(Section B: Immunology) Lecture 16: B Cell Immunity I Flashcards
(43 cards)
Antibodies
- Soluble polypeptide molecules manufactured and secreted by B cells
- Have neutralizing or cytotoxic activities (cell or complement-mediated)
- Can recognize any substance
- Enormous medical and commercial importance
What are antibodies technically?
Secreted form of B Cell Receptor
How does an antibody differ from a membrane-bound version of the BCR?
Membrane-bound BCRs have a hydrophobic segment to bind to membrane
Antibodies have a hydrophilic segement so that they are soluble
BCR Structure
- 2 heavy chains
- 2 light chains
Linked together by disulfide bonds
What are the areas of the BCR receptors/antibodies?
- Variable Region
- Hinge
- Constant Region
What can BCRs/Antibodies be modified by?
By carbohydrates
What variety of the protein components can there be in BCRs/antibodies?
Light Chain:
* κ, λ
Heavy Chain:
* μ, γ, α, δ, ε
What is the antigen binding region of BCRs/antibodies?
The light and heavy chains working together
What does Fab and Fc stand for?
Fab: Fragment Antigen Binding
Fc: Fragment Crystallization
What does the hinge in the BCR/antibody structure allow for?
Allows for flexibility
How are antibody types determined?
They are determined by the heavy chains
What gene determines the antibody class?
The heavy chain constant region (C gene segments)
IgM Structure
2 binding sites as monomers
* 10 binding sites as pentamers
What is the purpose of IgM?
First class produce by B cells (primary response)
* C1q binds to IgM to start classical complement pathway
* Opsonization by IgM enhances phagocytosis
What are the two conformations of IgM?
- Planar
- Staple
True or False:
IgM cannot bind to pathogens in planar conformation
False, they can bind to pathogens in planar or staple conformation
IgD Structure
2 Binding sites
IgD Function
Main function is to bind antigen as BCR
* Only 0.2% of circulating antibodies
* Function is not well understood
What antibodies do Immature B cells express?
IgM and IgD BCR at the same time
IgG Structure
2 binding sites
Subclasses:
1. IgG1
2. IgG2
3. IgG3
4. IgG4
IgG Function
- Most abundant antibody type in serum (plasma)
- Long-lived
- Efficient at activation of phagocytosis
- Efficient at activation of complement
IgA Structure
Exists in monomer form (2 binding sites)
* Exists predominantly in dimeric form in secretions (4 binding sites)
Subclasses:
* IgA1
* IgA2
IgA Function
- Mainly present in secretions (saliva, mucus of the gut, tears and breast milk etc.)
- Can be found in low lwevels in circulation
- Does not opsonize cells or activate complement
- Neutralizes pathogens and toxins
How does IgA work in the gut?
IgA is transported into the gut through the epithelial cells
