MHC Molecules

Major Histocompatibility Complex (MHC)

A key component of the immune system that helps distinguish between 'self' and 'non-self'.

Human Leukocyte Antigens (HLA)

The human variation of MHC, which refers to MHC molecules in humans.

Class I MHC molecules

Composed of a heavy chain and β2-microglobulin; presents peptide fragments to CD8+ T-cells.

Class II MHC molecules

Consists of α and β chains forming a heterodimer and primarily located on B cells, macrophages, and activated T cells.

Tissue distribution of Class I MHC

Present on all nucleated cells.

Tissue distribution of Class II MHC

Present on antigen-presenting cells (APCs) like B cells, dendritic cells, and macrophages.

Compatibility in MHC context

Refers to living together harmoniously, crucial for successful immune response.

MHC's role in autoimmunity

Autoimmune diseases arise when the immune system fails to distinguish between self and non-self.

Narcolepsy and MHC association

Strong association with HLA-DR2.

Ankylosing Spondylitis and MHC association

Associated with HLA-B27.

TAP (transporter associated with antigen processing)

Vital for transporting peptides to the cell surface in Class I MHC.

Disease susceptibility associated with HLA

Specific HLA types have been linked with susceptibility and resistance to various infectious diseases.

Class III MHC molecules

Involves polymorphic serum proteins related to immune functions, such as complement proteins.

Class IV MHC molecules

Associated with T-Cell leukemia (Thymus Leukemia Antigen).

Functions of MHC molecules

Facilitates recognition of infected and tumor cells by cytotoxic T lymphocytes (CTLs) and is essential for transplantation compatibility.

MHC Class I & II

MHC molecules present antigens to T cells, recognized by CD4-lymphocytes through T-cell receptors.

Polymorphism of HLA

High polymorphism with significant population variation and numerous amino acid substitutions contributing to immune diversity.

HLA Haplotype Inheritance

MHC genes are inherited as a haplotype from each parent, resulting in heterozygous expression.

Class I MHC Specificities

A maximum of 6 Class I specificities can be inherited from the three loci: A, B, and C.

Class II MHC Genes

Involves inheritance and expression of genes from DP, DQ, and DR loci.

Autoimmune Diseases and HLA

Over 40 autoimmune diseases linked to specific HLA haplotypes, such as narcolepsy and ankylosing spondylitis.

MHC and AIDS

HLA B35 and B70 are associated with susceptibility to AIDS, while HLA B44 and DR7 correlate with resistance.

MHC in Malaria

HLA B53 is linked with resistance to severe Plasmodium falciparum malaria.

Functions of MHC Molecules

Facilitates antigen recognition, enables immune response initiation, and contributes to organ transplantation compatibility.

Antigen Presentation by MHC Class I

Presents endogenous antigens to CD8+ T-cells after degradation of intracellular proteins.

Antigen Presentation by MHC Class II

Presents exogenous antigens to CD4+ T-cells after engulfing and processing in antigen-presenting cells.

MHC Class I and II Distribution

Class I MHC present on all nucleated cells; Class II MHC found predominantly on antigen-presenting cells.

MHC Biological Function

Essential for recognition of self vs. non-self, protection against intracellular pathogens, and facilitating T-cell responses.

MHC Structure

Located on chromosome 6p, MHC consists of Class I, II, III, and IV genes critical for immune functions.

Tissue Distribution of MHC

Class I MHC on all nucleated cells; Class II MHC on APCs and specific immune cells.