The B6-Igl KO mouse is a knockout model targeting the gene segment encoding the λ light chain. Through gene editing, the sequences encoding the V, J, and C regions of the mouse λ light chain (Igl) locus are completely ablated, resulting in the absence of B cells expressing immunoglobulin light chain λ. Consequently, B6-Igl KO mice serve as a valuable tool for investigating B cell development and function, generating κ light chain-only mouse antibodies, elucidating the role of the λ light chain in specific immune responses or autoimmune diseases, and exploring antibody diversity, immune regulatory mechanisms, and potential therapeutic strategies.