Fig 2: Dynamics and prognostic value of serum CXCL17 levels in influenza (A) Influenza patients (n = 68) were grouped according to their duration of symptoms on admission. Levels of CXCL17 were compared to healthy donors (HD; Kruskal–Wallis test and post hoc Dunn test; graph displays means and the standard error ( ± SE); *p = 0.05, **p = 0.01, ***p = 0.001, ****p = 0.0001). (B) We obtained a second serum sample in 54 influenza subjects seven days (D7) after hospital admission (D0). Levels of CXCL17 at D0 and D7 were compared with the Mann–Whitney U test. (C) Longitudinal change in CXCL17 levels in survivor and deceased influenza patients (Wilcoxon test). (D) Initial serum CXCL17 levels in survivor (n = 52) and deceased (n = 16) influenza patients (Mann–Whitney U test; plots display medians and interquartile ranges). (E) Random forest algorithm showing the most important factors that impact on influenza-associated mortality. (F) Receiver operating characteristic (ROC) curve of the levels of CXCL17 in survivor and deceased influenza subjects. The graph displays area under the curve (AUC) and 95% CI interval values. (G) Survival curves of influenza patients grouped according to their serum CXCL17 levels were compared with the log-rank test.

Fig 3: Overexpression of CXCL17 upregulated CCL20 expression. Eighty-nine DEGs (a) shared by CXCL17 and GPR35 were used for PPI analysis (b). CXCL17 mRNA level in the CCLE cell lines (c). The protein level of CCL20 was significantly upregulated after transfecting a CXCL17 overexpression plasmid into the HGC27 cells (d). The mRNA level of SFRP2 (e) was downregulated upon the overexpression of CXLC17, while the CDX1 level (f) remained unchanged. ** p < 0.01. ns, no significance; PPI, protein–protein interaction; CCLE, Cancer Cell Line Encyclopedia.

Fig 4: Extended predictive value of serum CXCL17 levels in influenza patients and cellular sources. (A) Multiple correlation analysis of the clinical variables and serum CXCL17 levels of influenza patients (n = 68). The heat color map gradient was constructed using Spearman R values. (B) Serum CXCL17 levels in influenza patients according to the severity of their acute respiratory distress syndrome (ARDS) on admission (mild, PaO2/FiO2 >200, n = 3; moderate, PaO2/FiO2 100–200, n = 27; severe, PaO2/FiO2 <100, n = 38; Kruskal–Wallis test and post hoc Dunn test). (C) Comparison of the levels of CXCL17 between COVID-19 patients that survived (n = 14) or died (n = 10). Mann–Whitney U test. (D) Serum levels of CXCL17 were compared between influenza patients that developed acute kindly injury (AKIN, n = 19), and individuals with normal renal function (n = 49). (E) Differences in CXCL17 levels between influenza patients according to their need for renal replacement therapy (RRT; n = 52 vs 16). (B–E) Plots display medians and interquartile ranges. Mann–Whitney U test. (F) Receiver operating characteristic (ROC) curve of the CXCL17 levels in influenza patients that developed AKIN and those that maintained normal renal function. The graph display area under the curve (AUC) and 95% CI interval values. (G) ROC curve analysis of the serum CXCL17 levels in patients requiring RRT. (H) Human A549 alveolar epithelial cells and (I) peripheral blood-monocyte derived macrophages were infected with a clinical isolate of the influenza A(H1N1) pdm09 virus for 24, 48, and 72 h n = 6–7 per group per time point). Levels of CXCL17 in supernatants from infected and uninfected cells were compared using the unpaired Student’s t test (n = 5 to 9 per group) at each time point. Values of p were corrected for multiple comparisons using the Holm–Sidak method. The data represent mean ( ± SE) values from 2 to 3 independent experiments per time point and experimental condition. *p = 0.05, **p = 0.01, ***p = 0.001, ****p = 0.0001.

Fig 5: Identification of DEGs of CXCL17 (a) and GPR35 (c); the red color is indicative of upregulated genes and the green color is indicative of downregulated genes. The heatmaps displayed the top 20 down- and upregulated genes of CXCL17 (b) and GPR35 (d). The top DEGs shared by CXCL17 and GPR35 are in red. DEGs, differentially expressed genes.