Many types of glomerulonephritis (GN) undergo tandem connected phases: inflammation and fibrosis. Fibrosis in human GNs leads to irreversible end stage disease. This study investigated how these two phases were controlled.
Using a rat anti-glomerular basement membrane (GBM) GN model, we established bone marrow (BM) chimeras between GN-resistant Lewis (LEW) and GN-susceptible Wistar Kyoto (WKY) rats. Glomerular inflammation and fibrosis were compared between chimeras.
LEW’s BM to WKY (WKYLEW) chimeras with or without co-transfer of host WKY’s T cells were GN-resistant. On the other hand, WKY’s BM to LEW (LEWWKY) chimeras developed glomerular inflammation and albuminuria upon immunization. Quantitative analysis showed that the number and composition of inflammatory cells in glomeruli of immunized LEWWKY chimeras were similar to those in immunized WKY rats at their inflammatory peak. Thus, glomerular inflammation was controlled by BM derived non-T cell populations. However, unlike WKY rats, LEWWKY rats did not develop fibrosis until the end of experiments (84 days) in spite of persistent inflammation and albuminuria.
Inflammation alone was not sufficient to trigger fibrosis, suggesting a critical role of glomerular cells in the fibrotic process. As LEWWKY chimera allows us to separate glomerular inflammation from fibrosis, this model provides a useful tool to study how fibrosis is initiated following inflammation.