Objective:To investigate the proliferative lesions of glomerular mesangial cell (GMC) in Thy-1 nephritis (Thy-1N) rats and the role of sublytic C5b-9 complexes in GMC proliferation. Methods:Thy-1N rat model was constructed. The expression of cyclin D2,proliferative cell nuclear antigen(PCNA) in the renal tissues of rats at mRNA and protein levels were observed at 18 h,on day 3 (3 d) and day 7 (7 d) after Thy-1 Ab injection. The deposition of C5b-9 was detected in the glomerulus. Meanwhile,the proliferation of glomerular cells in rats was assessed by BrdU incorporation,light microscopy(LM) and electron microscopy (EM). Furthermore,rat GMC were cultured and divided into different groups,and then the proliferation of GMC exposed to sublytic C5b-9 was evaluated by 3H-thymidine incorporation(3H-TdR) analysis. Results:The expression of cyclin D2 and PCNA in the renal tissues and the number of glomerular BrdU-positive cells became increasing at 18 h in Thy-1N rats,and continue increasing on 3 d and 7 d. The deposition of C5b-9 was found in the glomerulus,and some cells were intact. Moreover,the number of GMC and the secretion of ECM were increased on 3d and became obvious on 7 d under LM and EM. The proliferation of GMC was increased at 18 h after sublytic C5b-9 stimulation in vitro. The supernatant of GMC induced by sublytic C5b-9 could also promote GMC proliferation of rat. Conclusion:Glomerular lesions in rats with Thy-1N include early and secondary GMC proliferation,while sublytic C5b-9 complexes might be involved in early GMC proliferation.