Immunotherapies for cancers may cause severe and life-threatening cardiotoxicities.The underlying mechanisms are complex and largely elusive.Currently,there are several ongoing clinical trials based on the use of activated invariant natural killer T (iNKT) cells.The potential cardiotoxicity commonly associated with this particular immunotherapy has yet been carefully evaluated.The present study aims to determine the effect of activated iNKT cells on normal and β-adrenergic agonist (isoproterenol,ISO)-stimulated hearts.Mice were treated with iNKT stimulants,α-galactosylceramide (αGC) or its analog OCH,respectively,to determine their effect on ISO-induced cardiac injury.We showed that administration of αGC (activating both T helper type 1 (Th1)-and T helper type 2 (Th2)-Iiked iNKT cells) significantly accelerated the progressive cardiac injury,leading to enhanced cardiac hypertrophy and cardiac fibrosis with prominent increases in collagen deposition and TGF-β1,IL-6,and alpha smooth muscle actin expression.In contrast to αGC,OCH (mainly activating Th2-liked iNKT cells) significantly attenuated the progression of cardiac injury and cardiac inflammation induced by repeated infusion of ISO.Flow cytometry analysis revealed that αGC promoted inflammatory macrophage infiltration in the heart,while OCH was able to restrain the infiltration.In vitro coculture of αGC-or OCH-pretreated primary peritoneal macrophages with primary cardiac fibroblasts confirmed the profibrotic effect of αGC and the antifibrotic effect of OCH.Our results demonstrate that activating both Th1-and Th2-liked iNKT cells is cardiotoxic,while activating Th2-liked iNKT cells is likely cardiac protective,which has implied key differences among subpopulations of iNKT cells in their response to cardiac pathological stimulation.