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Classical pathway of complement activation in normal and diseased human glomeruli
J Zwirner1, E Felber, V Herzog
1Institut für Immunologie, Universität München, Munich, Federal Republic of Germany.
Insights
This study reveals that C4d fragment in normal glomeruli indicates continuous classical complement pathway activation. This activation is triggered by physiological deposition of IgM-containing immune complexes in the kidney.
Area of Science:
- Nephrology
- Immunology
- Histopathology
Background:
- The classical complement pathway plays a crucial role in immune responses and renal pathology.
- Understanding complement component deposition in renal tissues is vital for diagnosing kidney diseases.
Purpose of the Study:
- To investigate the deposition patterns of complement components in normal and diseased human renal tissues.
- To elucidate the role of C4d fragment in the classical complement pathway activation within the glomeruli.
Main Methods:
- Indirect immunoperoxidase technique using monoclonal antibodies against complement components.
- Histological examination of normal and glomerulonephritis kidney biopsies.
- Light and immunoelectron microscopy for detailed localization of C4d, IgM, and C4 binding protein (C4bp).
Main Results:
- Prominent C4d staining observed in glomeruli and renal arterioles of normal kidneys.
- C4d deposition localized to mesangial areas and subendothelial glomerular basement membrane (GBM).
- Diseased kidneys showed stronger, diffuse C4d staining patterns compared to segmental patterns in normal kidneys, correlating with IgM/IgG deposits and C4bp.
Conclusions:
- C4d fragment in normal human glomeruli signifies continuous local complement activation via the classical pathway.
- This activation is induced by physiological deposition of IgM-containing immune complexes.
- The findings provide insights into complement-mediated mechanisms in renal health and disease.
Abstract:
Monoclonal antibodies (mAb) reactive against complement components involved in the classical activation pathway were applied in an indirect immunoperoxidase technique for the histological study of normal and diseased human renal tissues. Prominent staining with antibodies against the C4d fragment was seen in all glomeruli and some renal arteriolar walls. The C4d staining was mesangial with light microscopy, whereas the subendothelial site of the glomerular basement membrane (GBM) also appeared to be positive in immunoelectron microscopy. In similar localization, albeit with distinctly weaker intensity, IgM and C4 binding protein (C4bp) were detected. In kidney biopsies from patients with various types of glomerulonephritis, C4d reactive antibodies stained the glomerular structures in a strong, diffuse or granular pattern in contrast to the more segmental distribution and weaker staining intensity in normal kidney specimens. Increased amounts of C4d, occasionally also of C4b, were paralleled in diseased kidney tissues by distinct deposits of IgM and/or IgG in the presence of C4bp. This study suggests that the C4d fragment in normal human glomeruli is indicative of a continuous, local complement activation via the classical pathway induced by the physiological deposition of IgM-containing immune complexes.