Antigens & Antibodies: reactions,
detection, and applications
Introduction
 Adaptive immune responses are not directed against
whole bacteria, protozoa, or viruses, but instead
against portions of cells, viruses, and even parts of
single molecules that the body recognizes as foreign
and worthy of attack.
 These biochemical shapes are called antigens
Adaptive Immunity Crash Course
Antigens & Antibodies
 antigens stimulate the production of one or
more antibodies by white blood cells.

The term originally came from antibody generator
Antigens are “molecules of
attack”. Our bodies
respond to foreign antigens
associated with pathogenic
bacteria/viruses/etc. rather
than the pathogen itself
Antigens & Antibodies
 Antibodies (Ab), or immunoglobulins (Ig), are
large Y-shaped proteins produced by B-cells in
response to the presence of an antigen.
 Antibodies bind to antigens and aid in defense of the
body by neutralizing the pathogens possessing the
antigens that stimulated their production
Actions of Antibodies
Antigens & Antibodies
 Each antibody binds to a specific antigen by way of
an interaction similar to the fit between a lock and a
key.
Antibodies bind to antigens
forming immune complexes
or antibody-antigen
complexes.
Applications
Antigen/Antibody Applications
 Antigens and Antibodies have many uses in Biotech
applications

Medical Diagnostics

Vaccine Production

Locating Cellular Proteins

Immunoprecipitation

ELISA
Medical Diagnostics
 Detection of particular antibodies is a very common
form of medical diagnostics
 In biochemical assays for disease diagnosis, a titer of
antibodies directed against Epstein-Barr virus is
estimated from the blood. If those antibodies are not
present, either the person is not infected, or the
infection occurred a very long time ago, and the B
cells generating these specific antibodies have
naturally decayed.
Medical Diagnostics
 Antibodies raised against human chorionic
gonadotropin (HCG) are used in over the counter
pregnancy tests
 These tests often work by using
immunochromatography to detect the presence of
HCG.
Immunochromotography
Test strips use antibodies to
capture a molecule of
interest (i.e. HCG).
Accumulation of the
molecule of interest causes
a color change on the test
strip, indicating a positive
result.
Vaccine Production
 A vaccine is a biological preparation that improves
immunity to a particular disease.
 Vaccines typically contain an agent that resembles a
disease-causing microorganism
 We can isolate antigenic surface proteins of
pathogens and use them to produce vaccines and
generate immunity.
Locating Proteins
 Antibodies linked to fluorescent molecules can be
used to locate proteins within cells and can be used
to differentiate between cell types based on what
proteins the cells are expressing.
Immunofluorescence image of the
eukaryotic cytoskeleton. Actin filaments are
shown in red, microtubules in green, and
the nuclei in blue.
Immunoprecipitation
 Is the technique of precipitating a
protein antigen out of solution using
an antibody that specifically binds to that particular
protein.
 This is often used to isolate and concentrate a
particular protein from a sample containing many
different proteins.
Immunoprecipitation
ELISA
 Enzyme-linked immunosorbent assay (ELISA)
is a test that uses antibodies and color change to
identify a substance.
ELISA
 Antigens from a sample are attached to a surface
 (usually they are immobilized by binding to embedded antibodies).
 A further specific antibody is applied over the surface so it can
bind to the antigen.

This antibody is linked to an enzyme
ELISA
 In the final step, a substance containing the
enzyme's substrate is added. The enzymes reaction
with its substrate produces a detectable signal, most
commonly a color change in the substrate
ELISA
ELISA
 The ELISA can been useful as a diagnostic tool in
medicine to check for the presence of certain
antigens
 ELISA is also often used for quality-control in
various industries (i.e. ELISA can be used to check
for the presence of allergens in food).