Expansion of innate CD5pos B cells expressing high levels of CD81 in hepatitis C virus infected liver

Rat Deconvolution as Knowledge Miner for Immune Cell Trafficking from Toxicogenomics Databases

Toxicogenomics databases are useful for understanding biological responses in individuals because they include a diverse spectrum of biological responses. Although these databases contain no information regarding immune cells in the liver, which are important in the progression of liver injury, deconvolution that estimates cell-type proportions from bulk transcriptome could extend immune information. However, deconvolution has been mainly applied to humans and mice and less often to rats, which are the main target of toxicogenomics databases. Here, we developed a deconvolution method for rats to retrieve information regarding immune cells from toxicogenomics databases. The rat-specific deconvolution showed high correlations for several types of immune cells between spleen and blood, and between liver treated with toxicants compared with those based on human and mouse data. Additionally, we found 4 clusters of compounds in Open TG-GATEs database based on estimated immune cell trafficking, which are different from those based on transcriptome data itself. The contributions of this work are three-fold. First, we obtained the gene expression profiles of 6 rat immune cells necessary for deconvolution. Second, we clarified the importance of species differences on deconvolution. Third, we retrieved immune cell trafficking from toxicogenomics databases. Accumulated and comparable immune cell profiles of massive data of immune cell trafficking in rats could deepen our understanding of enable us to clarify the relationship between the order and the contribution rate of immune cells, chemokines and cytokines, and pathologies. Ultimately, these findings will lead to the evaluation of organ responses in Adverse Outcome Pathway.

Recent Insights into the Role of B Cells in Chronic Hepatitis B and C Infections

Chronic viral hepatitis infections, caused by the hepatitis B or C virus, are a major global health problem causing an estimated one million deaths each year. Immunological studies have classically focused on T cells, while B cells have largely been neglected. Emerging evidence, however, highlights a role for B cells in the immunopathogenesis of chronic hepatitis B and C infections. B cell responses appear to be altered across different clinical phases of chronic HBV infection and across stages of disease in chronic HCV infection. These B cell responses show signs of a more activated state with a simultaneous enrichment of phenotypically exhausted atypical memory B cells. Despite the fact that studies show an activating B cell signature in chronic viral hepatitis infection, antibody responses to HBsAg remain impaired in chronic HBV infection, and glycoprotein E2-specific neutralizing antibody responses remain delayed in the acute phase of HCV infection. At the same time, studies have reported that a subset of HBV- and HCV-specific B cells exhibit an exhausted phenotype. This may, at least in part, explain why antibody responses in chronic HBV and HCV patients are suboptimal. Here, we summarize recent findings and discuss upcoming research questions while looking forward to how new single-cell technologies could provide novel insights into the role of B cells in chronic viral hepatitis infections.

The role of endometrial B cells in normal endometrium and benign female reproductive pathologies: a systematic review

STUDY QUESTION

What are the similarities and differences in endometrial B cells in the normal human endometrium and benign reproductive pathologies?

SUMMARY ANSWER

Endometrial B cells typically constitute <5% of total endometrial CD45⁺ lymphocytes, and no more than 2% of total cells in the normal endometrium, and while their relative abundance and phenotypes vary in benign gynaecological conditions, current evidence is inconsistent.

WHAT IS KNOWN ALREADY

B cells are vitally important in the mucosal immune environment and have been extensively characterized in secondary lymphoid organs and tertiary lymphoid structures (TLSs), with the associated microenvironment germinal centre. However, in the endometrium, B cells are largely overlooked, despite the crucial link between autoimmunity and reproductive pathologies and the fact that B cells are present in normal endometrium and benign female reproductive pathologies, scattered or in the form of lymphoid aggregates (LAs). A comprehensive summary of current data investigating B cells will facilitate our understanding of endometrial B cells in the endometrial mucosal immune environment.

STUDY DESIGN, SIZE, DURATION

This systematic review retrieved relevant studies from four databases (MEDLINE, EMBASE, Web of Science Core Collection and CINAHL) from database inception until November 2021.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The search strategy combined the use of subject headings and relevant text words related to ‘endometrium’, ‘B cells’ and B-cell derivatives, such as ‘antibody’ and ‘immunoglobulin’. Non-benign diseases were excluded using cancer-related free-text terms, and searches were limited to the English language and human subjects. Only peer-reviewed research papers were included. Each paper was graded as ‘Good’, ‘Fair’ or ‘Poor’ quality based on the NEWCASTLE-OTTAWA quality assessment scale. Only ‘Good’ quality papers were included.

MAIN RESULTS AND THE ROLE OF CHANCE

Twenty-seven studies met the selection criteria and were included in this review: 10 cross-sectional studies investigated B cells in the normal endometrium; and 17 case–control studies compared the characteristics of endometrial B cells in control and benign female reproductive pathologies including endometritis, endometriosis, infertility, abnormal uterine bleeding, endometrial polyps and uterine fibroids. In all studies, B cells were present in the endometrium, scattered or in the form of LAs. CD20⁺ B cells were more abundant in patients with endometritis, but the data were inconsistent as to whether B-cell numbers were increased in endometriosis and patients with reproductive pathologies.

LIMITATIONS, REASONS FOR CAUTION

Although only ‘good’ quality papers were included in this systematic review, there were variations in patients’ age, diagnostic criteria for different diseases and sample collection time among included studies. Additionally, a large number of the included studies only used immunohistochemistry as the identification method for endometrial B cells, which may fail to provide an accurate representation of the numbers of endometrial B cells.

WIDER IMPLICATIONS OF THE FINDINGS

Histological studies found that endometrial B cells are either scattered or surrounded by T cells in LAs: the latter structure seems to be under hormonal control throughout the menstrual cycle and resembles TLSs that have been observed in other tissues. Further characterization of endometrial B cells and LAs could offer insights to endometrial B-cell function, particularly in the context of autoimmune-associated pathologies, such as endometriosis. Additionally, clinicians should be aware of the limited value of diagnosing plasma cell infiltration using only CD138.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by Finox Biotech. The authors have no conflicts of interest to declare.

PROSPERO REGISTRATION NUMBER

This systematic review was registered in PROSPERO in January 2020 (PROSPERO ID: CRD42020152915).

