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

The variable fragment of mouse kappa light chain [V(κ)] 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 V(κ) by both sequence analysis and size. Rabbit antiserum raised against the purified V(κ) fragment precipitated the V(κ)25 fragment, the L25 chain, and only slightly the intact myeloma protein X-25. In double diffusion in agar against anti-V(κ) a line of identity was formed between L25 and V(κ)25. In radioimmunoassay, complete inhibition of L25 binding by V(κ)25 was observed. This fact and the lack of cross-reaction with V(λ)315 or with heavy chains demonstrate the V(κ) specificity of the antiserum. Other κ-chains did not give precipitin line in double diffusion but were found to cross-react with anti-V(κ) in radioimmunoassay, regardless of their subgroup or their respective antibody specificity. Pooled light chains from either BALB/c or AKR Ig also shared anti-V(κ)25 specificities. Anti-V(κ)25 was absorbed completely by Sepharose-pooled L chain. It follows that the antibody is specific to common V(κ) framework-related determinants and denoted variotypes, and may be useful for the detection of V(κ) domains in products or receptors of lymphatic cells. This anti-V(κ) antibody complements a series of V-region-specific antibodies, the first two of which, anti V(H) and anti V(λ), were already found to be useful in probing the presence of V regions on T cells.