Upregulation of the CD155-CD226 Axis Is Associated With Muscle Inflammation and Disease Severity in Idiopathic Inflammatory Myopathies

BACKGROUND AND OBJECTIVES: The CD155-CD226/T-cell Ig and immunoreceptor tyrosine-based inhibitory motif (ITIM) domain (TIGIT) pathway plays a critical role in regulating T-cell responses and is being targeted clinically. However, research on the role of this pathway in autoimmune diseases is limited. This study aimed to investigate the expression and tissue-specific roles of CD155-CD226/TIGIT pathway molecules in the inflamed muscles of patients with idiopathic inflammatory myopathies (IIMs). METHODS: Immunohistochemistry, Western blot analysis, and polychromatic immunofluorescence staining were performed to examine the expression of CD155, CD226, and TIGIT in skeletal muscle biopsies from 30 patients with dermatomyositis (DM), 10 patients with amyopathic DM (ADM), 20 patients with immune-mediated necrotizing myopathy (IMNM), 5 patients with dysferlinopathy, and 4 healthy controls. Flow cytometry analysis was used to analyze the functions of T cells with different phenotypes. RESULTS: Strong expression of CD155 was observed in patients with DM and IMNM, while its expression was largely negative in those with ADM and dysferlinopathy and healthy controls. The costimulatory receptor CD226 was highly expressed on muscle-infiltrating cells, while the coinhibitory receptor TIGIT was expressed at low levels. These infiltrating CD226+ cells were mainly activated effector T cells that localized adjacent to CD155-expressing myofibers, but were faintly detectable within the muscle fascicles lacking CD155. A strong positive correlation between CD155 and CD226 expression scores was also observed. Polychromatic immunofluorescence staining revealed that CD155+ muscle cells coexpressed major histocompatibility complex classes I and II, and tumor necrosis factor alpha expression was detected in CD226+ T cells at their close sites with the myofibers. Furthermore, the expression levels of CD155 and CD226 showed a positive correlation with creatine kinase, lactate dehydrogenase, and the muscle histopathology damage scores and an inverse correlation with the Manual Muscle Testing-8 scores. In addition, CD155 and CD226 expressions were significantly decreased in representative patients who achieved remission posttreatment. DISCUSSION: These findings demonstrate that the CD155-CD226 axis is highly activated in inflamed muscle tissues of patients with IIM and is associated with muscle disease severity. Our data uncover the immunopathogenic role of the axis in the pathology of IIMs.