Imaging α-GalCer-activated iNKT cells in a hepatic metastatic environment

Colorectal cancer patients frequently develop liver metastases after, and perhaps as a consequence of, lifesaving surgical resection of the primary tumor. This creates a potential opportunity for prophylactic metastatic treatment with novel immunostimulatory molecules. Here, we used state-of-the-art intravital imaging of an experimental liver metastasis model to visualize the early behavior and function of invariant (i)NKT cells stimulated with α-galactosylceramide (α-GalCer). Intravenous α-GalCer prior to tumor cell seeding in the liver significantly inhibited tumor growth. However, some seeding tumor cells survived. A multiple dosing regimen reduced tumor burden and prolonged the life of mice, whereas tumors returned within 5 days after a single dose of α-GalCer. With multiple doses of α-GalCer, iNKT cells increased in number and granularity (as did NK cells). As a result, the total number of contacts and time in contact with tumors increased substantially. In the absence of iNKT cells, the beneficial effect of α-GalCer was lost. Robust cytokine production dissipated over time. Repeated therapy, even after cytokine dissipation, led to reduced tumor burden and prolonged survival. Serial transplantation of tumors exposed to α-GalCer-activated iNKT cells did not induce greater resistance, suggesting no obvious epigenetic or genetic immunoediting in tumors exposed to activated iNKT cells. Very few tumor cells expressed CD1d in this model, and as such, adding monomers of CD1d-α-GalCer further reduced tumor growth. The data suggest early and repeated stimulation of iNKT cells with α-GalCer could have direct therapeutic benefit for colorectal cancer patients that develop metastatic liver disease.

Inflammatory processes in the liver: divergent roles in homeostasis and pathology

The hepatic immune system is designed to tolerate diverse harmless foreign moieties to maintain homeostasis in the healthy liver. Constant priming and regulation ensure that appropriate immune activation occurs when challenged by pathogens and tissue damage. Failure to accurately discriminate, regulate, or effectively resolve inflammation offsets this balance, jeopardizing overall tissue health resulting from an either  overly tolerant or an overactive inflammatory response. Compelling scientific and clinical evidence links dysregulated hepatic immune and inflammatory responses upon sterile injury to several pathological conditions in the liver, particularly nonalcoholic steatohepatitis and ischemia-reperfusion injury. Murine and human studies have described interactions between diverse immune repertoires and nonhematopoietic cell populations in both physiological and pathological activities in the liver, although the molecular mechanisms driving these associations are not clearly understood. Here, we review the dynamic roles of inflammatory mediators in responses to sterile injury in the context of homeostasis and disease, the clinical implications of dysregulated hepatic immune activity and therapeutic developments to regulate liver-specific immunity.

Anti-rods/rings autoantibody and IMPDH filaments: an update after fifteen years of discovery

Autoantibodies to unknown subcellular rod and ring-shaped structures were first discovered in sera from hepatitis C patients in 2005. Early studies showed a strong association between these anti-rods/rings antibodies (anti-RR) and the standard of care interferon-α plus ribavirin combination therapy (IFN/RBV), suggesting that anti-RR are drug-induced autoantibodies. In the context of hepatitis C, anti-RR have been linked with relapse from or lack of response to IFN/RBV in some patient cohorts. However, examples of anti-RR in other diseases and healthy individuals have also been reported over the years, although anti-RR remains a rare autoantibody response in general. The advent of new direct-acting antiviral drugs for chronic hepatitis C and studies of anti-RR from different parts of the world are also beginning to change the perception of anti-RR. The nucleotide biosynthetic enzyme inosine monophosphate dehydrogenase (IMPDH) has been identified as the major autoantigen recognized by anti-RR. Coincidentally, the assembly of IMPDH into micron-scale rod and ring-shaped structures was discovered around the same time as anti-RR. Knowledge of the fundamental biological properties and cellular functions of these structures, referred to as "IMPDH filaments" by cell biologists, has advanced in parallel to anti-RR antibodies. Recent studies have revealed that IMPDH filament assembly is a mechanism to prevent feedback inhibition of IMPDH and is therefore important for the increased nucleotide production required in hyperproliferating cells, like activated T cells. Fifteen years later, we review the history and current knowledge in both the anti-RR autoantibody and IMPDH filament fields. TAKE-HOME MESSAGE: Anti-rods/rings are recognized as an example of a drug-induced autoantibody in hepatitis C patients treated with interferon and ribavirin, although new studies suggest anti-rods/rings may be detected in other contexts and may depend on unknown environmental or genetic factors in different populations. Recent data suggest that the assembly of IMPDH into rod and ring structures, the targets of anti-rods/rings autoantibody, is a mechanism for hyperproliferating cells, like activated T cells, to maintain increased guanine nucleotide levels to support rapid cell division.

CD5/CD20 expression on circulating B cells in HCV-related chronic hepatitis and mixed cryoglobulinemia

The role of CD5⁺ B cells in patients with HCV infection and HCV-related disorders, including mixed cryoglobulinemia (MC), has been addressed in previous reports with conflicting results. We established a correlation between CD5/CD20 expression on circulating B lymphocytes, characterizing monoclonal B cell lymphocytosis (MBL), and clinical features in a cohort of 45 patients with chronic HCV hepatitis [without MC: 23 patients (MC- group); with MC: 22 patients (MC+ group)], and 45 HCV-negative healthy subjects as controls. By flow cytometry analysis, three B cells phenotypes were singled out: 1) CD5⁺CD20^dim (CLL-like phenotype); 2) CD5⁺CD20^bright (atypical phenotype); and 3) CD5^-CD20⁺ phenotype. CD5⁺CD20^bright cells were reduced in MC- patients (p=0.049). CD5⁺CD20^dim B cells were significantly higher in group B than in the control group (p=0.003). ROC curve analysis in MC+ patients showed the highest positive likelihood ratio at ≥7.35% (p=0.008) for CLL-like phenotype and at ≤63.6% (p=0.03) for the CD5^-CD20⁺ B cell phenotype. HCV infection was associated with a higher frequency of CLL-like (odds ratio=16, p=0.002) and a lower frequency of atypical (odds ratio: 3.1, p=0.02) and CD5^-CD20⁺ (odds ratio: 11, p=0.01) phenotypes. The association with higher levels of CLL-like phenotype progressively increased from group of MC- patients (odds ratio: 9.3, p=0.04) to the group of MC+ patients (odds ratio: 25.1, p=0.0003). CONCLUSIONS: The occurrence of a CLL-like pattern may allow to identify HCV-infected patients at risk of developing MC and eventually non-Hodgkin lymphoma, who should require a closer surveillance and a longer follow-up.

