MHC (Major Histocompatibility Complex) | Online Biotech Notes

Online Biotech Notes

MHC (Major Histocompatibility Complex):

•   It is a glycoprotein that present antigen to T_H cells.
•   T cells receptor can only recognize antigen that has been processed and presented by major histocompatibility complex (MHC).

Location of MHC

•  Collections of genes on chromosome 6 in humans (HLA complex) (Human leukocytes antigen) chromosome 17 in mice (H-2 complex).

Types of MHC:-

There are three type of MHC present in the body of human & mice.

• Class 1 MHC genes:- 
•  Encode glycoprotein expressed on all nucleated cells.
• Class 2 MHC genes:-
• Encode glycoprotein expressed on antigen presenting cells.(macrophage , B cells, Dendritic cell).
• Class 3 MHC genes:-
• Encode various product involved in complement and inflammation.

difference between MHC1 and MHC2

Structure of class 1 & class 2 molecule:-

Ø     It comprised of 2 molecules-

• α - chain (45 K D_a), transmembrane, cytoplasmic tail.
• β₂ – Macroglobulin (12K D_a).
• Non - covalently associated with each other.
•  Association of α – chain and β-2 is required for surface expression.
• α – chain made up of 3 domains (α – 1, α - 2, α – 3).
• β₂ – Macroglobulin similar to α – 3.
• α – 1 and α – 2 form peptide binding C left.
• Fits peptide of about 8-10 a/a long.
• α – 3 highly conversed among MHCI molecule.
• Interact with CD₈ (T_C) molecule.
• It presents indigenous & intraocular peptide of pathogen.

 

Ø   Peptide presented thru MHC

• Class 2 MHC molecule contain two different polypeptide chains, a 33- kD_­a α chain and 28 – kD_a β -  chain which associated by non covalent interactions.
• α – β chain contain Trans membrane segments and cytoplasmic tail.
• Association of α – β is required for surface expression.
•  α – chain made up of 2 domains (α – 1, α – 2).
• β - Chain is made up of 2 domains (β – 1, β – 2).
• α – 1  and β – 1 from antigen binding C left
• Peptide consists of 13 – 18 a/a.
• CD₄ molecule binds α – 2/ β – 2 domains.

Ø   MHC Restriction:-

• CD₈⁺ T_C cells are MHC class 1 restricted.
• Can only recognize antigen presented by MHC class 1 molecule.
• Therefore cells with MHC class 1 are called “Target cells”, killed by cytotoxic T cells.
• CD₄⁺ T_H cells are MHC class 2 restricted.
• Cells with MHC class 2 are called antigen presenting cell.(APCs)