Fig 1: IL-17A Trans-Signaling through Cardiac Fibroblasts Downregulates MerTK expression on Monocytes and MDMs(A and B) Representative EM images showing (A) apoptotic cells or apoptotic cellular debris internalized by Ly6Chi MDMs (arrowheads) and (B) engulfed cellular debris were largely absent in Ly6Clo MDMs. Scale bars: 2 µm.(C) Macrophage phagocytic index was calculated using the following formula: (number of engulfed apoptotic cells/total number of macrophages) × (number of macrophages with engulfed apoptotic cells/total number of macrophages) × 100.(D–G) Hearts from day 21 EAM mice.(D) Frequencies of F4/80hiCD64+ macrophages out of viable CD45+Ly6G–CD11b+ cells were assessed by flow cytometry.(E and F) MerTK MFI of F4/80hiCD64+ macrophages (E) and F4/80–CD64+ monocytes (F) in the hearts.(G) ELISA showing soluble Mer (sMer) in WT and IL-17Ra-/- EAM mice sera.(H and I) Cardiac fibroblasts were harvested from WT naive mice, whereas monocytes were sorted from EAM IL-17Ra-/- mice.(H) MerTK MFI of Ly6Chi or Ly6Clo monocytes and MDMs in vitro after 160 h post-co-culture with cardiac fibroblasts stimulated with or without IL-17A.(I) sMer detected in supernatants of the monocyte-fibroblast co-culture by ELISA.(J) Flow cytometric analysis of the frequencies of FITC+F4/80hiCD64+ macrophages in the myocardium of WT, IL-17Ra-/-, and non-treated controls.(K) Percentages of FITC+F4/80hiCD64+ macrophages out of viable CD45+Ly6G–CD11b+ cells.(L) MerTK MFI in patients with either myocarditis or ischemic cardiomyopathy.(D–G) Data are representative of five independent experiments. n = 8 – 9. (H and I) Data are representative of three independent experiments with technical triplicates. n = 3. (J and K) Data are representative of two independent experiments. n = 3. (C–G, I, K, and L) Groups were compared using Student’s t test. *p < 0.05; **p < 0.01. (H) Groups were compared using one-way ANOVA followed by Dunnett test. **p < 0.01; ****p < 0.0001. All data were presented as mean ± SD.See also Figure S7 and Tables S2 and S3.