The document discusses antigen-antibody reactions. Antigens induce an immune response and antibodies neutralize pathogens. Antigen-antibody reactions occur specifically between antigens and antibodies. These reactions form the basis of immunity and are used in blood banking. The reactions occur in three stages - antigen-antibody complex formation, visible events like precipitation or agglutination, and antigen destruction or neutralization.

2. Antigen Antibody Reactions
• Antigen:A toxin or any foreign substance
which induces an immune response in the
body, especially the production of antibodies.
Antibodies:
An antibody (Ab)is a protein produced mainly
by plasma cells that is used by the immune
system to identify and neutralize pathogens
such as bacteria and viruses etc.

3. INTRODUCTION:
• The antigens and the antibodies combine specifically
with each other. This interaction between them is
called Antigen-Antibody reaction.
• It may be abbreviated as Ag – Ab reaction.
• These form the basis for immunity
•Reactions observed in Blood banking

4. • When Ag – Ab reactions occur in vitro, they are
known as serological reactions.
• The reactions between Ag and Ab occur in three
stages.
In first stage the reaction involves formation of
Ag-Ab complex. Sensitization.
The second stage leads to visible events like
precipitation, “agglutination .
The third stage includes destruction of Ag or its
neutralization “Hemolysis.

5. Binding Site of Antigen – Antibody Reaction:
• In antigen - antibody reaction, the antibody attaches
with the antigen.
• The part of antigen which combines with antibody is
called Epitope.
• An epitope, also known as antigenic determinant, is
the part of an antigen
•The part of an antibody that recognizes the epitope is
called a paratope.

6. Agglutination & Haemolysis
Agglutination is the formation of aggregates of
particles,
e.g. Red blood cells that bear antigenic
determinants (epitope) on their surface and
combine with the antibodies present in the test
serum.
Can observed (ABO grouping) and indirect
techniques (antiglobulin procedures). :

7. Agglutination occurs in two stages
• Sensitization
• Zeta Potential
Antigen and Antibody to Show Epitope And
Paratope

8. Agglutination occurs in two stages:
Sensitization:
The antibody attaches itself specifically to the
polysaccharide/lipid/protein complexes that form
the antigen sites on the red cell.
Requires proper temperature,
ph and ionic Strength of the medium and
antigenantibody Ratio.

9. Clump formation:
• The second phase is the physical process of
Agglutination, in which cells come together
• To form clumps. This depends upon the type
of antibody involved, the antigen sites
available and the zeta‘ potential of the
medium in which the cells are suspended.

10. Zeta Potential:
• Red cells, when in a suspension, carry a negative
charge on their surface These charges serve to repel
the adjacent cells to avoid sledging. When the cells
are suspended in an electrolyte solution,This
determines the effective charge of the red blood cells
and is designated as the zeta potential.

11. Zeta Potential:
• In order to bring an antibody close to the
surface of the cell, this potential has to be
reduced. Even those antibodies that do not
exhibit agglutination normally can do so if this
potential is reduced.

12. Proteolytic Enzymes
• The enzymes that are used to enhance antigen-
antibodyreactions include papain, ficin and
bromelin.
• They also remove structures on the red cells
membranes, so as to facilitate the interaction of
the antibody with the corresponding antigen. The
red cell antigens that are enhanced by enzymes
include Rh,Kell, Kidd & Lewis blood groups.
Certain red cell antigens, including Duffy (Fy) and
M, N,S destroyed by enzymes.

13. Albumin:
• It is prepared from bovine sources and is
commercially available as a 22%
• preparation. Over time, the use of albumin
has been abandoned by many blood
banks,due to the availability of better
potentiators like LISS and Polyethylene Glycol.

14. LISS
Low-Ionic Strength Saline is widely used in
blood banks as an enhancing medium. The
incubation time is shortened to 10 minutes and
most antibodies are well detected by this
technique..
PEG (Polyethylene Glycol):
It potentiates agglutination by taking out water
in hydration, thus binding the cells together and
enhancing second-stage agglutination.

15. Assignment
• Reading & Interpreting agglutination
Reactions and Hemolysis

16. Haemolysis:
This is an important antigen-antibody reaction that results in
the lysis of cells. Free haemoglobin‘s red colour is an important
end point of an antigen-antibody reaction.
Haemolysis is a positive result that indicates the presence of a
complement activating antibody.
A haemolytic reactionoccurs in two stages:
1. The antibody combines with the antigen, thus sensitizing the
red cell.
2. Sensitized red cells lyse with the help of activated
complement components.

17. The chief use of antigen-antibody reactions are:
• Determination of blood groups for transfusion.
• Serological exposure to infectious agents.
• Development of immunoassays for the
quantification of various substances.
• To detect the presence or absence of protein in
serum.
• Determining the characteristics of certain immuno-
deficiency disease.
Application of Antigen – Antibody Reaction:

18. Conclusion:
we conclude up this topic with a quick review about
Antigen – Antibody Reaction.
The antigens and the antibodies combine specifically
with each other. This interaction between them is
called Antigen-Antibody reaction.

19. Thank
You