Classify antibodies into 5 types

There are 5 types of heavy chain constant regions in antibodies. The 5 types - IgG, IgM, IgA, IgD, IgE - (isotypes) are classified according to the type of heavy chain constant region, and are distributed and function differently in the body.

IgG	IgG is the main antibody in blood. It is the only isotype that can pass through the placenta, and IgG transferred from the mother's body protects a newborn until a week after birth. IgG widely distributed to the blood and tissue, and protects the body.
IgM	IgM is made up of 5 antibodies. IgM has a key role in the initial immune system. It is distributed to the blood.
IgA	Secreted IgA is made up of 2 antibodies. It is distributed to serum, nasal discharge, saliva, breast milk and bowel fluid. Breast milk protects the gastrointestinal tract of newborns from bacterial and viral infection (maternal immunity).
IgD	IgD is present on the surface of B cells and plays a role in the induction of antibody production.
IgE	IgE is believed to be related to immunity reactions to parasites, and has recently become known as a key factor of allergies such as pollinosis.

Population of 5 types of antibodies in blood (%)