Monoreactive and polyreactive rheumatoid factors produced by in vitro Epstein-Barr virus-transformed peripheral blood and synovial B lymphocytes from rheumatoid arthritis patients

Human IgM monoclonal antibodies block HIV-transmission to immune cells in cervico-vaginal tissues and across polarized epithelial cells in vitro

The importance of natural IgM antibodies in protection against infections is still emerging and these antibodies have a potential role in the maintenance of homeostasis through clearance of apoptotic bodies, complement-dependent mechanisms, inflammation and exclusion of misfolded proteins. Natural IgM act as a first line of defence against unknown hazardous factors and are present in most vertebrates. We investigated the functional capacity of anti-HIV-1 IgM monoclonal antibodies, from a combinatorial Fab library derived from healthy individuals, and evaluated their protective role in inhibiting HIV-1 in vitro when passing across the human mucosal epithelial barrier. Primary HIV-1 isolates were efficiently transmitted over the tight polarized epithelial cells when added to their apical surface. Efficient inhibition of HIV-1 transmission was achieved when anti-HIV-1 IgM monoclonal antibodies were added to the basolateral side of the cells. Two of these human IgM MoAbs had the ability to neutralize HIV and reduced infection of dendritic cells in primary cervico-vaginal tissue biopsies in vitro. This indicates a potential role of natural IgM antibodies in the reduction of HIV-1 transmission in mucosal tissues and improve our understanding of how natural IgM antibodies against a neutralizing epitope could interfere with viral transmission.

Increased rheumatoid factor interference observed during immunogenicity assessment of an Fc-engineered therapeutic antibody

Protein therapeutics may elicit an anti-therapeutic antibody (ATA) response in patients. This response depends on a number of factors including patient population, disease state, route of delivery or characteristics specific to the product. Therapeutics for immunological indications often target relatively young and healthy patients with hyperactive immune systems who have periodic flares and remissions. The hyperactive immune system of these patients can add several levels of bioanalytical complexity due to the presence of cross reactive molecules such as autoantibodies. In addition, the long-term chronic dosing regimen often necessary in this patient population can increase their risks of immunogenicity against the therapeutic and lead to safety concerns. Therefore, development of a sensitive and drug-tolerant ATA method is important. Bridging ATA assays are usually very sensitive and drug-tolerant methods for immunogenicity assessment; however these methods are particularly vulnerable to any factor that is able to bridge the conjugated therapeutics used as reagents and can generate false positive signal. Although there are many potential interfering factors in serum, rheumatoid factors (RFs), autoantibodies associated with rheumatoid arthritis (RA), are of particular concern in this type of assay. MTRX1011A is a non-depleting anti-CD4 monoclonal antibody therapeutic that was clinically tested in RA patients. This paper will discuss the bioanalytical challenges encountered during development of a clinical ATA assay for MTRX1011A. These challenges highlight interference due to patient disease state, in this case presence of RF in RA patients, as well as specific molecule-related interference caused by an engineered mutation in the Fc region of MTRX1011A designed to enhance its binding to the neonatal Fc receptor (FcRn). We will discuss the characterization work used to identify the cross-reactive epitope and our strategy to overcome this interference during development of an effective ATA assay to support clinical evaluation of MTRX1011A.

Reduced Fas ligand-expressing splenic CD5+ B lymphocytes in severe collagen-induced arthritis

Introduction

The objective was to study immune regulation in a mouse model of rheumatoid arthritis that exhibits considerable heterogeneity of disease activity.

Methods

T-cell receptor transgenic mice, in which nearly all CD4⁺ T cells recognize a single peptide of type II collagen, were immunized with collagen and observed for development of arthritis for 4 weeks. At 28 days post-immunization, splenocytes were analyzed by flow cytometry and in vitro assays for markers of immune activation and regulation.

Results

Disease severities ranging from 0 to 12 (on a 12-point scale) were observed. Among splenic lymphocyte populations, only the CD5⁺ B-cell subset displayed a decrease in relative numbers as arthritis severity increased. Splenic CD5⁺ B cells expressed higher levels of Fas ligand (FasL) than did CD4⁺ T cells or CD5^- B cells in all mice, and antigen-dependent T-cell death correlated with higher levels of CD5⁺ B cells in cocultures. Ratios of interleukin (IL)-17 to interferon-gamma production were higher in antigen-driven cultures of splenocytes from severely arthritic mice compared to mildly or nonarthritic mice. A correlation was established between the reduced production of IL-17 in antigen-driven T-cell/B-cell cocultures and FasL, but not IL-10. Confirmation of the direct killing effect of B cells on T cells was demonstrated using an antigen-specific T hybridoma cell line.

Conclusions

Reduced numbers of splenic FasL⁺ CD5⁺ B cells correlated with increasing arthritis severity and decreased T-cell death in a T-cell receptor transgenic mouse model of collagen-induced arthritis. These 'killer' B cells may provide a novel mechanism for inducing T-cell death as a treatment for arthritis.

Platinum Group Elements Enhance the Allergic Immune Response by Acting on Dendritic Cells

BACKGROUND

Atmospheric pollution may play a role in the immune response to allergens either directly or by entering the food chain. While particulate platinum group elements (PLGE) emitted by catalytic converters can be considered biologically inert, approximately 10% of these species accumulate in the environment as bioavailable soluble forms.

METHODS

We challenged in vitro human immature and mature monocyte-derived dendritic cells with subtoxic concentrations of soluble species of PLGE. Dendritic cells were studied both at baseline and following treatment with Na(2)PtCl(6), Na(2)PdCl(6) or Na(3)RhCl(6). (NH(4))(6)Mo(7)O(24) was included as control. The following end-points were considered: expression of differentiation markers, effectiveness of allergen presentation and Th2 cytokine production by cocultured T lymphocytes, expression of IgE-type I receptor and efficiency of IgE-dependent endocytosis.

