MHC Class II

Definition

MHC Class II molecules are proteins found on the surface of certain immune cells that present antigens from extracellular sources to CD4+ T helper cells. They play a crucial role in initiating and regulating adaptive immune responses by facilitating the communication between antigen-presenting cells and T cells, leading to a targeted immune reaction against pathogens such as bacteria and viruses.

5 Must Know Facts For Your Next Test

1. MHC Class II molecules are primarily expressed on professional antigen-presenting cells, which include dendritic cells, macrophages, and B cells.
2. The interaction between MHC Class II molecules and CD4+ T cells is vital for the activation of helper T cells, which then stimulate B cells to produce antibodies.
3. MHC Class II molecules present processed fragments of extracellular proteins, allowing the immune system to detect infections caused by bacteria or other extracellular pathogens.
4. Polymorphism in MHC Class II genes contributes to the diversity of the immune response among individuals, affecting susceptibility to diseases.
5. The binding of a peptide to an MHC Class II molecule stabilizes the complex, enabling effective signaling and activation of CD4+ T cells.

Review Questions

• How do MHC Class II molecules contribute to the activation of CD4+ T cells?
  • MHC Class II molecules present processed antigens from extracellular sources to CD4+ T cells. When a CD4+ T cell recognizes the antigen-MHC Class II complex through its T cell receptor (TCR), it becomes activated. This activation is crucial for the subsequent stimulation of other immune components, particularly B cells and cytotoxic T cells, thus playing a central role in orchestrating an effective immune response.
• Discuss the importance of MHC Class II polymorphism in adaptive immunity.
  • MHC Class II polymorphism is significant because it creates a diverse array of MHC molecules among individuals, enhancing the ability of the immune system to recognize and respond to a wide variety of pathogens. This genetic variation allows different individuals to present different sets of antigens, which can be critical during infections or vaccinations. It ensures that populations have a better chance of surviving against evolving pathogens due to this broad spectrum of antigen presentation capabilities.
• Evaluate the implications of impaired MHC Class II function in human health and disease.
  • Impaired MHC Class II function can lead to serious health issues, including autoimmune diseases where the body may fail to distinguish between self and non-self antigens. Conditions like rheumatoid arthritis or lupus may arise from such dysfunction. Furthermore, inadequate presentation of antigens can compromise the immune response, making individuals more susceptible to infections and reducing vaccine efficacy. Understanding these implications highlights the critical role MHC Class II plays in maintaining a balanced immune system.

Related terms

Antigen-Presenting Cells (APCs): Cells that process and present antigens to T cells, including dendritic cells, macrophages, and B cells, which express MHC Class II molecules.

CD4+ T Cells: A subset of T cells that recognize antigens presented by MHC Class II molecules and play a critical role in orchestrating immune responses.

Adaptive Immunity: The branch of the immune system that provides long-lasting protection against specific pathogens through the activation of lymphocytes, including B and T cells.