Heterogeneity and coexistence of oncogenic mechanisms involved in HCV-associated B-cell lymphomas

The association of HCV-infection with B-lymphomas is supported by the regression of most indolent/low-grade lymphomas following anti-viral therapy. Studies on direct and indirect oncogenic mechanisms have elucidated the pathogenesis of HCV-associated B-lymphoma subtypes. These include B-lymphocyte proliferation and sustained clonal expansion by HCV-envelope protein stimulation of B-cell receptors, and prolonged HCV-infected B-cell growth by overexpression of an anti-apoptotic BCL-2 oncogene caused by the increased frequency of t(14;18) chromosomal translocations in follicular lymphomas. HCV has been implicated in lymphomagenesis by a "hit-and-run" mechanism, inducing enhanced mutation rate in immunoglobulins and anti-oncogenes favoring immune escape, due to permanent genetic damage by double-strand DNA-breaks. More direct oncogenic mechanisms have been identified in cytokines and chemokines in relation to NS3 and Core expression, particularly in diffuse large B-cell lymphoma. By reviewing genetic alterations and disrupted signaling pathways, we intend to highlight how mutually non-contrasting mechanisms cooperate with environmental factors toward progression of HCV-lymphoma.

Hepatitis C virus infection in chronic kidney disease: paradigm shift in management

Hepatitis C virus (HCV) infection in chronic kidney disease (CKD) is associated with increased liver-related morbidity and mortality rates, accelerated progression to end-stage renal disease, and risk of cardiovascular events. CKD patients with HCV infection require antiviral therapy. Pegylated interferon (peg-IFN) plus ribavirin was the standard of care for HCV-infected CKD patients before the introduction of first-generation direct-acting antiviral (DAA) oral anti-HCV agents. Peg-IFN-based treatment has a low virologic response rate and poor compliance, resulting in a high dropout rate. Recently, several clinical trials of all-DAA combination regimens have reported excellent antiviral efficacy and few adverse drug reactions in HCV-infected patients with CKD. These positive results have revolutionized the treatment of chronic HCV infection in this population. In this review, we address the impact of chronic HCV infection in CKD patients, and discuss their management using next-generation DAAs.

Clinicopathologic characteristics and outcomes of transformed diffuse large B-cell lymphoma in hepatitis C virus-infected patients

Hepatitis C virus (HCV) causes a chronic but curable infection associated with the development of marginal zone lymphoma (MZL) and diffuse large B-cell lymphoma (DLBCL). Preliminary data have shown frequent transformation of indolent lymphoma to DLBCL in HCV-infected patients. To compare their clinicopathologic characteristics and oncologic outcomes, we reviewed the medical records and pathology reports of HCV-infected and uninfected patients with DLBCL that transformed from indolent lymphoma seen at The University of Texas MD Anderson Cancer Center (June 2004 to May 2015). To identify predictors of DLBCL relapse, patients with relapse after first-line chemotherapy were compared with those without it using univariate and logistic regression analyses. Compared with the uninfected patients (n = 63), HCV-infected patients (n = 21) were younger (median age =54 years [interquartile range= 49-62 years] vs. 62 years [53-66 years]; p = 0.01) and more often had advanced DLBCL (Ann Arbor stage 3-4; 95% vs. 76%; p = 0.05). Immunophenotypically, more HCV-infected than uninfected patients had CD10-negative B cells (76% vs. 43%; p = 0.008), CD5-positive B cells (39% vs. 7%; p = 0.004) and activated B-cell phenotypes (57% vs. 31%; p = 0.07). Comparison of the patients who had relapse after first-line chemotherapy (n = 42) and those who did not (n = 40) revealed that having CD5-positive B cells was the only factor associated with DLBCL relapse in multivariate analysis (odds ratio= 10.7; p = 0.02). HCV-infected patients with transformed DLBCL have unique clinicopathologic characteristics that make their lymphoma difficult to treat, potentially leading to unfavorable outcome. The impact of HCV eradication should be explored in such patients.

Programmed Cell Death 1 (PD-1) and Cytotoxic T Lymphocyte-Associated Antigen 4 (CTLA-4) in Viral Hepatitis

Virus-specific cluster of differentiation 8 (CD8+) cytotoxic T cells (CTL) recognize viral antigens presented on major histocompatibility complex (MHC) class I chains on infected hepatocytes, with help from CD4+ T cells. However, this CTL response is frequently weak or undetectable in patients with chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) infection. Programmed cell death 1 (PD-1) and cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) are receptors in the CD28 family of costimulatory molecules, providing inhibitory signals to T cells. The overexpressions of PD-1 and CTLA-4 in patients with viral infection have been shown to associate with functional impairment of virus-specific T cells. In acute viral hepatitis, PD-1 and CTLA-4 are up-regulated during the symptomatic phase, and then down-regulated after recovery. These findings suggest that PD-1 and CTLA-4 have protective effects as inhibitory molecules to suppress cytotoxic T cells which induce harmful destruction of viral infected hepatocytes in self-limited viral hepatitis. In chronic viral hepatitis, the extended upregulations of PD-1 and CTLA-4 are associated with T cell exhaustion and persistent viral infection, suggesting positive correlations between expression of immune inhibitory factors and the chronicity of viral disease. In this review, we summarize recent literature relating to PD-1, CTLA-4, and other inhibitory receptors in antigen-specific T cell exhaustion in viral hepatitis, including hepatitis A, B, C, and others.

Inflammatory myopathies and lymphoma

The inflammatory myopathies comprise a group of immune-mediated muscle diseases. Lymphoma is a term for a variety of lymphatic system malignancies. Autoimmune diseases and lymphoproliferative malignancies share a complex bidirectional relationship. A causal relationship between inflammatory mypathies and lymphoma has not been established. The diagnosis/treatment of inflammatory myopathy usually precedes the detection/diagnosis of lymphoma. Immune system dysregulation presumably underlies the evolution of lymphoma in patients with inflammatory myopathies. Inflammatory activity with chronic B-cell activation and/or antigen stimulation is deemed the major risk factor for lymphoma in patients with autoimmunity. A "paraneoplastic" phenomenon or the effects of immunosuppressive therapy may be alternative immune-based mechanisms. In chronic lymphocytic leukemia immune system disturbance rarely results in non-hematological autoimmune disease, including inflammatory myopathies.

