Genetic, structural and functional properties of an IgG DNA-binding monoclonal antibody from a lupus patient with nephritis

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Abstract
Antibodies binding to double‐stranded (ds) DNA are strongly associated with renal involvement in patients with systemic lupus erythematosus (SLE). We have generated two new IgG DNA‐binding monoclonal antibodies (mAb), RH‐14 and DIL‐6, from the peripheral blood lymphocytes of two SLE patients with glomerulonephritis using the heteromyeloma cell line CB‐F7. RH‐14 is an IgG1 λ antibody which also bound to single‐stranded (ss)DNA, histones and nucleosomes. DIL‐6 is an IgG3 λ antibody with restricted antigen binding specificity. cDNA encoding the variable regions of the heavy (VH) and light (VL) chains of RH‐14 was sequenced and the antigen binding site of this mAb was computer modelled. Sequence analysis of VH and VL regions of RH‐14 showed that VH is derived from germ‐line gene V3‐7, a member of the VH3 family, and VL is derived from DPL 11, a member of the Vλ2 family. Somatic mutations and basic amino acid residues are identified in the complementarity‐ determining regions of both VH and VL regions. The nephritogenic properties of these mAb were analyzed by implanting and growing the hybridoma cells secreting the mAb in the peri toneum of SCID mice. The animals that received the RH‐14 hybridoma produced higher levels of proteinuria (3 to ≥ 4) (p < 0.001) compared to the groups that received DIL‐6 (trace to ≥ 1) or CB‐F7 (trace). Electron microscopy of kidney sections from all the RH‐14‐ implanted animals showed granular immunoglobulin deposition in the renal glomerular capil laries and mesangium. In this study we have shown for the first time using electron micros copy that a human IgG anti‐dsDNA mAb, RH‐14, is nephritogenic and that deposition of such an antibody alone is sufficient to induce renal damage.