Rheumatoid Factor Activity Research Articles

Clonal CD27+ CD19+ B Cell Expansion through Inhibition of FCγIIR in HCV+ Cryoglobulinemic Patients

Persistent HCV infection may be associated with extrahepatic manifestations such as type II mixed cryoglobulinemia (II-MC), a clonal B cell proliferative disorder. In persistent HCV infection without II-MC, an increase in serum immunoglobulins (Ig) is commonly observed. This increase is polyclonal and is determined primarily by increased levels of IgG which include both HCV-specific and nonspecific antibodies. Nonetheless, memory CD27(+) B cells do not accumulate. This paradoxical phenomenon depends on heightened sensitivity of memory B cells to BCR-independent noncognate T cell help, which speeds up their terminal differentiation into antibody-secreting cells and makes them more prone to apoptosis. In persistent HCV infection with II-MC, serum Ig elevation is also a general occurrence, and characteristically includes IgM antibodies with rheumatoid factor activity, which are essential for the development of circulating, cryoprecipitable immune complexes. Hypergammaglobulinemia is sustained by a peripheral expansion of IgM(+)k(+)IgD(low/neg)CD21(low)CD27(+) B cells. These cells exhibit marked V(H), J(H), and V(K) gene segment usage restriction, indicating that a limited number of antigens drive their proliferation through BCR interaction. Recently, two epitopes, one of the human IgG and the second of the HCV(NS3) protein, had been identified and demonstrated able to link the BCR exposed on II-MC subjects. Based on the above findings, we propose a model whereby BCR binding the IgM/IgG/HCV(NS3) immune complexes deprives Fc gammaIIR of its natural ligand. This takes the brake off RF(+)CD27(+) B cell proliferation and promotes their selective accumulation, which is otherwise prevented by increased apoptosis susceptibility in persistent HCV infection without II-MC.

Characterization of Antibodies Directed against the Immunoglobulin Light κ Chain Variable Chain Region (VK) of Hepatitis C Virus‐Related Type‐II Mixed Cryoglobulinemia and B‐Cell Proliferations

Autoimmune type-II cryoglobulinemia (II-MC) is sustained by hepatitis C virus (HCV) infection and B-cell (oligo)clones. This is the reason why the disease may be considered an "indolent B-cell lymphoma (NHL)." B clones show a restricted use of immunoglobulin variable genes (BCR), in particular in the use of the variable kappa (VK)3-20/15 light chain, and show a homology between their BCR functional regions and those of autoimmune rheumatoid factors. We underlined the BCR unique repertoire with frequent rheumatoid factor activity also observed in other autoimmune disorders associated with NHL. The immunoglobulin idiotype is a clonal B-cell marker and an ideal target for immunotherapy. Five monoclonal antibodies were produced in our laboratory toward the VK3-20 of a subject with HCV infection and a II-MC-associated NHL. Epitope determination was performed using the epitope excision approach. Monoclonal antibody reactivity was tested in vitro in ELISA, Western blot, and cytofluorimetry. Data confirmed that a panel of antibodies, reactive against shared idiotypes, can be produced from patients with HCV-associated B-cell lymphoproliferative diseases, thus obviating the need to produce an anti-idiotype antibody for each patient.

