FUNCTIONAL PROTEOMIC ANALYSIS OF COMPLEMENT PROTEINS FROM PATIENTS WITH SYSTEMIC SCLEROSIS

Systemic sclerosis (SSc) is an autoimmune disease characterized by excessive collagen deposition in skin and internal organs. An abnormal immunological response and microvascular damage appear to be early events in the pathophysiology of SSc. This research project follows a previous proteomic comparative analysis on serum, which had identified Factor H as one of the proteins differently expressed between SSc patients and healthy controls. Since FH has a fundamental role either in complement fluid phase regulation and host cell membrane protection, we focused our attention on this molecule, in the attempt of clarifying its eventual role in SSc pathogenesis. First of all, we confirmed by two complementary techniques, WB and ELISA, increased FH serum levels in SSc patients. We also analyzed complement activation in our patients, whose involvement in SSc is still matter of debate, without detecting significative abnormalities. No defects were found either in FH fluid phase activity and interaction with some ligands, i.e. C3b and heparin, evaluated comparing purified FH samples from SSc patients and controls. We observed an high hemolytic activity of SSc sera towards sheep RBCs compared to control sera, which is reversed by pre-incubation with commercial or healthy purified FH. Anti-FH antibodies were detected in a small percentage of patients, although a further screening on a wider cohort of subjects and the epitope-mapping are still on course. Since the genetical analysis did not reveal mutations in FH, we think the reported observations might be explained by anti-FH antibodies or post translational modifications which could block FH membrane activity. Also abnormalities in FH dimerization or complexes between FH and any of its many ligands might have a pathogenetic effect. Finally, SSc patients might present alterations in other complement regulators directly or indirectly connected to FH. In conclusion, our study proposed a new hypothesis on SSc etiopathogenesis and, although not exploring all the existing connection among the complement players and not reaching definitive conclusions, provided some hints about a possible dysfunction in complement regulation, which could be the starting point of more targeted functional studies.