Rheumatoid factor, complement, and mixed cryoglobulinemia. Clin Dev Immunol. 2012;2012:439018. [PMID: 22956968 PMCID: PMC3432568 DOI: 10.1155/2012/439018]

Chronic Hepatitis C Virus Infection, Extrahepatic Disease and the Impact of New Direct-Acting Antivirals

Chronic hepatitis C virus infection is an important cause of liver cirrhosis, hepatocellular carcinoma and death. Furthermore, it is estimated that about 40-70% of patients develop non-hepatic alterations in the course of chronic infection. Such manifestations can be immune-related conditions, lymphoproliferative disorders and metabolic alterations with serious adverse events in the short and long term. The introduction of new Direct-Acting Antivirals has shown promising results, with current evidence indicating an improvement and remission of these conditions after a sustained virological response.

[Comparative analysis of the development mechanisms of cryoglobulinemic vasculitis and Sjögren's syndrome]

Cryoglobulinemic vasculitis is a disease characterized by damage of small vessels and in some cases can be a manifestation of mixed cryoglobulinemia. Mixed cryoglobulinemia is a condition in which immunoglobulins in the blood serum form precipitates at temperatures below 37 °C and dissolve again when it rises. Currently, hepatitis C (HCV) is considered the most common etiological factor of mixed cryoglobulinemia. In addition, mixed cryoglobulinemia may be associated with other infectious agents, as well as autoimmune and lymphoproliferative diseases. In the absence of such association, we can talk about essential mixed cryoglobulinemia. To understand how different nosologies in their clinical and morphological picture lead to the development of mixed cryoglobulinemia, it is necessary to carefully analyze the mechanisms of the development of some of them, namely, HCV-associated cryoglobulinemic vasculitis and Sjögren's syndrome. It is noteworthy that mixed cryoglobulinemia in relation to Sjögren's syndrome can be perceived both as its consequence and as a manifestation of the underlying disease. Such an ambiguous nature of mixed cryoglobulinemia makes it currently impossible to select clear diagnostic criteria. For this reason, it is necessary to carry out a comparison between different immunopathogenesis of mixed cryoglobulinemia in order to identify the features that form its classical manifestations.

Risk factors for relapse in non-infectious cryoglobulinemic vasculitis, including type I cryoglobulinemia: a systematic review

Background

Data on non-infectious cryoglobulinemic vasculitis (NICV) is scarce, especially concerning the management of relapses, which are troublesome. We aimed to investigate risk factors for relapse in NICV.

Methods

A systematic literature search of CINAHL, Embase, MEDLINE, Scopus, and the Web of Science databases was implemented until April 2023. Eligible studies included randomized control trials, observational studies, and case series with ≥4 patients. Two reviewers independently extracted data and assessed the quality of the eligible studies.

Results

A total of 3,724 articles were retrieved from a database search, with 27 studies meeting the inclusion criteria for review. Most studies (n = 23) detailed relapses, with the time to relapse varying between 1 and 80 months. The relapse rate was reported at 28% in Type I NICV and ranged from 22% to 60% in mixed NICV. Risk factors for relapse in NICV were identified based on the cryoglobulin subtype and correlated with clinical and immunological responses to varying treatment regimens. Type I NICV with an associated lymphoproliferative disorder exhibited a response-relapse pattern. Cutaneous and articular involvement and incomplete clinical and immunological responses to treatment, particularly corticosteroid monotherapy and occasionally rituximab, influence the risk of relapse in Type II and Type III NICV.

Conclusion

Our findings underscore the significance of attaining both clinical and immunological responses and identifying risk factors for relapse in NICV. Appropriate risk stratification for NICV patients is essential for the successful implementation of effective treatment strategies.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, identifier CRD42023408140.

Biomarkers of lymphoma in Sjögren's syndrome: what's the latest?

INTRODUCTION

Primary Sjögren's syndrome (pSS) is a chronic autoimmune disease standing in the crossroads of autoimmunity and lymphomagenesis, characterized by chronic B-cell hyperactivity and ectopic lymphoid tissue neoformation, potentially driving lymphoid malignant transformation. Lymphoma development is considered the most serious complication of pSS.

AREAS COVERED: “

Old-classical" biomarkers (clinical, serological, hematological, and histological) validated in the past are analyzed under the perspective of recently published research. Biomarkers that have emerged during the last decade are subdivided to "old-new" and "newly proposed-novel" ones, including biomarkers pathophysiologically related to B-cell differentiation, lymphoid organization, and immune responses, identified in serum and tissue, both at genetic and protein level. Upcoming new imaging biomarkers, promising for further patient stratification, are also analyzed.