Immunoglobulin G4: an odd antibody

Despite its well-known association with IgE-mediated allergy, IgG4 antibodies still have several poorly understood characteristics. IgG4 is a very dynamic antibody: the antibody is involved in a continuous process of half-molecules (i.e. a heavy and attached light-chain) exchange. This process, also referred to as 'Fab-arm exchange', results usually in asymmetric antibodies with two different antigen-combining sites. While these antibodies are hetero- bivalent, they will behave as monovalent antibodies in most situations. Another aspect of IgG4, still poorly understood, is its tendency to mimic IgG rheumatoid factor (RF) activity by interacting with IgG on a solid support. In contrast to conventional RF, which binds via its variable domains, the activity of IgG4 is located in its constant domains. This is potentially a source of false positives in IgG4 antibody assay results. Because regulation of IgG4 production is dependent on help by T-helper type 2 (Th2) cells, the IgG4 response is largely restricted to non-microbial antigens. This Th2-dependency associates the IgG4 and IgE responses. Another typical feature in the immune regulation of IgG4 is its tendency to appear only after prolonged immunization. In the context of IgE-mediated allergy, the appearance of IgG4 antibodies is usually associated with a decrease in symptoms. This is likely to be due, at least in part, to an allergen-blocking effect at the mast cell level and/or at the level of the antigen-presenting cell (preventing IgE-facilitated activation of T cells). In addition, the favourable association reflects the enhanced production of IL-10 and other anti-inflammatory cytokines, which drive the production of IgG4. While in general, IgG4 is being associated with non-activating characteristics, in some situations IgG4 antibodies have an association with pathology. Two striking examples are pemphigoid diseases and sclerosing diseases such as autoimmune pancreatitis. The mechanistic basis for the association of IgG4 with these diseases is still enigmatic. However, the association with sclerosing diseases may reflect an excessive production of anti-inflammatory cytokines triggering an overwhelming expansion of IgG4-producing plasma cells. The bottom line for allergy diagnosis: IgG4 by itself is unlikely to be a cause of allergic symptoms. In general, the presence of allergen-specific IgG4 indicates that anti-inflammatory, tolerance-inducing mechanisms have been activated. The existence of the IgG4 subclass, its up-regulation by anti-inflammatory factors and its own anti-inflammatory characteristics may help the immune system to dampen inappropriate inflammatory reactions.

Characterization of Antibodies Direct against the Idiotypic VK3 Chain of HCV-Related Type-II Mixed Cryoglobulinemia and B-Cell Proliferations

Autoimmune type-II cryoglobulinemia (MC) is sustained by clonal/oligoclonal B-cell populations such the disease may be considered an “indolent B-cell lymphoma (NHL) “ and may favor overt NHL development. HCV-antigen driven mechanism induces B-cell proliferations. Clonal B-cells demonstrate a restricted used of variable genes to construct the B-cell receptor (BCR) and a homology between BCR functional regions and autoimmune rheumatoid factor (RF) activity. We underline the BCR unique repertoire with frequent rheumatoid factor activity also in other autoimmune disorders associated to NHL development as Sjogren's syndrome and rheumatoid arthritis. All together these BCRs are characterized by their high degree of idiotypic (Id) cross reactivity. Particularly the K chain V3-20/15 is frequently found in subject with positive HCV antibody. Id is a clonamarker expressedby B cells, thus is an ideal target for immunotherapy. The evidence of few Id presented in the NHL subgroup above reported constitute the rational for the development of antibodies and recombinant proteins that use shared Id among different NHL. Five monoclonal antibodies have been produced in our laboratory toward the VK3-20 region of a subject HCV+ with NHL. Epitopes recognized has been performed using epitope excision approach. A fine determination of the antibodies activities toward specific amino acids, possibly common to different individuals, are in progress. Monoclonal antibodies reactivity has been tested in vitro in ELISA, western blot and cytofluorimetry. Apoptosis and SyK/ERK phosphorylation pathways induced following BCR cross-linking of antiId murine IgG will be performed. All the antibodies were reactive in Elisa against the VK3-Ig light chain. Two of these antibodies showed a reactivity against the light chain of cryoprecipitated immunocomplexes from several patients in western blot, and by cytofluorimter they recognised two lymphoma B-cell lines.

