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Loss of autoantibody activity by alteration in autoantigen
1Department of Pediatrics, SUNY Health Science Center, Syracuse, New York 13210, USA.
Abstract:
C3 nephritic factor (C3NeF) is an autoantibody produced by patients with membranoproliferative glomerulonephritis (MPGN); it is thought to be responsible for the continued breakdown of C3 in these patients. We have studied three patients with MPGN for periods of 7 to 17 years who were noted to develop a normal C3 and factor B level in the face of persistent circulating C3NeF. In addition, C3NeF obtained from other sera were inactive when added to these patients' sera. When C3NeF was isolated from these patients' sera, however, it was completely active when added to normal human serum as a source of C3 and factor B. Removal of the C3 and factor B from these patients' sera by passage over anti-C3 and anti-factor B columns followed by reconstitution with C3 and factor B isolated from normal serum allowed C3NeF to be active in these sera. Replacement of C3 alone did not restore activity to these sera but replacement with factor B alone restored full C3NeF activity. These data suggest some alteration in autoantigen (factor B) as a mechanism for reduction in autoantibody (C3NeF) activity.
Insights
C3 nephritic factor (C3NeF) autoantibodies in MPGN patients can become inactive due to alterations in factor B. Restoring factor B levels reactivates C3NeF, suggesting a key role for factor B in C3NeF activity.
Area of Science:
- Immunology
- Nephrology
Background:
- C3 nephritic factor (C3NeF) is an autoantibody implicated in membranoproliferative glomerulonephritis (MPGN).
- C3NeF drives continuous C3 breakdown, a hallmark of MPGN pathogenesis.
Purpose of the Study:
- To investigate the mechanism behind reduced C3NeF activity in long-term MPGN patients.
- To determine the role of serum components in modulating C3NeF function.
Main Methods:
- Studied three MPGN patients with persistent C3NeF but normal C3 and factor B levels.
- Assessed C3NeF activity in patient sera and isolated C3NeF.
- Utilized anti-C3 and anti-factor B columns to deplete and reconstitute patient sera.
Main Results:
- Isolated C3NeF was active in normal serum, but inactive in patient sera.
- Depletion and reconstitution experiments showed that factor B, not C3, restored C3NeF activity in patient sera.
- This suggests an alteration in the autoantigen (factor B) rather than the autoantibody (C3NeF).
Conclusions:
- Alterations in factor B may reduce C3NeF activity in MPGN patients.
- Factor B is crucial for C3NeF function in this context.
- This finding offers insights into MPGN pathogenesis and potential therapeutic targets.