APLN and silicosis: More strikingly, after adjusting for age and smoking, serum apelin levels were positively correlated to DLCO% (P=0.031), FVC% (P=0.004), FEV1% (P=0.006), FEF50% (P=0.033), and FEF25-75% (P<0.001) in silicosis patients (Figure 1C).