Clonal CD27+ CD19+ B-Cell Expansion through Inhibition of FCgIIR in HCV+ Lymphorpoliferative Disorders

HCV infection may or may not be associated with extra-hepatic manifestations such as type-II mixed cryoglobulinemia (MC), a clonal B cell proliferative disorder. In persistent HCV infection without MC a increase in serum immunoglobulins (Ig) is commonly observed. We found this increase is polyclonal and is determined primarily by increased levels of both HCV-specific and nonspecific IgG. Despite this hypergammaglobulinemia, memory CD27+ do not accumulate, depending on a heightened sensitivity of memory B cells to BCR-independent noncognate T cell help which speeds up their terminal differentiation into antibody secreting cells and make them more prone to activation induced cell death. In persistent HCV infection with MC, elevation of Ig is a general occurrence too. However, it is attributable to IgG and IgM. The latter include antibodies with rheumatoid factor (RF) activity, which are essential for the development of circulating, cryoprecipitable immune complexes. We found Hypergammaglobulinemia is sustained by a peripheral expansion of IgMk+restriction indicating that a limited number of antigens drives their proliferation through BCR interaction. We shown that IgM RF and their counterparts on the surface of bone marrow-resident monoclonal B cells react against a Fc-epitope of IgG and the HCV-NS3 protein. Based on the above findings, we propose a model whereby BCR, by binding the Fc of IgM/IgG/HCVNS3 immune complexes deprives FcgIIR of its natural ligand. This takes the brake off RF+CD27+ B cell proliferation and promotes their selective accumulation which is otherwise prevented by increased apoptosis susceptibility in persistent HCV infection without MC. By confocal microscopy analysis we found that both Fc and NS3 peptides are able to clusterize BCR. Cytofluorimetric analysis found activation of both SYK/ERK phosphorilation pathways. Both these observations are in agreement with the hypothesis of BCR activation in these samples. Data regarding FcR are in course.

Human IgG anti-F(ab′)2 antibodies possess rheumatoid factor activity

Individual preparations of affinity purified anti-F(ab')2 antibodies and anti-Fc antibodies isolated from the sera of patients with rheumatoid arthritis (RA), were examined for reactivity with the Fab and Fc fragments of human IgG. Western blot assays demonstrated specific interaction of affinity-purified anti-Fab antibodies with both Fab and Fc molecules. Approximately one-half of the anti-Fab antibody preparations studied contained IgG antibodies reactive with Fab and Fc fragments in ELISA, suggesting the existence of naturally occurring epibody-like autoantibodies in these patients. Thirteen of 14 affinity-purified anti-Fc antibody preparations contained IgG cross-reactive with Fab molecules in ELISA. Double-adsorption assays on affinity columns demonstrated that a minimum of 14%, and possibly as much as 50%, of the IgG anti-Fab antibodies reacted with the Fc of IgG. Conversely, a minimum of 12%, and possibly as much as 70%, of the IgG anti-Fc antibodies reacted with IgG Fab molecules. Anti-Fab antibodies isolated from non-RA individuals also exhibited anti-Fc reactivity in ELISA, demonstrating the presence of these dual-reactive antibodies in other autoimmune and normal individuals. These studies establish the presence of naturally occurring IgG autoantibodies reactive with both the Fab and Fc fragments of human IgG. Their existence emphasizes the potential of anti-immunoglobulin antibodies to recognize a multiplicity of antigens, possibly including other members of the immunoglobulin supergene family.

Quantitative measurement of cytomegalovirus-specific IgG and IgM antibodies in relation to cytomegalovirus antigenaemia and disease activity in kidney recipients with an active cytomegalovirus infection

