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Antibody to a cryptic, solid phase C1Q antigen in membranoproliferative nephritis
C F Strife1, A E Leahy, C D West
1Children's Hospital Research Foundation, Cincinnati, Ohio.
Kidney International
|March 1, 1989
Summary
In membranoproliferative nephritis (MPGN), IgG binding to solid phase C1q (spClq) is not due to immune complexes. This spClq-binding IgG targets a cryptic antigen revealed upon C1q fixation to surfaces.
Area of Science:
- Immunology
- Nephrology
- Biochemistry
Background:
- Membranoproliferative nephritis (MPGN) is often associated with immune deposits.
- Solid phase (sp) C1q ELISA detects IgG in MPGN serum, presumed to be immune complexes.
Purpose of the Study:
- To investigate the nature of spC1q-binding material in MPGN serum.
- To determine if spC1q-binding IgG represents true immune complexes or an artifact.
Main Methods:
- Sucrose density ultracentrifugation and sieve chromatography of MPGN serum.
- Isolation and characterization of MPGN IgG and its binding to spC1q.
- Pepsin digestion of IgG to yield F(ab')2 fragments.
- Solid phase C1q ELISA and fluid phase C1q binding assays.
Main Results:
- spC1q-binding protein in MPGN serum primarily sedimented at 7S or co-fractionated with IgG.
- Isolated MPGN IgG and its F(ab')2 fragments bound spC1q.
- No significant fluid phase C1q-binding material was detected in MPGN serum.
- spC1q-binding IgG was found in 54% of MPGN patients.
Conclusions:
- The 7S spC1q-binding IgG in MPGN is likely an antibody to a cryptic antigen.
- This antigen is revealed only when C1q binds to a solid surface, not in fluid phase.
- The findings challenge the traditional interpretation of spC1q-binding material as immune complexes in MPGN.