Liver immunology and its role in inflammation and homeostasis

The human liver is usually perceived as a non-immunological organ engaged primarily in metabolic, nutrient storage and detoxification activities. However, we now know that the healthy liver is also a site of complex immunological activity mediated by a diverse immune cell repertoire as well as non-hematopoietic cell populations. In the non-diseased liver, metabolic and tissue remodeling functions require elements of inflammation. This inflammation, in combination with regular exposure to dietary and microbial products, creates the potential for excessive immune activation. In this complex microenvironment, the hepatic immune system tolerates harmless molecules while at the same time remaining alert to possible infectious agents, malignant cells or tissue damage. Upon appropriate immune activation to challenge by pathogens or tissue damage, mechanisms to resolve inflammation are essential to maintain liver homeostasis. Failure to clear 'dangerous' stimuli or regulate appropriately activated immune mechanisms leads to pathological inflammation and disrupted tissue homeostasis characterized by the progressive development of fibrosis, cirrhosis and eventual liver failure. Hepatic inflammatory mechanisms therefore have a spectrum of roles in the healthy adult liver; they are essential to maintain tissue and organ homeostasis and, when dysregulated, are key drivers of the liver pathology associated with chronic infection, autoimmunity and malignancy. In this review, we explore the changing perception of inflammation and inflammatory mediators in normal liver homeostasis and propose targeting of liver-specific immune regulation pathways as a therapeutic approach to treat liver disease.

Glomerular Diseases Associated With Hepatitis B and C

Infections with hepatitis B virus (HBV) and hepatitis C virus (HCV) are prevalent worldwide. In this review, we discuss the epidemiology, pathogenesis, clinical manifestations, and treatment of HBV- and HCV-related glomerulonephritis (GN). The most common histopathologic presentation of HBV-GN is HBV-associated membranous nephropathy, which usually manifests clinically with varying grades of proteinuria and microscopic hematuria. The pathogenesis is likely to be immune complex mediated; however, other host and viral factors have been implicated. The treatment of HBV-GN revolves around antiviral therapy. Various histologic types of glomerular diseases are reported in association with HCV infection, the most frequent being Type 1 membranoproliferative glomerulonephritis, usually in the context of Type 2 mixed cryoglobulinemia. The pathogenesis of HCV-GN can be attributed to glomerular deposition of cryoglobulins or noncryoglobulin-immune complexes. Cryoglobulins typically comprised immunoglobulin Mκ with rheumatoid factor activity. Clinically, patients may present with proteinuria, microscopic hematuria, hypertension, and acute nephritic and/or nephrotic syndrome. The treatment of HCV-GN, especially cryoglobulinemic membranoproliferative glomerulonephritis, encompasses various options including contemporary antiviral therapy with or without conventional and novel immunomodulatory agents.

Lymphoma-associated dysimmune polyneuropathies

Lymphoma consists of a variety of malignancies of lymphocyte origin. A spectrum of clinical peripheral neuropathy syndromes with different disease mechanisms occurs in about 5% of lymphoma patients. There exists a complex inter-relationship between lymphoproliferative malignancies and autoimmunity. An imbalance in the regulation of the immune system presumably underlies various immune-mediated neuropathies in patients with lymphoma. This article reviews lymphoma and more-or-less well-defined dysimmune neuropathy subgroups that are caused by humoral and/or cell-mediated immune disease mechanisms directed against known or undetermined peripheral nerve antigens.

CD100 up-regulation induced by interferon-α on B cells is related to hepatitis C virus infection

Objectives

CD100, also known as Sema4D, is a member of the semaphorin family and has important regulatory functions that promote immune cell activation and responses. The role of CD100 expression on B cells in immune regulation during chronic hepatitis C virus (HCV) infection remains unclear.

Materials and Methods

We longitudinally investigated the altered expression of CD100, its receptor CD72, and other activation markers CD69 and CD86 on B cells in 20 chronic HCV-infected patients before and after treatment with pegylated interferon-alpha (Peg-IFN-α) and ribavirin (RBV) by flow cytometry.

Results

The frequency of CD5⁺ B cells as well as the expression levels of CD100, CD69 and CD86 was significantly increased in chronic HCV patients and returned to normal in patients with sustained virological response after discontinuation of IFN-α/RBV therapy. Upon IFN-α treatment, CD100 expression on B cells and the two subsets was further up-regulated in patients who achieved early virological response, and this was confirmed by in vitro experiments. Moreover, the increased CD100 expression via IFN-α was inversely correlated with the decline of the HCV-RNA titer during early-phase treatment.

Conclusions

Peripheral B cells show an activated phenotype during chronic HCV infection. Moreover, IFN-α therapy facilitates the reversion of disrupted B cell homeostasis, and up-regulated expression of CD100 may be indirectly related to HCV clearance.

The development of mixed cryoglobulinemia in Capillaria hepatica-infected mice is associated with the capillaria antigen-induced selective proliferation of splenic B-1a cells in response to interleukin-5 stimulation

Chronic infection by pathogens such as hepatitis C virus induces monoclonal or oligoclonal proliferation of B cells, which produce IgM rheumatoid factor, leading to the development of mixed cryoglobulinemia (MC). Antigen-driven lymphoproliferation is essential to the onset of MC; however, the underlying mechanism is largely unknown. Herein, we show that type II MC is induced by Capillaria hepatica infection through a mechanism in which splenic B-1a cells reacting to C. hepatica-specific antigen selectively proliferate, producing IgM rheumatoid factor under co-stimulation of the specific worm antigen and IL-5. In vitro assays using B-1a cells from infected mice showed that stimulation by C. hepatica soluble fraction promoted the proliferation of B-1a cells and the secretion of IgM, which reacted with the 75-kDa antigen in the soluble fraction. The severity of MC was correlated with the increase in serum IL-5 levels in the infected mice. Furthermore, i.p. injection of the soluble worm fraction caused MC without an inflammatory response in IL-5 transgenic mice, indicating that IL-5 is critical for the development of MC. These results indicate that the selective proliferation of IgM rheumatoid factor-secreting B-1a cells is induced by co-stimulation by the specific pathogen antigen and IL-5 in the development of MC in C. hepatica-infected mice.

Overexpression of Regulatory T Cells Type 1 (Tr1) Specific Markers in a Patient with HCV-Induced Hepatocellular Carcinoma

Hepatitis C virus (HCV) is an important causative agent of liver disease, but factors that determine the resolution or progression of infection are poorly understood. In this study, we suggested that existence of immunosuppressive mechanisms, supported by regulatory T cells and especially the regulatory T cell 1 subset (Tr1), may explain the impaired immune response during infection and thus the fibrosis aggravation to hepatocellular carcinoma (HCC). Using quantitative real-time PCR, we investigated the intra-hepatic presence of Tr1 cells in biopsies from a genotype 1b infected patient followed for an 18-year period from cirrhosis to HCC. We described a significant increase of gene expression in particular for the cytokines IL-10, TGF-β, and their receptors that were perfectly correlated with an increased expression of the Tr1 specific markers (combined expression of CD4, CD18, and CD49b). This was strongly marked since the patient evolved in the pathology and could explain the failure of the treatment. In conclusion, evidence of regulatory T cell installation in the liver of chronically infected patient with cirrhosis and HCC suggests for the first time a key role for these cells in the course of HCV infection.

