In IPF patients, the percentages of S100A9+CD163− monocytes showed a trend toward a moderate correlation with the serum levels of surfactant protein-D (SP-D) (r = 0.4158 [95% CI − 0.02042–0.7191], p = 0.051, Table 2). The gene discussed is S100A9; the disease is idiopathic pulmonary fibrosis.