EXPERT OPINION

Salivary gland enlargement and cryoglobulinemia still remain the best validated "classical-old" biomarkers for lymphoma development. Though new biomarkers still need to be validated, some can be used for the identification of high-risk patients long before lymphoma diagnosis, some might be more relevant in distinct age subgroups, while others have an added value in the assessment of lymphoma remission or relapse. Future development of composite indices integrating old and recently proposed biomarkers could contribute to a more precise lymphoma prediction model.

Practical Details for the Detection and Interpretation of Cryoglobulins

BACKGROUND

Cryoglobulins are immunoglobulins that precipitate at low temperature. Strict preanalytical and analytical conditions are critical for the detection of cryoglobulins.

CONTENT

This review will focus on practical recommendations for detection and characterization of cryoglobulins and the technical problems that may be encountered. A laboratory report format is proposed for presentation of these results that includes the parameters necessary for an optimal interpretation by clinicians. The first step of detection of cryoglobulins can be performed in any laboratory that has a 37 °C incubator and temperature-controlled centrifuge. The second step is the characterization of cryoglobulins, and this often must be performed in more specialized laboratories. Characterization includes immunoglobulin typing, for the classification of cryoglobulins and potential underlying disease(s); quantification of immunoglobulins and rheumatoid factor in the cryoprecipitate to define the pathogenicity; and quantification of serum complement, which is useful for diagnosis.

SUMMARY

These practical recommendations will be useful for the accurate detection of cryoglobulins, an essential step for the diagnosis of cryoglobulinemic vasculitis, a rare but severe clinical manifestation of cryoglobulins.

Selective decrease in complement C2 hemolytic activity is a sensitive marker for cryoglobulinemia and active disease in hepatitis C patients

BACKGROUND

Some HCV patients present low/non-detected C2 hemolytic activity (C2h) without apparent consumption of other Complement components (selective low/non-detected C2h).

AIM

Characterization of the immunologic/clinical basis of this phenomenon.

METHODS

C2h, HCV-viral load, cryoglobulinemia and Complement components were determined in 726 HCV patients, with sequential C2h determination in 189 patients.

RESULTS

C2h was non-detected in 15.9%, low in 16.9% and normal in 67.2% subjects and showed temporal oscillation in 30.7% of patients. Samples with selective non-detected C2h presented lower C3/C4 than those with normal C2h, but still within the normal C3/C4 range. Selective non-detected C2h was associated with higher aspartate aminotransferase (AST) (p<0.001), alanine transferase (ALT) (p = 0.03) and APRI (Aspartate aminotransferase-to-Platelet Ratio Index) (p<0.001), lower serum albumin (p = 0.01) and platelet count (p = 0.012), more individuals at pre-treatment stage, with detectable HCV-RNA p<0.001), cryoglobulinemia (p<0.001) and with HCV genotype 3 (p = 0.003). Elevated ALT, HCV genotype 3, active disease and viral load were independent predictors of low/non-detected C2h. In vitro exposure of normal serum to exogenous HCV cryoglobulins caused dose-dependent decrease in C2h.

CONCLUSIONS

Selective C2h decrease is a sensitive marker of Complement activation in HCV patients and is associated with cryoglobulinemia, active disease, elevated ALT, higher viral load, and HCV genotype 3.

Interactive Impacts from Hepatitis C Virus Infection and Mixed Cryoglobulinemia on Complement Levels

BACKGROUND/AIM

How hepatitis C virus (HCV) infection and mixed cryoglobulinemia interactively affect complement levels remains elusive, and we aimed to elucidate it.

METHODS

A prospective cohort study of 678 consecutive chronic HCV-infected (CHC) patients was conducted. Of 678, 438 had completed a course of anti-HCV therapy and 362 had achieved a sustained virological response (SVR). The baseline and 24-week post-therapy variables including complement levels and mixed cryoglobulinemia status were surveyed.

RESULTS

At baseline, lower complement component 3 (C3) and component 4 (C4) levels were noted in patients with than those without mixed cryoglobulinemia. The differences between pre-therapy (in 678 CHC patients) and 24-week post-therapy (in 362 SVR patients) factors associated with C3 levels were interferon λ3 (IFNL3) genotype, triglycerides, cirrhosis, and estimated glomerular filtration rate; the different associations with C4 levels were cirrhosis, sex and high sensitivity C-reactive protein. Compared with baseline, SVR patients without pre- and post-therapy mixed cryoglobulinemia had increased C3 levels, and SVR patients with pre-therapy mixed cryoglobulinemia had increased C4 levels. Lower C3 levels were noted in SVR patients with than those without post-therapy mixed cryoglobulinemia.

