetic variability in MHC Class I genes impacts individual susceptibility to diseases.
  • Genetic variability in MHC Class I genes can significantly influence an individual's immune response capabilities. Different alleles can result in varying efficiency at presenting specific peptide fragments to CD8+ T cells. Consequently, individuals with certain MHC Class I variants may be more susceptible or resistant to particular infections or cancers. This genetic diversity ensures that populations can better withstand various pathogens over time, but it can also lead to challenges in organ transplantation due to mismatched MHC alleles triggering rejection responses.

Related terms

CD8+ T Cells: A subtype of T cells that have a key role in the adaptive immune response by directly killing infected or cancerous cells.

MHC Class II:

MHC molecules that primarily present exogenous peptides to CD4+ T helper cells, playing a central role in orchestrating the immune response.

Antigen Presentation: The process by which proteins are displayed on MHC molecules on the cell surface to be recognized by T cells, crucial for initiating an immune response.