Anti-C1q in chronic hepatitis C virus genotype IV infection: association with autoimmune rheumatologic manifestations

In the Crosshairs: RNA Viruses OR Complement?

Complement, a part of the innate arm of the immune system, is integral to the frontline defense of the host against innumerable pathogens, which includes RNA viruses. Among the major groups of viruses, RNA viruses contribute significantly to the global mortality and morbidity index associated with viral infection. Despite multiple routes of entry adopted by these viruses, facing complement is inevitable. The initial interaction with complement and the nature of this interaction play an important role in determining host resistance versus susceptibility to the viral infection. Many RNA viruses are potent activators of complement, often resulting in virus neutralization. Yet, another facet of virus-induced activation is the exacerbation in pathogenesis contributing to the overall morbidity. The severity in disease and death associated with RNA virus infections shows a tip in the scale favoring viruses. Growing evidence suggest that like their DNA counterparts, RNA viruses have co-evolved to master ingenious strategies to remarkably restrict complement. Modulation of host genes involved in antiviral responses contributed prominently to the adoption of unique strategies to keep complement at bay, which included either down regulation of activation components (C3, C4) or up regulation of complement regulatory proteins. All this hints at a possible “hijacking” of the cross-talk mechanism of the host immune system. Enveloped RNA viruses have a selective advantage of not only modulating the host responses but also recruiting membrane-associated regulators of complement activation (RCAs). This review aims to highlight the significant progress in the understanding of RNA virus–complement interactions.

The Immunopathology of Complement Proteins and Innate Immunity in Autoimmune Disease

The complement is a powerful cascade of the innate immunity and also acts as a bridge between innate and acquired immune defence. Complement activation can occur via three distinct pathways, the classical, alternative and lectin pathways, each resulting in the common terminal pathway. Complement activation results in the release of a range of biologically active molecules that significantly contribute to immune surveillance and tissue homeostasis. Several soluble and membrane-bound regulatory proteins restrict complement activation in order to prevent complement-mediated autologous damage, consumption and exacerbated inflammation. The crucial role of complement in the host homeostasis is illustrated by association of both complement deficiency and overactivation with severe and life-threatening diseases. Autoantibodies targeting complement components have been described to alter expression and/or function of target protein resulting in a dysregulation of the delicate equilibrium between activation and inhibition of complement. The spectrum of diseases associated with complement autoantibodies depends on which complement protein and activation pathway are targeted, ranging from autoimmune disorders to kidney and vascular diseases. Nevertheless, these autoantibodies have been identified as differential biomarkers for diagnosis or follow-up of disease only in a small number of clinical conditions. For some autoantibodies, a clear relationship with clinical manifestations has been identified, such as anti-C1q, anti-Factor H, anti-C1 Inhibitor antibodies and C3 nephritic factor. For other autoantibodies, the origin and the functional consequences still remain to be elucidated, questioning about the pathophysiological significance of these autoantibodies, such as anti-mannose binding lectin, anti-Factor I, anti-Factor B and anti-C3b antibodies. The detection of autoantibodies targeting complement components is performed in specialized laboratories; however, there is no consensus on detection methods and standardization of the assays is a real challenge. This review summarizes the current panorama of autoantibodies targeting complement recognition proteins of the classical and lectin pathways, associated proteases, convertases, regulators and terminal components, with an emphasis on autoantibodies clearly involved in clinical conditions.

Rheumatologic manifestations of hepatic diseases

The course of hepatic diseases may be complicated by a multitude of rheumatologic manifestations, which can complicate the diagnostic approach and alter the natural history of primary liver disease, sometimes worsening prognosis due to associated multiple organ dysfunction. These manifestations can occur in association with a multitude of liver diseases, including viral hepatitis, autoimmune hepatitis, alcoholic liver disease, nonalcoholic fatty liver disease, hemochromatosis, or Wilson’s disease. It is necessary not only for rheumatologists, but also for other clinicians, to be aware that these atypical manifestations may reflect an undiagnosed hepatic disease. On the other hand, it is crucial that, in a patient with known hepatic disease presenting with rheumatologic symptoms, an accurate distinction be made between the rheumatologic manifestations of hepatic disease and primary rheumatologic disease, since the treatment is often different. This review aims to summarize the current evidence regarding rheumatologic manifestations of hepatic diseases, how to distinguish them from primary rheumatologic disorders, and how to provide adequate management.

Interleukin-17A and B-cell activating factor in chronic hepatitis C patients with or without asymptomatic mixed cryoglobulinemia: effects of antiviral treatment and correlations with vitamin D

BACKGROUND

Several studies have provided conflicting results regarding the immune responses in chronic hepatitis C (CHC) patients with mixed cryoglobulinemia (MC). The importance of B-cell activating factor (BAFF) in MC has been described, but the role of interleukin (IL)-17A is less clear.

METHODS

Serum concentrations of IL-17A, BAFF and 25-OH vitamin D were measured in CHC patients at baseline, end of treatment, and 6 months post-treatment with pegylated interferon-α and ribavirin, versus 12 healthy controls.

RESULTS

Thirty-four patients (20 male, mean age 40.7±9.2 years, 12 of genotype 1 or 4, 22 of genotype 2 or 3) were included, of whom 64.7% achieved a sustained virological response (SVR). MC was detected in 52.9% of the patients. Higher levels of both cytokines were found in patients with MC compared to those without. Patients who achieved SVR had higher pretreatment IL-17A and lower BAFF levels compared to those without SVR. IL-17A was downregulated during and following treatment in responders, whereas upregulation was observed in non-responders. CHC patients demonstrated low vitamin D levels compared to HC. Moreover, the changes in IL-17A over the treatment period were significantly associated with vitamin D changes (β=-0.04, SE=0.02, P=0.046). No difference in IL-17A, BAFF and vitamin D values was seen between patients with cirrhosis (n=14) and those without.

CONCLUSIONS

CHC patients with asymptomatic MC have increased levels of IL-17A and BAFF. IL-17A levels decline significantly while BAFF increases during treatment in responders. An interplay between IL-17A and vitamin D concentrations was revealed during the antiviral treatment.

The Complement System and C1q in Chronic Hepatitis C Virus Infection and Mixed Cryoglobulinemia

The complement system bridges innate and adaptive immunity against microbial infections, with viral infection being a major trigger. Activation of the classical, alternative, and lectin pathways have been reported in chronic hepatitis C virus (HCV) infection and/or cryoglobulinemia. HCV infection leads to dysregulation of complement-mediated immune responses. Clinical and experimental evidence support involvement of complement in intra- and extrahepatic manifestations of HCV infection, such as liver fibrosis and type II cryoglobulinemia. In this review, we summarize studies that have investigated the interplay between HCV and the complement system to establish chronic infection and autoimmunity, as well as the association between HCV pathogenesis and abnormal complement profiles. Several unanswered questions are highlighted which suggest additional informative lines of investigation.