In a longitudinal investigation 103 kidney recipients were studied with respect to the development of cytomegalovirus (CMV) specific antibodies of the IgG and IgM class, in relation to the detection of CMV antigenaemia (immediate early antigen, IEA), in weekly obtained blood samples during the first 3 months after transplantation. In 15 out of 49 (31%) seronegative patients a primary infection occurred, which was characterized by a quick rise in IgM antibody followed by a slower production of IgG antibody, high maximum numbers of IEA+ cells, and a CMV syndrome in 11 patients. In 35 out of 54 (65%) seropositive patients a secondary infection occurred. After a post-operative fall in the IgG antibody, which was also found in patients without an active infection and which was accompanied by a similar drop in serum albumin and IgG, a second dip in IgG antibody was found 6 days before the first IEA+ leucocyte appeared in the blood. This was followed by a significant increase, indicative of an active immune response in consequence of the infection, 18 days later. In 31 of these 35 patients an IgM response was found. This could be ascribed to the presence of rheumatoid factor activity in 20 of them. Eight patients who showed a transient rise in IgG antibody between the two dips could be distinguished from the remaining ones by a lower maximum number of IEA+ cells and less severe disease symptoms. The described results suggest that (i) an adequate humoral immune system may prevent symptomatic CMV disease in secondary infections; and (ii) CMV-specific antibodies may be removed from the circulation by antigens present in infected tissues before CMV antigenaemia becomes detectable.

Rheumatoid factors and glomerulonephritis

It is presently unknown whether rheumatoid factors have a pathogenic role in the development of various types of glomerulonephritis with immune deposits. Three isotypes of rheumatoid factors (RFs), which are autoantibodies to IgG, were measured using the solid-phase fluorescence immunoassay in sera from patients with diffuse proliferative lupus nephritis (DPLN), membranous lupus nephritis (MLN), IgA nephropathy (IgAN) and idiopathic membranous nephropathy (MN). RF activity of immunoglobulins deposited in the glomeruli from these patients was also studied by examining the binding of the FITC-conjugated human IgG and Fc portion of IgG to the glomeruli of renal biopsy specimens. IgG, IgA and IgM RFs were significantly increased in sera from patients with DPLN, and the increase was significantly lower in patients with MLN, IgAN and MN. Human IgG bound to immunoglobulin on the glomeruli only in DPLN, but not in MLN, IgAN or MN. The Fc portion of IgG was demonstrated to be involved in this reaction. It was suggested that RFs and IgG may play a major role in immune deposits on the glomeruli in DPLN and may be involved in the development of DPLN; however, this is not likely in MLN, IgAN or MN.

Prevalence of anti-Fab antibodies in patients with autoimmune and infectious diseases.

Sensitive ELISA were devised to examine the specificity of circulating IgM and IgA autoantibodies for whole human IgG, Fc and Fab fragments of human IgG. Sera from patients with autoimmune and infectious conditions such as rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), tuberculosis (TB), infectious mononucleosis (IM) and cystic fibrosis (CF) were studied. Results of the ELISA assays using whole human IgG as antigen revealed that a proportion of patients in each of the groups studied had circulating IgM and IgA rheumatoid factors (RF). Fifteen normal individuals studied were negative. In the latex positive RA group, IgM RF and IgA RF had primarily anti-Fc reactivity (100% and 93% respectively), although 3/15 patients also showed IgM anti-Fab reactivity and one patient had high IgA anti-Fab activity. Patients with SLE and TB who had detectable RF levels also revealed predominantly anti-Fc specificity. In contrast, examination of 25 patients with IM showed positivity for IgM RF activity in 8% of patients using whole IgG as antigen, 24% positivity using purified Fc fragments as antigen and 45% positivity when plates were coated with Fab fragments. Similarly, a large number of CF patients (54%) also showed predominantly IgM anti-Fab activity. Of interest, 69% of the CF patients who were all studied at the time of bacterial infection had detectable IgA RF levels, with 46% of these patients showing both IgA anti-Fc and anti-Fab activity. These findings suggest that autoantibody specificities in autoimmune and infectious diseases are different.

A novel immunoglobulin-immunoglobulin interaction in autoimmunity.

