MHC Complex class 1

The genes on chromosome 6 regulate the human leukocyte antigen (HLA) system, also known as the major histocompatibility complex (MHC) in humans, which is a crucial component of the immune system.

MHC molecules that present antigen (Ag) are divided into 2 main classes:

Class I MHC molecules

Class II MHC molecules

MHC class 1:

1. The MHC class 1 complex have alpha and beta chains and coded by HLA-A , HLA-B , HLA-C genes.

2. Class 1 MHC molecules are expressed in all nucleated cells in the body.

3. The alpha chain acts as the peptide binding groove and made up of 3 sub-units (⍺1 , ⍺2 & ⍺3) and on the other hand β sub-unit support the structure of alpha chain.

4. The peptide binding groove have the ability to bind with the peptide of size 8 - 10 amino acids.

5. These peptides are processed and expressed by the endogenous path way.

Endogenous pathway of antigen presentation:

Step 1: Recognition of the protein to be degraded.

Step 2: Protein degradation by proteasome complex.

Step 3: The TAP (Transporter of antigenic peptides] which are present on the surface of endoplasmic reticulum which facilitate the transport of the degraded peptide inside the ER.

Step 4: Structuring of MHC class 1 simultaneously happens in the ER.

Step 5: Tapasin protein help in the transfer of the peptide binding region of the class 1 MHC molecule.

Step 6: Now the peptide loaded MHC complex is transported to the golgi body, where the complex is enclosed inside a vesicle.

Step 7: This vesicle is transported to the membrane of the cell resulting in exposure of peptide to the immune cells.

Endogenous pathway of antigen presentation

Cytotoxic T cell and Natural Killer cells circulating in recognise the peptide presented on the MHC complex and kill the cell.