Interrogation of single-cell RNA-Seq data from 4 independent groups revealed highly enriched expression of MARCO in circulating and alveolar macrophages, as well as monocytes in both SSc and IPF lungs (Figure 1B and Supplemental Figure 1A; supplemental material available online with this article; https://doi.org/10.1172/jci.insight.151037DS1). Here, MARCO is linked to idiopathic pulmonary fibrosis.