Baseline serum syndecan-4 predicts prognosis after the onset of acute exacerbation of idiopathic interstitial pneumonia. 
BACKGROUND: Patients with idiopathic interstitial pneumonia can experience acute  respiratory worsening, also known as acute exacerbation, with a large deterioration on prognosis. The precise mechanism remains unclear; however, syndecan-4 may be involved. Syndecan-4, a transmembrane heparan sulfate proteoglycan expressed in a variety of cells (e.g., epithelial cells, macrophages, fibroblasts, etc.), performs various biological roles by binding to  several proteins through its heparan sulfate glycosaminoglycan side chains. The goal of this study was to clarify the role of syndecan-4 in acute exacerbation of idiopathic interstitial pneumonia. METHODS: Patients with idiopathic interstitial pneumonia who had been sequentially admitted to our hospital due to acute exacerbation were retrospectively analyzed. First, serum syndecan-4 levels in the acute exacerbation and clinically stable phases were compared. Second, the relationship between serum syndecan-4 levels and clinical parameters was analyzed. Third, the  relationship between serum syndecan-4 levels and prognosis was evaluated. RESULTS: Serum syndecan-4 levels were significantly lower in patients with acute  exacerbation of idiopathic interstitial pneumonia than in patients in the clinically stable phase. Serum syndecan-4 levels also showed a significant positive correlation with white blood cell count and a weak positive tendency with KL-6 and baseline %VC. Prognosis was significantly worse in patients with idiopathic interstitial pneumonia with high baseline serum syndecan-4 levels than with low baseline levels. Multiple logistic analysis indicated baseline serum syndecan-4 level as the only prognostic predictor following acute exacerbation. CONCLUSIONS: Baseline serum syndecan-4 is a possible prognostic biomarker after the onset of acute exacerbation of idiopathic interstitial pneumonia.