IMMUNOGLOBULINS

IMMUNOGLOBULINS
An immunoglobulin is a large Y-shaped glycoprotein that is produced by plasma cells (terminally differentiated B cells) in response to an immunogen exposure and function as an antibody. Each tip of the "Y" of an antibody contains a paratope (a structure analogous to a lock) that is specific for one particular epitope (similarly analogous to a key) on an antigen, allowing these two structures to bind together with precision (hand and glove specificity). The production of antibodies is the main function of the humoral immune response.

The terms antibody and immunoglobulin are often used interchangeably. The term antibody refers to the specific activity of immunoglobulin: e.g. anti-Salmonella antibody.

Activated B cells produce "soluble" antibodies. Un-activated and memory B-cells produce "surface, membrane-bound" antibodies. The membrane form gives the B-cell receptor.

Antibodies can recognize an extremely diverse set of antigens. A single B-cell produces antibodies that are homogenous in their specificity.

BASIC STRUCTURE OF IMMUNOGLOBULINS:
The basic functional unit of each antibody is an immunoglobulin (Ig) monomer (containing only one Ig unit); secreted antibodies can also be dimeric with two Ig units as with IgA, or pentameric with five Ig units, like mammalian IgM.
Although different immunoglobulins can differ structurally, they all are built from the same basic units.
All immunoglobulins are composed of two identical light chains and two identical heavy chains. There are five types of mammalian Ig heavy chain denoted by the Greek letters: ?, ?, ?, ?, and ?. The type of heavy chain present defines the class of antibody; these chains are found in IgA, IgD, IgE, IgG, and IgM antibodies, respectively.
There are two types of immunoglobulin light chain, which are called lambda(?) and kappa(?).
Each antibody contains two light chains that are always identical; only one type of light chain, ? or ?, is present per antibody. Each heavy chain has two regions, the constant region and the variable region. The constant region is identical in all antibodies of the same class(isotype), but differs in antibodies of different class. The variable region of