What is an Antibody? Types of Immunoglobulin

Antibody: An immunoglobulin, a specialized immune protein,
An antibody, also known as an Antibody, is a large, Y-shaped protein produced mainly by plasma cells / B cells of the immune system to neutralize pathogens such as pathogenic bacteria and viruses.
The antibody recognizes a unique molecule of the pathogen, called an antigen. There are five kinds of antibodies, such as Immunoglobulins M, G, E, D and A. An antibody is a serum protein that is generally found in blood.

This is how Antibodies works : Animation Video.

The immunoglobulin can be divided into
five different classes, based on difference in the amino acid sequence in the constant region of the heavy chains.

1. IgG – Gamma heavy Chains.
2. IgM – Mu heavy chains.
3. IgA – Alpha heavy chains.
4. IgD – Delta heavy chains.
5. IgE – Epsilon heavy chains.

(Short tricks – GAMED )

Immunoglobulin types –

Immunoglobulin can also be classified by the type of light chain that they have .
Light chain types are based on difference in the amino acid sequence in the constant region of the light chain .

    1. Kappa light Chains.
    2. Lambda light Chains.


Antibodies also called immunoglobulin or Igs. ( with molecular weight of 150 -900Md) Constituents the gamma globulin part of the blood protein. They are soluble protein secreted by the plasma offspring( clones) of primed B.Cells.

What is antibody

IgE – Responsible for autoimmune response , such as allergies and diseases like arthritis , multiple sclerosis and systemic lupus erythematosus.

IgG – is the only antibodies that can cross the placental barrier to the fetus and it is responsible for 3 to 6 month immune protection of newborn that is Conferred by the mother .

IgM – is the dominant antibody produced in primary immune response & physically much larger than the other immunoglobulin.

IgG – dominant in secondary immune response.

Structure and some properties of Immunoglobulin classes :

A. ImmunoglobulinG (IgG) –

1. Structure – All IgG’s are monomers ( 7S immunoglobulin )

2. Half life – 23 days.

3. % total serum antibodies – 75-80 ( most abundant in serum)

4. Properties – IgG is the most versatile immunoglobulin because it is capable of carrying out all of the functions of immunoglobulin molecules.

  • I. IgG is the Major Ig in serum – 75% of Serum Ig is IgG .
  • II. IgG is the major ig in extra vascular space and in blood and lymph .
  • III. Placental transfer – Transfer is mediated by a receptor on placental cell for the Fc region of IgG.
  • IV. Fix Complement – Not all subclasses fix equally well; IgG4 does not fix complement.

B. Immunoglobulin M (IgM ) –

1. Structure – IgM normally exists as a Pentamer (19S immunoglobulin) but it can also exists as a monomer.

2. Half life – 05 days

3. % total serum Antibodies – 5 -10 %

4. Properties –

  • I. IgM is the third most common serum Ig .
  • II. IgM is the first Ig to be made by the fetus and the first Ig to be made by a virgin B cells when it is stimulated by antigens.
  • III. As a consequences of its pentameric structure , IgM is a good complement fixing Ig . Thus IgM antibodies are very efficient in leading to the lysis of microorganisms .
  • IV. As a consequences of its structure, IgM is also a good agglutinating Ig .thus , IgM antibodies are very good in clumping microorganisms for eventual elimination from the body.

C. Immunoglobulin A ( IgA) –

1. Structure – serum IgA is a monomer but IgA found in secretion is a diamer .

2. Half Life – 06 days

3. % total serum Antibodies – 10 -15%

4. Properties

  • I. IgA is the 2nd most common serum Ig.
  • II. IgA is the major class of the Ig in Secretion – tears , saliva ,
    colostrums , mucus , IgA is importent
    in Local ( mucosal) immunity.

  • III. Normally , IgA does not fix coplement , unless aggregated.

D) Immunoglobulin D (IgD) –

1. Structure – IgD exist only as a monomer.
2. Half life – 03 days
3.% total serum Antibody – 0.2%
4. Properties –

  • I. IgD is found in low leval in serum, its role in serum is uncertain
  • II. IgD is primarily found on B cell surface where it functions as a receptor for antigens.
  • IV. IgD does not bind complement

E. Immunoglobulin E (IgE ) –

1. Structure – IgE Exists as a monomer and has an extra domain in the constant region.
2. Half life – 02 days
3. % total serum antibody – 0.002%
4. Properties

  • I. IgE is the least common serum Ig.
  • II. involved in allergics reaction .
  • III. IgE also plays a roles in parastic helminth diseases . Since serum IgE levals rise in parasitics diseases, Measuring IgE levals is helpful in diagnosing parasitic infections.
  • IV ) IgE does not fix Complement.


1. Type I Anaphylaxis –

*Characteristics – IgE bind to mast cell Or basophills causes degranulation of mast cell and release histamine.
*signs appear within.
– less than 30 min.

Example – Anaphylactic shock from drugs, venoms, common allergic conditions as hay fever, asthama.

2. Type II Cytotoxic –

*Characteristic – Antigen causes formation of IgM and IgG that bind to target cell, when combined with action of complement destroy target cell.

*Signs appear wihin – 5 – 12 hrs.

Example – Transfusion

3. Type III Immune Complex –

* Characteristics – Ag ( antigen) and Ab ( antibody ) form complex that causes inflammation .
* Signs appears within – 3 – 8 hrs

Example – Arthus reaction, serum Sickness .

4. Type IV Cell Mediated or delayed type

* Characteristics – Aantigen causes formation of Tc that kills target cell.

Examples – Rejection of transplanted tissue poison ivy , such chronic diseases like tuberculosis, leprosy.


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