CONCLUSIONS

HCV might affect C3 levels through IFNL3 genotype, triglycerides, cirrhosis, and renal function; and affect C4 with a link to sex, inflammation, and cirrhosis. That C3 levels decreased in CHC patients without mixed cryoglobulinemia or in SVR patients with post-therapy mixed cryoglobulinemia, and C4 levels decreased in CHC patients with mixed cryoglobulinemia, suggested that mixed cryoglobulinemia and HCV infection antagonistically and synergistically decrease C3 and C4 levels, respectively.

Cryoglobulinemic vasculitis: pathophysiological mechanisms and diagnosis

PURPOSE OF REVIEW

Cryoglobulins (CG) are immunoglobulins that precipitate in the cold, and dissolve at 37°C. In vivo, in cold exposed tissues and organs, they can induce vasculitis and occlusive vasculopathy after deposition on vascular endothelium under low temperature and high concentration conditions. Clinical manifestations are cutaneous (purpura, ulcers, vasomotor symptoms, and livedo reticularis), rheumatological (arthralgia and arthritis), and peripheral neuropathy (paresthesia and pain in the lower limbs). In profound organs such as the kidneys, CG deposition is less temperature-dependent, favored by local protein and anion concentrations, and can lead to glomerulonephritis. This review will focus on cryoglobulinemic vasculitis and vascular lesion, and their diagnosis.

RECENT FINDINGS

The mechanisms of vascular lesions of pathogenic CG in function of CG type and their characteristics are better defined. Optimal conditions for CG detection are critical. The importance of looking for underlying diseases, especially hepatitis C virus status in mixed CG, is reminded.

SUMMARY

A decision diagram for CG vasculitis diagnosis based on clinical and biological parameters is proposed.

Contribution of Hepatitis C Infection to a Large Cohort of Cryoglobulin-Positive Patients: Detection and Characteristics

Cryoglobulins (CGs) are cold precipitating immunoglobulins, and hepatitis C virus (HCV) infection is its most common cause. The purpose of the study was to determine the contribution of HCV in a large cohort of CG. Biological characteristics and specificity of CGs in HCV patients were compared to non-HCV subjects. Cryoglobulin analysis included isotype, clonality, concentration, and rheumatoid factor (RF) in cryoprecipitate and serum complement and RF. This study is an extension of the study carried out on a cohort of 13,439 patients tested for CGs from all medical units, in which 1,675/13,439 (12.5%) patients had a CG, and 680/1,675 (40.6%) had HCV serology or viral load determination (HCV RNA). Among these 680 CG patients tested for HCV, 325 of 680 (47.8%) HCV patients (272 HCV RNA⁺ and 45 HCV RNA⁻ patients) were compared to 355/680 (52.2%) non-HCV subjects. After a positive detection of CG, HCV status was determined only for 37.7% (256/680) of patients, allowing the diagnosis of a previously unknown HCV infection for 39.8% (102/256). Concentration of HCV RNA⁺ CGs (median = 80.5 mg/L) was significantly higher than that of HCV RNA⁻ CG (median = 50.5 mg/L, p = 0.001) and HCV⁻ CG (median = 32 mg/L, p < 0.0001). There was no difference of median CG concentration between HCV RNA⁻ patients and non-HCV subjects. Rheumatoid factor titer was significantly higher in type II CG compared to type III CG in HCV RNA⁺ patients (254 ± 720 vs. 15 ± 21 IU/mL, p < 0.0001) and non-HCV subjects (333 ± 968 vs. 16.8 ± 26 IU/mL, p = 0.0004). Complement functional activity CH50 was lower in HCV RNA⁺ patients (36 ± 24 U/mL) and in HCV RNA⁻ patients (32 ± 21 U/mL) than in non-HCV subjects (50 ± 25 U/mL, p = 0.001 and p = 0.004). In conclusion, HCV infection and treatment influence CG characteristics. It is essential, and far from always tested, to determine the HCV status of patients with mixed CG, and conversely to search for CG in patients with HCV infection.

Cryoglobulins Today: Detection and Immunologic Characteristics of 1,675 Positive Samples From 13,439 Patients Obtained Over Six Years

OBJECTIVE

Cryoglobulins are cold-precipitating immunoglobulins. Through progress in techniques, we undertook this study to update information on the biologic characteristics of cryoglobulins in a very large population.

METHODS

A cohort of 13,439 patients was tested for cryoglobulins from January 2010 to December 2016. The analysis included cryoglobulin isotype, clonality, concentration, and IgM rheumatoid factor (IgM-RF) in cryoprecipitate, as well as serum complement and RF. Markers of gammopathy, viral infection, and autoimmunity were also investigated.

