Antibodies and Antigens- Lecture 6 Flashcards
Antibodies are associated with the _____ _____
Humoral response
Antibodies respond to ____ ______ ONLY
extracellular pathogens
Antibodies are produced by B cells as part of _____ _____ ____
ADAPTIVE immune system
What are the 5 main effector functions of antibodies?
- Agglutination (bind pathogens together)
- Neutralization of toxins (similar feature- blocks receptors from binding toxins)
- Activation of complement (to facilitate phagocytosis)
- Opsonization (to facilitate phagocytosis)
- Regulatory properties with production of cytokines (antibody-dependent cellular cytotoxicity) –> Initiates a T cell or inflammatory response
What is the structure of the antibody?
4 chains:
2 light- Kappa or Lambda (one or the other on each Ab)
2 heavy- Alpha, epsilon, gamma, delta, mew (mu)
Describe the 3 components of each chain on an antibody
Fab: binds Ag
Fc carries out effector functions and is found on only heavy chains
Hinges connect Fab to Fc allows binding of two antigens at a time
ALL Abs start as membrane-bound ___ or ___
IgM or IgD
What is the difference between membrane-bound and secretory antibodies?
Membrane-bound:
- Has extra Ch domain
- NO TAIL PIECE
- Includes IgM and IgD (Which are all B cell receptors (BCR’s))
Secretory:
- Tailpiece
- Includes IgE, IgA, and IgG (this can be both secretory and membrane-bound)
Papain verses Pepsin. Describe Papain
Found in papayas!
Cleaves at the hinges
Leaves 2 separate Fab regions and one Fc region
Papain verses Pepsin. Describe Pepsin
Digestive enzyme in humans
Cleaves below hinges
Leaves one Fab region (can bind 2 Ags) and 1 Fc region that dissociates. The Fab region is denoted as F(ab’)2
Note that is you over digest with pepsin then you can get 2 Fab regions
Describe the Ab recognition of Ag
Proteins- In conformational, linear or cut (via proteolysis) forms
Nucleic Acids
Polysaccharides
*Note that T cells can only recognize protein Ags!
Affinity verses Avidity. Describe Affinity
Affinity: How tight an Ag binds to an Ab
Increases with secondary exposure
Affinity verses Avidity. Describe Avidity
Avidity: Strength of an Ag-Ab complex
Depends on affinity and valence
Increases as valence increases
What is valence number?
Valence: Number of ags that can bind to an Ab
Minimum is 2 ags for each Ab
Describe B cell receptors (IgM and IgD) in terms of:
Antigen binding site
Type of antigen that binds
Binding affinity
B Cells:
Antigen binding site: Binds to variable heavy and light chains
Type of antigen that binds: Proteins (can be any conformation), polysaccharides, lipids
Binding affinity: Higher affinity than T cells
Describe T cell receptors in terms of:
Antigen binding site
Type of antigen that binds
Binding affinity
Antigen binding site: Binds to variable alpha and beta
Type of antigen that binds: PROTEIN ONLY (linear only)
Binding affinity: Lower than B cell binding
Pre-B cells will always make __ first
µ
Immature B cells will always make ___ ___ first
Membrane IgM
Mature B cells: produce membrane ____ and ____
IgM and IgD
Actavated B cells can do what?
Maintain membrane IgM, IgD
Form secretory Abs IgA, IgG, and IgE
For Abs secreted by active B cells IgA, IgG, and IgE what determines which one will be made?
Abs determination will be dependent on T cells and the cytokines they produce
What do plasma cells do? And do they need to be activated?
Constant secretion of Abs (secretory only)
Describe Isotype switching. What changes and what stays the same?
Causes change of HEAVY CHAIN Fc portion
Fab stays the same
What does isotype switching require?
Requires cytokines for CD4+ T cells
What are the 3 types of cells that can release cytokines to stimulate isotype swithing?
T cells
Macrophage activating cells
Neutrophils
Describe the Structure, Location, and Stimulating Cytokine for the Ig: IgG (gamma)
Structure: Monomer
Location: Serum- highest in serum, can invade tissues
Stimulating Cytokines: IFN-gamma
Describe the Structure, Location, and Stimulating Cytokine for the Ig: IgM (µ)
Structure: Pentamer with J chain
Location: Serum, naïve B cells
Stimulating Cytokines: IL-2, 4, 5
Describe the Structure, Location, and Stimulating Cytokine for the Ig: IgE (epsilon)
Structure: Monomer
Location: Mast cells
Stimulating Cytokines: IL-4
Describe the Structure, Location, and Stimulating Cytokine for the Ig: IgA (alpha)
Structure: Dimer with J chain + Secretory Component
Location: Mucosal areas- highest in whole body
Stimulating Cytokines: TGF-beta
Describe the Structure, Location, and Stimulating Cytokine for the Ig: IgD (delta)
Structure: Monomer
Location: Naive B cells
Stimulating Cytokines: N/A
What are the 5 functions of IgG (gamma)?
**High in serum** Phagocytosis Can pass between mother and child Can be secreted Highest during secondary response
What are the 5 functions of IgM (µ)?
**Always present first** Complement activation Membrane bound Highest during primary response High avidity- low affinity
What are the 3 functions of IgE (epsilon)?
Allergic response (mast cell activation)
Can be secreted
Acute inflammation and infections by worms
What are the 3 functions of IgA (alpha)?
Mucosal Defense
Can be secreted and can cross endothelial membranes (GI tract as a dimer)
Transferred in breast milk)
What is the function of IgD (delta)?
Only found on B cells
