VMC 221: Veterinary Immunology and Serology (1+1)

Agglutination tests

INTRODUCTION- AGGLUTINATION TESTS

• The interaction between antibody and a particulate antigen results in visible clumping called agglutination.
• Antibodies that produce such reactions are called agglutinins. IgM is more efficient than IgG in causing agglutination.
• Agglutination reactions are similar in principle to precipitation reactions; they depend on the cross linking of polyvalent antigens.
• Antigen and antibody must be present in correct proportion (Zone of equivalence) for agglutination to occur.
• Just as an excess of antibody inhibits precipitation reactions, such excess can also inhibit agglutination reactions. This inhibition is called the prozone effect.
• The causes of prozone effect are
  • In antibody excess, each antigenic particle may be so coated by antibody that agglutination is inhibited.
  • Presence of non agglutinating antibodies called incomplete antibodies.
• The lack of agglutinating activity of such antibodies may be because of the restricted flexibility of the hinge region and or the epitopes that they bind lie deep with in the antigen.
• For detecting presence of non agglutinating antibodies on the surface of particles a direct antiglobulin test may be used. 
• The washed particles are mixed with antiglobulin and if immunoglobulins are present, agglutination will occur.
• Post zone effect is seen when antigens are present in excess.
•   Agglutination does not occur in prozone and post zone.