Differential expression of complement C3 and C4 in the human kidney

Area of Science:

• Nephrology
• Immunology
• Molecular Biology

Background:

• Complement activation is implicated in various immune-mediated renal diseases.
• Proximal tubular epithelial cells constitutively express complement C4 messenger RNA (mRNA) and can produce C3.
• The in situ localization of complement C3 and C4 mRNA in renal tissues requires further investigation.

Purpose of the Study:

• To compare the in situ localization of complement C3 and C4 mRNA in renal biopsy and nephrectomy specimens.
• To investigate the relationship between C3 mRNA distribution and histological abnormalities.
• To determine if tubular C3 and C4 mRNA are translated into proteins.

Main Methods:

• In situ hybridization to detect C3 and C4 mRNA in 23 renal tissue samples.
• Northern hybridization for mRNA detection.
• Immunohistochemistry using monoclonal antibodies to detect C3c and C4c proteins.

Main Results:

• C4 mRNA was consistently detected in the cortical tubular epithelium of all adequate samples.
• C3 mRNA expression varied significantly, with no detection in normal specimens.
• Focal C3 mRNA correlated with focal histological abnormalities, while diffuse C3 mRNA was associated with diffuse inflammatory processes.
• Cytoplasmic staining for C3c and C4c indicated translation of the respective mRNAs.
• Infiltrating inflammatory cells and glomerular cells were negative for C3 and C4 mRNA.

Conclusions:

• Renal tubular epithelial cells express both C3 and C4 mRNA, with C4 expression being constitutive and C3 expression varying with disease state.
• Local production of complement components within the kidney may contribute to the pathogenesis of renal diseases.
• Inflammatory mediators could induce C3 synthesis, potentially enhancing complement-mediated damage in the renal interstitium.