Background: Mast cells (MCs) have been implicated in the pathogenesis of atherosclerosis and tissue fibrosis. However, the role of MC in the development of renal fibrosis has not been fully elucidated. Stem cell factor (SCF; the ligand for MC c-kit receptor) is thought to attract and activate MCs.
Methods: The intensity of MC infiltration and SCF expression in renal biopsies from 56 patients with different forms of primary and secondary glomerulonephritis and five controls were investigated by immunohistochemistry, using a monoclonal anti-human MC tryptase antibody and a polyclonal antihuman SCF antibody.
Results: A large number of MCs were detected in the renal interstitium of the diseased kidneys. Immunostainable SCF was detected in tubular as well as interstitial cells. MC infiltration was significantly higher in glomerulonephritis (16.9 +/- 10.2 cells/field) compared with controls (2.8 +/- 2.1 cells/field, P = 0.03). Similarly, immunostainable SCF was 0.6 +/- 0.3% for controls and 3.3 +/- 2.1% in the glomerulonephritis group (P = 0.02). MC infiltration was highly correlated with SCF expression in diseased kidneys (r = 0.93, P = 0.0001). Double immunostain showed them to colocalize in some interstitial cells. Analysis of MC proliferation [proliferating cell nuclear antigen (PCNA) positivity] and apoptosis (in situ end labeling of DNA) showed these cells to be terminally differentiated. Both MCs and SCF were correlated with interstitial fibrosis (R = 0.71 for MC and R = 0.62 for SCF, P = 0.0001) and interstitial alpha-smooth muscle actin (R = 0.69 for MC and R = 0.60 for SCF P = 0.0001). Using regression analysis, the number of MC infiltration was found to be a very powerful determinant of interstitial fibrosis in the glomerulonephritis group (R2 = 91.4%).
Conclusion: MCs as an infiltrating hematopoietic cell and its growth factor (SCF) seem to be up-regulated in glomerulonephritis, and may play a role in the development of renal fibrosis.