Lymphocyte Activation Gene 3 Regulation of Profibrotic Cytokines and Type I Collagen Production in Patients With Systemic Sclerosis.

OBJECTIVE: Diffuse cutaneous systemic sclerosis (dcSSc) is characterized by skin and internal organ fibrosis. The regulatory aspects of the immune system involved in maintaining tolerance are still poorly understood in dcSSc. The late checkpoint inhibitory lymphocyte activation gene 3 (LAG-3) is implicated in T cell inhibition by interacting with its ligand, major histocompatibility complex class II. Its role in dcSSc has yet to be established. METHODS: Plasma soluble LAG-3 (sLAG-3) levels of 35 patients with dcSSc were compared with the levels of 20 healthy controls (HCs). Peripheral blood mononuclear cell (PBMC) samples from patients with dcSSc (n = 8) and HCs (n = 8) were analyzed by flow cytometry for the surface expression of LAG-3 on CD4+ and CD8+ T cells after CD3/CD28 stimulation. The dcSSc PBMCs were stimulated (anti-CD3/CD28), kept as monocultures, or cocultured with autologous dermal fibroblasts and treated with a LAG-3 agonistic antibody or isotype control. The supernatants were analyzed for proinflammatory cytokines, extracellular matrix proteins, and bioactive type I interferon (IFN). RESULTS: Patients with dcSSc had a two-fold decreased sLAG-3 level compared with HCs (P < 0.0001). Increased surface expression of LAG-3 was observed in activated CD4+ T cells and CD8+ T cells in patients with dcSSc compared to HC PBMCs. The LAG-3 agonistic antibody decreased IFNγ, interleukin-4, and tumor necrosis factor α levels in supernatants from PBMCs and dermal fibroblast cocultures. Furthermore, we observed decreased pro collagen, fibronectin, and IFNα/β bioactivity in the cocultures. CONCLUSION: LAG-3 is immunoregulatory in dcSSc, and a LAG-3 agonistic antibody is a potential treatment modality.