Heavy chain diseases

[Jason Yan]

Heavy chain diseases are plasma cell cancers in which a clone of plasma cells produces a large quantity of pieces of abnormal antibodies called heavy chains.
(See also Overview of Plasma Cell Disorders.)
Plasma cells develop from B cells (B lymphocytes), a type of white blood cell that normally produces antibodies (immunoglobulins). Antibodies are proteins that help the body fight infection. If a single plasma cell multiplies excessively, the resulting group of genetically identical cells (called a clone) produces a large quantity of a single type of antibody. Because this antibody is made by a single clone, it is called a monoclonal antibody and also is known as the M-protein. People with a large quantity of the M protein often have reduced levels of other antibodies. In some cases, the antibody produced is incomplete, consisting of only light chains or heavy chains (functional antibodies normally consist of two pairs of two different chains called a light chain and heavy chain).
There are 5 classes of antibodies— IgM, IgG, IgA, IgE, and IgD. Each class has its own type of heavy chain.
Heavy chain diseases are categorized according to the type of heavy chain produced:

Alpha (from IgA)
Gamma (from IgG)
Mu (from IgM)