Major histocompatibility complex (MHC)

Definition

The major histocompatibility complex (MHC) is a set of cell surface proteins essential for the adaptive immune system to recognize foreign molecules. MHC molecules present peptide fragments derived from pathogens to T cells, playing a crucial role in the activation of the immune response. This system allows the body to distinguish between self and non-self, which is vital for effective immune surveillance and defense.

5 Must Know Facts For Your Next Test

1. MHC molecules are divided into two main classes: MHC class I and MHC class II, each serving distinct roles in immune response.
2. MHC class I molecules are present on almost all nucleated cells and present peptides from intracellular proteins to CD8+ cytotoxic T cells.
3. MHC class II molecules are expressed primarily on professional antigen-presenting cells, such as dendritic cells, macrophages, and B cells, presenting extracellular antigens to CD4+ helper T cells.
4. The diversity of MHC alleles in a population contributes to varying immune responses among individuals, influencing susceptibility to diseases.
5. Incompatibility of MHC molecules between donors and recipients can lead to transplant rejection, making MHC matching crucial in organ transplantation.

Review Questions

• How do MHC molecules contribute to the recognition of pathogens by T cells in adaptive immunity?
  • MHC molecules play a critical role in adaptive immunity by presenting peptide fragments from pathogens on the surface of cells. When a pathogen infects a cell, it generates peptides that are processed and displayed by MHC class I or class II molecules. CD8+ cytotoxic T cells interact with MHC class I, recognizing infected cells, while CD4+ helper T cells engage with MHC class II on antigen-presenting cells. This interaction is vital for activating T cells and initiating an appropriate immune response.
• Discuss the significance of MHC diversity in a population regarding immune responses and disease susceptibility.
  • MHC diversity within a population is significant as it affects how well individuals can respond to various pathogens. Different MHC alleles can present a unique set of peptides, allowing populations to collectively recognize and respond to a wider range of infectious agents. This genetic variability can lead to differential susceptibility to diseases; individuals with certain MHC types may be more adept at mounting effective immune responses against specific pathogens, while others may be at higher risk for infections or autoimmune diseases due to less effective recognition.
• Evaluate the implications of MHC matching in organ transplantation and its relevance to transplant success.
  • MHC matching is critical in organ transplantation because it minimizes the risk of transplant rejection. When the recipient's immune system recognizes foreign MHC molecules from the donor as non-self, it can mount an immune response leading to rejection of the transplanted organ. Successful matching reduces this risk by ensuring compatibility between donor and recipient MHC alleles, improving graft survival rates. Understanding this concept emphasizes the importance of immunological compatibility in achieving successful outcomes in transplantation medicine.

Related terms

T Cells: A type of white blood cell that plays a central role in cell-mediated immunity, helping to recognize and respond to pathogens.

Antigen Presentation: The process by which MHC molecules display peptide fragments on the cell surface to T cells, initiating an immune response.

Cytotoxic T Cells:

A subtype of T cells that directly kill infected or cancerous cells, relying on MHC class I molecules to identify their targets.