Preparation and characterization of anti-framework antibodies to the kappa-chain variable region (V kappa) of mouse immunoglobulins.

The variable fragment of mouse kappa light chain (Vκ) was prepared from myeloma protein XRPC-25. The preparation included tryptic digestion of the light chain, anion exchange chromatography, and preparative SDS polyacrylamide gel electrophoresis. The end product was identified by N terminal amino acid sequence and was proven to be pure Vκ by both sequence analysis and size. Rabbit antiserum raised against the purified Vκ fragment, precipitated the Vκ25 fragment, the L25 chain, and only slightly the intact myeloma protein X-25. In double diffusion in agar against anti-Vκ, a line of identity was formed between L25 and Vκ25. In radioimmunoassay, complete inhibition of L25 binding by Vκ25 was observed. This fact and the lack of cross-reaction with Vλ 315 or with heavy chains demonstrate the Vκ specificity of the antiserum. Other κ-chains did not give precipitin line in double diffusion but were found to cross-react with anti-Vκ in radioimmunoassay, regardless of their subgroup or their respective antibody specificity. Pooled light chains from either BALB/c or AKR Ig also shared anti-Vκ25 specificities. Anti-Vκ25 was absorbed completely by Sepharose-pooled L chain. It follows that the antibody is specific to common Vκ framework-related determinants and denoted variotypes, and may be useful for the detection of Vκ domains in products or receptors of lymphatic cells. This anti-Vκ antibody complements a series of Vregion-specific antibodies, the first two of which, anti VH and anti Vλ, were already found to be useful in probing the presence of V regions on T cells.