Abstract 16000: β-arrestins Mediate Cardiac Infiltration of Cytotoxic CD8+ T Cells and Macrophages in Acute CVB3 Viral Myocarditis

Abstract

Introduction: In response to Coxsackievirus B3 (CVB3) infection, immune cells infiltrate the heart affecting viral clearance, tissue damage, and cardiac remodeling. However, the molecular mechanisms regulating the immune response during acute CVB3-induced myocarditis are not well understood. β arrestins (βarrs), scaffolding proteins that mediate G protein-coupled receptor internalization, desensitization, and signaling are known to regulate immune responses. Hypothesis: We hypothesized that the immune populations infiltrating the heart during acute CVB3 infection are dependent on βarrs. Methods: To test our hypothesis, 5- to 7-week-old mice lacking βarr1 (βarr1 KO; n=8), βarr2 (βarr2 KO; n=4), or C57BL/6 controls (WT; n=7) were injected intraperitoneally with 1x10 4 plaque forming units (PFU) of CVB3 or saline and immune cell populations were measured in the heart at 7 days post infection (dpi) using flow cytometry. Results: At 7 dpi, there was a marked increase in cytotoxic CD8+ T cells in hearts of WT mice that positively correlated with the level of viral infection as assessed by heart tissue PFU (slope= 1.34, Y-intercept= -3.77). In contrast, the degree of infiltration of CD8+ T cells was significantly blunted in βarr KO hearts over a broad range of heart PFU (βarr1 KO: Slope=-0.3, Y-intercept=1.65; p=0.03 vs WT; βarr2 KO: Slope=-0.32, Y-intercept= 1.3; p=0.003 vs WT). Helper CD4+ T cell populations remained unaltered at 7 dpi among all groups. Macrophages at 7 dpi were significantly reduced in βarr KO hearts over a range of PFU (WT: Slope= 18.6, Y-intercept -52.32; βarr1 KO: Slope= -5, Y-intercept=32; βarr2 KO: Slope=3.46, Y-intercept=-8.4; p=0.04 vs WT). To assess cardiac injury, we measured the level of apoptosis by TUNEL staining and found that CVB3 infected βarr KO hearts showed significantly fewer TUNEL positive cells than WT CVB3 infected controls (WT 8.7%± 2.74; βarr1 KO 1.7%±0.51; βarr2 KO 1.7%±0.37; p=0.04 vs. WT). Conclusions: These data indicate that βarrs participate in the cardiac infiltration of CD8+ T cells and macrophages in response to CVB3 infection and that blocking the action of βarrs may diminish the cardiotoxicity with the acute phase of CVB3-induced myocarditis.