IgE : Structure, Property & Role in defence and Allergic reaction

  Immunoglobulin E (IgE) is a monomer. It contains 2 epsilon(ε) heavy chains.

• IgE contains 2 Heavy chains (MW 170 kDa) and 2 light chains (MW 23 kDa).

• Each heavy chain has 4 constant domains like IgM.

• Molecular weight of IgE is 190 kDa

• IgE is found in trace amount in serum. It is the least abundant immunoglobulin in serum (0.002%).

• It has a half-life of Two days.

• IgE does not participate in complement fixation, optimization etc.

• IgE is very crucial antibody because it play important role in allergic reactions.
IgE is also important in defense against parasitic worms.

Structure of Immunoglobulin E

Role of immunoglobulin E in our body

Role of immunoglobulin E in Defense against parasitic worms :

When there is an invasion by parasitic worms. The T-helper cells secrete cytokines such as interleukin-4 and stimulate B-cells to secrete IgE antibodies.

• The concentration of IgE antibodies in the serum rises. These antibodies then coat the surface of the worm by binding to their surfaced antigens.

• These bound IgE antibodies are recognised by the Eosinophils.

• This recognition is mediated by specific Fc receptors (FcεR) present on the eosinophils.

• These receptors recognise and bind FC region of IgE antibodies.

• Once bound they undergo to granulation. The released granule content destroys the parasitic worm.

Role of IgE in allergic reactions :

  The immune system of some people is sensitive to substances such as pollen, nuts, dust mites etc.

• These substances are known as allergens and ordinarily harmless in most people, But the immune system of sensitive or allergic people recognise these substances as dangerous.

• When there is an initial or first exposure to an allergen B-cells are activated.

• These B-cells differentiate into IgE producing plasma cells, These IgE antibodies attach themselves to the mast cells and basophils by their FC regions. Now the antigen binding sites of these lgE antibodies are free.

• When there is second exposure of the allergen, the allergen binds to these antigen binding sites of IgE antibodies.

• This binding of allergen to IgE antibodies results in the cross-linking of IgE antibodies.

• This cross-linking sends signal to the cell and results in  Degranulation.

• As a result of degranulation there is a rapid release of preformed mediators from the granules. For example, Histamine, Heparin etc.

• These mediates further result in viscodilation, increased vascular permeability, smooth muscle contractions etc. This reaction is known as allergic reaction.

• Thus elevated levels of IgE antibodies in the body of diagnostic significance.

Elevated levels of immunoglobulin indicates the possibility of allergic reaction or parasitic infection. 

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