RESULTS

Of the 13,439 patients, 1,675 (12.5%) tested positive for cryoglobulins: 155 patients (9.3%) with type I, 788 (47%) with type II, and 732 (43.7%) with type III cryoglobulins. Nine percent of patients who were retested after initially testing negative for cryoglobulins showed a positive result on a follow-up test (196 of the 2,213 retested patients). In type I cryoglobulins, IgM was more frequent but occurred at lower concentrations than IgG. Mixed cryoglobulins were found in 34.8% of the tested patients who were positive for hepatitis C virus and <5% of those who were positive for hepatitis B virus or HIV. Of the patients with anti-double-stranded DNA, anti-SSA, or anti-cyclic citrullinated peptide autoantibodies, 25.4% tested positive for mixed cryoglobulins, with type III occurring more frequently than type II. Both cryoprecipitate and serum were RF-positive in 21.6% of type II and 10.1% of type III cryoglobulins. A decrease of C4, with or without accompanying decreases of C3 and CH50, was found in 23.6% of cryoglobulin samples.

CONCLUSION

Obtained with the use of modern assays, our findings from this very large collection of cryoglobulins provide an update on cryoglobulin distribution and characteristics, with minimal selection bias. Despite strict preanalytical conditions, a negative finding for the presence of cryoglobulin must be confirmed in a second sample. RF activity and complement decreases were rarely detected.

Laboratory Assessment of Patients with Suspected Rheumatic Musculoskeletal Diseases: Challenges and Pitfalls

Current patient care in rheumatology relies primarily on a combination of traditional clinical assessment and standard laboratory tests. Investigators seek to discover new biomarkers and novel technologies to boost the research in this field. Mechanistic biomarkers such as cytokines, cell types, antibodies, signaling molecules, are rooted in the mechanism underlying the disease and can guide the clinical management of the disease. Conversely, descriptive biomarkers are byproducts of the disease process, depict the state of a disease but are not involved in its pathogenesis. In this article, we reviewed the field of common laboratory biomarkers in rheumatology, highlighting both their descriptive or mechanistic value as well as their role in clinical practice.

Rheumatoid factor as predictor of response to treatment with anti-TNF alpha drugs in patients with rheumatoid arthritis: Results of a cohort study

We determined whether rheumatoid factor (RF) and anti-cyclic citrullinated peptide antibody (ACPA) can predict remission or severe disability in rheumatoid arthritis (RA) patients treated with anti-tumor necrosis factor (TNF) alpha drugs.We performed a cohort study based on the clinical data from a referral center for the treatment of RA in Bogotá, Colombia, were included patients aged ≥18 years with diagnosis of RA with an active disease and for whom a treatment scheme was begun with anti-TNF alpha medication, with a minimum follow-up time of 12 months. Disease activity of Rheumatoid Arthritis was assessed through measurement of RF, ACPA, disease activity score (DAS28), and health assessment questionnaire (HAQ). We calculated the incidence rates (IRs) for remission and severe disability. We also calculated the incidence rate ratio (IRR) for each outcome by adjusting for possible confounders using the Poisson regression method. The hypothesis was tested with a P value of <.05. Statistical analysis was performed in Stata 15.We included 400 patients receiving an anti-TNF alpha agent. Median age was 60 years, and 322 patients were women (80.5%). RF was positive in 357 patients (89%), ACPA in 348 patients (87%), and co-positivity in 324 patients (81%). Median follow-up was 41 months (range, 12-79 months). The IR for remission was 23 per 100 person-years in RF-negative patients and 16 per 100 person-years in RF-positive patients. The adjusted IRR (age sex, treatment, and ACPA) was 1.51 (95%CI, 1.05-2.18). The IR for severe disability was 10.8 per 100 person-years in the RF-positive cohort and 2.3 per 100 person-years in the RF-negative cohort. The IRR adjusted for these factors was 4.37 (95%CI, 1.6-12). Co-positivity had a similar behavior to RF. No differences were recorded in the rates of remission or disability in ACPA-positive and ACPA-negative patients.Our findings suggest that remission is less frequent and severe disability more frequent in RF-positive patients treated with anti-TNF alpha agents than in RF-negative patients.

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.

