Antibodies Flashcards
What are the three secondary effector functions of antibodies once bound to antigens?
Opsonisation
Complement activation
Cell activation (e.g. mast cells)
Which immunoglobulin category do antibodies fall into?
Gamma immunoglobulins
What type of bond holds together the chains in the immunoglobulin?
Disulphide bonds
What is an immunoglobulin domain?
Internal intrachain disulphide bond
What did scientists find when sequencing the amino acid sequence of the variable region on antibodies?
There are three hypervariable regions called the complementarity determining regions
What part of the variable region of the antibody binds to the antigen?
The complementarity determining regions are found at the end of the variable regions and interact with antigens
What forces are involved in antibody-antigen binding?
THEY ARE ALL NON-COVALENT
Hydrogen bonding, ionic bonding, van der waals, hydrophobic interactions
Define affinity.
The strength of the total non-covalent interactions between a single antigen-binding site and a single epitope
What equation shows affinity mathematically?
K = [Ab-Ag]/[free Ab][free Ag]
Define avidity.
The overall strength of the multiple interactions between an antibody with multiple binding sites and a complex antigen with multiple epitopes
What is antibody cross-reactivity? Give an example.
Antibodies that are produced in response to one antigen can cross-react and bind to a different antigen with a similar structure. E.g. cow pox and small pox
What are isotypes and allotypes of antibodies?
Isotypes vary in the constant regions – everyone has isotypes
Allotypes – polymorphic variables – some people have them others don’t
How do the different classes of antibodies (GAMED) differ?
They vary in the constant region of their heavy chain
What are the two classes of light chain?
Kappa and lambda
Which immunoglobulin classes have subclasses and how many subclasses do they have?
IgG = 4 (in order of abundance – 1 is the most abundant) IgA = 2
How do the different subclasses vary?
They vary in the hinge region
Describe the formation of secretory IgA.
Dimeric IgA is produced by plasma cells
It binds to the Poly-Ig receptor on the basolateral surface of the epithelia
This binding stimulates endocytosis
Once inside the cell, the poly-Ig receptor is cleaved and the dimeric IgA is secreted with the secretory component
The secretory component is derived from the poly-Ig receptor
How can IgE activate cells?
It binds to the Fc (Fc-epsilon-RI) receptor on mast cells
When antigens bind to the IgE, which is attached to the mast cell, it stimulates degranulation
Which two Ig classes are mainly responsible for activating complement?
IgM and IgG
