Hinge region is found in IgG, IgA, and IgD to provide flexibility in its structure. These regions are rich in proline and cysteine and basically found between two Fab arms of the Y-shaped antibody.

IgG is the only antibody which can pass through the placenta, except IgG2 all other subtypes of IgG can cross the placenta and transfer immunity from mother to fetus.

IgM is the first antibody to produce during the primary response to antigen and it is also the first antibody which is made by the developing B-cells. It is composed of five units and formed pentameric structure with a J-chain.

IgA is the predominant immunoglobulin which is present in the external secretion such as saliva, breast feed, tears, and mucus. It constitutes 10-15% of total immunoglobin in serum.

IgE mediates hypersensitivity reaction which is responsible for the symptoms of hay fever, asthma, and anaphylactic shock. It includes degranulation of basophils and mast cells.