classes of immunoglobulin

classes of immunoglobulin

1. Classes of immunoglobulin Roll-no- 933 Ritu sheoran

2. There are five immunoglobulin classes Of antibody molecules found in serum:- IgA (immunoglobulin A) IgD (immunoglobulin D) IgE (immunoglobulin E) IgG( immunoglobulin G) IgM (immunoglobulin M)

3. IgA:- Structure-dimer Percentage serum antibodies-10-15%. Location:-IgA found in high concentrations in the mucous membranes, particularly those lining the respiratory passages and gastrointestinal tract, as well as in saliva and tears. It has two subclass (IgA1 and IgA2) bind fragment crystallization(Fc) receptors. The J chain is a 15-kD polypeptide consisting of 129 amino acids residues and one carbohydrate group. Domestic IgA binds to the blood side of the epithelial cells through Fc receptors.these receptors are also called secretory,or S ,proteins. Function:-Its main function is to prevent attachment of virus and bacteria to the epithelial surfaces. Its presence in first milk produced helps in protecting the infant from GI infection.

4. IgD:- Structure:-Its is a monomer but it does not activate the complement system and also can not cross the placenta. 2 heavy chain of Delta class and two light chains .IgD apparently is also able to bind basophils and mast cells and activate these cells to produce antimicrobial factors that are functional in respiratory immune defense in humans. They are mostly found on surface of B cells probably functioning as antigen receptor that helps to initiate the differentiation of B cells into plasma cells and memory cells. IgD is also produced in a secreted form that is found in very small amounts in blood serum,representing 0.25% of immunoglobulins in serum. IgD may be a regulator of immune responses through its role in antigen internalization . The chain C region is divided into three domains and consists of 383 amino acid residues . The hinge region of IgD consists of 64 amino acid residues ,longer than any other antibody class.

5. IgE:- Structure- it is a monomer.However they are slightly larger than igG They represent only very small fraction of the antibody of the blood . The tails attach to the mast cells and basophils whenever they are trigered by an antigen . They cause release of histamine and other chemical that cause an allergic reaction. Percentage serum antibodies :-0.002%. IgE is made up of about 13% carbohydrate. IgE also has an essential role in type 1 hypersensitivity, which manifests in various allergic diseases,such as allergic asthma,food allergies.

6. IgG:- Structure:-It is the monomer ,is the predominant Ig class present in human serum produced as part of the secondary immune response to an antigen IgG have different subclass which are IgG1,IgG2,IgG3,IgG4 and are differentiated on the basis of the size of the hinge region,position of the size of the hinge region,position of interchain disulfide bond,and molecular weight. It is the most abundant circulatory antibody. IgG readily crosses walls of blood vessel and enter tissue fluid .IgG is the only class of Ig that can cross the placenta in humans.and it is largely responsible for protection of the newborn during the first month’s of life. IgG protest against bacteria,viruses and various other toxin. It also trigger actions of the complement system. IgG3 is the most effective complement activator,followed by IgG1;IgG2 is less effevent ,and IgG4 is not able to activate complement at all. IgG1 and IgG3 bind with high affinity to Fc receptors phagocytic cells and thus mediate opsonization.

7. IgGM:- S tructure :-It is a pentamer molecule.IgM has heavy chains ,is always the first class of antibody made by developing B cell. The monomers are held together by the interconnection formed in Fc region by disufide bonds and J (joining chain).J chain, whichimmunoglobulin before secretion of pentamer helps in the plymerization of the monomers. IgM is the first immunoglobin class produced in a primary response to an antigen . IgM antibodis are relatively short lived,disappearing earlier than IgG. Pentameric IgM has 10 antigen binding sites and 5 Fc portions held together by disufide bridge bonds and J chains . IgM is to large and it cannot cross the placenta and does not help in conferring maternal immunity. Percentage serum antibodies -5-10% IgM can bind complement Component C1 and activate the classical pathway,leading to opsonization of an antigen.

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