noun, plural: antibodies
Any of the numerous Y-shaped gamma globulin proteins found in the blood or lymph, and produced by B cells as an immune defense against foreign agents (antigens). Each antibody has a region that binds specifically to a particular antigen which it neutralizes. It is typically made up of large heavy chains and small light chains.
An antibody, also referred to as immunoglobulin, is a Y-shaped glycoprotein. It belongs to the immunoglobulin superfamily, i.e. a large protein superfamily whereby members possess an immunoglobulin domain and involved in recognition, binding, or adhesion process of cells.
The term antibody originates from the combination of anti- (meaning "against") and body. The antibodies are produced by plasma (B) cell as an immune response against antigens. They may be produced by direct exposure to foreign agents (active immunity). They may also be passed on from mother to offspring via milk (passive immunity).
Antibodies are grouped based on their mode of action. Some of which are as follows:
In placental mammals (including humans), there are five classes (or isotypes) of antibodies or immunoglobulins based on structure and biological activity:
- immunoglobulin A (IgA) – a dimer with α (alpha) heavy chain
- immunoglobulin D (IgD) – a monomer with δ (delta) heavy chain
- immunoglobulin E (IgE) – a monomer with ε (epsilon) heavy chain
- immunoglobulin G (IgG) – a monomer with γ (gamma) heavy chain
- immunoglobulin M (IgM) – a pentamer with μ (mu) heavy chain