Major Histocompatiblity Complex Flashcards
MHC
First recognized as the site of genes that cause T cells to reject tissues transplanted from unrelated donors to recipients
- MHC in humans is called Human leukocyte antigen complex
Isotypes
Products of the different MHC 1 and 2 genes
Alleles
Different forms of any given gene
Allotypes
Different products of any given gene
MHC diversity
Much smaller than that of TCR
- multiple gene families
- genetic polymorphism
How many MHC class 1 isotypes do you have?
6 classes, get each one from your parent = 12 isotypes
MHC class 1 locus
A-G
Heterozygous
Individual that inherited 2 different forms (alleles) of the gene from parents
- better to be heterozygous than homozygous
Homozygous
Individual that inherited the same forms (alleles) of the gene from parents
HLA haplotype
Particular combination of HLA alleles found on a given chromosome 6
HLA type
Combination of all HLA alleles a person has
T cells can not recognize an _____ in the absence of _____
Antigen; MHC
Difference between survivors and fatalities when an infectious disease strikes a population
The complement of MHC molecules present in each individual
- species wide MHC polymorphisms dramatically reduce likelihood that a single infectious agent will destroy an entire population
Species most prone to genetic bottlenecking
- African cheetahs
- Florida panthers
- Lions in Tanzani
Advantage of multiple MHC genes that arise from balancing selection
- contribute different peptide binding specificities
- greater number of pathogen derived peptides is presented during any infection
- strength of immune response against the pathogen is improved by increasing number of activated pathogen specific T cells
- high degree of MHC polymorphism ensures that most members of population are heterozygotes
Directional selection
Favors certain MHC alleles at the expense of others and is imposed by specific, epidemic disease
- replaces older alleles with newer variants
- outcome is change, not balance
MHC in domestic animals
- all mammals have MHC 1,2, and 3
- express differences in their conserved and variable regions
- MHC class 2 and 3 are orthologous
- MHC class 1 genes are paralogous
- overall molecular structure and function of MHC molecules does not differ significantly
MHC class 3
- 4 genes for complement receptors, P450, TNF alpha, lymphotoxins, NK receptors, HSP
Why do we have 2 different classes of MHC?
Helps to discriminate between different pathogens, do not need to send all pathogens thru the same pathway
