Major histocompatibility complex (MHC): introduction, types and differences

Introduction

The Major Histocompatibility Complex (MHC) is a set of genes that code for cell surface proteins essential for the immune system to recognize foreign antigens. MHC molecules play a key role in antigen presentation to T cells, enabling immune defense against pathogens and abnormal cells. MHC is a group of cell surface glycoproteins that bind peptide fragments derived from pathogens and display them to T lymphocytes, triggering an immune response.

• MHC products play an important role in intracellular recognition and discrimination between self and non self.
• MHC participates in development of humoral and cellular immune responses.

One chromosome pair coding for three different classes of protein:

•  Class 1 Protein that determined histocompatibility and the acceptance or rejection of allograft.
•  Class 2 Protein that regulate the immune response.
•  Class 3 Protein that include some components of the complement system and a few others.

• HLA (Human Leucocyte antigens) complex: The HLA complex of genes is located on the short arm of chromosome 6.
• It consists of three separate cluster of:
  • HLA class 1 comprising A, B and C loci.
  • HLA or D region consists of DR, DQ, and DP loci.
  • Class3 or the complement reason containing genes for complement component C4B, BFC2 to TNF.

Type of major Histocompatibility complex

1. MHC type 1
2. MHC type 2
3. MHC type 3

MHC type 1

• The gene of this MHC is Coat glycoprotein expressed on the surface of nearly all the nucleated cells. The main function of MHC type 1 presentation of peptide to antigen to Tc cells.
• Consists of two polypeptide chain:
  1. Alpha chain– Alpha molecule is of 45 kDa. Each molecule consists of 30 amino acids.
  2. Beta chain- It is of 12KDa.
     • Beta-2 microglobulin: Similarly size in organisation to alpha-3.
     • Bound non-covalently to alpha domain.

MHC type 2

• Glycoprotein are present value on specialised (APC) including macrophages dendritic cell to present T-cell or B- cell. For production of antibody as well as neutralizing cell mediated immunity.
• T- helper cells are finally activated upon binding with macrophages and dendritic cell, MHC to antigen.
• Consists of two different polypeptide chain
  1. Alpha chain- 33KDa
  2. Beta chain – 28KDa

MHC type 3

• It is group of protein which structure and function are two poorly known.
• They are not involved in antigen binding; only few of them are actively involved in immunity, while most of them engage in cell communication.
• They are mainly known from these genes because the cluster is present in between class 1 and class 2 MHC.
• The genes of type 3 molecules are signaling molecules of TNF and HSP.

Diseases

• Insulin dependent diabetes mellitus.
• Multiple sclerosis
• Rheumatoid arthritis

Difference between MHC TYPE 1 and TYPE 2

Also Read:

• Animal and plant viruses, prions, and viroids
• Difference between Prokaryotes and Eukaryotes
• Antibody or Immunoglobulin

References and Sources

• https://healthengine.com.au/info/blood-function-and-composition
• https://quizlet.com/36017580/biol-2114-chapter-19-blood-flash-cards/
• https://www.sciencedirect.com/topics/immunology-and-microbiology/major-histocompatibility-complex
• https://www.researchgate.net/publication/328546257_Discrimination_Between_Self_and_Non-Self-Nucleic_Acids_by_the_Innate_Immune_System