Preparation and characterization of antibodies to the λ chain variable region (V_λ) of mouse immunoglobulins

The variable portion (V_L) of the mouse myeloma protein MOPC‐315 (α, λ₂) was obtained from its Fv fragment and was used to immunize rabbits. Anti‐V_L antibodies were found to be specific to the V_L region of protein 315 and to precipitate V_L, Fv or light chain but not Fab' or intact M315. Anti‐V_L 315 precipitates also the light chain of MOPC‐104E (μ, λ₁) but not the intact protein. Intact immunoglobulins (Ig) containing λ chains, although they do not precipitate with anti‐V_L, inhibit the binding of anti‐V_L to V_L in the radioimmunoassay. Radioimmunoassay inhibition studies demonstrated that V_λ1 and V_λ2 cross‐react extensively and that anti‐V_L 315 can be used as a general anti‐V_λ reagent to detect molecules containing λ chains in mouse serum. Analysis of sera from several mouse strains indicated that V_λ‐containing molecules are present in approximately 3% of the Ig population, whereas the SJL strain has no detectable V_λ‐bearing molecules. In some of the antisera, anti‐V_L 315 slightly cross‐reacted with V_K‐bearing molecules. Anti‐V_L 315 antibodies are not anti‐idiotypes since they react with myeloma proteins M315 (anti‐2,4‐dinitrophenyl MOPC‐104E (anti‐dextran) and HOPC‐1 (specificity unknown) and with most serum Ig containing λ chains. In view of the similarity of mouse λ chain sequences, it is suggested that most anti‐V_L 315 is “anti‐framework” antibody.