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Immunology and Serology (DVT2153)

Antigen-Antibody Interactions (Lecture)_Week VI Lecture

By: Dr. Erkihun Aklilu

12 March 2012

Universiti Malaysia KelantanFaculty oF veterinary medicine

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Antigen-Antibody Interactions

The binding of antibody to antigen is a reversibleprocess, involving non-covalent bonds

The specific association of antigens and antibodiesis dependent on:

Hydrogenbonds

hydrophobic interactions,

electrostatic forces, and

van der Waals forces.

It is a reversible reaction

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Antigen-Antibody Interactions

The law of mass actionAt the beginning, a chemical reaction proceeds

predominantly in one direction, but the reverse rateprogressively increases until the forward and reverse speedsare equal. At this point, the reaction is said to have reachedits equilibrium.

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Antigen-Antibody Interactions

FIGURE- Precipitation reactions in fluids yield a precipitin curve.

( Lattices or large aggregates )

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Antigen-Antibody Interactions

Antigen-Antibody Interaction involves various non-covalent interactions between the epitope of theantigen & the variable-region (VH/VL) domain of theantibody molecule.

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Antigen-Antibody Interactions

Terminologies

Affinity: Is the strength of the reaction betweena single antigenic determinant and a singlecombining site on the antibody.

Avidity: Is a measure of the overall strength ofbinding of an antigen with many antigenicdeterminants and multivalent antibodies.

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Antigen-Antibody Interactions

Specificity:-The ability of an individual antibodycombining site to react with only oneantigenic determinant

OR

-The ability of a population of antibodymolecules to react with only one antigen.

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Antigen-Antibody Interactions

Cross reactivity: the ability of an individualantibody combining site to react with morethan one antigenic determinant or the ability ofa population of antibody molecules to reactwith more than one antigen.

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Antigen-Antibody Interactions

Factors Affecting Antigen-AntibodyReactionsFactors acting on the equilibrium constant

- Temperature- pH- Ionic strength- Enzyme treatment of red cells

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Antigen-Antibody Interactions

Other factors

- Concentrations of antigen and antibody- Zygosity (number of antigen sites per cell)- Duration of incubationFactors affecting the antigen-antibody reaction.pdf