Kevytketjut

Kevytketjut, literally "light chains," is a term most often used in immunology to refer to the light chains of antibodies (immunoglobulins). In humans, these light chains come in two isotypes, kappa and lambda, and they pair with heavy chains to form the antigen-binding sites of antibodies. Light chains are produced by B cells through gene rearrangements during B cell development and can be secreted as part of complete antibodies or circulate freely in the blood or be excreted in the urine.

In the structure and function of antibodies, the light chain contributes to antigen recognition via its variable region, while its constant region helps define the antibody subclass and effector interactions. The two types, kappa and lambda, are produced by different genetic loci, and a healthy individual normally maintains a regulated balance between them; a notable predominance of one type can be a sign of abnormal B cell activity.

Clinical relevance centers on the concept of free light chains and light chain–restricted monoclonal production. Free light chains are light chains not bound to heavy chains and can be detected in serum; in urine, they appear as Bence Jones proteins in some plasma cell disorders. The serum free light chain assay measures unbound kappa and lambda chains and their ratio, aiding diagnosis and monitoring of plasma cell dyscrasias such as multiple myeloma and light chain amyloidosis. Abnormal levels can also reflect kidney dysfunction, since the kidneys clear light chains from circulation.

Beyond medicine, the term kevytketjut may appear in other disciplines to describe lightweight chain materials, but in biomedicine it most often denotes immunoglobulin light chains and their clinical implications. See also: immunoglobulin, light chain restriction, monoclonal gammopathy, multiple myeloma.