Well over six decades since its first description, the Rheumatoid Factor (RF)—autoantibodies recognizing Fc (constant) portion of IgG through their own Fab (antigen binding variable segments)—is believed to have come of age. Autoimmune pancreatitis is a unique form of pancreatitis, biologically characterized by an elevated serum IgG4 concentration. Given the fact that IgG4 myeloma proteins can act as RF, we initially hypothesized that IgG4 in autoimmune pancreatitis might do likewise, hence potentially contributing to disease pathogenesis. Indeed Western blotting clearly showed that IgG4 binds to IgG1 κ, IgG2 κ, IgG3 κ myeloma proteins, as well as to IgG Fc, in line with a typical RF activity. Further experiments however unraveled the unexpected fact that unlike hitherto known RF, IgG4 does not engage IgG Fc through its Fab, but its very own Fc. These data therefore collectively describe a Novel RF (NRF) in autoimmune pancreatitis. In the future, the relevance of NRF, beyond autoimmune pancreatitis, in both diagnosis/prognosis as well as pathophysiology of autoimmune and other systemic diseases where IgG4's role seems paramount, needs to be systematically assessed.

Cryoglobulinemic glomerulonephritis: an extrahepatic manifestation of hepatitis C virus (HCV) infection

A 66-year-old woman was admitted to our Department for evaluation of a nephrotic syndrome. Physical examination revealed ankle edema, palpable purpura of the legs and hypertension. There was no hepatosplenomegaly. The main laboratory findings were haemoglobin 11.4 g/dl, serum creatinine 1.4 mg/dl, proteinuria 3.5 g/day with reduced serum albumin (3.1 g/dl), rheumatoid factor (RF) activity 125 IU/ml, and serum C4 levels 2.3 mg/dl. Cryocrit was 24%, with type II (IgG-IgM-κ) cryoglobulins. The patient was positive for HCV antibodies and serum HCV RNA; the genotype was 1b. A percutaneous renal biopsy showed a cryoglobulinemic membranoproliferative glomerulonephritis with moderate histologic severity. The primary goal in patients with mild-to-moderate disease is viral clearance, so combination therapy with interferon-α (3 MU thrice weekly) and ribavirin (800 mg/day) was started. Twelve weeks later, serum HCV RNA had disappeared, a result that was confirmed at the end of antiviral therapy in week 48, and during the post-treatment follow-up. Proteinuria returned to the normal range, cryoglobulins decreased to undetectable levels and serum C4 levels normalized. RF activity decreased, but remained above normal. The message provided by this illustrative case is that antiviral therapy represents the first-line treatment for HCV-related cryoglobulinemic patients with mild-to-moderate kidney involvement, because it provides the best chance of viral clearance and subsequent disease improvement.

Anti‐chromatin antibodies drive in vivo antigen‐specific activation and somatic hypermutation of rheumatoid factor B cells at extrafollicular sites

A dominant type of spontaneous autoreactive B cell activation in murine lupus is the extrafollicular generation of plasmablasts. The factors governing such activation have been difficult to identify due to the stochastic onset and chronic nature of the response. Thus, the ability to induce a similar autoreactive B cell response with a known autoantigen in vivo would be a powerful tool in deciphering how autoimmune responses are initiated. We report here the establishment and characterization of a system to initiate autoreactive extrafollicular B cell responses, using IgG anti-chromatin antibodies, that closely mirrors the spontaneous response. We demonstrate that exogenously administered anti-chromatin antibody, presumably by forming immune complexes with released nuclear material, drives activation of rheumatoid factor B cells in AM14 Tg mice. Anti-chromatin elicits autoreactive B cell activation and development into antibody-forming cells at the T zone/red pulp border. Plasmablast generation occurs equally in BALB/c, MRL/+ and MRL/lpr mice, indicating that an autoimmune-prone genetic background is not required for the induced response. Importantly, infused IgG anti-chromatin induces somatic hypermutation in the absence of a GC response, thus proving the extrafollicular somatic hypermutation pathway. This system provides a window on the initiation of an autoantibody response and reveals authentic initiators of it.

