Selective losses of large immune complexes during density gradient ultracentrifugation and an approach for prevention of these losses

T cells and in situ cryoglobulin deposition in the pathogenesis of lupus nephritis

We discuss a 53-year-old woman with systemic lupus erythematosus who presented with vasculitis, hypocomplementemia and nephritis. Although her serum complement 4 (C4) levels were zero, she had four copies of C4 gene. Renal biopsy revealed membranoproliferative glomerulonephritis and the presence of cryoglobulins, detected by electron microscopy, and significant numbers of T cells in the interstitium. Cryoglobulins were considered responsible for the complete consumption of C4 in the serum the levels of which improved gradually after treatment. T cells in the kidney were found to express CD44 and phosphorylated ezrin/radixin/moiesin which explain why they homed to the kidney inappropriately. The contribution of cryoglobulins and T cells in the expression of kidney pathology is discussed.

Antibodies to human myeloperoxidase in glomerular immune deposits of systemic lupus erythematosus

Antibodies to human myeloperoxidase and cathepsin G have been detected in the serum of some patients with systemic lupus erythematosus. Therefore, the presence of antibodies to human myeloperoxidase and cathepsin G was examined in glomerular immune deposits. Glomerular basement membrane fragments were prepared from renal tissues obtained at autopsy from 19 patients with systemic lupus erythematosus. IgG was extracted from the glomerular basement membrane fragments and tested with sensitive immunoassays for antibodies to myeloperoxidase and cathepsin G. Antibodies to cathepsin G were not detected in the extracts but antibodies to human myeloperoxidase were found in extracts of one specimen. In the extract with 6M guanidine hydrochloride these antibodies were enriched 103-fold, compared to the initial supernatant of glomeruli, which served as a serum surrogate. The recovered antibodies to myeloperoxidase accounted for 12% of the recovered IgG. These findings add autoantibodies to human myeloperoxidase to the list of antibodies that have been shown to be present in glomerular immune deposits of patients with lupus glomerulonephritis.

Deposition of antibodies to the collagen-like region of C1q in renal glomeruli of patients with proliferative lupus glomerulonephritis

OBJECTIVE

To determine if antibodies to the collagen-like region of C1q (C1q-CLR) are present in the glomerular immune deposits of patients with systemic lupus erythematosus (SLE).

METHODS

Kidney tissues were obtained at autopsy, glomeruli were isolated, and glomerular basement membrane fragments were prepared. Antibodies were extracted with low pH or with DNase.

RESULTS

The concentrations of antibodies to C1q-CLR recovered from the glomeruli were > or =50-fold higher per unit of IgG than that found in the serum or in the serum and interstitial fluid entrained in glomeruli. Antibodies to C1q-CLR were recovered from glomeruli of 4 of 5 patients with proliferative glomerulonephritis at autopsy.

CONCLUSION

This is the first demonstration that antibodies to C1q-CLR are deposited and concentrated in the renal glomeruli of patients with SLE. These antibodies, thus, have the potential of contributing to the pathogenesis of lupus glomerulonephritis.

Antibodies to the collagen-like region of C1q in sera of patients with autoimmune rheumatic diseases

Antibodies to the collagen-like region of C1q have recently been observed in sera of patients with systemic lupus erythematosus (SLE). In this study, we documented that these antibodies were present in 47.3% of SLE patient sera, whereas they were uncommon in sera from patients with rheumatoid arthritis (2.8%) and Sjögren's syndrome (12.8%), as well as in normal sera (6.4%). Markedly elevated antibody levels (greater than 4 SD above the normal mean) were observed almost exclusively in sera of patients with SLE. Levels of antibodies to the collagen-like region correlated highly with levels of solid-phase C1q-binding IgG when analyzed by the C1q solid-phase assay for immune complexes (r = 0.87). We previously found that, after sucrose density gradient ultracentrifugation, a predominance of the solid-phase C1q-binding IgG in SLE sera sediments as monomeric IgG. These findings, together with the present data, indicate that reactivity of SLE patients' sera in the C1q solid-phase assay reflects primarily the presence of antibodies to the collagen-like region, and not the presence of immune complexes.