Role of Natural IgM Autoantibodies (IgM-NAA) and IgM Anti-Leukocyte Antibodies (IgM-ALA) in Regulating Inflammation

Natural IgM autoantibodies (IgM-NAA) are rapidly produced to inhibit pathogens and abrogate inflammation mediated by invading microorganisms and host neoantigens. IgM-NAA achieve this difficult task by being polyreactive with low binding affinity but with high avidity, characteristics that allow these antibodies to bind antigenic determinants shared by pathogens and neoantigens. Hence the same clones of natural IgM can bind and mask host neoantigens as well as inhibit microorganisms. In addition, IgM-NAA regulate the inflammatory response via mechanisms involving binding of IgM to apoptotic cells to enhance their removal and binding of IgM to live leukocytes to regulate their function. Secondly, we review how natural IgM prevents autoimmune disorders arising from pathogenic IgG autoantibodies as well as by autoreactive B and T cells that have escaped tolerance mechanisms. Thirdly, using IgM knockout mice, we show that regulatory B and T cells require IgM to effectively regulate inflammation mediated by innate, adaptive and autoimmune mechanisms. It is therefore not surprising why the host positively selects such autoreactive B1 cells that generate protective IgM-NAA, which are also evolutionarily conserved. Fourthly, we show that IgM anti-leukocyte autoantibodies (IgM-ALA) levels and their repertoire can vary in normal humans and disease states and this variation may partly explain the observed differences in the inflammatory response after infection, ischemic injury or after a transplant. Finally we also show how protective IgM-NAA can be rendered pathogenic under non-physiological conditions. IgM-NAA have therapeutic potential. Polyclonal IgM infusions can be used to abrogate ongoing inflammation. Additionally, inflammation arising after ischemic kidney injury, e.g., during high-risk elective cardiac surgery or after allograft transplantation, can be prevented by pre-emptively infusing polyclonal IgM, or DC pretreated ex vivo with IgM, or by increasing in vivo IgM with a vaccine approach. Cell therapy with IgM pretreated cells, is appealing as less IgM will be required.

Role of Natural Autoantibodies and Natural IgM Anti-Leucocyte Autoantibodies in Health and Disease

We review how polyreactive natural IgM autoantibodies (IgM-NAA) protect the host from invading micro-organisms and host neo-antigens that are constantly being produced by oxidation mechanisms and cell apoptosis. Second, we discuss how IgM-NAA and IgM anti-leukocyte antibodies (IgM-ALA) inhibits autoimmune inflammation by anti-idiotypic mechanisms, enhancing removal of apoptotic cells, masking neo-antigens, and regulating the function of dendritic cells (DC) and effector cells. Third, we review how natural IgM prevents autoimmune disorders arising from pathogenic IgG autoantibodies, triggered by genetic mechanisms (e.g., SLE) or micro-organisms, as well as by autoreactive B and T cells that have escaped tolerance mechanisms. Studies in IgM knockout mice have clearly demonstrated that regulatory B and T cells require IgM to effectively regulate inflammation mediated by innate, adaptive, and autoimmune mechanisms. It is, therefore, not surprising why the host positively selects such autoreactive B1 cells that generate IgM-NAA, which are also evolutionarily conserved. Fourth, we show that IgM-ALA levels and their repertoire can vary in normal humans and disease states and this variation may partly explain the observed differences in the inflammatory response after infection, ischemic injury, or after a transplant. We also show how protective IgM-NAA can be rendered pathogenic under non-physiological conditions. We also review IgG-NAA that are more abundant than IgM-NAA in plasma. However, we need to understand if the (Fab)(2) region of IgG-NAA has physiological relevance in non-disease states, as in plasma, their functional activity is blocked by IgM-NAA having anti-idiotypic activity. Some IgG-NAA are produced by B2 cells that have escaped tolerance mechanisms and we show how such pathogenic IgG-NAA are regulated to prevent autoimmune disease. The Fc region of IgG-NAA can influence inflammation and B cell function in vivo by binding to activating and inhibitory FcγR. IgM-NAA has therapeutic potential. Polyclonal IgM infusions can be used to abrogate on-going inflammation. Additionally, inflammation arising after ischemic kidney injury, e.g., during high-risk elective cardiac surgery or after allograft transplantation, can be prevented by pre-emptively infusing polyclonal IgM or DC pretreated ex vivo with IgM or by increasing in vivo IgM with a vaccine approach. Cell therapy is appealing as less IgM will be required.

