Igk

IGK refers to the immunoglobulin kappa light chain, one of the two light chain isotypes that partner with heavy chains to form antibodies in vertebrate immune systems. In humans and many other mammals, the kappa light chain is a key component of the B cell receptor and secreted antibodies, contributing to antigen binding in conjunction with the heavy chain.

The IGK gene locus comprises variable (Vκ) segments, joining (Jκ) segments, and a constant (Cκ) region. During B cell development, Vκ and Jκ gene segments undergo V(D)J recombination mediated by the RAG1/2 enzymes to create diverse Vκ-Jκ combinations, which are then paired with a Cκ exon to produce a functional light chain transcript. Expression of a functioning IGK rearrangement is tightly regulated by allelic exclusion to ensure that each B cell expresses a single light chain type, typically either kappa or lambda.

Functionally, the mature Igκ light chain contributes to the antigen-binding site of the antibody, pairing with a heavy chain to form a complete immunoglobulin molecule. In humans, roughly two-thirds of circulating antibodies include a kappa light chain, with the remaining third containing a lambda light chain; the exact ratio can vary among individuals and species.

Clinical relevance lies in the use of IGK rearrangements for clonality testing in diagnostics. Abnormal IGK rearrangements or light chain restriction patterns can be observed in B-cell malignancies such as chronic lymphocytic leukemia, multiple myeloma, and acute lymphoblastic leukemia, where analysis of IGK can aid in identifying clonal B-cell populations.

See also: Immunoglobulin light chains, IGH, IGL.