Antibody to a cryptic, solid phase C1Q antigen in membranoproliferative nephritis

IgG containing material detected in membranoproliferative nephritis (MPGN) serum with a solid phase (sp) Clq ELISA has been presumed to be immune complexes. However, in serum from 13 MPGN patients containing large amounts of spClq-binding material, sucrose density ultracentrifugation and sieve chromatography showed spClq-binding protein to sediment at 7S or cofractionate with IgG. One serum (stored for 12 years) contained, in addition, spClq-binding material sedimenting at more than 19S. Isolated MPGN IgG was shown to bind to spClq. SpClq-binding material could be totally removed from MPGN serum by absorption with BSA-anti-BSA immune precipitates, and by acid elution of the precipitates IgG binding to spClq could be recovered. F(ab')2, isolated from pepsin digested MPGN IgG, continued to bind spClq. Binding of MPGN IgG or F(ab')2 to spClq was not inhibited by 2 M NaCl. Incubation of MPGN serum with 125I Clq followed by sucrose density ultracentrifugation resulted in a peak of radioactivity at 11S, the sedimentation rate of Clq, giving evidence that material binding fluid phase Clq is not present. SpClq-binding IgG was detected in 54% of 68 MPGN patients. These results indicate that the 7S spClq-binding IgG represents antibody to a cryptic antigen revealed only when Clq fixes to a solid surface.

Low-molecular weight C1q-binding immunoglobulin G in patients with systemic lupus erythematosus consists of autoantibodies to the collagen-like region of C1q

The majority of C1q-binding IgG in sera of some patients with systemic lupus erythematosus (SLE) cosediments with monomeric IgG. This study was undertaken to provide definitive proof that the low-molecular weight C1q-binding IgG consists of autoantibodies to C1q. Monomeric C1q-binding IgG was isolated from five SLE plasmas by C1q affinity chromatography and gel filtration. All C1q-binding IgG preparations and their F(ab')2 fragments bound to both C1q and the collagen-like region of C1q by an ELISA. To rule out the possibility that small DNA-antiDNA immune complexes caused this binding activity, Fab' fragments of the C1q-binding IgG preparations were digested with DNase I to degrade any DNA. The Fab' fragments continued to bind to C1q and its collagen-like region after this treatment. C1q-binding IgG was heterogenous on isoelectric focusing. Interaction of C1q-binding IgG with solid-phase C1q was retained in 1 M NaCl, whereas the binding of DNA or heat-aggregated IgG to solid-phase C1q was abrogated or markedly diminished. The association constant of C1q-binding IgG with solid-phase C1q was 2.7 X 10(7) M-1. We conclude that low-molecular weight C1q-binding IgG in the studied patients with SLE consists of autoantibodies to the collagen-like region of C1q.

Characterization of circulating Yersinia-specific immune complexes in patients with yersiniosis

The size of immune complexes (ICs) containing Yersinia enterocolitica antigens was studied by size exclusion high-pressure liquid chromatography and sucrose density gradient ultracentrifugation in sera of patients with recent yersiniosis. The ICs detected were relatively small, i.e., of equal size to or slightly larger than the corresponding anti-Yersinia antibodies. The size of the ICs was equal in the patients with Yersinia-triggered reactive arthritis and in those recovering without complications. No changes were observed during a follow-up. The equal size of ICs in the patients with and without arthritis also suggests that antigens and antibodies involved are similar in both patient groups. Taken together with our earlier findings indicating occurrence of high concentrations of Yersinia IgM ICs in the arthritic patients, the present results suggest that Yersinia--IgM ICs have a role in the pathogenesis of Yersinia-triggered reactive arthritis.