How many classes of immunoglobulins (antibodies) are there?

Five. Briefly:

• IgG - the most common immunoglobulin (around 70-75%)


• IgA - the second most common; found mainly around mucous membranes (e.g. genitourinary and respiratory systems, and the oral cavity) and in body secretions (e.g. saliva, milk).


• IgM - the third most common one, often produced first amongst the antibodies, in response to a new infection.


• IgE - found principally on the membranes of basophils and mast cells and plays an important role in allergic responses.


• IgD - also rare, but a major component of the surface of many B cells.

The various antibody classes can look quite different - for instance, IgG looks like a single 'Y', IgA looks like to 'Y's joined to each other, and IgM can be broadly described as five 'Y's joined together. There's lots more to say about antibodies, but let's leave things there for now, shall we?