The main difference between HLA and MHC is that the HLA is a form of MHC antigens in humans whereas the MHC is a group of antigens that occur in other vertebrates. Furthermore, the class I HLA contains HLA-A, HLA-B, and HLA-C molecules and class II HLA contains HLA-D molecules. Also, the three classes of MHC are MHC class I, II, and II. Moreover, in humans, the HLA gene family occurs on chromosome 6.
HLA and MHC are two types of cell surface proteins in vertebrates. They play a key role in the acquired immune system by presenting foreign antigens which in turn determines histocompatibility.
Key Areas Covered
1. What is HLA
– Definition, Polymorphism, HLA Typing
2. What is MHC
– Definition, Classes, Importance
3. What are the Similarities Between HLA and MHC
– Outline of Common Features
4. What is the Difference Between HLA and MHC
– Comparison of Key Differences
Key Terms
Class I, Class II, HLA (Human Leukocyte Antigen), HLA Typing, MHC (Major Histocompatibility Complex), Polymorphism
What is HLA
The HLA (human leukocyte antigen) is a form of MHC gene complex present in humans. It consists of around 200 genes located close together on chromosome 6. These genes are expressed on all nucleated cells. The main function of the HLA molecules is to present antigens produced inside the cell on the cell surface in order to be recognized by T cells. Therefore, T cells can recognize foreign antigens upon self-antigens, initiating an acquired immune response. On the other hand, the recognition of antigens by T cells as self allows determining histocompatibility. But, the recognition of self-antigens as non-self by the immune system leads to autoimmune diseases.
Figure 1: Human Chromosome 6
However, HLA complex is the most polymorphic loci of the human genome. The two main classes of HLA complex are Class I, which contains HLA-A, HLA-B, and HLA-C genes, and Class II, which contains HLA-D genes. The most polymorphic HLA gene is the HLA-B, which has 425 alleles recognized up to date. Likewise, the HLA-DRB1 gene has 289 recognized alleles, and HLA-A gene has 214 recognized genes. The IPD-IMGT/HLA database contains all the reported and named sequences of HLA alleles up to date. According to the basic genetic principles, children inherit HLA alleles from parents.
Figure 2: MHC Complex Function
Furthermore, for successful organ transplantation, the HLA alleles of the donor and the recipient have to be matched to each other. The organs with unmatching or non-self HLA alleles will be rejected from the body by the immune system. Therefore, scientists have developed a number of techniques to type HLA alleles in individuals for various purposes, including organ transplantation, paternity tests to determine the percentage of a child, and to identify carriers of certain hereditary diseases such as cancer, diabetes, lupus, etc.
What is MHC
MHC (major histocompatibility complex) is a group of cell surface proteins expressed on all nucleated cells of vertebrates. Same as the HLA complex, the main function of the MHC proteins is to present antigens to the T cells. In addition, the three subgroups of MHC complex are Class I, Class II, and Class II MHC complexes. Moreover, the TCR receptor of the CD8+ T cells recognizes the β2 subunit of Class I MHC molecules while the TCR receptor of the CD4+ T cells recognizes the β1 and the β2 subunits of the Class II MHC molecules. On the contrary, the Class III MHC molecules have a physiological role in the immune system, secreting components of the complement system.
Figure 3: MHC Class I and II
Moreover, the MHC complex in mice is known as the H-2 complex. This complex allows the sexual selection in order to make mate choices of females.
Similarities Between HLA and MHC
- HLA and MHC are two types of surface antigens that occur in all nucleated cells in vertebrates.
- Their main function is to present foreign antigens to T cells.
- The three gene families of HLA and MHC are Class I, II, and III.
- Also, these antigens occur in all nucleated cells of vertebrates.
Difference Between HLA and MHC
Definition
HLA (human leukocyte antigen) refers to a gene complex encoding the major histocompatibility complex (MHC) proteins in humans while MHC refers to a set of cell surface proteins essential for the acquired immune system to recognize foreign molecules in vertebrates, which in turn determines histocompatibility. Thus, this is the fundamental difference between HLA and MHC.
Correspondence
So, the main difference between HLA and MHC is that the HLA is the form of MHC complex that occurs in humans while the MHC complex occurs in all vertebrates.
Types
The class I HLA genes are HLA-A, HLA-B, and HLA-C and class II HLA genes are HLA-D while three classes of MHC complex are Class I, II, and III. Hence, this is another major difference between HLA and MHC.
Conclusion
HLA is the form of MHC gene complex occurs in humans. However, MHC is a gene complex, which expresses surface antigens on all nucleated cells in vertebrates. The main function of MHC molecules to present antigens to the T cells. It allows the T cell recognition of foreign antigens upon self-antigens. Further, the three main classes of MHC are Class I, II, and III. Still, the main difference between HLA and MHC is their occurrence in vertebrates.
References:
1. Williams, T M. “Human leukocyte antigen gene polymorphism and the histocompatibility laboratory” Journal of molecular diagnostics : JMD vol. 3,3 (2001): 98-104. Available Here
2. “Histocompatibility Complex – Genetics Home Reference – NIH.” U.S. National Library of Medicine, National Institutes of Health, Available Here
Image Courtesy:
1. “HLA” By HLA.jpg: Original uploader was Pdeitiker at en.wikipediaderivative work: Faigl.ladislav (talk) – HLA.jpg (Public Domain) via Commons Wikimedia
2. “Antigen presentation alt” By Fred the OysteriThe source code of this SVG is valid.This vector image was created with Adobe Illustrator. – The Immune System (pdf) (Public Domain) via Commons Wikimedia
3. “MHC classe 1 i 2” By BQmUB2011048 – Own work (CC BY-SA 3.0) via Commons Wikimedia
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