CM from M1 macrophages induces a pro-inflammatory HDF. HDFs upregulated the gene expression of pro-inflammatory genes CCL2, IL6 and CCL7 after stimulation with CM of M1 polarized macrophages compared to M2 polarized and unstimulated macrophages (A). HDFs stimulated with CM of M1 macrophages secreted significantly more CCL2, IL6 and CCL7 after 24 h and 48 h, whereas secretion levels of these proteins by fibroblasts stimulated with CM of M2 macrophages or unstimulated macrophages were below the detection limit (B). ** p < 0.01, Difference between HDFs stimulated with CM of M1 polarized and CM of M2 polarized macrophages, *** p < 0.001. # p < 0.05, Difference between HDFs stimulated with CM of M1 polarized and CM of unstimulated macrophages, ## p < 0.01, ### p < 0.001. Gene expression analysis data were analyzed using two-way ANOVA followed by Bonferroni’s post-test, n = 4. Protein secretion data were analyzed using one-way ANOVA followed by Tukey’s post-test n = 3.