Hepatitis C-associated B-cell non-Hodgkin lymphomas. Epidemiology, molecular signature and clinical management

There is ample epidemiologic evidence for an association of chronic hepatitis C virus (HCV) infection with B-cell non-Hodgkin lymphoma (B-NHL). B-NHL subtypes most frequently associated with HCV are marginal zone lymphoma and diffuse large B-cell lymphoma. The most convincing evidence for a causal relationship between HCV infection and lymphoma development is the observation of B-NHL regression after HCV eradication by antiviral therapy (AVT). In fact, for indolent HCV-associated B-NHL, first-line AVT instead of standard immune-chemotherapy might be considered. Molecular mechanisms of HCV-NHL development are still poorly understood. Three general theories have emerged to understand the HCV-induced lymphomagenesis: (1) continuous external stimulation of lymphocyte receptors by viral antigens and consecutive proliferation; (2) HCV replication in B cells with oncogenic effect mediated by intracellular viral proteins; (3) permanent B-cell damage, e.g., mutation of tumor suppressor genes, caused by a transiently intracellular virus ("hit and run" theory). This review systematically summarizes the data on epidemiology, interventional studies, and molecular mechanisms of HCV-associated B-NHL.

Early-stage splenic diffuse large B-cell lymphoma is highly associated with hepatitis C virus infection

Splenic marginal zone lymphoma (SMZL) and splenic diffuse large B-cell lymphoma (DLBCL) are the most common types of lymphomas involving the spleen. Geographic variation in hepatitis C virus (HCV) seroprevalence is characteristic of splenic lymphomas. In Italy, HCV seroprevalence was higher in patients with SMZL and splenic DLBCL than in patients with all types of lymphoma. In Japan, HCV seroprevalence was higher in patients with splenic DLBCL than in patients with all types of lymphoma; however, HCV seroprevalence in patients with SMZL was similar to that in patients with all types of lymphoma. In this study, clinicopathological data of 74 splenic lymphoma cases between 1988 and 2011 collected from the Department of Pathology at National Taiwan University Hospital were analyzed. Serology for HCV infection was available for 41 cases. Splenic DLBCL and SMZL accounted for 36% (n = 27) and 42% (n = 31) of splenic lymphomas, respectively. Microscopically, most cases of DLBCL (26/27) presented with circumscribed tumor and most cases of SMZL (28/31) presented with white pulp expansion. HCV seroprevalence in patients with DLBCL and SMZL was 44% and 10%, respectively (7/16 vs. 2/20, p = 0.020). The pattern identified in this study is closer to that in Japan than in Italy. HCV seroprevalence in patients with early-stage (I/II) and late-stage (III/IV) DLBCL was 100% and 10%, respectively (6/6 vs. 1/10, p < 0.001). Early-stage DLBCL is clinically considered a form of primary splenic lymphoma rather than a systemic lymphoma with splenic involvement. High HCV seroprevalence in patients with early-stage DLBCL suggests a role of HCV in the pathogenesis of primary DLBCL.

Hepatitis C virus-mediated modulation of cellular immunity

The hepatitis C virus (HCV) is a major cause of chronic liver disease globally. A chronic infection can result in liver fibrosis, liver cirrhosis, hepatocellular carcinoma and liver failure in a significant ratio of the patients. About 170 million people are currently infected with HCV. Since 80 % of the infected patients develop a chronic infection, HCV has evolved sophisticated escape strategies to evade both the innate and the adaptive immune system. Thus, chronic hepatitis C is characterized by perturbations in the number, subset composition and/or functionality of natural killer cells, natural killer T cells, dendritic cells, macrophages and T cells. The balance between HCV-induced immune evasion and the antiviral immune response results in chronic liver inflammation and consequent immune-mediated liver injury. This review summarizes our current understanding of the HCV-mediated interference with cellular immunity and of the factors resulting in HCV persistence. A profound knowledge about the intrinsic properties of HCV and its effects on intrahepatic immunity is essential to be able to design effective immunotherapies against HCV such as therapeutic HCV vaccines.

Pathogenetic mechanisms of hepatitis C virus-induced B-cell lymphomagenesis

Hepatitis C virus (HCV) infection is probably the most common chronic viral infection and affects an estimated 180 million people worldwide, accounting for 3% of the global population. Although the liver is considered to be the primary target, extrahepatic manifestations are well recognized among patients with chronic HCV infection. Epidemiological studies have clearly demonstrated a correlation between chronic HCV infection and occurrence of B-cell non-Hodgkin's lymphomas (B-NHL). The clinical evidence that antiviral therapy has a significant role in the treatment at least of some HCV-associated lymphoproliferative disorders, especially indolent B-NHL, further supports the existence of an etiopathogenetic link. However, the mechanisms exploited by HCV to induce B-cell lymphoproliferation have so far not completely clarified. It is conceivable that different biological mechanisms, namely, chronic antigen stimulation, high-affinity interaction between HCV-E2 protein and its cellular receptors, direct HCV infection of B-cells, and "hit and run" transforming events, may be combined themselves and cooperate in a multifactorial model of HCV-associated lymphomagenesis.

Hepatitis C virus infection and mixed cryoglobulinemia

Hepatitis C virus (HCV) chronic infection is recognized as the major cause of mixed cryoglobulinemia (MC). Its persistence represents a continuous stimulus for host immune system with production of circulating immune complexes (ICs), one-third of them with cryoprecipitate property. Several factors contribute to the biological activities of ICs, many of which are not completely known. Among them, complement factors play a crucial role in the cold-insoluble ICs-mediated vasculitis, involving primarily small blood vessels in different tissues including skin, kidney, peripheral, and central nervous system. Liver represents the major target of HCV infection with inflammatory infiltrates, resembling secondary lymphoid follicles. Cytokine like CXCL13 contribute to B-cell homing in intraportal lymphoid aggregates, in which B-cell clonal selection may arise. B-cell clonal expansion starts as an antigen-driven event and expands towards indolent and malignant B-cell proliferation. Occurrence of intrahepatic B-cell clonalities correlates with extrahepatic clinical manifestations of HCV infection. In this context, cryoglobulinemic patients should be considered a peculiar HCV-infected population that needs a clinical multidisciplinary approach and more articulated therapeutic measures.

