IMMUNOCHEMISTRY
PREPARED BY MR. ABHIJIT DAS
IMMUNOGLOBULINS:
Immunoglobulins, also
known as antibodies, serve as vital components within the body's defense
mechanisms.
They're made by special cells called plasma cells, which come from another type of cell
called B lymphocytes, or B cells.
These antibodies are super important because they
help our body recognize and fight off pathogens like
bacteria, viruses, and toxins.
STRUCTURE OF IMMUNOGLOBULINS:
1. The
structure of immunoglobulins comprises a tetrapeptide
framework composed of two heavy chains and
two light chains, interconnected
by disulfide bonds.
2. Within this structure, there exists an antigen-binding site formed at the junction between a segment of the heavy chain and a portion of the light chain.
3. This
arrangement enables the specificity of
antibodies, ensuring that each antibody will selectively bind to a particular
antigen.
FUNCTIONS OF IMMUNOGLOBULINS:
1.
Neutralization:
Immunoglobulins can bind to viruses, bacteria, and toxins, preventing them from infecting cells or causing harm.
2.
Opsonization:
They coat pathogens, marking them for destruction
by immune cells such as macrophages and neutrophils.
3.
Activation of complement:
Immunoglobulins can trigger the complement cascade,
leading to the destruction of pathogens by forming pores in their membranes.
4.
Maternal immunity:
Maternal antibodies, primarily IgG, are
transferred to the fetus during pregnancy and provide temporary protection
against infections until the newborn's immune system matures.
5.
Mucosal immunity:
Immunoglobulins, particularly IgA, play a
crucial role in protecting mucosal surfaces such as the respiratory, gastrointestinal,
and urogenital tracts by neutralizing
pathogens before they can penetrate tissues.
6.
Allergic reactions:
Immunoglobulin E (IgE) is involved in
allergic reactions by binding to allergens and triggering the release of histamine and other inflammatory mediators from mast cells.
ENZYME LINKED IMMUNO SORBENT ASSAY (ELISA):
DIRECT ELISA:
Ø First,
the antigen is supplied and sticks to the surface.
Ø Then,
enzyme-linked antibodies specific to the
antigen is added.
Ø This
enzyme produces a colorful product when a substrate is added.
Ø If
the antigen is present, the color change is detected, indicating its presence.
Advantage:
simple and quick.
Disadvantage:
sometimes it may produce a weak color change that's
hard to detect, especially when the concentration of the target antigen is low.
INDIRECT ELISA:
Ø The
antigen is supplied and sticks to the surface.
Ø Then,
specific primary antibodies to the antigen
are added.
Ø After
washing, secondary antibodies linked to an
enzyme are added. These secondary antibodies bind to the primary antibodies.
Ø An
enzyme reaction produces a colorful product when a substrate is added.
Ø The
intensity of the color change indicates the presence of the antigen, amplifying
the signal for detection.