Slpi, also known as Secretory Leukocyte Protease Inhibitor, is a multifunctional protein. It acts as a serine antiprotease, protecting airways from proteolytic damage caused by neutrophil and other immune cell-derived serine proteases. It has antimicrobial and anti-viral properties, and can control inflammation in the lung by interfering with NF-κB-induced pro-inflammatory gene expression. It is expressed at mucosal surfaces, mainly by epithelial cells, and maintains homeostasis at barrier tissues [1,2].

In a muco-obstructive lung disease model, when ENaC-Tg mice (replicating COPD and CF features) were crossed with SLPI knock-out (SLPI-/-) mice, SLPI deficiency altered airway protease activity and induced cell recruitment, suggesting a role of decreased SLPI levels in the pathogenesis of muco-obstructive lung disease [4]. In bone metabolism, genetic ablation of Slpi in mice severely impaired PTH-induced bone formation, as Slpi in osteoblasts enhances their differentiation and suppresses osteoclastic function, regulating communication between the two cell types [3].

In conclusion, Slpi plays essential roles in maintaining mucosal tissue homeostasis, especially in the airways and bone. Gene knockout mouse models have revealed its significance in muco-obstructive lung disease and PTH-induced bone formation, providing insights into disease mechanisms and potential therapeutic targets in these areas.