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T follicular helper–like cells and IL-21 are drivers of skin fibrosis in systemic sclerosis. Scleroderma's little helpers: Scleroderma, also known as systemic sclerosis, is a devastating disease involving multi-organ fibrosis. Taylor et al. examined immune cells from patients and in the skin of a graft-versus-host disease–based mouse model to elucidate the key players in this disease. They observed that a subset of T follicular helper–like cells expressing inducible costimulator (ICOS) correlated with disease scores. Blocking these cells with anti-ICOS or anti–IL-21, an important T follicular helper cell cytokine, ameliorated disease in the mouse model. Targeting these not-so-helpful T cells could dampen dermal fibrosis and bring relief to scleroderma patients. Systemic sclerosis (SSc) is a debilitating inflammatory and fibrotic disease that affects the skin and internal organs. Although the pathophysiology of SSc remains poorly characterized, mononuclear cells, mainly macrophages and T cells, have been implicated in inflammation and fibrosis. Inducible costimulator (ICOS), which is expressed on a subset of memory T helper (TH) and T follicular helper (TFH) cells, has been shown to be increased in SSc and associated with disease pathology. However, the identity of the relevant ICOS+ T cells and their contribution to inflammation and fibrosis in SSc are still unknown. We show that CD4+ ICOS-expressing T cells with a TFH-like phenotype infiltrate the skin of patients with SSc and are correlated with dermal fibrosis and clinical disease status. ICOS+ TFH-like cells were found to be increased in the skin of graft-versus-host disease (GVHD)–SSc mice and contributed to dermal fibrosis via an interleukin-21– and matrix metalloproteinase 12–dependent mechanism. Administration of an anti-ICOS antibody to GVHD-SSc mice prevented the expansion of ICOS+ TFH-like cells and inhibited inflammation and dermal fibrosis. Interleukin-21 neutralization in GVHD-SSc mice blocked disease pathogenesis by reducing skin fibrosis. These results identify ICOS+ TFH-like profibrotic cells as key drivers of fibrosis in a GVHD-SSc model and suggest that inhibition of these cells could offer therapeutic benefit for SSc. [ABSTRACT FROM AUTHOR]

Objective Systemic sclerosis (SSc) is a fibrotic disease characterized by an obliterative vasculopathy with thrombosis and impairment of the coagulation-fibrinolysis balance. Plasminogen activator inhibitor 1 (PAI-1) is the major inhibitor of profibrinolytic plasminogen activators (PAs). This study was undertaken to evaluate the contribution of PAI-1 to SSc pathology in the skin. Methods PAI-1 was evaluated in skin from patients with diffuse SSc (dSSc) and those with limited SSc (lSSc) by immunohistochemistry. The contribution of PAI-1 to SSc pathology was tested in vivo in murine graft-versus-host disease (GVHD) and bleomycin models of progressive skin fibrosis and in vitro in dermal human microvascular endothelial cells (HMVECs) using a monoclonal antibody that selectively prevents the binding of PAI-1 to PA. Results Skin from patients with dSSc and those with lSSc showed increased PAI-1 levels in the epidermis and microvessel endothelium. PAI-1 neutralization in the GVHD model led to a dramatic, dose-dependent improvement in clinical skin score, concomitant with vasculopathy resolution, including a reduction in fibrinolysis regulators and vascular injury markers, as well as reduced inflammation. Resolution of vasculopathy and inflammation was associated with resolution of skin fibrosis, as assessed by reduction in collagen content and expression of key profibrotic mediators, including transforming growth factor β1 and tissue inhibitor of metalloproteinases 1. Similar to the GVHD model, PAI-1 neutralization reduced dermal inflammation and fibrosis in the bleomycin model. PAI-1 neutralization stimulated plasmin-mediated metalloproteinase 1 activation in dermal HMVECs. Conclusion Our findings indicate that neutralization of the antifibrinolytic function of PAI-1 resolves skin fibrosis by limiting the extent of initial vascular injury and connective tissue inflammation. These data suggest that PAI-1 represents an important checkpoint in disease pathology in human SSc. [ABSTRACT FROM AUTHOR]