Major Histocompatibility Complexes Flashcards
(41 cards)
MHC is a…
genetic complex
in ALL vertebrate species
MHC stands for
Major Histocompatibility Complex
MHC genes are….
polymorphic (come in MANY genetic forms)
Classes of MHC
MHC Class I
MHC Class II
MHC I Structure
PART PRESENTED TO T-CELLS:
alpha-1 bind to membrane. alpha-2 & -3 combined form peptide-binding cleft. B-2 microglobulin doesn’t contribute to it’s function.
MHC II Structure
PART PRESENTED TO T-CELLS:
B-2 and a-2 bind to cell membrane. b-1 and a-1 form peptide-binding cleft.
MHC I expressed by
ALL nucleated cells
MHC I present Ag to…
CD8 T-cells
MHC I presents Ags that are…
sythesized inside the cell
cytosolic pathogens
Types of Ags presented by MHC I
viral antigens
intracellular parasites
MHC II expressed by…
dendritic cells
macrophages
B-cells
MHC II present Ags to…
CD4 T-cells
MHC II presents Ags that are…
made outside the cell and internalized
intravesicular pathogens & extracellular pathogens & toxins
Types of Ags presented by MHC II
extracellular parasites
extracellular phase of intracellular parasites
MHC functions
transport intracellular antigens to the surface of a cell where the TCR can “see” it
MHC I Antigen Processing
Tumer antigen coding region in nueclues –> endogenously synthesized Ag –> proteasome –> peptides –> peptide enters ER & binds to MHC I –> MHC I + Ag go to Golgi then DGN –> cell membrane
MHC II Antigen Processing
endocytosis of protein antigen –> Ag endosome joins MHC II containing endosome –> Ag binds to MHC II –> MHC II on plasma membrane
Peptide-Binding Selectivity of MHC I and II
MHC I and II bind to many different peptides but have preferences for certain amino acids that must be present to bind.
the requirements for binding aren’t as strict as Ag:Ab binding.
SELECTIVE rather than SPECIFIC binding
What happens when MHC is less polymorphic?
limited polymorphism
a more limited number of antigenic peptides that can be present to T-cells.
examples of diseases related to limited polymorphism
- Feline infectious peritonitis in Cheetahs
2. Tasmanian devil facial tumors that are “transplanted” from biting (they don’t make MHC)
MHC alleles associated with susceptility & sometimes resistance to…
mostly autoimmune diseases
MHC polymorphism means…
each groove on the various MHC molecules is different from the others, making it highly specific to TCRs
Canine Disease Associations with MHC alleles
probably due to the way Ags are presented by the MHC which leads to an increased risk of disease.
Infectious Disease Resistance/Susceptibility
- has potential associations with MHC alleles
- probably because viruses have lots of antigenic peptides and at least one of them will bind to MHC and be presented. THEREFORE, the diseases aren’t as effective.