The expanding spectrum of HCV-related cryoglobulinemic vasculitis: a narrative review

Cryoglobulinemic vasculitis (CV) is a small-to-medium-vessel vasculitis that appears in 10-15 % of patients chronically infected with hepatitis C virus (HCV). The classic symptom triad of CV, purpura/asthenia/arthralgia, is accompanied by clinical features that include glomerulonephritis, neuropathy, interstitial pneumonitis, and cardiomyopathy, ranging in their severity from mild to life threatening. The risk of developing non-Hodgkin lymphoma is also higher. The cumulative 10-year survival rate of CV patients is significantly lower than in the age- and sex-matched general population, with death typically caused by nephropathy, malignancies, liver involvement, and severe infections. Unfailing serological stigmata include both a cryoglobulin IgM fraction with rheumatoid factor activity and decreased complement C4 levels. On peripheral B cells, the expression of the CD81 B cell receptor is reduced while that of the CD19 receptor is increased. A monoclonal B cell lymphocytosis develops in almost one-third of patients. HCV-related proteins (but not HCV-RNA genomic sequences) can be detected on biopsy samples by immunofluorescence and immunohistochemistry and involve the vessel lumen, vessel walls, and the perivascular spaces of the skin, kidney, and peripheral nerves, supporting the pathogenetic role of HCV in the onset of a widespread microvasculitis. Based on the demonstration of HCV infection in the large majority of CV patients, a therapeutic regimen consisting of once-weekly pegylated interferon-α and the daily administration of ribavirin results in a sustained virologic response in ~50 % of patients. In those with refractory and relapsing disease, addition of the anti-CD20 monoclonal antibody rituximab has significantly increased the overall response rates. The extension to CV of latest-generation direct-acting antivirals, strikingly successful in non-CV HCV-positive patients, has yielded high complete response rates according to the few studies published thus far.

Overview of Laboratory Testing and Clinical Presentations of Complement Deficiencies and Dysregulation

Historically, complement disorders have been attributed to immunodeficiency associated with severe or frequent infection. More recently, however, complement has been recognized for its role in inflammation, autoimmune disorders, and vision loss. This paradigm shift requires a fundamental change in how complement testing is performed and interpreted. Here, we provide an overview of the complement pathways and summarize recent literature related to hereditary and acquired angioedema, infectious diseases, autoimmunity, and age-related macular degeneration. The impact of complement dysregulation in atypical hemolytic uremic syndrome, paroxysmal nocturnal hemoglobinuria, and C3 glomerulopathies is also described. The advent of therapeutics such as eculizumab and other complement inhibitors has driven the need to more fully understand complement to facilitate diagnosis and monitoring. In this report, we review analytical methods and discuss challenges for the clinical laboratory in measuring this complex biochemical system.

Diagnostics and treatment of cryoglobulinaemia: it takes two to tango

Cryoglobulins are immunoglobulins that reversibly precipitate in the cold. They come in different flavours and, as such, are differentially associated with lymphoproliferative diseases (type I), or systemic autoimmune diseases, and/or infectious diseases (type II/III). The clinical manifestations of cryoglobulinaemia result from either hyper-viscosity or small vessel vasculitis. Hepatitis C virus (HCV) is a well-known factor in the aetiology of cryoglobulinaemia, but substantial geographical differences exist in the association between cryoglobulins and HCV. In the absence of any underlying disease, cryoglobulinaemia is referred to as 'idiopathic' or 'essential'. Detection of cryoglobulins in the laboratory is hampered by several pitfalls, in particular in the pre-analytical stage as well as in the quantification. In addition, our personal experience reveals that the detection of rheumatoid factor, most often present in high concentrations in patients with mixed cryoglobulinaemia, relies on the choice of the test system. Hence, interpretation of the laboratory results in relation to the clinical manifestations requires a partnership between the clinician and the laboratory specialist in order to make a correct diagnosis. Treatment options are primarily directed by identification of underlying diseases, i.e. infections or systemic autoimmune diseases. Idiopathic cryoglobulinaemia is treated with corticosteroids and immunosuppression, or B cell depleting anti-CD20 biologicals. In this overview, the recent literature on current laboratory and clinical practice of cryoglobulinaemia is discussed from a personal perspective.

Hepatitis C virus syndrome: A constellation of organ- and non-organ specific autoimmune disorders, B-cell non-Hodgkin's lymphoma, and cancer

