AB0193 Semaphorin4a induces th17 cytokine production in systemic sclerosis
Authors: S. García Pérez, T. Carvalheiro, A.J. Affandi, B. Malvar Fernandez, I. Dullemond, M. Cossu, W. Marut, K.A. Reedquist, T.R. Radstake
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> Systemic sclerosis (SSc) is an autoimmune disease characterised by inflammation, vascular injury and excessive fibrosis in different organs. Different studies have shown that Th17 cells and Th17 cytokines (IL-17, IL-21 and IL-22) play a key role in the pathogenesis of the disease. Semaphorin 4A (Sema4A) is a transmembrane protein that belongs to a large family of proteins initially described as ligands essential for neuronal development. Further studies have shown that they also play a role in other biological processes including the control of immune responses. Importantly, Sema4A has a critical role in the skewing of CD4<sup>+</sup> T cells towards a Th17 phenotype. However, it is unknown if Sema4A contributes to the elevated number of Th17 cells observed in SSc patients. <h3>Objectives</h3> The aim of this study was to analyse the potential role of Sema4A as a regulator of Th17-skewing in SSc. <h3>Methods</h3> Plasma levels of Sema4A were measured by ELISA. Expression of Sema4A and its receptors PlexinB2, PlexinD1 and neuropilin-1 (NRP-1) was determined by (q)uantitative PCR, western blot and flow cytometry in monocytes and CD4<sup>+</sup> T cells of healthy donors (HD) and SSc patients. Monocytes were stimulated with Poly IC (5 µg/ml) or CXCL-4 (5 µg/ml) and Sema4A expression was analysed by qPCR and ELISA. CD4<sup>+</sup> T cells were stimulated with anti-CD3/anti-CD28 beads (ratio 1 bead: 5 cells) alone or in combination with recombinant human Sema4A (200 ng/ml), in the presence or absence of neutralising anti-NRP1 or PlexinD1 antibodies, and the expression of PlexinB2, PlexinD1, NRP-1 and the production of Th17 cytokines was analysed by qPCR, ELISA and flow cytometry. <h3>Results</h3> Plasma levels of Sema4A were significantly higher in SSc patients compared to healthy controls (HC) and positively correlated (r=0.611) with the skin disease severity. Sema4A and PlexinB2 expression was significantly higher in monocytes and CD4<sup>+</sup> T cells from SSc patients, respectively. Moreover, Poly IC and CXCL-4 significantly up-regulated the expression and secretion of Sema4A in monocytes from SSc patients, and CD4<sup>+</sup> T cells stimulation with anti-CD3/anti-CD28 beads increased the expression of PlexinB2 and NRP-1 in both HC and SSc patients. Finally, functional assays showed that Sema4A significantly enhanced the expression of Th17 cytokines induced by CD3/CD28 in CD4<sup>+</sup> T cells from both HC and SSc patients, and the blocking of the Sema4A signalling using neutralising antibodies anti-PlexinD1 and anti-NRP-1 significantly reduced this expression. Importantly, the Sema4A-induced IL-17 secretion was significantly higher in stimulated CD4<sup>+</sup> T cells from SSc patient compared to HC. <h3>Conclusions</h3> Sema4A signalling is deregulated in SSc patients and plays an important role in Th17 skewing. Therefore, Sema4A and its receptors could be promising therapeutic targets for the treatment of SSc. <h3>Disclosure of Interest</h3> None declared