CCR4 and idiopathic pulmonary fibrosis: Overall, differential gene expression results derived from single cell and bulk RNA expression data suggested that a monocyte-macrophage chemoattractant axis (including potentially CCL2-CCR2 and CCL17-CCR4) was highly activated in ‘Ciliated_low’ (Myeloid-enriched IPF subset) patients and was possibly responsible for recruiting inflammatory macrophages in this subset, whereas ciliated epithelium-derived chemokine production (e.g. CCL15) may play an important role in cell recruitment in the Ciliated epithelium-enriched IPF subset of patients.