Immunoglobulin (English Version)

Immunoglobulin (Ig) is a protein secreted by plasma cells, the differentiated B cells, and binds with a particular antigen. Immunoglobulin is also called antibody. All antibodies have the same Y-shaped structure and in their monomer form consists of two identical heavy chains and two identical light chains.¹ Immunoglobulin is divided by five classes, namely IgG, IgM, IgA, IgD and IgE.² Those classes are determined by the structure difference in heavy-chain constant region. For this reason, those classes have no effects towards the antibody specifity, whereas the antibody specifity is determined by antigen binding sites.³

Immunoglobulins belong to the group of glycoproteins called globulins. Immunoglobulin consists of four polypeptides chains, that is two identical Heavy (H) chains and two identical Light (L) chains. In every H and L chain are two distinct regions. In the tips of the chain, there is V (variable) region as the sites of antigen binding. It is V region that recognizes and attaches specifically to particular antigen.³ The remainder L and H is the constant (C) region, nearly the same to all antibodies in the same class, is responsible on the kind of antigen-antibody reactions occurs.²

Immunoglobulin and antibody is the important part of body’s defense in protecting body from antigens (strange objects) that go inside the body. Immunoglobulin can be found in blood plasma.⁴ When an antigen go inside the body, B cell, or B lymphocyte, encounters by binding immunoglobulin molecules, exist as integral proteins within plasma membrane of B cell, towards the antigen. When immunoglobulin molecule binds with specific epitope on the antigen, particular cytokines is secreted by T-helper cells, then B cell becomes activated, proliferates into plasma cells and memory cells.^1,4 Each of plasma B cells is the manufacturer of immunoglobulin that the specifity is the same as parent B cells that binds with antigens. Next, these antibodies go inside blood and lymphatic circulations, as well as in extracellular fluid, and then bind with proper antigen epitopes in anywhere in the body. Once the antibody has coated proper antigen, other cells and chemical processes will be activated to eliminate the antigen.⁴ The ways of antibodies inactivating antigens are neutralizing antigens, immobilizing bacteria, agglutinating and precipitating antigens, activating complement system, enhancing phagocytosis, opsonizing, stimulating inflammation and preventing bacterial and viral adhesions.^3,4

There are five classes of immunoglobulin (Ig). IgM plays a role by coating (opsonizing) antigen for destructing and fixing complement system. IgM antibody is associated with primary immune response and frequently used to diagnosing acute exposure to an immunogen or pathogen. IgD has unclear functions, as it is unknown participating within major antibody effector mechanisms.⁵ IgG antibody is responsible in resistance against many viruses, bacteria and bacterial toxins. IgE plays an important role in allergy response and when this antibody binds with antigen, it will stimulate the cell to release histamine and other chemicals for accelerating inflammation in the immediate region.³ Then, IgA is found in a huge quantities in mucous membranes of digestive, urogenital and respiratory systems, and functions in preventing pathogens attach on the surface of cells.⁶

References

1.    Reece JB, Urry LA, Cain ML, Wasserman SA, Minorsky PV, Jackson RB. Campbell biology, 9th ed. San Francisco (CA): Pearson Benjamin Cummings; 2011.

2.    Tortora GJ, Derrickson B. Principles of anatomy and physiology, 12th ed. Danvers (MA): John Wiley adn Sons, Inc; 2009.

3.    Martini FH, Nath JL, Bartholomew EF. Fundamentals of anatomy and physiology, 10th ed. San Francisco: Pearson Benjamin Cummings; 2014.

4.    Raven PH, Johnson GB, Mason KA, Losos JB, Singer SR. Biology, 9th ed. New York: McGraw-Hill; 2011.

5.    Schroeder HW, Cavacini L. Structure and function of immunoglobulins. J Allergy Clin Immunol. 2010 Feb; 125(202): S41–S52

6.    Enger ED, Ross FC, Bailey DB. Concepts in biology, 14th ed. New York: McGraw-Hill; 2012.

 *proudly written by using Vancouver Writing System