GPR68 and idiopathic pulmonary fibrosis: Furthermore, TDAG8 was shown to be upregulated in lung fibroblasts from patients with idiopathic pulmonary fibrosis compared to healthy individuals, whilst OGR1 was downregulated in these cells, and GPR4 was not detected in primary human lung fibroblasts [65], hence mirroring expression patterns of bronchial smooth muscle cells.