Early lesions in lymphoid neoplasia: Conclusions based on the Workshop of the XV. Meeting of the European Association of Hematopathology and the Society of Hematopathology, in Uppsala, Sweden

The increasing use of immunophenotypic and molecular techniques on lymphoid tissue samples without obvious involvement by malignant lymphoma has resulted in the increased detection of "early" lymphoid proliferations, which show some, but not all the criteria necessary for a diagnosis of malignant lymphoma. In most instances, these are incidental findings in asymptomatic individuals, and their biological behaviour is uncertain. In order to better characterize these premalignant conditions and to establish diagnostic criteria, a joint workshop of the European Association for Haematopathology and the Society of Hematopathology was held in Uppsala, Sweden, in September 2010. The panel reviewed and discussed more than 130 submitted cases and reached consensus diagnoses. Cases representing the nodal equivalent of monoclonal B-cell lymphocytosis (MBL) were discussed, as well as the "in situ" counterparts of follicular lymphoma (FL) and mantle cell lymphoma (MCL), topics that also stimulated discussions concerning the best terminology for these lesions. The workshop also addressed the borderland between reactive hyperplasia, and clonal proliferations such as pediatric marginal zone lymphoma and pediatric FL, which may have very limited capacity for progression. Virus-driven lymphoproliferations in the grey zone between reactive lesions and manifest malignant lymphoma were covered. Finally, early manifestations of T-cell lymphoma, both nodal and extranodal, and their mimics were addressed. This workshop report summarizes the most important conclusions concerning diagnostic features, as well as proposals for terminology and classification of early lymphoproliferations and tries to give some practical guidelines for diagnosis and reporting.

Comparative analysis of portal cell infiltrates in antimitochondrial autoantibody-positive versus antimitochondrial autoantibody-negative primary biliary cirrhosis

Substantial evidence supports dysregulated B-cell immune responses in patients with primary biliary cirrhosis (PBC), including the presence of serum antimitochondrial antibodies (AMAs). However, recent reports from murine models of PBC suggest that B cells may also provide regulatory function, and indeed the absence of B cells in such models leads to exacerbation of disease. The vast majority of patients with PBC have readily detectable AMAs, but a minority (<5%) are AMA negative (AMA(-)), even with recombinant diagnostic technology. This issue prompted us to examine the nature of B-cell infiltrates surrounding the portal areas in AMA-positive (AMA(+)) and AMA(-) patients, because they display indistinguishable clinical features. Of importance was the finding that the degree of bile duct damage around the portal areas was significantly milder in AMA(+) PBC than those observed in AMA(-) PBC patients. The portal areas from AMA(-) patients had a significant increase of cluster of differentiation (CD)5(+) cells infiltrating the ductal regions, and the levels of B-cell infiltrates were worse in the early phase of bile duct damage. The frequency of positive portal areas and the magnitude of CD5(+) and CD20(+) cellular infiltrates within areas of ductal invasion is associated with the first evidence of damage of biliary duct epithelia, but becomes reduced in the ductopenia stage, with the exception of CD5(+) cells, which remain sustained and predominate over CD20(+) cells.

CONCLUSION

Our data suggest a putative role of B-cell autoimmunity in regulating the portal destruction characteristic of PBC.

Hepatitis viruses and non-Hodgkin lymphoma: epidemiology, mechanisms of tumorigenesis, and therapeutic opportunities

Over the past 2 decades considerable evidence has accumulated on the association between hepatitis C virus (HCV) and hepatitis B virus (HBV) and several hematologic malignancies, most notably B-cell non-Hodgkin lymphoma (NHL). In this review we summarize this evidence, address possible mechanisms whereby hepatitis viruses may contribute to lymphomagenesis, and discuss the therapeutic fallouts from this knowledge. Most of this evidence is on HCV, and this is the main focus of the review. Moreover, we mainly address the association with NHL, the most prevalent hematologic malignancy, and the most extensively investigated with regard to an association with hepatitis viruses. Available evidence on the association with other hematologic malignancies is also addressed briefly.

Differential susceptibility of peripheral blood CD5+ and CD5- B cells to apoptosis in chronic hepatitis C patients

A body of evidence has suggested a close link between chronic hepatitis C virus (HCV) infection and B cell abnormalities, including mixed cryoglobulinemia, rheumatoid factor (RF) production, and lymphoproliferative disorders that may develop into non-Hodgkin's lymphoma. Recent studies have demonstrated the expansion of CD5(+) B cells in the peripheral blood of chronic hepatitis C patients (CHC). As CD5(+) B cells, which are capable of producing autoantibodies and RF, are apparently crucial for the development of HCV-associated pathogenesis, the fate of both the CD5(+) and CD5(-) B cell subsets upon chronic HCV infection is of interest. In this study, the degree to which chronic HCV infection induces apoptosis in each B cell subset was investigated. Our results demonstrated that peripheral CD5(-) B cells were more susceptible to apoptosis than CD5(+) B cells in CHC. Furthermore, plasma levels of IL-4, IL-10, and IL-12 were significantly elevated in CHC, thus suggesting that these interleukins protect CD5(+) B cells from apoptosis. The rationale for the differential susceptibility of distinct B cell subsets in CHC is also discussed with regard to extrahepatic manifestations associated with chronic HCV infection.

Microanatomy of the liver immune system

The critical metabolic functions of the liver often eclipse any perception of its role as an immune organ. However, the liver as a mediator of systemic and local innate immunity and an important site of immune regulation is now an accepted concept. Complex repertoires of lymphoid and non-lymphoid cells are key to hepatic defense and immunoregulation. Hepatic cells of myeloid lineage include Kupffer cells and dendritic cells. Intrahepatic lymphocytes are distinct both in phenotype and function from their counterparts in any other organ and include both conventional (CD4+ and CD8+ alphabeta T cell receptor (TCR)+ T cells, B cells, natural killer (NK) cells) and nonconventional lymphoid cells (natural killer T (NKT) cells, gamma delta TCR+ T cells, CD4- CD8- T cells). Many hepatic T cells express the TCR at an intermediate level and the great majority of them either coexpress NK cell markers (NKT cells) or they are apoptosing peripheral T cells. The percentage of activated (CD69+) and memory (CD45RB low+) lymphocytes is much higher while naive (CD62L high) and resting T cells as well as B lymphocytes are underrepresented in the liver. The discovery of major populations of lymphoid cells in the liver that differ phenotypically, functionally and even perhaps developmentally from populations in other regions has been key to the evolving perception of the liver as a regulatory lymphoid organ. This chapter will focus on these populations and how they contribute to immune surveillance against malignant, infectious and autoimmune disease of the liver.

