Antibodies Flashcards
What secondary effector functions do antibodies initiate? (3)
Complement activation, opsonisation and cell activation via specific antibody binding receptors
Which end is the amino terminus and which end is the carboxyl terminus of an antibody?
The carboxyl is closest to the constant region, amino furthest from constant region
How are the four polypeptide chains of an antibody held together?
Disulphide bridges
Are antibodies symmetrical?
YES
Which is Fab and which is Fc?
The constant part of the two heavy chains is Fc, the variable regions are Fab
Are antibodies flexible? Why?
Yes so they can bind to many widely or narrowly spaced epitopes
What regions do both light and heavy chains have?
Constant and variable
Which part of the antibody is the antigen binding site?
The variable region
What are immunoglobulin domains?
Internal intrachain disulphide bonds
What does the Fc part do?
Undergoes conformational changes when antigen binds, and can perform effector functions such as activating complement
What are the three hyper variable regions called?
Complementarity Determining Regions (CDR)
Where are the CDR and what do they do?
At the end of the protein/line up at the end of the V domain and interact with antigen
What is antibody affinity?
The strength of the total non-covalent interactions between a single antigen-binding site and a single epitope on an antigen
What is antibody avidity?
The overall strength of multiple interactions between an antibody with multiple binding sites and a complex antigen with multiple epitopes
What is antibody cross reactivity? Example?
Antibodies produced in response to one antigen can cross-react and bind to a different antigen of similar structure, e.g. cowpox vaccine working for smallpox
What is difference in different classes of antibodies?
The constant regions of their heavy chains vary
What are the five classes?
IgG, IgA, IgM, IgD, IgE
Which classes of immunoglobulin have subclasses?
IgG and IgA
What are the two types of light chain?
Kappa and lambda
Which classes have three constant heavy domains?
IgG, IgA, IgD
Which classes have four constant heavy domains?
IgM and IgE
How many subclasses in IgG?
4
How many subclasses in IgA?
2
What is the difference in subclasses? (3)
Variance in the hinge region (e.g. loads of disulphide bonds between the heavy chains), ability to activate complement (IgG4 doesn’t) and effector function domains
Which is the only class of immunoglobulins that can move across the placenta?
IgG
Which is class of immunoglobulins is a major activator of the complement pathway?
IgG
Which is the most abundant class of immunoglobulins?
IgG
What are the subclass numbers representative of?
Abundance, 1 being the most abundant
What is the difference between IgA in blood and scripted?
Monomer in blood, dimer in secretions
Main function of IgA?
Protect mucosal surfaces
Which is the second most abundant class of immunoglobulins?
IgA
What produces IgA?
Plasma cells (activated B cells)
Describe the process of IgA secretion
The IgA is produced by a plasma cell (activated B cell) and then binds to the Poly-Ig Receptor on the basolateral membrane of the epithelial cell. The poly-Ig receptor is cleaved which leaves the secretory component attached to the dimeric IgA.
What does the secretory component of a secreted IgA dimer do?
Helps protect the secreted antibody from degradation
What is the stand out feature of IgM?
Pentameric
Which is the first Ig produced after exposure to an antigen?
IgM
What are IgM useful for?
Agglutination
Can IgM activate complement?
Yes
What is the problem with IgD?
Not useful for fighting infection directly
What is the main purpose in IgD?
Involved in B cell development and activation
What is IgE useful for?
Fighting parasitic infections and allergic disease
What does IgE bind to?
High affinity Fc receptors of mast cells and basophils
What does IgE do?
Triggers mast cell activation and histamine release. Fc part binds to mast cell, allergen binds to Fab and triggers mast cell activation and histamine release.
What are atopic individuals?
Individuals more susceptible to making IgE and having allergic reactions
Which antibodies are generally found in blood?
IgG and IgM
Which antibodies are generally found in extracellular fluids?
IgG
Which antibodies are generally found in secretions?
IgA
Which antibodies are generally found in the foetus?
IgG
Which antibodies are generally found in mast cells below epithelia?
IgE
What type of antibodies do NK cells work well with?
IgG
