Major Histocompatibility Complex 02/28/06
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Transcript Major Histocompatibility Complex 02/28/06
Principles of Immunology
Major Histocompatibility
Complex
2/28/06
“Change is not merely necessary for life. It is life.”
A Toffler
Word List
Congenic
Haplotype
HLA complex
MHC
Polygenic
Syngeneic
MHC
Cluster of genes that influence:
1. Intercellular recognition
2. Self vs. non-self
HLA complex in humans
HLA Complex
Three regions
Class I genes
MHC I molecules
Nucleated cells
T cytotoxic cells (CD8)
Class II genes
MHC II molecules
APCs
T helper cells (CD4)
Class III genes
Complement components (C2 and C4) plus TNF
MHC I Molecules
Membrane bound glycoprotein (Ig super family)
Alpha chain
Three domains
Encoded by HLA complex
Anchored in cell membrane
Cytoplasmic tail
Beta chain
A single domain
Encoded by a different gene on another chromosome
Not anchored in cell membrane
Bound to alpha chain non covalently
Necessary for MHC I expression
MHC I Molecules
Antigen presenting features
Alpha 1 and alpha 2 domains form
peptide-binding cleft
8-10 amino acid peptides can bind to
MHC I molecule
Alpha 3 interacts with CD 8 on T
cytotoxic cells
MHC II Molecules
Membrane bound glycoprotein (Ig super family)
Alpha chain
Two domains
Encoded by HLA complex
Anchored in cell membrane
Cytoplasmic tail
Beta chain
Two domains
Encoded by HLA complex
Anchored in cell membrane
Cytoplasmic tail
MHC II Molecules
Antigen presenting features
Alpha 1 and beta 1 domains form
peptide-binding pocket
13-18 amino acid peptides can bind to
MHC II molecule
Alpha 2 and beta 2 interact with CD 4 on
T helper cells
Fig 7-5
MHC I – Peptide Interaction
Stable associations
Endogenously processed antigens
Up to six allelic variants
~100,000 MHC molecule variants per
cell
~ 100 MHC-peptide complexes
required for T cytotoxic cell
recognition
MHC II – Peptide Interaction
Stable associations
Exogenously processed antigens
Up to 12 allelic variants
MHC Diversity
Genetically determined
Polygenic characteristic
Different alleles
Genes with overlapping functions
~12 million haplotypes
Diversity in HLA type
MHC I Expression
Varies by cell type
Lymphocytes high
Hepatocytes low
Regulated by cytokines
Interferons
TNF
Suppressed by viruses
Herpes family
Hepatitis B
Inheritance of MHC(HLA) Type
Polymorhisms
Many allelic types within a species
Haplotype
The genetic loci of MHC are closely linked
Inherited as a group (haplotype)
One haplotype from each parent
Co-dominant expression
Inheritance of MHC
Inbred mice
Homozygous parents
F 1 generation has MHC loci from both
(heterozygous)
F1 generation can accept grafts from
either parent
Neither parent can accept graft from F1
offspring
WHY?
Inheritance of MHC
Humans
Heterozygous parents
F 1 generation has MHC loci from both
(heterozygous)
Four combinations
F1 generation can not accept grafts from
either parent
Neither parent can accept graft from F1
offspring
1 in 4 F1 generation are HLA compatible