Fig. 5

Endogenous S100A9 enhances PD-L1 expression in monocytes to inhibit T-cell cytotoxicity. a KEGG pathway enrichment analysis of DEGs between S100A9⁺CD14⁺ monocytes and other circulating cells. b Percentage of S100A9⁺ cells (left) and PD-L1⁺ cells (right) in PBMC from healthy donors (HD, n = 5) and patients with hepatocellular carcinoma (HCC, n = 7), colorectal cancer (CRC, n = 5), and biliary tract cancer (BTC, n = 7). c-e PD-L1 levels in S100A9^high or S100A9^low cells in CD14⁺monocytes from patients with HCC, CRC, and BTC. f-h Correlation analysis between PD-L1 and S100A9 levels in CD14⁺monocytes from patients with HCC, CRC, and BTC. i S100A9 and CD274 (j) mRNA levels of S100A9-knockdown THP-1 cells transfected with si-S100A9#1, si-S100A9#2, and si-S100A9#3. k Representative flow cytometric plot (left) and quantification (right) of S100A9 levels in S100A9-knockdown THP-1 cells transfected with sh-S100A9#1 and sh-S100A9#2. l Representative flow cytometric plot (left) and quantification (right) of PD-L1 levels in S100A9-knockdown THP-1 cells transfected with sh-S100A9#1 and sh-S100A9#2. m the percentage of highly proliferated CFSE^low of T cells co-cultured with S100A9-knockdown THP-1 cells at 96 h (n = 3). n TBX21, PRF1, IL2, and GZMB mRNA levels of T cells after co-cultured with S100A9-knockdown THP-1 cells for 24 h. P value in (b) was evaluated using the Mann–whitney U-test. P values in c-e were determined by two-tailed paired sample t-test. P values in i-m were determined by one-way ANOVA. P value in (n) was evaluated using 2-way ANOVA. Correlations were analyzed using the Spearman rank correlation test. *P < 0.05, **P < 0·01, ***P < 0.001 and ****P < 0.0001