This presentation gives information about antigen-antibody interaction as a precipitate and a graph related to it.

1. Precipitation in Fluids
Submitted to: Submitted by:
Dr. Payal Mehtani Aparajita Sharma
Associate Professor MSc Biotech 2nd Sem

2. Antigen-Antibody interaction
• A biomolecular association which does not
lead to an irreversible chemical alteration in
either the antibody or the antigen.
• Development of a variety of immunological
assays, which can be used to detect the
presence of either antibody or the antigen.

3. Precipitation reactions in fluids
• Antibody and soluble antigen interacting in
aqueous solution form a lattice that
eventually develops into a visible precipitate.
• Antibodies that aggregate soluble antigens are
called precipitins.
• Formation of an Ag-Ab lattice depends on the
valency of both the antigen and antibody:
the antibody must be bivalent, the antigen
must be either bivalent or polyvalent.

4. Precipitation reactions in fluids yields
a precipitin curve
• A quantitative precipitation reaction can be performed
by placing a constant amount of antibody in a series of
tubes and adding increasing amounts of antigen to the
tubes.
• After the precipitate forms, each tube is centrifuged to
pellet the precipitate, the supernatant is poured off,
and the amount of precipitate is measured.
• Plotting the amount of precipitate against increasing
antigen concentration s yields a precipitin curve.
• In the equivalence zone, the ratio of antibody to
antigen is optimal.

6. • This plot of the amount of antibody precipitated versus
increasing antigen concentration (at constant total
antibody) reveals three zones:
• Zone of antibody excess, in which precipitation is
inhibited and antibody not bound to antigen can be
detected in the supernatant; an equivalence zone of
maximal precipitation in which antibody and antigen
form large insoluble complexes and neither antibody
nor antigen can be detected in the supernatant; and a
zone of antigen excess in which precipitation is
inhibited and antigen not bound to antibody can be
detected in the supernatant.

7. Thank you