Profilin is a cytoplasmic protein that binds to actin monomer and regulates actin polymerization. In a number of experimental and human glomerular diseases, the mesangial cell expresses alpha-smooth muscle actin and undergoes a phenotypic change to myofibroblast. We used a rat model of mesangial proliferative nephritis induced with antibody to the Thy 1 antigen present on mesangial cells to investigate whether profilin is upregulated. We amplified and sequenced rat profilin cDNA by the reverse-transcribed-polymerase chain reaction (RT-PCR). The nucleotide and amino acid sequences were highly conserved across the mammalian profilins. We raised affinity purified antibody to rat profilin in rabbits immunized with a synthetic profilin peptide (EFTMDLRTKS). At 7 days after disease induction, enhanced expression in both profilin mRNA and protein was demonstrated in the isolated glomeruli by RT-PCR and Western blot analysis. These results suggest that profilin may be involved in the pathogenesis of glomerulonephritis by reorganizing actin cytoskeleton.