Serological and genetic characterization of a human monoclonal immunoglobulin G anti-DNA idiotype.

This study analyzed the distribution of an idiotype, B3-Id, in patients with active SLE, classified according to organ involvement, normal controls, and other autoimmune rheumatic diseases. A polyclonal anti-idiotype was raised by immunizing a rabbit with a monoclonal IgG anti-double-stranded (ds) DNA antibody, B3, generated from a patient with SLE who had active arthritis. The idiotype is present on the lambda chain and is at or near the binding site for double-stranded DNA. The lambda chain, which was characterized by nucleotide sequencing, was 90% homologous to the V lambda 2.1 germline, which is known to be involved in coding for nephritogenic anti-DNA antibodies carrying the 8.12 idiotype. There were four changes to positively charged amino acids, known to be involved in DNA binding, in the complementarity determining regions of B3 lambda chain compared with a non-DNA binding, 8.12 positive antibody, PV11. Only one change to a positively charged amino acid occurs in the heavy chain of B3, which is 93.5% homologous to VH-26. The B3-Id was present on IgG antibodies in the serum of 20% of patients with SLE but was not found in the normal controls. Within the SLE group, there is a statistically significant association of B3-Id on IgG in the arthritis group (42%) compared to the other manifestations (9%) (P < 0.001). In four B3-Id-positive SLE patients tested serially, the level of B3-Id reflected the arthritis disease activity more closely than the overall disease activity (P < 0.05). The B3-Id was also present on IgM antibodies in one third of patients with rheumatoid arthritis. This idiotype is the first to be derived from a human monoclonal anti-DNA antibody of the IgG class, the isotype associated with active disease. Sequence analysis shows that positively charged amino acids on the lambda chain may contribute to DNA binding.