The VKIIIb light chain sub-subgroup: restricted association with mu heavy chain in normal human serum

The VKIII human kappa light chain subgroup has been serologically and structurally divided into two sub-subgroups, VKIIIa and VKIIIb. VKIIIb has been shown by others to be strikingly prevalent in IgM autoantibodies, but no studies have been performed to determine heavy chain isotype association with VKIIIb light chain in normal human serum. The VKIIIb sub-subgroup was shown here to be associated with mu heavy chain in normal human serum, but was not detected in association with gamma or alpha heavy chain. Approximately 25 +/- 15% of IgM-kappa was determined to be VKIIIb. Both intact IgG and purified light chains from pooled IgG did not bind monoclonal anti-VKIIIb, indicating that the determinants recognized by anti-VKIIIb are not merely masked in intact IgG. These results are the first report of a light chain sub-subgroup showing preferential association with a heavy chain isotype.