Immunoglobulin Kappa (Igk) is a type of light chain found in antibodies, which are critical components of the adaptive immune system . It associates with immunoglobulin heavy chains to constitute complete, functional antibody molecules, including but not limited to IgG and IgM classes. This pairing is essential for the structural integrity and antigen-binding capability of these immunoglobulins. In humans, the IGK gene located on chromosome 2 encodes this essential protein, which represents one of the two major light chain types - either kappa or lambda. The production of Igk chains is subject to stringent regulatory mechanisms to guarantee correct antibody formation. Impairments in Igk function may result in various immunological disorders, including immunodeficiency states and B-cell derived cancers. Clinically, kappa light chains have significant diagnostic value as biomarkers for detecting monoclonal gammopathies, particularly multiple myeloma.To detect the activity of recombinant Igk, a functional ELISA assay was performed to evaluate the interaction between recombinant mouse Igk and recombinant human IgM.Briefly, Igk was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to IgM-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-Igk pAb, then aspirated and washed 3 times. After incubation with HRP labelled secondary antibody for 1h at 37℃, wells were aspirated and washed 5 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50 µL stop solution to the wells and read at 450/630nm immediately. The binding activity of recombinant mouse Igk and recombinant human IgM was shown in Figure 1, and this effect was in a dose dependent manner.