Cover Picture: Autoreactive B cells get activated in extrafollicular sites – Eur. J. Immunol. 12/2007

AbstractThe cover image schematically depicts the mechanisms proposed by Winkler and colleagues (pp. 3330–3333) as underlying the extrafollicular activation of rheumatoid factor B cells by chromatin–immune complexes. The follicular region is shown in orange, the marginal sinus in green, the marginal zone in turquoise, and the red pulp in red. The scheme is based on the data obtained by Shlomchik and colleagues (pp. 3339–3351) in their new mouse model of extrafollicular somatic hypermutation, a characteristic of murine lupus. The model importantly uses IgG anti‐chromatin antibodies rather than conventional immune complexes.

In this issue

In this issue

B-cell depletion in the treatment of mixed cryoglobulinemia

A controlled study has been carried out to assess the efficacy of rituximab (RTX), a chimeric antibody that binds to the B-cell surface antigen CD20, in twenty patients with mixed cryoglobulinemia (MC) and HCV-positive chronic active liver disease, resistant to interferon-α(IFN-α) therapy. They received an intravenous infusion of 375 mg/m 2 RTX once a week for 4 consecutive weeks. Infusion of RTX had a good safety profile, and no severe side-effects were reported. Sixteen patients (80%) had a complete response (CR), characterized by rapid improvement of clinical signs (disappearance of purpura, weakness, arthralgias and improvement of peripheral neuropathy), and decreased cryocrit. CR was associated with a significant reduction in rheumatoid factor (RF) activity and anti-HCV antibody titers. Decline of IgG anti-HCV titers in the cryoprecipitates was usually associated with a favorable response (r 0.81; p <0.005). No differences in the dynamics of B-cell depletion and recovery were found between responders and non-responders. Molecular monitoring of the B-cell response revealed disappearance/deletion of peripheral clones in the responders and great stability in the non-responders. RTX had a deep impact on hepatitis C viremia: HCV RNA increased to approximately twice the baseline level in the responders, whereas it remained much the same in the non-responders. Twelve out of 16 responders (75%) remained in remission throughout the follow-up. The results indicate that RTX has clinical and biological activity in HCV-positive MC patients. However, in view of the increased viremia in the responders, additional modes of application and combination of RTX with other agents need to be investigated.

Mixed cryoglobulinemia: a model of virus-related disease in internal medicine

Like other hepatotropic viruses, hepatitis C virus (HCV) exhibits the property of inducing hepatocellular damage, possibly through induction of immune mechanisms that lead to hepatocellular necrosis. The early activated mechanisms include production of non-specific and specific antibodies, which represent the first line of defence against invading foreign pathogens. As a consequence, circulating immune complexes are promptly formed and antigen uptake and processing by specialized cells are enhanced. A major fraction of circulating immunoglobulins (Igs) are part of the spectrum of so-called "natural" antibodies, which include anti-idiotypic antibodies and molecules with rheumatoid factor (RF) activity. They mainly belong to the IgM class, are polyclonal and have no intrinsic pathogenetic potential. In 20-30% of HCV-infected patients, RFs share characteristics of high affinity molecules, are monoclonal in nature, and result in the production of cold-precipitating immune complexes and mixed cryoglobulinemia (MC). The persistent production of monoclonal RF molecules implies the existence of a further mechanism capable of restricting the reactivity and reflects a distinct selection of a cell population that can be maintained throughout life because it is continuously exposed to antigen pressure. Either polyclonal or monoclonal profiles of B-cell expansion are demonstrable in the liver of the majority of HCV-infected patients. The frequent detection of oligoclonal B cell expansion may, indeed, represent a key pathobiologic feature which sustains non-malignant B-cell lymphoproliferation. The preferential expansion of one clone would in turn lead to a monoclonal pattern, which could favor stochastic oncogenic events. Thus, it can be postulated that HCV is the stimulus not only for the apparent benign lymphoproliferative process underlying a wide spectrum of clinical features, but also for the progression to frank lymphoid malignancy in a subgroup of patients.

