Heme Synthesis & Antigen Presentation Flashcards
Structure of heme
Conjugated double bonds = color
oxygenated = red
deoxygenated = blue
Protoporphyrin IX
Tetrapyyrole ring
4 nitrogen’s
Fe2+ at center
If heme is not associated with protein, its a ____
Lipophilic pro-oxidant
Pro-oxidant forms ____
ROS - induces oxidative stress
How does lead affect heme synth
It inhibits ALA dehydratase and ferrochelatase
Produced in liver when Fe levels are high
Why does it make sense
Hepcidin
Because we want to control Fe levels and hepcidin inhibits the transporter ferroportin (the dude on the basolateral side)
What does Hepcidin do
Inhibits transport of Fe from the mucosal cell
Inflammatory cytokines increase _______ in the liver, contribute to the ______
Synthesis of hepcidin
Anemia of chronic diseases
Where is most heme made
Bone marrow and liver
ALAS1 vs ALAS2
1: short half life, highly regulated, negative feedback by heme
2: regulated in response to levels of iron
Sideroblastic anemia genetic
What else can cause this is acquired not from genes
X-linked mutation of the ALAS2 gene
Most common cause of Sideroblastic anemia
-B6 deficiency also causes this
Sideroblastic anemia acquired
Vitamin B6 deficiency
Bad diet
Alcohol abuse
______ are dominantly inherited with low penetrance
Genetic porphyrias
Most common porphyrias
Porphyria cutanea tarda
_____ has intermittent attacks
AIP - acute intermittent porphyria
Where is heme converted to bilirubin
Macrophages
Steps of heme to bilirubin
Heme—1—->Biliverdin—2—->bilirubin
1=heme oxygenase
need NADPH —>NADP+
need O2
release CO
release Fe3+
2=biliverdin reductase
NADPH —>NADP+
At HOME we first make BILI VERDE (chili verde is harder to make so we need more ingredients) then BILI RUBINS.
Direct vs indirect bilirubin
Direct = conjugated, soluble
conjugated by bilirubin glucuronyl transferase
actively transported by MRP2
Indirect = unconjugated, insoluble
carried on albumin to liver
How do you find indirect bilirubin
Total -direct
PREHEPATIC jaundice causes
Indirect hyperbilirubinemia
If post is directly creepy. This is just the opposite.
What is a common cause of indirect hyperbilirubinemia
Over production of bilirubin
From hemolysis = more than one heme being released
INTRAHEPATIC jaundice causes
Direct and indirect hyperbilirubinemia
INTRA means inside
If you’re on the inside you’ve got the inside scoop and have both direct and indirect
Mech behind intrahepatic jaundice
Something wrong with the liver
It can’t uptake, conjugate and/or secrete bilirubin
How does newborn jaundice happen?
Bilirubin glucuronyl transferase is developmentally expressed
This enzyme is low in newborns and even lower in premature newborns
What’s the concern with newborn jaundice
Albumin can be at full capacity
This leaves excess bilirubin floating around
It accumulates at the basal ganglia and can cause toxic brain damage called “kernicterus”
How does phototherapy work
It converts bilirubin to more soluble isoforms that can be excreated into bile WITHOUT conjugation
What are the genetic conditions causing intrahepatic jaundice
Crigler-Najjar Syndrome
Gilbert Syndrome
Dubin Johnson Syndrome
Key points of Craigler-Najjar Syndrome
Type 1
Type 2
Rare
Autosomal recessive
Deficiency in bilirubin glucuronyl transferase
Unconjucated hyperbilirubinemia at birth
Type 1 = totally deficient
Type 2 = less severe
Gilbert syndrome key points
Common
Mild increase of indirect bilirubin
There is a mutation in the PROMOTER of bilirubin glucuronyl transferase gene
Not very noticeable
GILBERT - GENE
The Gilberts are indirectly creepy
Dubin-Johnson syndrome key points
Rare Mutation in MRP2
Causes defective transport of conjugated bilirubin OUT of hepatocytes
Posthepatic jaundice causes
Direct hyperbilirubinemia
Post is directly creepy but if you let him be creepy long enough it can lead to indirect
Posthepatic jaundice key points
Dark pee
Bile acids can accumulate in plasma
Prolonged obstruction can lead to liver damage and increase of indirect bilirubin
Haptoglobin mech/func
Hapto:
binds αβ dimers in blood
This creates a complex too big to be filtered by glomerulus
This big boi dimers get delivered to macrophages thru a specific receptor
Then its taken up for release and degradation of heme the normal way
Hemopexin mech/func
Hemop:
Free Hb is oxidized to metHb
This turns into goblin and
Metheme
Metheme and Hemopexin bing
Takes it to the liver
This action triggers heme oxygenase
When does haptoglobin decrease
With a lot of hemolysis going on
When would haptoglobin increase
During inflammation or infection
When could hemopexin decrease
When there is a lot of hemolysis
antigens
Molecule or molecular fragment capable of inducing an immune response
What are antigens recognized by
By specific receptors on T and B cells
Immunogen
Molecule that stimulate immune response
Antigen focuses more on binding
What can be a good immunogen
Proteins
Polysaccharides
What can be a bad immunogen
Nucleic acids - cuz they are inside the cell
Lipids - not water soluble
Increasing immunogenicity
Worst
amino acids
happens
lipids
steroids
carbohydrates
proteins
Best
What are epitopes
It’s the part of a macromolecule that the antibody binds to.
