The immunoglobulin light chain is the small polypeptide subunit of an antibody.
A typical antibody have two Ig heavy chains linked by disulfide bonds to two Ig light chains.
There are two types of light chains.
kappa (κ) chain, encoded by the immunoglobulin kappa locus (IGK@) on chromosome 2.
lambda (λ) chain, encoded by the immunoglobulin lambda locus (IGL@) on chromosome 22.
Antibodies are produced by B lymphocytes, each expressing only one class of light chain.
Light chain class remains fixed for the life of the B lymphocyte.
In a healthy person, the total kappa-to-lambda ratio is roughly 2:1 in serum.
The free light chain ratio ranges from 0.26 to 1.65.
Both the kappa and the lambda chains can increase proportionately, maintaining a normal ratio.
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:
one constant (CL) domain
one variable domain (VL) that is important for binding antigen.
The approximate length of a light chain protein is from 211 to 217 amino acids.
The constant region determines what class (kappa or lambda) the light chain is.
The lambda class has 4 subtypes
λ
lambda 1,
lambda 2,
lambda 3, and
lambda 7
Individual 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.
A lymph node 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.
Free immunoglobulin light chains secreted by neoplastic plasma cells, such as in multiple myeloma, can be called Bence Jones protein when detected in the urine=urinary free light chains.
Increased levels of free Ig light chains have also been detected in various inflammatory diseases, but in contrast to increased levels in lymphoma patients, these Ig light chains are polyclonal.
Ig light chains can bind to mast cells and, using their ability to bind antigen, facilitate activation of these mast cells.
Activation of mast cells results in the release of various pro-inflammatory mediators which are believed to contribute to the development of the inflammatory disease.
Ig light chains activate mast cells but also dorsal root ganglia and neutrophils, expanding their possible role as mediators in inflammatory disease.