Subclasses

1. IgG has gamma heavy chains and 4 subclasses exist: IgG1 to IgG4 Only IgG1 and IgG3 appear to be clinically significant because macrophages in the spleen only have receptors for these two subclasses.

2. IgM has MU heavy chains, and no subclasses exist.

3. IgA has alpha heavy chains and two subclasses exist, IgA1 and IgA2.

   NOTE: Only IgG, IgM and IgA play a role in IH because blood group antibodies consist of only these immunoglobulins.

4. IgD has delta heavy chains, and two subclasses, IgD1 and IgD2. Its biological role is unknown, but it may play a role as a surface receptor on lymphocytes.

5. IgE has epsilon heavy chains. IgE is sometimes called a cytophilic antibody because it occurs on the membrane of mast cells or circulating basophilic granulocytes. IgE is also sometimes called reagin (or is said to have reaginic activity) because it reacts with allergens to produce the symptoms of an allergic reaction (e.g., to plant pollen or animal danders).

Subclasses