Aka determinant
What are haptens
Small molecule (hapten) attached to large carrier to induce immune response
The hapten carrier complex acts as a immunogen
T-dependent antigen process
Needs helper T and B lymphocytes to stimulate antibody response
Antigen taken up by dendritic cell
Then the antigen is presented to naive T helper cell
T helper cell interacted with B cell
B cell proliferates
Becomes plasma cell
Secreate antibodies
Example: protein
T-independent antigen
NON protein antigen that can stimulate antibody response without T cell help
Ex: polysaccharides and lipids
Antigen types
Metabolites
Sugars
Lipid
Hormones
Macromolecule like complex carbs
Phospholipids
Nucleic acids
Proteins
How does T-independent antigen usually work
A bunch of epitopes that cross link a bunch of B cell receptors
Directly from there the B cell can proliferate
usually IgM, low affinity antibodies; short-lived plasma cells produced
What does Major Histocompatibility Complex do (MHC)
Molecule that displays antigen on T cells
Inheritance pattern of MHC
Codominant expression!
Alleles from both parents are expressed equally amongst children
Typically children won’t have the same inheritance
MHC Ι vs MHC II
I: present antigen to cytotoxic T cells (CD8)
II: present antigen to T-helper cells (CD4)
Cellular expression of Class I MHC
6 types
3 independent domains
Stable
If we want to change, we need to mutate
Some are very diverse!
More diversity, more protection against infection
Cellular expression of Class II MHC
Target extracellular stuff that can’t hide inside cell
they can get microbes that are INTRACELLULAR but they are really good at targeting the extracellular ones
5 isotypes
What cells are good at targeting microbes that are INTRACELLULAR
NK cells
CD8 T lymphocytes
Most polymorphic MHC class I genes
HLA locus A, B
Most polymorphic MHC class II locus
HLA- DRB1
Why is it important that there is polymorphism for antigen processing and transplatation?
You want the most polymorphic loci to be used because it will have the most likely chance to not be rejected by the new host
The more epitopes there are the more we have a chance of recognizing them
Tissue distribution of MHC class I
ALL NUCLEATED CELLS IN BODY
Tissue distribution of MHC class II:
-some activated T cells
-B cells
-macrophages/APC
-thymic epithelial cells
Big function of NK cells
Kill cells that don’t have MHC I
Which MHC has 2 anchors
MHC I
One anchor domain allows for what
Longer peptide to dangle out
MHC II
Exogenous antigen presentation via MHC class II
- Endocytos protein (with antigen) into cell
- Process protein in endosome and lysosome
break it down - At same time in RER
a. ER is making MHC II with CLIP and friends (invariant chain) (CLIP is just a dude filling the hole. His friends make sure no one else fills the hole)
b. MHC II with CLIP goes to golgi
c. From golgi, it is now in a exocytic vesicle
here CLIPS friends leave - Exocytic vesicle with MHC II and CLIP combine with endosome/lysosome that has antigen
- NOW antigen and MHC II are in the same place
as well as HLA-DM
function of this is to accept CLIP does this by catalyses - Antigen fills in hole at MHC II spot
- It is presented on the outside of the cell
Exogenous vs endogenous antigen presentation basics
EXO: antigen presented and created outside cell
ENDO: antigen presented and created inside cell
MHC II do what kind of presentation of antigen
Exogenous
____ is only in antigen presenting cells
Exogenous presentation
MHC I do what kind of antigen presentation
Endogenous
Endogenous antigen processing is used for processing ______
Cytosolic proteins
Endogenous proteins include
Viral gene products
Proteins from phagocytoses microbes
Mutated/altered host cell genes
Endogenous peptide processing steps
- Production of proteins in CYTOSOL
- Transported to proteasome
- Breaks down protein to peptides
- Peptides transported to ER by TAP transporter
- At the same time MHC I and β2m transported to ER
here they form weak connection with TAP and other chaperone molecules
6.Tapsasin forms bridge btw MHC I and TAP
this allows the peptide to enter the peptide binding cleft of MHC I - MHC I gets folded properly and is exported to cell surface
Describe cross presentation
APC can take in either exogenous or endogenous and load it to MHC I
Benefit of cross-presentation
Don’t want APC to get infected
this would effect T cells in the long run
Process of cross presentation
1.Transfer of antigen from Endocytic pathway to cytosol
2. Picked up by proteosome
3. Processed
4. Transported to ER for presentation on class I MHC
Endogenous antigen processing includes
Viral gene products
Proteins from phagocytoses microbes
Mutated/altered host cell genes
Define porphyria
Abnormal build up of heme sythesis intermediates
What is the goal of having haptoglobin and Hemopexin?
They salvage proteins Hb fragments from intravascular hemolysis
(Put in own words)
Where is ALAS1
Liver, and other tissues