The clinical course of chronic hepatitis C virus (HCV) infection is characterized by possible development of both liver and extrahepatic disorders. The tropism of HCV for the lymphoid tissue is responsible for several immune-mediated disorders; a poly-oligoclonal B-lymphocyte expansion, commonly observed in a high proportion of patients with HCV infection, are responsible for the production of different autoantibodies and immune-complexes, such as mixed cryoglobulins. These serological alterations may characterize a variety of autoimmune or neoplastic diseases. Cryoglobulinemic vasculitis due to small-vessel deposition of circulating mixed cryoglobulins is the prototype of HCV-driven immune-mediated and lymphoproliferative disorders; interestingly, in some cases the disease may evolve to frank malignant lymphoma. In addition, HCV shows an oncogenic potential as suggested by several clinico-epidemiological and laboratory studies; in addition to hepatocellular carcinoma that represents the most frequent HCV-related malignancy, a causative role of HCV has been largely demonstrated in a significant percentage of patients with isolated B-cells non-Hodgkin's lymphomas. The same virus may be also involved in the pathogenesis of papillary thyroid cancer, a rare neoplastic condition that may complicate HCV-related thyroid involvement. Patients with HCV infection are frequently asymptomatic or may develop only hepatic alteration, while a limited but clinically relevant number can develop one or more autoimmune and/or neoplastic disorders. Given the large variability of their prevalence among patients' populations from different countries, it is possible to hypothesize a potential role of other co-factors, i.e., genetic and/or environmental, in the pathogenesis of HCV-related extra-hepatic diseases.

Anti-nuclear antibody detection in cryoprecipitates: distinctive patterns in hepatitis C virus-infected patients

BACKGROUND

Anti-nuclear antibodies are immunoglobulins directed against nuclear antigens. They are associated with many autoimmune disorders, but are frequently found in patients infected with hepatitis C virus, possibly indicating an underlying common origin. Likewise, mixed cryoglobulinemia often accompanies autoimmune diseases and hepatitis C infection.

AIM

To compare anti-nuclear antibodies and immunoglobulin content of cryoprecipitates from hepatitis C virus-positive patients in order to assess their predictive value in the onset of hepatitis C virus-driven extrahepatic disorders.

METHODS

Serum from 40 hepatitis C virus-positive patients and 50 controls with rheumatoid arthritis was processed for cryoglobulin detection: all subjects presented with Type III mixed cryoglobulinemia. Immunoglobulin content and immunoglobulin subclasses of cryoprecipitates were assessed by immunofixation and tested by ELISA for rheumatoid factor. Cryoprecipitates were also analysed for anti-nuclear antibodies by indirect immuno-fluorescence to identify specific patterns typical of each condition.

RESULTS

Anti-nuclear antibody patterns differed significantly; 26 infected subjects (65%) were IgG3 positive: of these, 25 were also anti-nuclear antibody-positive (96.1%).

CONCLUSIONS

IgG3 are autoreactive clones unrelated to viral recognition and possibly involved in autoimmune disorders. Altogether, these results may represent useful diagnostic device for early detection of hepatitis C virus-induced autoimmune diseases.

Vasculitis: determinants of disease patterns

The vasculitides are a large group of heterogeneous diseases for which it has been assumed that pathogenesis is largely autoimmune. As clinicians, we distinguish one form of vasculitis from another on the basis of observed patterns of organ injury, the size of the vessels affected and histopathological findings. The terms 'small-vessel', 'medium-vessel' and 'large-vessel' vasculitis are useful clinical descriptors, but fail to inform us about why vessels of a certain calibre are favoured by one disease and not another. Classification based on vessel size also fails to consider that vessels of a specific calibre are not equally prone to injury. Distinct vulnerabilities undoubtedly relate to the fact that same-size vessels in different tissues may not be identical conduits. In fact, vessels become specialized, from the earliest stages of embryonic development, to suit the needs of different anatomical locations. Vessels of the same calibre in different locations and organs are as different as the organ parenchymal cells through which they travel. The dialogue between developing vessels and the tissues they perfuse is designed to meet special local needs. Added to the story of vascular diversity and vulnerability are changes that occur during growth, development and ageing. An improved understanding of the unique territorial vulnerabilities of vessels could form the basis of new hypotheses for the aetiopathogenesis of the vasculitides. This Review considers how certain antigens, including infectious agents, might become disease-relevant and how vascular diversity could influence disease phenotypes and the spectrum of vascular inflammatory diseases.

Vasculitis with renal involvement in essential mixed cryoglobulinemia: Case report and mini-review

The discovery of a strong association between hepatitis C virus (HCV) infection and mixed cryoglobulinemia (MC) has led to an increasingly rare diagnosis of idiopathic essential MC (EMC). The incidence of EMC is high in regions where there is a comparatively low HCV infection burden and low in areas of high infection prevalence, including HCV. The diagnosis of EMC requires an extensive laboratory investigation to exclude all possible causes of cryoglobulin formation. In addition, although cryoglobulin testing is simple, improper testing conditions will result in false negative results. Here, we present a 46-year-old female patient with a case of EMC with dermatological and renal manifestations, highlighting the importance of extensive investigation to reach a proper diagnosis. We review the need for appropriate laboratory testing, which is often neglected in clinical practice and which can result in false negative results. This review also emphasizes the significance of an extended testing repertoire necessary for better patient management. Despite a strong association of MC with HCV infection and other causes that lead to cryoglobulin formation, EMC remains a separate entity. Correct diagnosis requires proper temperature regulation during sample handling, as well as characterization and quantification of the cryoprecipitate. Inclusion of rheumatoid factor activity and complement levels in the cryoglobulin test-panel promotes better patient management and monitoring. Consensus guidelines should be developed and implemented for cryoglobulin detection and the diagnosis of cryoglobulinemic syndrome, which will reduce variability in inter-laboratory reporting.

