Fig 2: Cytokine secretion by the heart is influenced by MI and lack of CD73 on T cells.(A) Cytokine secretion was assessed in the coronary effluent of isolated perfused hearts from sham-operated CD4-Cre–/– CD73fl/fl mice (A) and 3 days after MI (B). Sham-operated mice, n = 3; MI mice, n = 6. (C) Influence of CD73 deficiency on T cells on the cardiac release of IL-6, MCP-1, and IL-9 measured in control (CD4-Cre–/– CD73fl/fl) and T cell–specific CD73-KO (CD4-Cre+/– CD73fl/fl) mice 3 days after MI (n = 6). Values are the mean ± SD. *P ≤ 0.05, **P ≤ 0.01, and ***P ≤ 0.001, by 2-tailed Student’s t test (A and B) and 2-way ANOVA using the 2-stage step-up method of Benjamini, Krieger, and Yekutieli (C).

Fig 3: Il6 expression in the infarcted heart as measured by RNAscope.Sections from hearts of C57BL/6J mice were analyzed 3 days after MI. (A) Representative WGA staining (bright green) delineates the infarcted area. Close-ups on the right were stained for Il6 mRNA (blue) with RNAscope without counterstaining. (B) Representative section stained for Ptprc (CD45) (red) and Il6 (blue) mRNA. Close-up in the upper right panel shows chromogenic staining at higher magnification. The chromogenic Fast Red dye could additionally be visualized in the red fluorescence spectrum, as shown in the lower panel of the close-up. The fluorescence image was overlaid with the bight-field image (gray). (C) Representative staining for Postn (blue) and Il6 (red) mRNA. The upper and lower close-ups are the chromogenic and fluorescence images, respectively. Representative images of the same heart are shown. n = 3. Scale bars: 300 μm and 20 μm (close-up insets). LV, left ventricle; RV, right ventricle.

Fig 4: Quantification of IL-6 secretion from cardiac ECs, granulocytes, macrophages, and CFs by ELISPOT.Cells were isolated 3 days after MI and seeded at a density of 10,000 cells per well. The number of IL-6–secreting cells was determined by ELISPOT assay after overnight incubation. n = 5. Values are the mean ± SD. *P ≤ 0.05, by 1-way ANOVA with Tukey’s multiple-comparison test. Gran, granulocytes.

Fig 5: Scheme of the proposed mechanism by which purinergic crosstalk between T cells and CFs controls IL-6 production.In the post-MI heart during scar formation, ATP is derived mainly from noncardiomyocytes. Fibroblasts, in contrast to T cells, cannot further degrade AMP to adenosine, such that accumulating AMP diffuses to neighboring T cells, which highly express CD73. Similarly, granulocytes and monocytes contribute to this extracellular AMP pool. Supply of AMP to T cell CD73 augments local adenosine formation, which stimulates IL-6 production by fibroblasts via the A2bR in a Gq-dependent manner. T cells are not only the hub for extracellular adenosine formation, as adenosine can also modulate in an autacoid feedback loop the production of INF-γ and IL-17 (14). IL-6 predominantly acts via trans-signaling (sIL-6R) to confer proinflammatory activity in the post-MI heart (37).