cell infiltration whereas genetic inactivation of A2AR exerted the opposite effect. Noteworthy, while macrophages played an important role in renal fibrosis in a model of immune-associated chronic inflammation [13] and in aristolochic acid-induced RIF [36], in the presented UUO model no significant amount of macrophage (with CD68+ and F4/80+ staining) was observed participating in leukocyte infiltration around vessels post-UUO. Treg cells are critical to maintain immune-cell homeostasis by enforcing a dominant negative regulation on other immune cells. Thus, Tregs are of great interest due to its immunosuppressive effect and inhibitory effect against fibrosis [37]. Most recent, it wasAdenosine A2AR and Renal Interstitial Fibrosisreported that Tregs’ negative regulation on immune cells was mediated by A2AR activation whereas deletion of A2AR abolished Tregs’ regulatory effect [38]. These reports support our findings that A2AR activation by CGS21680 significantly increased the ratio of Tregs to CD4+ T lymphocytes, whereas this ratio was significantly decreased in A2AR KO mutants post-UUO. Thus, regulation of Tregs recruitment and (CD4+) T lymphocyte infiltration acts as underlying mechanism of A2AR-mediated effects against RIF. Another important finding in this study is that A2AR could affect EMT-related changes in E-cadherin and SMA. While more direct evidence and evaluations are needed in human studies, EMT is recently proposed as a 15755315 crucial mechanism in RIF [5]. During the EMT process, renal tubular epithelial cell lost the E-cadherin phenotype and acquire the myofibroblast phenotype a-SMA. Our findings demonstrated that activation of A2AR restored expression level of a-SMA and E-cadherin to a basal level in sham animals (Figure 4). Though indirectly based on Western blot reflecting total renal tissue rather than TECs-specific on-site changes, this finding indicates that A2AR activation maintained intrinsic phenotypes of epithelia and myofibroblast, i.e., inhibited the process of EMT. To find the mechanism by which A2AR affects EMT, we demonstrated that activation of A2AR significantly reduced the expression of TGF-b1, a key profibrotic mediator in EMT, along with ROCK1, the regulatory protein in the TGF-b1 downstream pathway Rho/ROCK signaling. In UUO, the enhanced TGF-b1 may (i) act as a mitogenic factor to affect collagen synthesis and (ii) facilitate the EMT process [6,39]. Importantly, activation of A2AR restored.Ortance in phenotypic conversion of RIF, 1516647 suggesting A2AR may become a potential therapeutic target against RIF. Regulation of the infiltration of T lymphocytes is the principal mechanism of A2AR manipulation in UUO-induced RIF in mice. The infiltration of lymphocyte, as a macrophage-independent response, plays an important role in the process of RIF and nephritis [19,25,26,27,28]. T cell infiltration was observed in the kidneys of patient with chronic kidney disease [29] and in the models of UUO 
[30,31,32]. Furthermore, there is reduced lymphocyte infiltration and fibrosis in the kidney after UUOwhen CC-chemokine receptor-1 mediated migration of lymphocytes into inflamed tissue is blocked [31,33]. Activation of A2AR, as a Gs coupling protein receptor, can significantly increase cAMP level in immune cells, and in turn, alter immune responses including antigen presentation, T cell activation, clonal expansion, and the survival of immune memory [34,35]. This study shows that activation of A2AR significantly reduced the CD4+ T cell infiltration whereas genetic inactivation of A2AR exerted the opposite effect. Noteworthy, while macrophages played an important role in renal fibrosis in a model of immune-associated chronic inflammation [13] and in aristolochic acid-induced RIF [36], in the presented UUO model no significant amount of macrophage (with CD68+ and F4/80+ staining) was observed participating in leukocyte infiltration around vessels post-UUO. Treg cells are critical to maintain immune-cell homeostasis by enforcing a dominant negative regulation on other immune cells. Thus, Tregs are of great interest due to its immunosuppressive effect and inhibitory effect against fibrosis [37]. Most recent, it wasAdenosine A2AR and Renal Interstitial Fibrosisreported that Tregs’ negative regulation on immune cells was mediated by A2AR activation whereas deletion of A2AR abolished Tregs’ regulatory effect [38]. These reports support our findings that A2AR activation by CGS21680 significantly increased the ratio of Tregs to CD4+ T lymphocytes, whereas this ratio was significantly decreased in A2AR KO mutants post-UUO. Thus, regulation of Tregs recruitment and (CD4+) T lymphocyte infiltration acts as underlying mechanism of A2AR-mediated effects against RIF. Another important finding in this study is that A2AR could affect EMT-related changes in E-cadherin and SMA. While more direct evidence and evaluations are needed in human studies, EMT is recently proposed as a 15755315 crucial mechanism in RIF [5]. During the EMT process, renal tubular epithelial cell lost the E-cadherin phenotype and acquire the myofibroblast phenotype a-SMA. Our findings demonstrated that activation of A2AR restored expression level of a-SMA and E-cadherin to a basal level in sham animals (Figure 4). Though indirectly based on Western blot reflecting total renal tissue rather than TECs-specific on-site changes, this finding indicates that A2AR activation maintained intrinsic phenotypes of epithelia and myofibroblast, i.e., inhibited the process of EMT. To find the mechanism by which A2AR affects EMT, we demonstrated that activation of A2AR significantly reduced the expression of TGF-b1, a key profibrotic mediator in EMT, along with ROCK1, the regulatory protein in the TGF-b1 downstream pathway Rho/ROCK signaling. In UUO, the enhanced TGF-b1 may (i) act as a mitogenic factor to affect collagen synthesis and (ii) facilitate the EMT process [6,39]. Importantly, activation of A2AR restored.