Antibodies, also known as immunoglobulins, are Y-shaped glycoproteins produced by plasma cells that bind to pathogens and toxins. They have two functions: recognition and binding of foreign substances, and triggering their elimination. Each antibody consists of two heavy chains and two light chains that form regions for binding antigens (Fab) and initiating immune responses (Fc). There are five classes of heavy chains that determine the isotype: IgM, IgG, IgA, IgE, and IgD. Structural differences in antibodies lead to differences in effector functions and polymerization state.

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2. Content
Introduction on antibody
Its structure
Reference
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3. 3
• Antibodies are immune system-related proteins also called immunoglobulins.
• Y-shaped glycoproteins produced by differentiated B-cells called plasma cells.
They are present in bodily fluids, secretions and on the surface of B-cells.
• Bind pathogenic microorganism and their toxins in extracellular
compartments
• The binding of antibodies to microorganisms or other such antigens can result
in the microorganism being immobile or preventing them from penetrating the
cells
• Antibodies carry out two principal functions in the immune system. The first
function is the recognition and binding to foreign bodies. The second more
important function is to trigger the elimination of the attached foreign
material.
Introduction on antibody
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4. 4  Structure of an antibody
a) Teach me Physiology
b) The biology project
c) Encyclopedia Britannica, Inc.
Image Source:
a) 3D illustration of antibody structure
b) Basic structure of antibody
c) Schematic structure of an antibody
a)
b) c)
Figure
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• Each antibody consists of four polypeptides– two heavy chains and two
light chains joined to form a "Y" shaped molecule.
• It is composed of a variable region and a constant region. The variable
region changes to various structures depending on the differences in the
antigens. The constant regions are constant and do not change with
antigens.
• Each heavy chain is connected to a light chain by a disulfide bond, and the
two heavy chains are connected to the light chains by two sulfide bonds.
• The Fab regions (fragment antigen binding) contain
the variable domains of the light and heavy chains. The Fc
region (fragment crystallisable) consists of the remaining constant
domains from the two heavy chains.
 Structure of an antibody
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• There are five different types of heavy chains in mammals that are μ (Mu), γ (Gamma), α
(Alpha), ε (Epsilon) and δ (Delta), which classify IgM, IgG, IgA, IgE and IgD respectively.
There are two types of light chains κ (kappa) and λ (lambda)
• The differences in the immunoglobulins are more pronounced in the Fc regions of the
antibody, which leads to the triggering of different effector functions.
• The structural differences in the antibodies also result in differences in the polymerization
state of the monomer unit.
 Structure of an antibody
Figure: Types of antibodies | Source: The Biology Notes
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7. 7  Reference
i. Sedlacek, H.H., Gronski, P., Hofstaetter, T. et al. The biological properties of
immunoglobulin G and its split products [F(ab’)2 and Fab]. Klin Wochenschr 61, 723–
736 (1983). https://doi.org/10.1007/BF01497399
ii. Judith A. Owen, Jenni Punt, Sharon A. Stranford (2013). Kuby Immunology. Seventh
Edition. W. H. Freeman and Company.
iii. Vidarsson, Gestur et al. “IgG subclasses and allotypes: from structure to effector
functions.” Frontiers in immunology vol. 5 520. 20 Oct. 2014,
doi:10.3389/fimmu.2014.00520
iv. Peter J. Delves, Seamus J. Martin, Dennis R. Burton, and Ivan M. Roitt(2017). Roitt’s
Essential Immunology, Thirteenth Edition. John Wiley & Sons, Ltd.
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