IgG is found in the serum in the highest concentration as compared to other immunoglobulins. IgG helps fight infections in serum by opsonisation, complement activation, neutralising toxins and viruses and causes agglutination /precipitation by cross linking. IgG has a long life and is passed from the mother to the fetus through the umbilical cord. If there is presence of IgG in the blood we can conclude that there is an ongoing infection. IgG is further divided into 4 subclasses: IgG1, IgG2, IgG3, IgG4.

Function of IgG

IgM is the first immunoglobulin produced by a newborn and the primary antibody secreted during an initial immune response. It plays an important role in B cell maturation and acts as a fast-acting but short-lived first line of defense against infections. Because it cannot pass through the placenta to the fetus, elevated levels of IgM in a newborn indicate an active, newly acquired infection.

Functions of IgM

IgA is the second highest immunoglobulin in serum concentration. It exists as a monomer in the serum where it has a minimal function. The primary function of IgA is in the secretions, where it exists as a dimer, it prevents pathogens from entering the body. It also prevents the adhesion of bacteria, virus and toxins. IgA is not passed through the placenta from the mother to the child, however it is present in the colostrum (i.e. the initial milk produced by the mother). There are two sub classes of IgA: IgA1 and IgA2. 

Functions of IgA

IgE is present in the lowest concentration in the serum. It's basic function is in allergic reactions. When a allergic antigen enters the body, IgE bind to mast cells which leads to the degranulation of these cells. And they release substances like histamine and heparin which cause the symptoms of allergy like vomiting, sneezing, diarrhoea , hives, asthma, hay fever and anaphylactic death. This immunoglobulin is also linked to allergic hypersensitivity. IgE also plays an additional role in anti parasitic reactions. It is not passed through the placenta to the child. 

Functions of IgE

IgD is found on the surface of mature B cells. It plays a role in helping B cells respond to signals from T cells and also helps B cells in IgA, IgE and IgG synthesis. These antibodies are involved in antigen-specific B cell activation and are maturity markers for B cells. IgD binds to basophils and mast cells to cause activation of the cells. They are not passed through the placenta. 

Function of IgD

Immunoglobulins (antibodies) are proteins produced by plasma B cells that recognize and bind antigens, making it easier for phagocytic cells to destroy them. The five classes of immunoglobulins are distinguished by the type of heavy chain in their structure: IgG, IgM, IgA, IgE, and IgD.

State University of New York at Buffalo

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Plasma B cells produce antibodies (also called immunoglobulins) that bind to the antigens which makes it easier for phagocytic cells to target and kill them. There are five classes of immunoglobulins:
1. IgG
2. IgM
3.IgA
4. IgE
5. IgD

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