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

Introduction

ANTIGEN-ANTIBODY INTERACTIONS

• Antigen and antibody binds when they are specific to each others.
• The non covalent interactions that form the basis of antigen (Ag) and antibody (Ab) binding include hydrogen bonds, ionic bonds, hydrophobic interactions and vander Waal’s interactions.
• These interactions are weaker when compared to covalent bonds and hence a large number of such interactions are required to form a strong Ag-Ab interaction.
• The combined strength of the non-covalent interactions between a single Ag binding site on an antibody and a single epitope is the affinity of the antibody for that epitope.
• The association between a binding site on an antibody with a monovalent Ag can be described by the equation:

• K₁ -  forward (association) rate constant 
• K _-1 - reverse (dissociation) rate constant.
• K₁/K _-1 - association constant Ka, a measure of affinity.
• Avidity is the strength of Ag-Ab binding when multiple epitopes on an antigen interact with multiple binding sites of an antibody.
• The measurement of Ag-Ab interactions for diagnostic purposes is known as serology.