Murine and human antibodies to native DNA that cross-react with the A and D SnRNP polypeptides cause direct injury of cultured kidney cells.

Murine monoclonal and human affinity-purified Abs to native DNA (anti-nDNA) that cross-react with the A and D SnRNP polypeptides were analyzed for direct injurious effects against cultured pig kidney (PK15) cells under ordinary cell-culture conditions. Of the two murine nephritogenic Abs derived from NZB/NZW F1 mice (BWds1 and BWds3), BWds1 initially bound to the cell surface and subsequently penetrated into cells localizing in nuclei and cytoplasm. BWds3 was consistently and abundantly associated with the surface of live cells without penetration. In the presence of rabbit C, BWds3 caused massive cell lysis (85% dead cells) whereas BWds1 had only a modest lytic effect (24% dead cells). One of the nonpathogenic murine anti-nDNA Abs (5GD5) that did not cross-react with the A and D polypeptides showed no interaction with PK-15 cells and had no injurious effects. Affinity-purified autoantibodies to nDNA isolated from two SLE patients with high anti-nDNA titers and clinically active lupus nephritis showed properties similar to the murine mAbs. They both strongly cross-reacted with the A and D SnRNP polypeptides and interacted with live PK-15 cells. One of them (Cr) penetrated into live cells and localized within cytoplasm and nuclei whereas the other (Pe) bound mostly to the cell surface and caused significant cell lysis in the presence of C. Results of this study suggest that the nephritogenic murine anti-nDNA as well as subpopulations of human anti-nDNA Abs could exert their injurious influence through direct interactions with kidney cells using two different pathogenic mechanisms (i.e., C-mediated cytotoxicity and potential cell cycle dysfunctions. Interestingly, cross-reactivity of anti-nDNA Abs with the A and D SnRNP polypeptides appears to be a prerequisite for their direct pathogenicity.