ARG1 and myositis disease: M2-like macrophages have previously been characterized by their expression of arginase gene Arg1 (39, 40), but in RRV-induced myositis, two studies showed that specific depletion of Arg-1-expressing myeloid cells enhanced viral clearance and reduced pathology (52, 53), and our findings showing that Arg1 mRNA is highly expressed in the muscle during the acute phase of the disease (6 to 9 dpi) are consistent with these findings.