Hydroxychloroquine cures autoimmune myocarditis by inhibiting the innate immune system via the C‐X‐C motif chemokine ligand 16 and C‐X‐C motif receptor 6 axis between macrophages and T cells

Abstract Background and Purpose Myocarditis is a life‐threatening inflammatory disease, but lacks effective treatment options. Hydroxychloroquine (HCQ), an established antimalarial agent, is used widely to manage rheumatic disorders. This research aimed to evaluate the efficacy of HCQ in treating myocarditis. Experimental Approach A mouse model of experimental autoimmune myocarditis (EAM) was used to evaluate the therapeutic effects of HCQ on cardiac function, inflammation and fibrosis. Echocardiography, histology and cytokine assays were performed to assess cardiac function and inflammatory responses. Single‐cell RNA sequencing was employed to analyse immune cell populations and chemotactic activity. C–X–C motif chemokine ligand 16 (CXCL16) levels were measured in cardiac tissue and serum, while YY1 expression was measured by western blotting in macrophages and cardiac tissue. Flow cytometry was used to evaluate immune cell infiltration and migration. Key Results HCQ improved cardiac function in acute and chronic myocarditis. HCQ treatment reduced inflammation, fibrosis and immune cell infiltration in myocarditis models. Single‐cell RNA sequencing revealed that HCQ lowered inflammatory cell proportions and suppressed macrophage chemotaxis. HCQ reduced YY1 levels, leading to the down‐regulation of CXCL16 expression in macrophages and inhibition of CXCL16‐mediated chemotaxis to Th17 and natural killer T (NKT) cells. CXCL16 neutralizing antibodies improved cardiac function and reduced inflammation in myocarditis. Conclusion and Implications HCQ improves cardiac function and reduces inflammation in myocarditis by inhibiting CXCL16 expression in macrophages, by suppressing its transcription factor YY1, which in turn reduced the chemotaxis of Th17 and NKT cells. HCQ is a promising therapeutic agent for myocarditis.