THE ROLE OF SEMAPHORIN 7A IN SYSTEMIC SCLEROSIS

INTRODUCTION: Semaphorins are a large group of membrane bound and secreted proteins. The semaphorins were first recognized for their important role in neurodevelopment and specifically their repulsive axonal growth guidance during embryonic development. Recently, semaphorins have also been found to have an important role in the regulation of the immune system, thus denoted as "immune semaphorins". Semaphorin 7A is a membrane bound protein which mediated its effect by two receptors: the β1 integrin subunit and plexin C1. Interactions between semaphorin 7A and its receptors contribute to inflammation and immunity by the stimulation of macrophage chemotaxis and cytokine production, regulation of dendritic cell migration and modulation of T cell function. Recently, semaphorin 7A has been found to have a role in the induction of fibrosis by tumor growth factor β1 (TGF β1). TGFβ1 activates semaphorin 7A and its receptors plexin C1 and β1 integrin subunit and induces proliferation of fibroblasts, lung fibrosis and remodeling in mice. A small study of 4 patients with systemic sclerosis (SSc) has recently demonstrated increased expression of semaphorin 7A mRNA on fibroblasts and B lymphocytes in peripheral blood. AIMS: To evaluate the expression of semaphorin 7A on regulatory T cells and B cells from peripheral blood of patients with SSc compared to healthy controls and to try and correlate the expression of semaphorin 7A with pulmonary fibrosis, skin fibrosis and other clinical characteristics of SSc patients. METHODS: Twenty six SSc patients were compared to 10 healthy controls. The expression of semaphorin 7A was evaluated by flow cytometry analysis of B cells using monoclonal antibodies to CD 108 and CD 19 and on peripheral regulatory T cells using monoclonal antibodies to CD 3 and CD 108. The analysis was conducted using flow-cytometry. Demographic, clinical and laboratory data were prospectively collected. Further data collection included: Systolic pulmonary artery pressure as assessed by echocardiography, lung function tests including diffusing capacity, nailfold video capillaroscopy pattern, modified Rodnan skin score (MRSS), Valentini activity index and Medsger severity score. Pulmonary involvement was determined by high resolution CT scan if it was suspected, according to impaired lung functions or auscultatory findings. RESULTS: Ten patients with diffused SSC (8 of whom suffered from pulmonary fibrosis) and 16 patients with limited disease were compared with 10 healthy controls. There was no difference between the groups with regard to age, gender, BMI or smoking habits. Semaphorin 7A expression on regulatory T cells was not different between SSc patients and healthy controls 4.2±6.5 % vs. 2.3±1.1 % (p< 0.35) nor was a difference found between SSC patients with diffuse disease compared to limited disease 2.5±8 % vs. 5.1±14 % (p< 0.3). Comparing the expression of semaphorin 7A on B cells did not reveal a difference between SSc patients and healthy controls as well 9.7±9.4 % vs. 4.9±1.7% (p< 0.12). No correlation was found between skin score, activity score or severity score and levels of expression of sempahorin 7A on B cells or regulatory T cells. CONCLUSIONS: In this small scale study we were not able to validate the role of semaphorin 7A as a mediator of fibrosis in SSc, as was suggested by a previous pilot study. Larger scale studies and investigation of semaphorin 7A on other peripheral cells and in tissues are needed in order to delineate the exact role of semaphorin as a mediator of fibrosis in SSc.