The complement system is a component of the innate immune system. Its main function was initially believed to be limited to the recognition and elimination of pathogens through direct killing or stimulation of phagocytosis. However, in recent years, the immunoregulatory functions of the complement system were demonstrated and it was determined that the complement proteins play an important role in modulating adaptive immunity and in bridging innate and adaptive responses. When the delicate mechanisms that regulate this sophisticated enzymatic system are unbalanced, the complement system may cause damage, mediating tissue inflammation. Dysregulation of the complement system has been involved in the pathogenesis and clinical manifestations of several autoimmune diseases, such as systemic lupus erythematosus, vasculitides, Sjögren's syndrome, antiphospholipid syndrome, systemic sclerosis, dermatomyositis, and rheumatoid arthritis. Complement deficiencies have been associated with an increased risk to develop autoimmune disorders. Because of its functions, the complement system is an attractive therapeutic target for a wide range of diseases. Up to date, several compounds interfering with the complement cascade have been studied in experimental models for autoimmune diseases. The main therapeutic strategies are inhibition of complement activation components, inhibition of complement receptors, and inhibition of membrane attack complex. At present, none of the available agents was proven to be both safe and effective for treatment of autoimmune diseases in humans. Nonetheless, data from preclinical studies and initial clinical trials suggest that the modulation of the complement system could constitute a viable strategy for the treatment of autoimmune conditions in the decades to come.

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Purpose of review Complement system dysfunction in terms of upregulation, downregulation, or dysregulation can create an imbalance of both host defense and inflammatory response leading to autoimmunity. In this review, we aimed at describing the role of complement system in host defense to inflection and in autoimmunity starting from the evidence from primary and secondary complement system deficiencies. Recent findings Complement system has a determinant role in defense against infections: deficiencies of complement components are associated with increased susceptibility to infections. Primary complement system deficiencies are rare disorders that predispose to both infections and autoimmune diseases. Secondary complement system deficiencies are the result of the complement system activation with consumption. Complement system role in enhancing risk of infective diseases in secondary deficiencies has been demonstrated in patients affected by systemic autoimmune disorders, mainly systemic lupus erythematosus and vasculitis. Summary The relationship between the complement system and autoimmunity appears paradoxical as both the deficiency and the activation contribute to inducing autoimmune diseases. In these conditions, the presence of complement deposition in affected tissues, decreased levels of complement proteins, and high levels of complement activation fragments in the blood and vessels have been documented.

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BackgroundBiologic agents are currently the strongest immunosuppressive drugs able to induce remission in rheumatoid arthritis (RA). One of the objectives of the medical scientific community now is how to maintain remission or low disease activity (LDA). The aim of this trial is to evaluate the contribution of low-dose sequential kinetic activation (SKA) IL-4, IL-10, and anti-IL-1 antibodies (10 fg/mL) in patients affected by RA in maintaining LDA or remission obtained after biological therapy.MethodThis is a randomized, open, active-controlled, prospective, Phase IV trial. Disease activity score (DAS28), clinical disease activity index, simplified disease activity index, erythrocyte sedimentation rate and C-reactive protein levels, global health assessment, and pain visual analog scale were evaluated at baseline visit and then every 3 months together with an assessment of side effects till 12 months. Thirty-nine RA patients were enrolled and randomized to continue disease-modifying antirheumatic drugs (DMARDs) therapy or to receive a combination of SKA low-dose cytokines formulated in concentration of 10 fg/mL orally administered at a dose of 20 drops/d for 12 consecutive months.ResultsThe rate of maintenance of LDA at 12 months was superior in the group treated with low-dose cytokines compared with patients treated with DMARDs, 66.7% and 42.1%, respectively; however, the difference between the groups was not statistically significant. No side effects were reported in both groups.ConclusionThis is the first study using a combination of three low-dose cytokines in RA, after data published on psoriasis. These data suggest that the use of a combination of low-dose SKA cytokines may be an opportunity to explore in the management of RA.

The first two authors contributed equally to this work Autoantibodies (rheumatoid factor, RF; anti-citrullinated-protein antibodies,ACPA) and complement system are involved in rheumatoid arthritis (RA). ACPA and anti-TNF agents are capable of in vitro modulating complement activity. We investigated the relationships between complement, autoantibodies, and anti-TNF treatment in vivo. One-hundred fourteen RA patients (89F/25M), diagnosed according to 1987 ACR criteria, and 30 healthy controls were enrolled. Serological analysis included ESR, CRP, complement C3, C4 and CH50, RF and ACPA (ELISA, cut-off>20U/ml). Split-products (SP) of C3 and B were studied by immunoelectrophoresis/counterimmunoelectrophoresis. Seventy-six patients started anti-TNF treatment and were studied at baseline and after 22 weeks. Disease activity was measured with DAS28 and response to therapy with EULAR criteria. At baseline, RA patients showed significantly higher levels of C3 and C4 than controls (C3 127.9±26.5 vs 1l0±25mgldl, P=O.0012; C4 29.7±10.2 vs 22.7±8.3mgldl, P=0.0003). No differences in C3, C4 and CH50 levels were observed between ACPA+ (n=76) and ACPA-(n=38) patients. After 22 weeks of anti-TNF, C3, C4 and RF were significantly reduced (P<0.003, <0.005 and <0.04, respectively) and RF changes showed negative correlation with CH50. SP of C3 and B were observed neither at baseline nor after 22 weeks. DAS28 significantly improved after 22 weeks. Patients showing higher baseline C3 or lower reduction of C3 levels after 22 weeks had a worse EULAR outcome (x2=22.793, P