Utility of immunologic testing in suspected rheumatologic disease

The use of diagnostic testing in the clinical practice of medicine has been a shifting landscape from the time that the first blood test was utilized. This is no different in the field of immunology and in particular rheumatology. As the field of immunology is relatively young, the clinical tests are not well established and therefore guidelines for use are still under debate. In this review, we seek to look at some of the key autoantibodies, as well as other tests that are available to diagnose suspected rheumatologic disease, and examine how to best use these tests in the clinic. In particular, we will focus on the anti-nuclear antibodies, anti-neutrophil cytoplasmic antibodies, complement, cryoglobulins, rheumatoid factor, and anti-citrullinated protein antibodies.

Isolation, characterization, and molecular modeling of a rheumatoid factor from a Hepatitis C virus infected patient with Sjögren's syndrome

We have previously isolated several IgG rheumatoid factors (RFs) from patients with both rheumatoid arthritis and idiopathic thrombocytopenia purpura using phage display system. To study IgG RFs in patients with other autoimmune diseases, phage display antibody libraries from a hepatitis C virus infected patient with Sjögren's syndrome were constructed. After panning, a specific clone RFL11 was isolated for characterization in advance. The binding activity and specificity of RFL11 to IgG Fc fragment were comparable to those of RFs previously isolated. The analysis with existed RF-Fc complex structures indicated the homology model of RFL11 is similar to IgM RF61 complex with high binding affinity of about 6 × 10⁻⁸ M. This effect resulted from longer complementarity-determining region (CDR) combining key somatic mutations. In the RFL11-Fc interfaces, the CDR-H3 loop forms a finger-like structure extending into the bottom of Fc pocket and resulting in strong ion and cation-pi interactions. Moreover, a process of antigen-driven maturation was proven by somatically mutated VH residues on H2 and H3 CDR loops in the interfaces. Taken together, these results suggested that high affinity IgG RFs can be generated in patients with Sjögren's syndrome and may play an important role in the pathogenesis of this autoimmune disease.

Complement C3c as a biomarker in heart failure

Introduction. Experimental data indicates an important role of the innate immune system in cardiac remodeling and heart failure (HF). Complement is a central effector pathway of the innate immune system. Animals lacking parts of the complement system are protected from adverse remodeling. Based on these data, we hypothesized that peripheral complement levels could be a good marker for adverse remodeling and prognosis in patients with HF. Methods and Results. Since complement activation converges on the complement factor C3, we measured serum C3c, a stable C3-conversion product, in 197 patients with stable systolic HF. Subgroups with normal and elevated C3c levels were compared. C3c levels were elevated in 17% of the cohort. Patients with elevated C3c levels exhibited a trend to better survival, slightly higher LVEF, and lower NTpro-BNP values in comparison to patients with normal C3c values. No differences were found regarding NYHA functional class. Significantly more patients with elevated C3c had preexisting diabetes. The prevalence of CAD, arterial hypertension, and atrial fibrillation was not increased in patients with elevated C3c. Conclusion. Elevated C3c levels are associated with less adverse remodeling and improved survival in patients with stable systolic heart failure.

Molecular signatures of hepatitis C virus (HCV)-induced type II mixed cryoglobulinemia (MCII)

The role of hepatitis C virus (HCV) infection in the induction of type II mixed cryoglobulinemia (MCII) and the possible establishment of related lymphoproliferative disorders, such as B-cell non-Hodgkin lymphoma (B-NHL), is well ascertained. However, the molecular pathways involved and the factors predisposing to the development of these HCV-related extrahepatic complications deserve further consideration and clarification. To date, several host- and virus-related factors have been implicated in the progression to MCII, such as the virus-induced expansion of selected subsets of B-cell clones expressing discrete immunoglobulin variable (IgV) gene subfamilies, the involvement of complement factors and the specific role of some HCV proteins. In this review, we will analyze the host and viral factors taking part in the development of MCII in order to give a general outlook of the molecular mechanisms implicated.