Use of Phage Expression to Analyze Regions of a Human V4‐34(VH4‐21)‐encoded IgG Autoantibody Required for Recognition of DNA No Involvement of the 9G4 Idiotope a

The V4-34 gene encodes the majority of autoanti-red cell antibodies of Vi specificity’ as well as a number of IgM and IgG anti-DNA antibodies from patients with systemic lupus erythematosus (SLE).2 Nucleotide sequence analysis of a panel of monoclonal antibodies (MoAbs) that use this gene has indicated that discrimination between different autoantigens may arise from the CDR3 sequence of VH. Specifically, anti-DNA activity may require basic amino acids, such as arginine, found in this region. To test this, we have expressed VH and VL sequences from a patient’s IgG anti-DNA MoAb, as Fab molecules at the surface of phage. The influence of the basic CDR3, of somatic mutations in VH, and of the VL gene on recognition of DNA has been assessed. The 9G4 idiotope, located in FWRl of VH and known to be involved in red cell recognition, has been found to have no influence on DNA binding.