In addition to the determination of PD-L1 expression, studies have also observed changes in the expression of soluble PD-L1 (sPD-L1), with one study showing significantly higher sPD-L1 levels in the serum of IPF patients without surgical biopsy than in healthy controls [66], and another study observing a similar presentation [70]. The gene discussed is SPDL1; the disease is idiopathic pulmonary fibrosis.