Immunoglobulin,-Antibody structure, definition, structure, types, functions,

Antibody structure, definition, structure, types, functions,
IGg, IGm, IGa, IGd, IGe

1. By S.D.Mankar Assistant Professor Department Of Pharmaceutics Pravara Rural College Of Pharmacy,Pravaranagar Immunoglobulin

2. Definition:- Antibodies are globulin proteins(Compact/globular form) therefore we have come to use the term immunoglobulin( Ig ) for antibodies. Globulin protein are relatively soluble. Immunoglobulin is a glycoprotein that is made in response to an antigen and can recognize and bind to the antigen that caused its production. Protects us from microbial infection.

3. Each antibody has at least two identical sites that bind to epitopes . These sites are known as antigen-binding sites. The number of antigen-binding sites on an antibody is called valence of that antibody. E.g most of human Ab have two binding sites therefore they are bivalent.

4. Structure:- Bcz a bivalent antibody has simplest molecular structure, is called monomer. A typical antibody monomer has four protein chains- Two identical light chains & two identical heavy chains. ( as per molecular wt) The chains are joined by disulfide links & other bonds to form Y shaped molecule. It is flexible & can assume a T shape. The two sections located at the end of the Y’s arms are called variables(V) regions.

5. These binds to epitopes . Their structure reflects the nature of the antigen for which they are specific-they are specific to the two antigen-binding sites found on each antibody monomer. The stem of the antibody monomer and the lower parts of the arms of the Y are called constant(C) regions. They are the same for particular class of immunoglobulin. There are five major type of C regions, which account for the five major classes of immunoglobulins .

6. The stem of the Y shaped antibody monomer is called the Fc region, so named bcz when antibody structure was first being identified, it was a fragment(F) that crystallized(c) in cold storage. The Fc region are often important for immunological reactions.

7. CLASSES (ISOTYPES) OF IMMUNOGLOBULINS Classes based on constant region of heavy chains Immunoglobulin A (IgA) Immunoglobulin D (IgD) Immunoglobulin E (IgE) Immunoglobulin G (IgG) Immunoglobulin M (IgM) Differentiation of heavy chains Length of C region, location of disulfide bonds, hinge region, distribution of carbohydrate Classes have different effector functions Dr.T.V.Rao MD 8

8. Immunoglobulin Classes I . IgG Structure: Monomer Percentage serum antibodies: 80% Location: Blood, lymph, intestine Half-life in serum: 23 days Complement Fixation: Yes Placental Transfer: Yes Known Functions: Enhances phagocytosis, neutralizes toxins and viruses, protects fetus and newborn. Dr.T.V.Rao MD 9

9. Immunoglobulin Classes II. IgM Structure: Pentamer Percentage serum antibodies: 5-10% Location: Blood, lymph, B cell surface (monomer) Half-life in serum: 5 days Complement Fixation: Yes Placental Transfer: No Known Functions: First antibodies produced during an infection. Effective against microbes and agglutinating antigens. Dr.T.V.Rao MD 10

10. Immunoglobulin Classes III. IgA Structure: Dimer Percentage serum antibodies: 10-15% Location: Secretions (tears, saliva, intestine, milk), blood and lymph. Half-life in serum: 6 days Complement Fixation: No Placental Transfer: No Known Functions: Localized protection of mucosal surfaces. Provides immunity to infant digestive tract. Dr.T.V.Rao MD 11

11. Immunoglobulin Classes IV. IgD Structure: Monomer Percentage serum antibodies: 0.2% Location: B-cell surface, blood, and lymph Half-life in serum: 3 days Complement Fixation: No Placental Transfer: No Known Functions: In serum function is unknown. On B cell surface, initiate immune response. Dr.T.V.Rao MD 12

12. Immunoglobulin Classes V. IgE Structure: Monomer Percentage serum antibodies: 0.002% Location: Bound to mast cells and basophils throughout body. Blood. Half-life in serum: 2 days Complement Fixation: No Placental Transfer: No K n o w n F u nctions: Allergic re a ct i o n s. P o ss i bly lysis of worms. Dr.T.V.Rao MD 13

13. Properties and biological activities of Immunoglobulins Ig G Ig A Ig M Ig D Ig E 1. Structure Monomer Monomer in serum/ Dimer in secretion Pentamer / monomer Monomer Mo n om er Heavy chain CH domain Mol. Wt. Serum concentration (mg/ml) G amm a Three 1 , 50 , 000 12 Alfa T h r ee 1, 6 , 000 2 Mu Four 9 , 00 , 000 1.2 Delta T h r e e 1 , 80 , 000 0.03 E p s ilon Four 1,9 , 00 0.00004 _ _ + + _ 45 42 80 75 50 - + + - + + - - - - - - - - - + - - + + + - - - 5. Present on membrane of mature B cell Intravascular Distribution (%) Crosses placenta Present in milk Selective secretion by seromucous glands Activation of complement Classical Alternate 10 Binds to FC receptor of phagocytes 11 Induces mast cell degranulation - - - - - - - - - - +