The immunoglobulin light chain is the small polypeptide subunit of an antibody (immunoglobulin).
A typical antibody is composed of two immunoglobulin (Ig) heavy chains and two Ig light chains.
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There are two types of light chain in humans (as in other mammals),
Antibodies are produced by B lymphocytes, each expressing only one class of light chain. Once set, light chain class remains fixed for the life of the B lymphocyte. In a healthy individual, the total kappa to lambda ratio is roughly 2:1 in serum (measuring intact whole antibodies) or 1:1.5 if measuring free light chains, with a highly divergent ratio indicative of neoplasm.
The exact normal ratio of kappa to lambda ranges from 0.26 to 1.65. Both the kappa and the lambda chains can increase proportionately, maintaining a normal ratio. This is usually indicative of something other than a blood cell dyscrasia, such as kidney disease.
The immunoglobulin light chain genes in tetrapods can be classified into three distinct groups: kappa (κ), lambda (λ), and sigma (σ). The divergence of the κ, λ, and σ isotypes preceded the radiation of tetrapods. The σ isotype was lost after the evolution of the amphibian lineage and before the emergence of the reptilian lineage.[1]
Other types of light chains can be found in lower vertebrates, such as the Ig-Light-Iota chain of Chondrichthyes and Teleostei.[2][3]
Camelids are unique among mammals as they have fully functional antibodies which have two heavy chains, but lack the light chains usually paired with each heavy chain.[4] The functional role of this separate repertoire is unknown as yet.
Only one type of light chain is present in a typical antibody, thus the two light chains of an individual antibody are identical.
Each light chain is composed of two tandem immunoglobulin domains:
The approximate length of a light chain protein is from 211 to 217 amino acids.[2]
B-cells in lymphoid tissue possess either kappa or lambda light chains, but never both together. Using immunohistochemistry, it is possible to determine the relative abundance of B-cells expressing kappa and lambda light chains. If the lymph node or similar tissue is reactive, or otherwise benign, it should possess a mixture of kappa positive and lambda positive cells. If, however, one type of light chain is significantly more common than the other, the cells are likely all derived from a small clonal population, which may indicate a malignant condition, such as B-cell lymphoma.[5]
Ig light chains produced in neoplastic plasma cells, such as in multiple myeloma, are called Bence Jones proteins.
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