Abstract
IntroductionInterleukin-6 (IL-6) is a pleiotropic cytokine for which preliminary data have suggested that it might contribute to systemic sclerosis (SSc). Our aims were to investigate, firstly, IL-6 expression in patients with SSc and, secondly, the efficacy of both passive and active immunization against IL-6 to reduce skin fibrosis in complementary mouse models of SSc.MethodsHuman serum levels and skin expression of IL-6 were determined by enzyme-linked immunosorbent assay and immunohistochemistry, respectively. We first evaluated the antifibrotic properties of the monoclonal anti-IL-6R antibody, MR16-1, in the bleomycin-induced dermal fibrosis mouse model, reflecting early and inflammatory stages of SSc. Then, we assessed the efficacy of MR16-1 in tight skin-1 (Tsk-1) mice, an inflammation-independent model of skin fibrosis. Additionally, we have developed an innovative strategy using an anti-IL-6 peptide-based active immunization. Infiltrating leukocytes, T cells, and B cells were quantified, and IL-6 levels were measured in the serum and lesional skin of mice after passive or active immunization.ResultsSerum and skin levels of IL-6 were significantly increased in patients with early SSc. Treatment with MR16-1 led in the bleomycin mouse model to a 25% (P = 0.02) and 30% (P = 0.007) reduction of dermal thickness and hydroxyproline content, respectively. MR16-1 demonstrated no efficacy in Tsk-1 mice. Thereafter, mice were immunized against a small peptide derived from murine IL-6 and this strategy led in the bleomycin model to a 20% (P = 0.02) and 25% (P = 0.005) decrease of dermal thickness and hydroxyproline content, respectively. Passive and active immunization led to decreased T-cell infiltration in the lesional skin of mice challenged with bleomycin. Upon bleomycin injections, serum and skin IL-6 levels were increased after treatment with MR16-1 and were significantly reduced after anti-IL-6 active immunization.ConclusionsOur results support the relevance of targeting IL-6 in patients with early SSc since IL-6 is overexpressed in early stages of the disease. Targeting IL-6 by both passive and active immunization strategies prevented the development of bleomycin-induced dermal fibrosis in mice. Our results highlight the therapeutic potential of active immunization against IL-6, which is a seductive alternative to passive immunization.
Highlights
Interleukin-6 (IL-6) is a pleiotropic cytokine for which preliminary data have suggested that it might contribute to systemic sclerosis (SSc)
Preliminary data suggest that IL-6 might contribute to human SSc: levels of IL-6 are increased in the serum and in the lesional skin of patients with SSc, spontaneous production of IL-6 by peripheral blood leukocytes from patients with SSc is elevated compared with healthy controls, and IL-6 levels correlate with skin thickness score [3,4,5,6,7,8,9,10,11,12]
Serum levels and skin expression of IL-6 are increased in patients with early systemic sclerosis We first evaluated IL-6 and IL-6 receptor (IL-6R) expression in the serum of 187 patients with SSc as compared with 48 healthy controls
Summary
Interleukin-6 (IL-6) is a pleiotropic cytokine for which preliminary data have suggested that it might contribute to systemic sclerosis (SSc). As an alternative and innovative strategy, our group has developed peptidebased anti-cytokine active immunization, which consists in inducing autoantibodies through an immunization against peptides of cytokines linked to a carrier protein (for example, keyhole limpet hemocyanin, or KLH) [15,16,17]. This promising strategy has not been used so far for IL-6 but has been successfully established for other cytokines, including tumor necrosis factor-alpha (TNFα) and IL-1β and IL-23 in different autoimmune diseases [15,16,17,18]. In this study, our aim was to compare the antifibrotic properties of both passive and active immunization against IL-6 in complementary mouse models of SSc
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