INTRODUCTION AND DEFINITION OF ANTIGEN AND ANTIBODY REACTION WITH THEIRE TYPES.

1. SHRI SHANKRACHARYA COLLEGE OF NSG.
HUDCO, BHILAI
SEMINAR PRESENTATION
ON
Antigen-Antibody Reaction
Presented By:- Guided By:-
Mrs. Biji Ramesh
Lecturer SSCN
SESSION
2013-14

2. Precipitation reaction
Agglutination reaction
Complement fixation test
Immunofluorescence
Immunoblotting
Neutralization test

3. An antigen has been defined as any
substance which, when introduced
parenterally into the body, stimulates
the production of an antibody with
which it reacts specifically and in an
observable manner.

5.  Antigen-antibody reactions have the
following general characteristics:
 The reaction is specific, an antigen combing
only with its homologous antibody and vice
versa.
 Entire molecules react and not fragments.
When an antigenic determinant present in a
large molecule or on a ‘carrier’ particle
reacts with its antibody, whole molecules or
particles are agglutinated.

6. 3. There is no denaturation of the antigen or the
antibody during the reaction.
4. The combination occurs at the surface.
Therefore, it is the surface antigen that are
immunologically relevant.
5. The combination is firm but reversible. The
firmness of the union is influenced by the
affinity and avidity of the reaction.
6. Both antigens and antibodies participate in the
formation of agglutinates or precipitates.
7. Antigens and antibodies can combine in varying
proportions, unlike chemicals with fixed
valencies.

7.  SENSITIVITY:- Sensitivity refers to the ability
of the test to detect even very minute quantities
of antigen or antibody.
 SPECIFICITY:- Specificity refers to the ability
of the test to detect reactions between
homologous antigens and antibodies only, and
with no other.

8.  Precipitation reaction:- When soluble antigen
combines with its antibody in the presence of
electrolytes (NaCl) at a suitable temperature
and pH, the antigen-antibody complex forms
an insoluble precipitate.
 MECHANISM OF PRECIPITATION:-
According to Marrac (1934) multivalent
antigens combine with bivalent antibodies in
varying proportions, depending on the
antigen-antibody ratio in the reacting mixture.

9.  Types of precipitation test:-
1. Ring test- This, the simplest type of
precipitation test, consists of layering the
antigen solution over a column of antiserum in
a narrow tube, a precipitate forms at the
junction of the two liquids.
2. Slide test- when a drop each of the antigen and
antiserum are placed on a slide and mixed by
shaking, floccules appear. The VDRL test for
syphilis is an example of slide flocculation.

10. 3. TUBE TEST- A quantitative tube flocculation
test is employed for the standardization of
toxins and toxoids. Serial dilutions of the
toxin/toxoids are added to the tubes
containing a fixed quantity of the antitoxin.
4. IMMUNODIFFUTION (PRECIPITATION
IN GEL)- There are several advantages in
allowing precipitation to occur in a gel
rather than in a liquid medium. The reaction
is visible as a distinct band of precipitation,
which is stable and can be stained for
preservation, if necessary. As each antigen-
antibody reaction gives rise to a line of
precipitation, the number of different
antigens in the reacting mixture can be
readily observed.

11.  When a particulate antigen is mixed
with its antibody in the presence of
electrolytes at a suitable temperature
and pH, the particles are clumped or
agglutinated.
 Agglutination is more sensitive than
precipitation for the detection of he
antibodies.

12.  SLIDE AGGLUTINATION- When a drop
of appropriate antiserum is added to a
smooth, uniform suspension of a
particulate antigen in a drop of saline on a
slide or tile, agglutination takes place.
 TUBE AGGLUTINATION- When a fixed
volume of a particulate antigen suspension
is added to an equal volume of serial
dilution of an antiserum in test tubes, the
agglutination titre of the serum can be
estimated.

13.  THE ANTIGLOBULIN (COOMBS)
TEST- The antiglobulin test was
devised by coombs, mourant and Race
(1945) for the detection of the anti-Rh
antibodies that do not agglutinate Rh
positive erythrocytes in saline.
 PASSIVE AGGLUTINATION TEST-
By attaching soluble antigens to the
surface of carrier particles, it is possible
to convert precipitation test into
agglutination test. which are more
convenient and more and more sensitive
for detection of antibodies. Such tests are
known as passive agglutination test.

14.  The ability of activated complement to lyse
RBCs is made use of in complement fixation
test for detection of antibodies or antigens.
This reaction is not visible. An indicator
system is used to detect the fixation of
complement. This indicator system consists of
sheep erythrocytes coated with amboceptor
(rabbit antibody to sheep RBCs).

15. PROCEDURE
The first step consists of adding antigen to serial
dilutions of patients serum followed by
complement. It is then incubated for one hour.
In the second step, the indicator system s added to
the mixture and is again incubated at 37 degree
Celsius for one hour after which haemolysis is
observe.

17.  VIRUS NEUTRALISATION TESTS:
Neutralization of bacteriphages can be
demonstrated by the plaque inhibition test.
When bacteriophages are seeded in
appropriate dilution on lawn culture of
susceptible bacteria, plaques of lysis are
produced. Specific antiphage serum inhibits
plaques information. Neutralisation of animal
viruses can be demonstrated in three systems-
animals, eggs and tissue culture.

18.  TOXIN NEUTRALISATION: Toxin
neutralisation can be tested in vivo or in
vitro. Neutralization tests in animals
consists of injecting toxin-antitoxin
mixture and estimating the least amount
of antitoxin that prevent death or disease
in animals.

19. PRESESNTED BY:- PRAFULL PAL