SIRPA and fibrosis: In addition, further studies are needed to determine the alternative mechanisms, including oxidative stress, protease/anti-protease imbalance, or increase the inhibitory macrophage receptor signal regulatory protein-alpha (SIRPα), which all play important roles in the regulation of apoptotic cell clearance,30, 31 in bleomycin-induced fibrosis, using simvastatin, PPARγ agonists/antagonists, or RhoA inhibitors.