In systemic lupus erythematosus (SLE), immune complexes (ICs) containing pathogenic IgG anti–double‐stranded DNA (anti‐dsDNA) autoantibodies are deposited in renal capillaries and initiate glomerulonephritis (GN) by the activation of complement and effector cells. In contrast, it has been demonstrated that the presence of IgM anti‐dsDNA antibodies correlates negatively with the development of GN in SLE. The aim of this study was to determine whether anti‐dsDNA antibodies of the IgM isotype protect against IC‐mediated organ damage in SLE.

Lupus‐prone (NZB × NZW)F₁ mice (females) were treated with murine monoclonal IgM anti‐dsDNA antibodies. Treatment was delivered by subcutaneous injection at a dosage of 100 μg/week starting at 16 weeks of age (prophylactic) or at 24 weeks of age (therapeutic).

Mice treated with IgM anti‐dsDNA exhibited a delayed onset of proteinuria and a reduced degree of renal pathology, which resulted in significantly improved survival as compared with control mice. Serum concentrations of IgG anti‐dsDNA antibodies were not significantly modified. However, glomerular deposition of ICs was markedly reduced in both treatment protocol groups. In contrast, higher amounts of IgG and IgM and increased expression of Fcγ receptor were demonstrated in liver sections from the treated mice compared with the untreated mice, suggesting an enhanced clearance of soluble ICs from phagocytic cells of the reticuloendothelial system.

These data demonstrate the efficacy of IgM anti‐dsDNA treatment in inhibiting the pathologic changes of lupus in (NZB × NZW)F₁ mice. Lower glomerular IC deposition is associated with a reduced inflammatory response and impaired organ damage. The reduced frequency of GN in SLE patients who have IgM anti‐dsDNA antibodies may therefore reflect a disease‐modifying effect of this class of autoantibodies that has potential therapeutic implications. Our findings should encourage the development of new therapeutic modalities using IgM anti‐dsDNA antibodies in humans with SLE.