Antibodies

Question 1

define antibody

Answer 1

specific protein produced in response to an antigen

Question 2

How can antibodies bind to both closely and widely spaced cell surface determinants?

Answer 2

flexibility at hinge region

Question 3

What forces are involved in antigen antibody binding? Why are there many point of interaction?

Answer 3

hydrogen bonds, ionic, hydrophobic, vanderwaals

individually weak bonds

Question 4

define antibody affinity

Answer 4

strength of total non-covalent interactions between single antigen binding site and single episode on the antigen

Question 5

define antibody avidity

Answer 5

the overall strength of multiple interactions
between an antibody with multiple binding sites and
a complex antigen with multiple epitopes

Question 6

Is antibody avidity or affinity a better measure of binding capacity?

Answer 6

avidity

Question 7

define antibody cross reactivity

Answer 7

Antibody elicited in response to one antigen can sometimes recognise a different antigen of similar structure

Question 8

How do different classes of antibodies differ?

Answer 8

constant region of heavy chains

Question 9

Name the different classes of antibodies and their heavy chain

Answer 9

IgG - gamma
IgA - alpha
IgM - mu
IgD - delta
IgE - epsilon

Question 10

Give characteristics of IgG

Answer 10

most abundant Ig
4 subclasses
actively transported across placenta
major activator of classical components pathway 
in blood and EC fluid

Question 11

Give characteristics of IgA

Answer 11

second most abundant
occurs as monomer in blood, dimer in secretions
protects mucosal surfaces

Question 12

How is secretory IgA formed

Answer 12

plasma cell secretes dimeric IgA which binds to poly -Ig receptor on epithelial cell
endocytosis into cell
enzymatic cleavage
release into lumen

Question 13

Give characteristics of IgM

Answer 13

pentameric molecule
mainly in blood
first Ig synthesised after antigen exposure
multiple binding sites
low affinity 
effect at agglutination
activate complement

Question 14

Give characteristics of IgD

Answer 14

low serum concentration
involved in B cell development and activation
surface IgD
expressed early in B cell development

Question 15

Give characteristics of IgE

Answer 15

present at very low levels
produced in response to parasites and allergies
binds to high affinity Fc receptors of mast cells and basophils
triggers mast cell activation and histamine release

Question 16

What are the consequences of antigen antibody binding

Answer 16

neutralisation, agglutination, opsonisation, complement activation, bids to cells expressed Fc receptors