The 1F7 idiotype is selectively expressed on CD5+ B cells and elevated in chronic hepatitis C virus infection

Antibodies against different chronic viruses, including hepatitis C virus (HCV), express a public cross-reactive idiotype (Id) designated as 1F7. The prominence of this Id may reflect selective engagement of B1 B cells by chronic pathogens. We investigated this by comparing 1F7 Id expression on CD5(+) and CD5(-) B cells, total IgG, total IgM and anti-HCV core antibodies in different HCV exposure settings. By flow cytometry, we observed a selective increase in 1F7 Id(+)CD5(+) B cells in chronic HCV infection. 1F7 Id levels in different immunoglobulin compartments were measured by enzyme-linked immunosorbent assay. 1F7 Id expression was prominent in anti-HCV core antibodies of approximately 90% of 141 HCV-exposed individuals tested. In the Canadian and Armenian study groups, participants who spontaneously cleared HCV infection had lower median 1F7 Id levels on total plasma IgG and anti-HCV core antibodies. Armenian spontaneous clearers, who were younger and more recently infected than their Canadian counterparts, also had had lower median 1F7 Id levels on total plasma IgM. Engagement by HCV of B-cell receptors within, or overlapping with the CD5(+) B1 B-cell repertoire is reflected in the production of 1F7 Id(+) anti-HCV antibodies and expansion of 1F7 Id(+)CD5(+) B cells. Higher 1F7 Id expression levels are associated with chronic infection.

Clonal expansion of immunoglobulin M+CD27+ B cells in HCV-associated mixed cryoglobulinemia

Hepatitis C virus (HCV) is associated with B-cell lymphoproliferative disorders such as mixed cryoglobulinemia (MC) and B-cell non-Hodgkin lymphoma (B-NHL). The pathogenesis of these disorders remains unclear, and it has been proposed that HCV drives the pro-liferation of B cells. Here we demonstrate that certain HCV(+)MC(+) subjects have clonal expansions of immunoglobulin M (IgM)(+)kappa(+)IgD(low/-)CD21(low)CD27(+) B cells. Using RT-PCR to amplify Ig from these singly sorted cells, we show that these predominantly rheumatoid factor-encoding V(H)1-69/J(H)4 and V(kappa)3-20 gene segment-restricted cells have low to moderate levels of somatic hypermutations. Ig sequence analysis suggests that antigen selection drives the generation of mutated clones. These findings lend further support to the notion that specific antigenic stimulation leads to B-cell proliferation in HCV MC and that chronic B-cell stimulation may set the stage for malignant transformation and the development of B-NHL. The finding that these hypermutated, marginal zone-like IgM(+)CD27(+) B cells are clonally expanded in certain subjects with MC offers insight into mechanisms of HCV-associated MC and B-cell malignancy. This study was registered at www.clinicaltrials.gov as NCT00219999.

Altered expression of the tetraspanin CD81 on B and T lymphocytes during HIV-1 infection

CD81 is a member of the tetraspan superfamily and plays a role in immune responses and in hepatitis C virus (HCV) pathogenesis. We analysed CD81 cell surface and mRNA expression in different lymphocytic subpopulations in human immunodeficiency virus (HIV)-1, HCV and dually infected subjects. CD81 cell surface expression was evaluated with fluorescence activated cell sorter (FACS) analysis; mRNA quantification was performed with semiquantitative polymerase chain reaction (PCR). CD81 cell surface expression on CD4(+) T lymphocytes was significantly different by analysis of variance (anova) test (P < 0.001), with reduced expression in HIV-1(+) patients. In B lymphocytes, higher cell surface expression was present in HIV-1, in HCV and in dually infected subjects compared to healthy controls. CD81 expression on B lymphocytes showed a positive correlation with plasma HIV-RNA. CD81 mRNA levels in B lymphocytes were significantly higher in HIV-1(+) patients compared to healthy controls. The potential consequence of the down-regulation of CD81 in CD4(+) cells during HIV-1 infection in conjunction with diverted CD28, CD4 and CD3 expression is the disruption of T cell function. Increased CD81 expression on B lymphocytes might explain the higher prevalence of lymphoproliferative disorders in HIV-1 and HCV infection. Up-regulation of CD81 mRNA on CD4(+) T cells indicates that down-regulation of CD81 occurs at the post-transcriptional/translational level.

Virological analysis and phenotypic characterization of peripheral blood lymphocytes of hepatitis C virus-infected patients with and without mixed cryoglobulinaemia

In clinical and pathological terms hepatitis C virus (HCV)-infected patients can be subdivided into two main groups with and without mixed cryoglobulinaemia (MC). Involvement of blood mononuclear cells by HCV has potentially important implications. To this end, HCV-RNA levels in peripheral blood lymphocytes (PBL) preparations of 20 chronically HCV-infected patients with MC were measured and compared with those found in a group of 20 patients without MC matched for age, serum HCV-RNA, infectious genotype, source and presumable duration of infection. Phenotypic abnormalities of PBL subsets in each group of patients were determined by cell surface marker expression and compared. Results showed a significant enrichment of HCV-RNA in PBL of MC patients compared with a non-MC group (P = 0.01). Different distribution of HCV-RNA was accompanied by evidence of an increased frequency of circulating B cells. These data indicate that MC patients are characterized distinctly by a higher quota of cell-associated viral load.

Type II mixed cryoglobulinaemia as an oligo rather than a mono B-cell disorder: evidence from GeneScan and MALDI-TOF analyses

OBJECTIVE

To identify and characterize rheumatoid factor (RF)-producing B-cells and cryoprecipitate immunoglobulin (Ig) M in hepatitis C virus (HCV)-positive patients.

METHODS

We purified and characterized, by peptide mass fingerprinting integrated with an NCBI IgBlast data bank search, the IgM component of cryoprecipitate and analysed the VDJ pattern of bone marrow B-cells by gene scan analysis of 17 HCV-positive patients with type II mixed-cryoglobulinaemia.

