Immunoglobulin G (IgG)

Immunoglobulin A (IgA)

Immunoglobulin M (IgM) Immunoglobulin D (IgD)

Immunoglobulin E (IgE)

1. IgG is the serum immunoglobulin. The normal serum concentration is about 8-16mg/ml

2. Molecular weight is 150,000

3. It is the only immunoglobulin that is transported through placenta & provides natural passive immunity to newborn

4. It is distributed equally between the intravascular & extravascular compartments

5. IgG appears late but persists for long period. It appears after the initial immune response which IgM in nature

6. It participates in precipitation, complement fixation & neutralization of toxin & viruses

7. It is protective against those microorganisms which are active in the blood & tissues

1. IgA is the second major serum immunoglobulin. The normal serum concentration is 0.6-4.2mg/ml

2. IgA occurs in two forms, serum IgA & secretory IgA

3. Serum IgA is a monomeric 7S molecule, while IgA found by two monomer units joined together by a glycoprotein named the J chain

4. Secretory IgA contains another polypeptide called the secretory piece or secretory component

5. IgA is the principal immunoglobulin present in secretions such as milk, saliva, tears, sweat, nasal fluids, colostrum & in secretions of respiratory, intestinal & genital systems. It protects the mucus membranes against microorganisms

6. IgA is mainly synthesized locally by plasma cells & little is derived from serum

1.IgM is a pentamer consisting of 5 immunoglobulin subunits & one molecule of J chain, which joins the Fc region of the basic subunits

2.It constitutes about 5-8% of total serum immunoglobulins. The normal level in serum is 0.5-2mg/ml

3.It is heavy molecule with a molecular weight 900,000 to 1,000,000 hence also called the ‘millionaire molecule’

4.IgM is mainly distributed intravascularly

5.It is the earliest synthesized immunoglobulin by fetus

6.It appears early in response to infection before IgG. IgM antibodies are short lived, & disappear earlier than IgG. Hence, its presence in serum indicates recent infection

7.It cannot cross the placenta, presence of IgM antibody in serum of newborn indicates congenital infection

8.It is very effective antibody in agglutination & complement fixation. It is more efficient than IgG in these reactions

9.IgM provides protection against blood invasion by microorganisms

1. IgD resembles IgG structurally

2. IgD is present in a concentration of 3mg per 100ml in serum. It is mostly intravascular in distribution.

3. Molecular weight is 1,80,000.

1. IgE is mainly produced in the linings of respiratory & intestinal tracts. Serum contains only traces. It is distributed extravascularly.

2. It is also referred to as regains

3. Molecular weight is 1,90,00

4. It resembles IgG in structure

5. It is heat labile whereas other immunoglobulins are heat stable

6. It has affinity for surface of tissue cells, particularly mast cells of the same species.

7. IgE mediates type I hypersensitivity reaction. This responsible for asthma, hay fever & eczema

8. It cannot cross the placental barrier or fix the complement

9. IgE is responsible for anaphylactic type of reaction