Immunology- Major Histocompatibility Complex (MHC)

MHC does what?

1)MHC encodes molecules presenting the antigen to CD4+ and T-Ly 2) MHC encode complement and cytokine molecules 3) MHC encode molecules presenting the antigen to CD8+T-Ly

How is MHC a unique system?

Alleles code for proteins differing in 10-20 amino acids instead of 2-3 amino acids Blocks of alleles, the combinations are inherited together and are identical in families It is a typical exon-intron structure. Lack of recombination in MHC chromosomal segments

BCR

B cell receptor

BCR function

BCR directly recognises and binds non self antigens

genes of minor histocompatibility complex

Encode minor histocompatibility antigens. More than 50 in humans. H-Y (male specific transplantation antigen)- AD coded by a gene (Smcy) on Y-chromosome. Found in tissues of males and is lacking in female tissues

MHC function

MHC binds nonself peptide antigens and serve as ligands for TCR

Where is MHC class I located?

MHC class 1 is located on the surface of all nucleated somatic cells It is most abundant on T cells

Where is MHC class II found?

MHC class 2 is located on immune cells such as B lymphocytes, antigen presenting cells, macrophages and DCs

MHC consists of what?

MHC consists of a short arm of chromosome 6 (224 loci, above 4 million base pairs). It is polygenic and polyallelic system. MHC encodes antigen recognition molecules

MHC genes are what?

MHC genes are codominant

MHC molecules class 2

MHC molecules class 2 encoded by MHC genes class 2

MHC molecules class 3

MHC molecules class 3 encoded by MHC genes class 3

MHC Molecules Class I

MHC molecules class I encoded by MHC genes class I

Functions of MHC molecules

MHC molecules help the recognition of self nonself and regulate the immune response. MHC 1= Tc. Tc kills cells that produce and later present the foreign antigen MHC 2= Th. Th helps cells that engulf foreign antigen from extracellular fluids

MHC restriction

MHC restriction is the ability of T lymphocytes to recognise antigens bound to a definite class of self MHC molecules. Each TCR recognises a definite antigen, bound to a definite MHC molecule

Polygenicity is responsible for what?

Polygenicity is responsible for the diversity of MHC gene expression at the level of each individual

polymorphism is responsible for what?

Polymorphism is responsible for the diversity of MHC gene expression at the level of the population as a whole.

Antigen presentation

Regulation of immune response Pathogenesis of autoimmune diseases (antigenic mimicry, HIV- MHC class 2 A.lumbricoides

TCR

T cell receptor

TCR function

TCR recognises and binds nonself antigens and self MHC molecule

MHC restriction (table)

The TCR repertoire in the thymus is a result of selection on the thymus of T cells educated to distinguish self MHC molecules

Polymorphism

The coexistence of two or more distinct forms in the same population.

Polygenicity

The fact that each trait is affected by several different genes

heterozygosity

having different alleles at a gene locus. It's an advantage

MHC

major histocompatibility complex

Homozygosity

the chance of drawing 2 identical alleles. MHC class 1- AIDS MHC class 2- chronic course of HBV infections Presence of rare alleles

functions of MHC class 1 molecules

viral and tumoral immunity (Tc) components of hormones and receptors (insulin) similar to genes for olphactorial receptors. MHC is a source of unique fragrances which affect recognition, sexual preferences, nesting, bringing up of offspring etc