short notes

1. ANTIBODY AFFINITY:
 Affinity measures the strength of interaction between an epitope
and an antibodys antigen binding site
 It is the sum of the attractive and repulsive forces between them
 Affinity is the equilibrium constant that describes the antigen
antibody reaction
 Antibody affinity is measured as Ka
KA = affinity constant
[Ab] = molar concentration of unoccupied binding sites
on the antibody
[Ag] = molar concentration of unoccupied binding sites
on the antigen
[Ab-Ag] = molar concentration of the antibody-antigen
complex
 A low affinity antibody binds the concerned antigen weakly
and it tends to dissociates readily
 A high affinity antibody binds the concerned antigen more
tightly and tends to reamin longer
ANTIBODY AVIDITY:
 Avidity gives a measure of the overall strength of an antibody-
antigen complex.
 It is dependent on three major parameters:

2.  Affinity of the antibody for the epitope
 Valency of both the antibody and antigen
 Structural arrangement of the parts that interact
 All antibodies are multivalent e.g. IgGs are bivalent and
and IgMs are decavalent.
 The greater an immunoglobulin’svalency (number of antigen
binding sites), the greater the amount of antigen it can bind.
 Similarly, antigens can demonstrate multivalency because they
can bind to more than one antibody.
 Multimeric interactions between an antibody and an antigen
help their stabilization.
 High avidity can compensate for low affinity
PentamericIgM has a lower affinity than IgG but has a higher avidity
than IgG due to its multivalence