Antibody or Immunoglobulin

Antibody or Immunoglobulin


  • Introduction
  • Structure
  • Types


  • Antibody antigen binding glycoprotein present on B-cell membrane and secreted by plasma cells.
  • The term antibody was first used by the scientists Paul Ehrlich.
  • Membrane on antibodies refers antigenic specificity on B-cells.
  • Secreted antibodies circulated, where they act as enhancer for stimulation of humoral mediated response, to neutralize antigens from the system.

Antibody or Immunoglobulin

The main categories of antibody action include:

    1. Neutralization
    2. Agglutination
    3. Precipitation
    4. Complement activation
  • All antibodies share structural features bind to antigen and participate in several functions.

Structure of antibodies

  • Antibody molecules have common structure of four polypeptide chains.i.e.2-light chains and 2 heavy chains respectively.
  • Heavy chains consist of about 25000 molecular weight and light chain of 12000 molecular weight.

Structure of antibodies

  • Each Light chain is bound to heavy chain by non-covalent interaction.
  • The light chain consists 220 amino acids while heavy chain consists of 440 amino acids.
  • The Monomer has two kappa and two lambda
  • Each antibody contains one or another type of light chains while consists of five types of heavy chains.
  • Due to linkage of heavy chain and light chain antibody look like Y- shaped.

Types of antibodies

There are five classes of immunoglobulin molecules such as:

    1. IgG- Gamma
    2. IgA- Alpha
    3. IgE- Epsilon
    4. IgD- Delta
    5. IgM- Mu
  • Heavy chains of antibodies had been named on Greek words each class of Ig plays important role in defense system.


The basic structure of human IgG

  • 50 to 80% antibodies contribute in the form of IgG in our serum.
  • The maternal molecules can pass through placenta and provide passive immunity to fetus.
  • These can also pass the cell walls of blood vessel.
  • They are Monomer and molecular weight about 1,50,000 KD.
  • They are responsible for neutralizing microbes and their toxins.
  • They also enhance effectiveness of phagocytic cells to engulf and ingest them.


Structure of IgM
The pentameric structure of human IgM. The disulfide bonds linking peptide chains are shown in black; carbohydrate side chains are in red. Note that 10 antigen-binding sites are present.
  • They constitute about 5 to 10% in blood serum.
  • It has pentamer structure.
  • When expose to antigen, it is IgM that appears first.
  • This specially cross linked particulate antigen and caused the aggregation due to numerous antigen binding site.
  • Molecular weight about 900000 KD.
  • It is very much effective as agglutination.


The Structure of Immunoglobulin IgA
The dimeric structure of human secretory IgA. Notice the secretory component (tan) wound around the IgA dimer and attached to the constant domain of each IgA monomer. Carbohydrate side chains are shown in red.
  • Concentration of IgA in human blood remains about 15%.
  • It consists J- chain with dimer.
  • Molecular weight is about 3,20,000 KD.
  • It is present in blood serum and surface of lymphocytes.
  • It checks the attachment of pathogens to mucosal surfaces and protect the infants from infections.


The structure of human IgD
The disulfide bonds linking protein chains are shown in black; carbohydrate side chains are in red.
  • It accounts only 0.2% of serum.
  • It is also Monomer and consist of 1,85,000 KD molecular weight.
  • These are present on the upper surface of T- cells and it cannot pass across placenta.
  • They assist initiation of immune responses and their population remains very high on the surface of the B – cells.


The structure of human IgE

  • The concentration of IgE is 0.02% of the total antibodies.
  • They are larger than IgG.
  • It responses quickly to the receptor of the mast cells and basophils.
  • Mast cell and basophils are spread cells that take part in allergic reaction.
  • Molecular weight is about 2 lakh KD.
  • They raise in infections and responsible for allergic symptoms.

Reference and Sources

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