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Significance of C3 nephritic factor (C3NeF) in non-hypocomplementaemic serum with membranoproliferative
1Department of Internal Medicine II, Nihon University School of Medicine, Tokyo, Japan.
Abstract:
C3NeF is an autoantibody of C3 convertase (C3bBb) and is often detected in the serum of hypocomplementaemic MPGN patients. Serum samples from 104 non-hypocomplementaemic MPGN patients (C3NeF) were studied. C3NeF, which cannot activate the alternative pathway, was found in the sera of 6 patients. We examined the C3NeF in purified IgG from five of the non-hypocomplementaemic serum samples (non-hypo C3NeF) and four hypocomplementaemic serum samples (hypocomplementaemic C3NeF) to determine why C3NeF does not induce C3 splitting and hypocomplementaemia. Purified IgG from non-hypo C3NeF stabilized EAC4b3bBb cells in a manner similar to IgG from hypocomplementaemic C3NeF in EDTA gelatin veronal buffer. However, the non-hypo C3NeF IgG did not stabilize C3 convertase (EAC4b3bBb cells) in the presence of control proteins (factors H and I), whereas the hypocomplementaemic C3NeF IgG did. The C3NeF in the hypocomplementaemic serum displayed two characteristics: (i) inhibition of intrinsic decay of Ce convertase (C3bBb); and (ii) inhibition of extrinsic decay by factors H and I. Although the C3NeF in the non-hypocomplementaemic sera did inhibit the intrinsic decay in a manner similar to the hypocomplementaemic C3NeF IgG, it did not inhibit the extrinsic decay. Due to the different characteristics of hypocomplementaemic C3NeF and non-hypo C3NeF in the serum samples, the non-hypo C3NeF did not activate C3. Therefore, we conclude that C3NeF exhibits a heterogeneity which is very important in relation to the pathogenesis of MPGN.
Insights
Complement C3 Nephritic Factor (C3NeF) autoantibodies show heterogeneity in MPGN patients. Non-hypocomplementaemic C3NeF stabilizes convertase but doesn't inhibit decay, unlike hypocomplementaemic C3NeF, impacting C3 activation and MPGN pathogenesis.
Area of Science:
- Immunology
- Complement System Biology
- Nephrology
Background:
- C3NeF, an autoantibody against the C3 convertase (C3bBb), is linked to hypocomplementaemic MPGN.
- The role of C3NeF in non-hypocomplementaemic MPGN remains unclear.
- Understanding C3NeF heterogeneity is crucial for MPGN pathogenesis.
Purpose of the Study:
- To investigate the functional differences between C3NeF from hypocomplementaemic and non-hypocomplementaemic MPGN patients.
- To determine why non-hypocomplementaemic C3NeF does not induce C3 splitting and hypocomplementaemia.
Main Methods:
- Serum samples from 104 non-hypocomplementaemic MPGN patients were analyzed.
- Purified IgG from non-hypocomplementaemic and hypocomplementaemic C3NeF samples were characterized.
- Functional assays assessed C3 convertase stabilization and decay inhibition in the presence of factors H and I.
Main Results:
- C3NeF was detected in 6 out of 104 non-hypocomplementaemic MPGN patients.
- Both hypocomplementaemic and non-hypocomplementaemic C3NeF IgG stabilized EAC4b3bBb cells.
- Non-hypocomplementaemic C3NeF IgG failed to inhibit extrinsic decay by factors H and I, unlike hypocomplementaemic C3NeF IgG.
Conclusions:
- C3NeF exhibits significant heterogeneity in its functional properties.
- Non-hypocomplementaemic C3NeF's inability to inhibit extrinsic decay explains its lack of C3 activation.
- This heterogeneity is critical for understanding the diverse pathogenesis of MPGN.