<<–2/”>a href=”https://exam.pscnotes.com/5653-2/”>p>Let’s break down the differences between MHC class I and MHC class II proteins, followed by their advantages, disadvantages, similarities, and some FAQs.
Introduction
The Major Histocompatibility Complex (MHC) is a group of genes that code for proteins on the surface of cells. These proteins are crucial for the adaptive immune response. They function by presenting antigens (small pieces of pathogens) to T cells, which are key players in the immune response. There are two main classes of MHC proteins:
- MHC class I: Primarily found on all nucleated cells. They present antigens derived from inside the cell (e.g., viral proteins) to cytotoxic T cells (CD8+ T cells).
- MHC class II: Found mainly on antigen-presenting cells (APCs), such as dendritic cells, macrophages, and B cells. They present antigens derived from outside the cell (e.g., bacterial fragments) to helper T cells (CD4+ T cells).
Key Differences between MHC Class I and MHC Class II Proteins
| Feature | MHC Class I | MHC Class II |
|---|---|---|
| Distribution | Present on almost all nucleated cells. | Primarily on antigen-presenting cells (APCs): dendritic cells, macrophages, B cells. |
| Encoding Genes | HLA-A, HLA-B, HLA-C | HLA-DR, HLA-DP, HLA-DQ |
| Antigen Origin | Endogenous (intracellular): Viral proteins, tumor antigens, self-proteins. | Exogenous (extracellular): Bacteria, parasites, ingested particles. |
| Peptide Size | Binds shorter peptides (8-10 amino acids). | Binds longer peptides (13-18 amino acids). |
| Processing ENZYMES | Cytosolic proteasomes. | Endosomal and lysosomal proteases. |
| Peptide Loading | In the endoplasmic reticulum (ER). | In specialized endosomal compartments. |
| Responding T cells | Cytotoxic T cells (CD8+). | Helper T cells (CD4+). |
| Function | Triggers cell destruction by cytotoxic T cells if presenting a foreign antigen. | Activates helper T cells to coordinate the immune response. |
Advantages and Disadvantages
| Advantages | Disadvantages | |
|---|---|---|
| MHC Class I | Allows detection of intracellular infections, tumor surveillance, and rejection of transplants. | High polymorphism leads to difficulty in finding suitable organ donors for transplants. |
| MHC Class II | Allows detection of extracellular infections and coordination of the immune response. | Susceptibility to autoimmune diseases due to self-antigen presentation. |
Similarities between MHC Class I and MHC Class II Proteins
- Both are cell surface glycoproteins.
- Both are involved in antigen presentation to T cells.
- Both are highly polymorphic (have many different forms), contributing to individual immune diversity.
FAQs on MHC Class I and MHC Class II Proteins
Q: Why is MHC polymorphism important?
A: MHC polymorphism ensures that the Population as a whole can recognize a wide variety of pathogens. It also makes finding compatible organ donors more difficult.
Q: How do MHC proteins contribute to autoimmune diseases?
A: Sometimes, MHC proteins mistakenly present self-antigens (proteins from the body’s own Tissues) to T cells, triggering an autoimmune response.
Q: Can MHC proteins be targeted therapeutically?
A: Yes, research is ongoing into developing drugs that modulate MHC function to treat cancer, autoimmune diseases, and transplant rejection.
Let me know if you’d like more details on any of these aspects!