Natural History and Clinical Impact of Cryoglobulins in Chronic Hepatitis C: 10-Year Prospective Study of 343 Patients

Serum cryoglobulins (CGs) are present in patients with chronic hepatitis C virus (HCV) infection, but their long-term clinical importance has not been established. We assessed the development rates, morbidity, and influence on the evolutionary course of hepatitis C of CG. A cohort of 343 HCV-RNA seropositive outpatients (173 men; age, 58 y; 82 with cirrhosis; 61 treated with interferon) with persistently increased aminotransferase levels and histologically defined liver disease was investigated. Patients initially were investigated for the presence, amount, and type of CG and prospectively followed up with clinical and laboratory examinations every 6 months. At enrollment, CGs were found in 163 (47%) patients at a mean level of 173 +/- 142 mg/L; 80% were type III, and associated to female sex (61% vs 40%, P = .0002) and cirrhosis (29% vs 19%, P = .04). Over the course of 17-130 months (median, 116 mo), de novo CG developed in 25 patients (2.3% per year), including 5 with cryoglobulinemic syndrome (.3% per year). The 10-year rates of progression to cirrhosis and of liver and extrahepatic complications were similar in CG (+) and CG (-) patients (32% vs 34%; 23% vs 16%; 5% vs 3%). The 10-year survival rates were lower for cirrhotic than for noncirrhotic patients (57% vs 91%, P < .00001), independently of CGs. CGs are common in patients with chronic HCV infection, mainly are type III, and do not influence the clinical course of hepatitis C during the first decades, except for the few rare cases of cryoglobulinemic syndrome.

56-Year-Old Man With Rash, Abdominal Pain, and Arthralgias

56-Year-Old Man With Rash, Abdominal Pain, and Arthralgias

Hepatitis C-associated mixed cryoglobulinaemia: a crossroad between autoimmunity and lymphoproliferation

Hepatitis C virus (HCV) infection is the second most cocmmon chronic viral infection in the world with a global prevalence of about 2%. Chronic HCV infection is commonly associated with a number of extrahepatic complications. Circulating mixed cryoglobulins (MCs) are detected in 40-60% of HCV-infected patients whereas overt cryoglobulinaemia vasculitis develops in only 5-10% of the cases. MC reflects the expansion of B cells producing a pathogenic IgM with rheumatoid factor (RF) activity. Because cryoglobulin-producing B cells in HCV are mostly monoclonal, HCV-associated MC can be viewed as a benign B cell lymphoproliferative condition. The disease expression of MC vasculitis is variable, ranging from mild clinical symptoms (purpura, arthralgia) to fulminant life-threatening complications (glomerulonephritis, widespread vasculitis). The overall risk of non-Hodgkin's lymphoma in patients with HCV-MC is estimated to be 35 times higher than that in the general population. This review will focus on recent advances in our understanding of the clinical course, complications, pathophysiology and treatment of those immune-mediated disorders.

Iron Ions and Haeme Modulate the Binding Properties of Complement Subcomponent C1q and of Immunoglobulins

The complement system and circulating antibodies play a major role in the defence against infection. They act at the sites of inflammation, where the harsh microenvironment and the oxidative stress lead to the release of free iron ions and haeme. The aim of this study was to analyse the consequences of the exposure of C1q and immunoglobulins to iron ions or haeme. The changes in target recognition by C1q and in the rheumatoid factor activity of the immunoglobulins were investigated. The exposure of C1q to ferrous ions increased its binding to IgG and to IgM. In contrast, haeme inhibited C1q binding to all studied targets, especially to IgG1 and C-reactive protein. Thus, the haeme released as a result of tissue damage and oxidative stress may act as a negative feedback regulator of an inappropriate complement triggering as seen in ischaemia-reperfusion tissue injury. The results also show that iron ions and haeme were able to reveal rheumatoid factor activity of IgG. The modulation of the C1q-target binding as well as the revealing of rheumatoid factor activity of IgG by exposure to redox-active agents released at the sites of inflammation may have important consequences for the understanding of the immunopathological mechanisms of inflammatory and autoimmune diseases.