A coculture system of macrophages and mesangial cells was established in vitro. The changes in levels of the fibrotic markers α-SMA and Collagen I of mesangial cells were observed using confocal microscopy, and the findings revealed that the interaction between macrophages and mesangial cells was involved in the process of DKD fibrosis. The gene discussed is ACTA1; the disease is diabetic kidney disease.