Polyclonal and Monoclonal antibodies
• Antibodies that arise in response to typical antigens
are heterogeneous, because they are formed by
several different clones of plasma cells; i.e., they
are polyclonal.
• Antibodies that arise from a single clone of cells, e.g.,
in a plasma cell tumor (myeloma), are homogeneous;
i.e., they are monoclonal.
• Monoclonal antibodies can also be made in the
laboratory by fusing a myeloma cell with an
antibody-producing cell. Such hybridomas
produce virtually unlimited quantities of monoclonal
antibodies that are useful in diagnostic tests and
in research.
• Hence, hybridoma are hybrid cell culture formed
of antigen sensitised cells, fused with myeloma
cancerous bone marrow cells for indefinite
production of monoclonal antibodies.
• Monoclonal antibodies are used in immuno-
assay.
• They are also used to detect the hormones present in
urine (pregnancy test kits), in detecting drugs in urine
(for athletes) and in detecting HIV virus.AntIgen-AntIBody InterACtIon
• Interaction between antigen and antibody involves
non-covalent binding of an antigenic determinant
(epitope) to the variable region (complementary
determining region, CDR or paratope) of both heavy
and light immunoglobulin chains.
• Antibodies bind to antigen forming antigen-antibody
complex using the following methods:
(a) Neutralization : Antibodies completely surround
the pathogen and block its attachment sites,
rendering the pathogen harmless.
(b) Agglutination : More than one bacteria and many
antibodies form clumps, due to cross-linking of
antibodies, thus making it easier for macrophages
to target and destroy.
(c) Activation : Uses complement proteins (non-
specific defense) forming membrane-attack
complex (MAC) that embeds itself into the
plasma membrane of the pathogen. Salts enter the
pathogen, facilitating water to cross the membrane,
thereby swelling and bursting the pathogen.
ACtIvAtIon of AdAptIve/ACquIred
ImmunIty
• Every antigen is scanned by antigen presenting cells
like macrophages, B-lymphocytes, etc. The processed
antigen is present on the surface of these cells.
• After a microbe or non cellular antigen gets
phagocytosed by a macrophage or dendritic cell in
non specific response, it is partially broken into smaller
peptide fragments by cell’s proteolytic enzymes.• The resulting digested fragments then bind to class
II MHC proteins synthesized by the cell.
• This entire complex is then transported to the cell
surface, where it is displayed on the plasma membrane
to this complex.
• Specific helper T-cells bind to this complex.
• This is the link between non-specific (innate) immune
response and specific (adaptive) immune response.