imunoglobulin.pptx

immunoglobulin
structure,types

1. Immunoglobulin By Swetha smenon 2 nd msc

2. Specialized group of proteins mostly associated with γ globulin fraction. Immunoglobulins is a functional term while γ globulin is a physical term. Abbreviated as Ig Ig are produced by plasma cells in response to an antigen and which function as antibodies.

3. Structure of immunoglobulins  All immunoglobulin molecules basically consist of : two identical heavy chains and two identical light chains held together by disulfide linkages (Inter-chain and Intra-chain ) and non-covalent interactions . It is Y shaped tetramer (H2L2) Each heavy chain contains 450 amino acids Light chain has 212 amino acids Heavy chain of Ig are linked to carbohydrates hence Ig are glycoproteins .

4.  Amino acid sequence of variable regions of light and heavy chains is responsible for specific binding of immunoglobulin (antibody) with antigen. There are certain hypervariable regions interspersed between the relatively invariable regions . Light chain has 3 hypervariable regions Heavy chain has 4. The hypervariable regions more specifically determine the antigen-antibody binding.

5. Immunoglobulin Classes   IgG - Gamma heavy chains IgM - Mu heavy chains IgA - Alpha heavy chains IgD - Delta heavy chains IgE - Epsilon heavy chains

6.  Two types of light chains : kappa ( Κ ) and lambda (λ ) An Ig contains two Κ or two λ light chain and never a mixture . Kappa chain (60%) is more common in human.

7. Ig G Major serum Ig – 75 -80 % Single Y shaped unit (monomer ) It is the antibody seen in secondary immuno response. It can transverse blood vessels readily. IgG is only Ig that can cross the placenta and transfer the mothers immunity to developing fetus

8.   Ig M J Chain Largest Ig composed of 5 Y shaped units held together by a J polypeptide chain . Pentamer –bind with 5 antigenic sites Due to its large size, IgM cannot transverse blood vesssels , hence it is restricted to the blood stream . IgM is first antibody to be produced in response to an antigen and is most effective against invading micro-organism.

9. IgM Ab cannot cross placenta So if the fetus even though it carries an incompatible Ag , is protected from natural Ab of the mother

10.   IgA Single (monomer) or double unit ( dimer ) held together by J chain Mostly found in body secretions such as saliva, tears, sweat, milk and the walls of intestine . Most predominant Ab in colostrum . Ig A molecules bind with bacterial Ag present on body surface and remove them. So IgA prevents the foreign substances from entering the body cells.

11. IgE Single Y shaped (Monomer) Normally present in minute conc in blood – 0.3g/ml IgE levels are elevated in individuals with allergies as it is associated with the body’s allergic response – Hay fever, Asthma, Anaphylactic shock . IgE tightly binds with Fc receptors on basophils and mast cells which release histamine and cause allergy . Immediate type Hypersensitivity reaction – peak at 30 min

12.   IgD Single Y shaped unit (Monomer ) Present in low concentration in circulation. Present on surface of B cells Their function is not known

13. Immunoglobulin Major Functions     IgG Main antibody in the secondary response . Opsonizes bacteria, making them easier to phagocytose . Fixes complement , which enhances bacterial killing. Neutralizes bacterial toxins and viruses. Crosses the placenta . IgA   Secretory IgA prevents attachment of bacteria and viruses to mucous membranes. Does not fix complement   IgM  Produced in the primary response to an antigen. Fixes complement . Does not cross the placenta   IgD  Found on the surfaces of B cells where it acts as a receptor for antigen. 

14. IgE Mediates immediate hypersensitivity (allergy) by causing release of mediators from mast cells and basophils upon exposure to antigen (allergen). Does not fix complement.  Main host defense against helminthic infections.

15. REFERNCE A text of microbiology ,Dr. R.C Dubey & Dr. D.K Maheswari https://www.dianova.com/en/faq/antibody-structure-what-is-a-secondary-antibody/ https://www.biologyexams4u.com/2012/11/different-types-of-immunoglobulins-igg.html