RESULTS

IgM purified from all of the patients presented an RF specificity. In three of these patients a high and predominant B-cell clone (>or=30%) was found in the bone marrow. B-cell-receptor sequences were determined and immunophenotyping of these clones was performed. Peptide masses originating after tryptic digestion of the B-cell-receptor combinatory regions and those originating by tryptic digestion of the cryoprecipitated IgM from the same patient were comparable. In the remaining patients an oligoclonal/polyclonality was found. However, in some of these patients we were able to find peptides that matched with the B-cell-receptor sequences of overexpanded B cells, indicating that, even in the absence of a clear monoclonal expansion, a fraction of total cryoprecipated IgM may derive from overexpanded B-cell clones found in patients' bone marrow.

CONCLUSIONS

In the majority of mixed cryoglobulinaemia-HCV-positive patients, both in the serum and in B cells from the bone marrow, an oligoclonal pattern is the main molecular picture. When a monoclonal B-cell clone is found, its B-cell-receptor shows an antigen-binding fragment identical to that of cryoprecipitable RF-IgM. Phenotypically, B cells are CD20-positive but CD5-negative, suggesting that the B-1 B-cell subset is not likely to produce high-affinity IgM-RF molecules.

HCV-associated B cell clonalities in the liver do not carry the t(14;18) chromosomal translocation

Infection with HCV can be associated with B-cell non-Hodgkin lymphoma. Polymerase chain reaction (PCR) amplification assays for Bcl-2/IgH rearrangement were performed on nucleic acids extracted from portal tract inflammatory infiltrates, isolated with laser capture microdissection (LCM), from liver biopsy sections of 16 hepatitis C virus (HCV)-infected patients with and without extrahepatic B cell-related disorders. Results were compared with total DNA extracted from core liver biopsy specimens and from peripheral blood mononuclear cells (PBMCs). We failed to demonstrate specific Bcl-2/IgH amplicons either in liver tissue or in PBMCs in all patients of the current series. Multiple PCR assays for variable diversity joining (VDJ) IgH gene rearrangements were also performed in the liver compartment. Selective amplification compatible with mono or oligoclonal B cell clonotypes was demonstrated in 80% (6/8) and 25% (2/8) of patients with and without clinical evidence of B-cell disorders. V(H)1 and V(H)3 were the most represented V(H) families. In situ expression of Bcl-2 protein was carried out by immunohistochemistry on liver biopsy sections. Bcl-2 protein was detected in 2 (12.5%) patients who did not associate extrahepatic disorders. In conclusion, current data support the concept that production of IgH gene rearrangements is not associated with Bcl-2/IgH chromosomal translocation in hepatic compartment. Liver overexpression of Bcl-2 protein may occur in at least a minor proportion of HCV-infected patients.

Screening of hepatocyte proteins binding to complete S protein of hepatitis B virus by yeast-two hybrid system

AIM: To investigate the biological function of complete S protein and to look for proteins interacting with complete S protein in hepatocytes.

METHODS: We constructed bait plasmid expressing complete S protein of HBV by cloning the gene of complete S protein into pGBKT7, then the recombinant plasmid DNA was transformed into yeast AH109 (a type). The transformed yeast AH109 was mated with yeast Y187 (α type) containing liver cDNA library plasmid in 2 ×YPDA medium. Diploid yeast was plated on synthetic dropout nutrient medium (SD/-Trp-Leu-His-Ade) containing X-α-gal for selection and screening. After extracting and sequencing of plasmids from positive (blue) colonies, we underwent sequence analysis by bioinformatics.

RESULTS: Nineteen colonies were selected and sequenced. Among them, five colonies were Homo sapiens solute carrier family 25, member 23 (SLC25A23), one was Homo sapiens calreticulin, one was human serum albumin (ALB) gene, one was Homo sapiens metallothionein 2A, two were Homo sapiens betaine-homocysteine methyltransferase, three were Homo sapiens Na⁺ and H⁺ coupled amino acid transport system N, one was Homo sapiens CD81 antigen (target of anti-proliferative antibody 1) (CD81), three were Homo sapiens diazepam binding inhibitor, two colonies were new genes with unknown function.

CONCLUSION: The yeast-two hybrid system is an effective method for identifying hepatocyte proteins interacting with complete S protein of HBV. The complete S protein may bind to different proteins i.e., its multiple functions in vivo.

Hepatitis C virus, cryoglobulinaemia, and vasculitis: immune complex relations

Several viruses are involved in the development of systemic vasculitides. Hepatitis C virus (HCV) has been shown to be closely related to mixed cryoglobulinaemia, an immune complex-mediated vasculitis. HCV particles and non-enveloped nucleocapsid protein participate in the formation of immune complexes. Once formed, immune complexes precipitate in many organs, including the skin, kidneys, and peripheral nerve fibres. Viral proteins confer peculiar physical and chemical properties on cryoimmunoglobulins. Since expansion of rheumatoid factor-synthesising B cells is the biological hallmark of mixed cryoglobulinaemia, it may be that the combination of rheumatoid factor activity and cryoprecipitability is responsible for the vasculitis. B-cell clonal expansion occurs primarily in the liver and correlates with a high intrahepatic viral load, pointing to a major role for HCV in the emergence and maintenance of B-cell clonalities. Recognition of HCV as an aetiological factor in most cryoglobulinaemic vasculitides has dramatically changed the approach to their treatment. Emphasis, in fact, is now placed on abatement of the viral load and deletion of B-cell clonalities.

Cryoglobulinemia

Mixed cryoglobulinemia (MC) type II is a disorder characterized by circulating cold-precipitable immune complexes composed of polyclonal immunoglobulin IgG and monoclonal IgM rheumatoid factor (RF). The systemic vasculitis which characterizes the disease is caused by the deposition of immune complexes on the walls of small vessels, and by the subsequent activation of the complement cascade. MC may be asymptomatic or lead to clinical manifestations characterized by a typical triad--purpura, arthralgia, and weakness--and in some cases by a more serious vasculitis with neurologic and renal involvement. In the vast majority (more than 90%) of patients, MC is associated with hepatitis C virus (HCV) infection, which is considered the triggering factor of the disease. The association between cryoglobulinemia and HCV infection, and the possible evolution to B-cell lymphomas usually after long-term follow-up, suggest the role of HCV infection both in the pathogenesis of MC and in lymphomagenesis. In fact, the virus chronically stimulates the polyclonal proliferation of B cells from which a monoclonal population may emerge. This paper also reviews the treatment strategies for MC syndrome, emphasizing the issue of the eradication of HCV, and the clinical and biological activity of rituximab for selective B-cell control.