Arginines in the CDR of anti-dsDNA autoantibodies facilitate cell internalization via electrostatic interactions

Internalization of autoantibodies against double-stranded DNA (anti-dsDNA) is crucial to the pathogenesis of systemic lupus erythematosus. Anti-dsDNA may bind to cell-surface targets in order to facilitate the subsequent cell penetration of the anti-dsDNA. In this study, we observed that the 9D7 monoclonal anti-dsDNA autoantibody (9D7 mAb) penetrates into Jurkat cells via a novel alternative pathway. Endocytosis inhibitors or a lipid-raft inhibitor did not significantly change the penetration of 9D7 mAb into the Jurkat cells. However, heparin sulfate, chondroitin sulfate B, decaarginine and chondroitinase ABC significantly suppressed the internalization and the 9D7 mAb inhibited the internalization of Tat-GFP. Moreover, the penetration of the 9D7 mAb was significantly reduced in proteoglycan-deficient cells (pgs A-745). Positively charged amino acids including arginine are commonly found in the CDR of the 9D7 mAb. Point mutations to the arginine residues in the CDR of the H chain of the recombinant 9D7 mAb significantly attenuated its DNA-binding and cell-penetration abilities. These findings indicate that cell penetration of anti-dsDNA is due to the electrostatic interactions of arginine residues in the CDR with the negatively charged sulfated polysaccharides on the cell surface.