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

Major Histocompatibility complex (MHC): Introduction, Types and Differences


  • Introduction
  • Types of Major Histocompatibility complex (MHC)
  • Difference between Type 1 and Type 2


  • 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.

Structure of MHC 1 and MHC 2 proteins

  • 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

Types of Histocompatibility complex


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.


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

Difference between MHC TYPE 1 and TYPE 2

Type 1          Type 2
  • Alpha and beta globulins are present on most of the cells.
  • Present on only specialized cell.
  • Bind endogenous antigen synthesized in the cell.
  • Bind to exogenous antigens.


  • It consists of 3-alpha Chain and 1-beta chain
  • Alpha and beta chains are equal.
  • Antigen is presented on Tc cells.
  • Antigens are Present on T- helper cells.
  • Bind to CD-8 molecules
  • Bind to CD-4 molecules.

Major Histocompatibility complex (MHC): Introduction, Types and Difference

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