Fig. 3.

Growth and differentiation factor 15 (GDF15) is upregulated in idiopathic pulmonary fibrosis (IPF) and expressed by epithelial cells. A: box-and-whisker plot of GDF15 expression data from the Lung Genomics Research Consortium (LGRC). Horizontal line marks the median value, box boundaries show the upper and lower quartiles, and whiskers show high and low values. Relative expression was calculated from normalized hybridization signal from microarray data. Welch’s t test, two tailed, was used to compare groups. B: correlation between natural log of GDF15 expression from IPF patients and carbon monoxide diffusion capacity (Dl_CO) in LGRC samples (Pearson correlation = −0.24). C: violin plots of GDF15 and EPCAM (epithelial cell adhesion molecule) expression in scRNA-seq data demonstrating epithelial specific expression of GDF15 (43). Data were processed and clustered exactly as described (43). The identity of each cluster is listed in the legend on the right. D: violin plot comparing GDF15 expression in donor and IPF lungs. AEC1 and AEC2, type I and II alveolar epithelial cell, respectively; NK, natural killer.