Agglutination is the clumping or clustering of antigens by antibodies. It occurs when antibodies bind to particulate antigens in equivalent proportions, causing the antigens to crosslink and aggregate. Better agglutination is seen with IgM antibodies than IgG antibodies. Agglutination involves antigen-antibody binding at the zone of equivalence according to the lock-and-key principle. This binding leads to the formation of a visible lattice structure as antibodies crosslink multiple antigen molecules.

1. AGGLUTINATION

2. AGGLUTINATION REACTIONS
 The interaction between antibody and a particulate antigen results in visible clumping called
agglutination.
 Antibodies that produce such reactions are called agglutinins. Better agglutination takes place with
IgM antibody than with IgG antibodies.
 Excess of an antibody also inhibits agglutination reaction; this inhibition is called prozone
phenomenon.
 Agglutination is more sensitive than precipitation for the detection of antibodies.
 Agglutination occurs optimally when antigens and antibodies react in equivalent proportions.

3. PRINCIPLE OF AGGLUTINATION REACTION
 The principle of agglutination reaction is based on the “Clumping of antigen and antibody”.
 Like precipitation reaction, it also involves the binding of antigen and antibody at the zone of
equivalence, where both are present in equal proportion.
 As the antibodies are y-shaped structure and there are two Fab sites made of “Hypervariable
region” will target the specific antigenic determinants or epitopes of an antigen.
 The binding of antigen and antibody is similar to the “Lock-key model”.
 Therefore, the epitopes of an antigen are the key which fits into the cleft of the Fab sites of the
antibody that works as a lock.

5. STEPS OF
AGGLUTINATION
 Sensitization: It can define as the
primary stage where binding of antigen
and antibody takes place. Temperature,
pH, ionic strength and incubation period
influence the efficiency of sensitization or
binding. Sensitization is not a visible
reaction.
 Lattice formation: It can define as the
secondary stage where the antibody and
multivalent antigen forms a Stable
network refers as “Lattice”. A lattice is a
net-like configuration which consists of a
network between sensitized antigen and
antibody. It takes much time to occur than
that of sensitization. Lattice is a visible
reaction.