Analysis of an IL-10 polymorphism in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive fibrotic disorder of the lung parenchyma. We have demonstrated changes in IL-10 protein production by alveolar macrophages (AMs) from patients with IPF, which we hypothesise could be because of an IL-10 gene polymorphism. We have screened the coding sequence and 3′ untranslated region of IL-10 for polymorphisms using single-standard conformational polymorphism analysis. A novel polymorphism was identified resulting in a G to A substitution of +43 nucleotides from the start codon changing glycine to arginine at amino acid 15 of the signal peptide sequence. We have introduced the signal peptide mutation into the IL-10 gene and compared secretion of the mutant and wild-type forms after transient transfection of COS-7 cells. Our studies showed that the signal peptide mutation did not have a significant effect on secretion at 24 h post-transfection ( P =0.4529 by Mann-Whitney test). However, by 48 h there are significantly lower levels of mutant IL-10 ( P =0.0515). There were no differences in the level of cell-associated IL-10 at either 24 or 48 h ( P =0.9296 and 0.4268). We suggest that the mutation could affect the efficiency of protein translocation and signal peptide cleavage resulting in lower levels of IL-10 protein secretion.