IgE historically protected us against parasites, worms etc. but now drives the allergic processes in the majority of allergy cases. It can trigger rapid immune reactions in allergic children exposed to an allergen that their immune system deems to be nasty and foreign.
IgG is our memory immunoglobulin, so once vaccinated or infected you will have circulating IgG against, for example, measles immunity for life, to protect you. Infrequently for sick children, it is often worth looking at IgG levels, to assess their immune system and particularly their response to vaccinations.
IgM is the immunoglobulin that goes up when you are infected with a ‘bug’ and disappears after the infection has been cleared, so is important in fighting the bugs as well as a marker for us doctors, to diagnose certain infections where needed.
IgA is the surface immunoglobulin that sits on our surfaces, gut, skin, lungs, nose etc. and grabs bags to present to our cellular immune system. A lack of IgA is the commonest minor immunodeficiency seen and can lead to TOO frequent respiratory and GIT infections, especially in kids.