What Is the Immunoglobulin Light Chain?

The immunoglobulin light chain is one chain in a group of four that forms an antibody molecule. There are two light chains, called either lambda or kappa type, and two heavy chains that have specific variables in their structure to accommodate for binding and precise functioning within the body. Light chains are “light” because they are composed of around 220 amino acids, whereas heavy chains are usually composed of over 500. Complete immunoglobulins assume two different roles within the human system; they may act as an antigen receptor on the surface of a cell or circulate freely in cellular fluids to recognize and eliminate antigenic compounds or pathogens. The determination of which function the immunoglobulin will perform is related to its genesis and differentiation process.

An antibody molecule is produced by a white blood cell known as a B lymphocyte (B-cell). Each immunoglobulin-producing B-cell is only encoded to express and produce a single form of the immunoglobulin light chain. The kappa chain has a specific site on chromosome 2 that is encoded by immunoglobulin kappa locus (IGK) and the alternative, the lambda chain, has a site encoded by immunoglobulin lambda locus (IGL) on chromosome 22. The ratio of total serum immunoglobulin light chain population, kappa chains to lambda chains, is around 2:1. Testing that indicates a significantly divergent ratio may be a sign of neoplasm, which can be indicative of a number of conditions, like kidney disease and multiple myeloma.

Due to an immunoglobulin light chain being a structure composed of a sequence of amino acids, the definition of a protein, it can also act as an antigen, as can many proteins in some circumstances. In this case, the body produces anti-immunoglobulin antibodies to try to eliminate the molecule. This event can be classified as an autoimmune disorder. Animal’s immunoglobulin light chains are often significantly different than the human variety. For example, introducing certain classes of immunoglobulins into a rabbit ensures a quick and usually fatal reaction due to the antibody response.

The human immune system has the inherent ability to recognize and attend to around 10⁷ different pathogens and types of antigens. The immune system’s diverse capabilities are attributed, in part, by the formation of the immunoglobulin light chain. The germinal cells that eventually produce the B-cells that produce immunoglobulins have a vast array of multiple genes in their deoxyribonucleic acid (DNA). This fact, coupled with the variable recombination and unique structuring of the germ cells as they differentiate and mature into B-cells, lends to a great diversification of antigen binding sites. An abundance of mutations are seen during this process as well, lending to the immune system’s remarkably innovative variances.