RESULTS

We found that treatment with PLGE (but not with the control metal) increased costimulatory molecule expression and antigen presentation, amplified IL-5 production by cocultured T lymphocytes, upregulated IgE-type I receptor membrane expression, and augmented IgE-type I receptor-mediated endocytosis.

CONCLUSIONS

We conclude that PLGE have an adjuvant-like effect on dendritic cells that can favor and amplify the immune response to allergens.

Viral replication-independent blockade of dendritic cell maturation and interleukin-12 production by human herpesvirus 6

Human herpesvirus 6 (HHV-6) is a potentially immunosuppressive CD4(+)-T-lymphotropic betaherpesvirus that causes severe human thymocyte depletion in heterochimeric SCID-hu thy/liv mice and has been implicated as a potential cofactor in the progression of AIDS. However, the mechanisms of HHV-6-mediated immunosuppression have not yet been fully elucidated. We investigated the phenotypic and functional alterations induced by HHV-6 on peripheral blood-derived human dendritic cells (DC). The infection of DC with HHV-6 A or B was nonproductive, as revealed by calibrated real-time PCR measuring the accumulation of viral genome equivalents over time. Nevertheless, preexposure to HHV-6 markedly impaired the maturation of DC driven by gamma interferon and lipopolysaccharide, as shown by the reduced surface expression of major histocompatibility complex class I molecules, HLA-DR, CD40, and CD80. Moreover, HHV-6, but not the closely related betaherpesvirus HHV-7, dramatically suppressed the secretion of interleukin-12 (IL-12) p70 by DC, while the production of other cytokines that influence DC maturation, i.e., IL-10 and tumor necrosis factor alpha, was not significantly modified. Likewise, the secretion of the CC chemokines macrophage inflammatory protein 1beta and RANTES was unaltered. Functionally, a pretreatment with HHV-6 impaired the ability of DC to stimulate allogeneic T-cell proliferation. Altogether, these data identify interference with the functional maturation of DC as a potential mechanism of HHV-6-mediated immunosuppression.

Rheumatoid factors induce signaling from B cells, leading to Epstein-Barr virus and B-cell activation

B-cell antigen receptor signaling is initiated upon binding of the antigen to membrane-bound immunoblobulin (Ig), and the anti-Ig antibody (Ab) mimics this signaling. In B cells latently infected with Epstein-Barr virus (EBV), the same signals induce virus activation. We examine here whether rheumatoid factors (RFs), autoantibodies directed against the Fc portion of IgG, induce EBV and B-cell activation. As a source of RFs, RF-producing lymphoblastoid cell line (LCL) clones were isolated from peripheral blood mononuclear cells (PBMC) and synovial cells from patients with rheumatoid arthritis (RA) by EBV transformation. Burkitt's lymphoma-derived Akata cells, which are highly responsive to EBV activation by anti-Ig Abs, were used for the assay of EBV activation. Akata cells expressed IgG3 as membrane-bound Ig. RFs from a synovium-derived LCL were directed to IgG3 and induced EBV activation in 16 to 18% of Akata cells, whereas RFs from another synovium-derived LCL were directed to IgG1 and did not induce EBV activation. Pretreatment of RFs with the purified Fc fragment of human IgG completely abolished EBV activation. Furthermore, B-cell activation was assessed by incorporation of [3H]thymidine. RFs from synovium-derived LCLs efficiently induced B-cell activation, and the addition of CD40 ligand had a synergistic effect. On the other hand, RFs from PBMC-derived LCLs were polyreactive, had a lower affinity to IgG, and did not induce EBV and B-cell activation. The present findings imply a possible role for RFs as EBV and B-cell activators.

Synergism of nitric oxide and maturation signals on human dendritic cells occurs through a cyclic GMP-dependent pathway

Nitric oxide (NO), generated by phagocytes at inflammation sites, contributes to regulate immune responses through autocrine and paracrine actions on bystander cells. Among the latter are dendritic cells (DCs). Little is known about regulation of DC function by NO, especially in the human system. We exposed human monocyte-derived DCs to the NO donor (z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl)amino] diazen-1-ium-1,2 diolate (DETA-NO) during their maturation process induced by treatment with tumor necrosis factor alpha or lipopolysaccharide or by CD40 activation. We report here that after exposure to DETA-NO, DCs exhibit a significantly increased ability to activate T lymphocytes stimulated by mycobacterial antigens, Staphylococcus aureus Cowen strain B, allo-antigens, or cross-linking of the CD3-T cell receptor complex. This effect persists after removal of DETA-NO, depends on the generation of cyclic guanosine 5'-monophosphate, and is a result of enhanced release by DCs of soluble factors, in particular interleukin (IL)-12. This modulation of DC function is a result of a synergism between NO and the various maturation stimuli, as neither enhanced T cell activation nor IL-12 release was observed after DC exposure to DETA-NO only. These results provide the first evidence that NO acts as a cosignaling molecule regulating human DC response to maturation stimuli.

Interference of rheumatoid factor activity by aspartame, a dipeptide methyl ester

Circulating autoimmune complexes of IgM rheumatoid factors (RF) bound to the Fc portions of normal, polyclonal IgG antibodies are frequently present in humans with rheumatoid arthritis (RA). The sweet tasting methyl ester of L-Asp-L-Phe (aspartame or APM) was found to relieve pain and improve joint mobility in subjects with osteo- and mixed osteo/rheumatoid arthritis [Edmundson, A. B. and Manion, C. V. (1998). Clin. Pharmac. Ther. 63, 580-593]. These clinical observations prompted the testing of the inhibition by APM of the binding interactions of human IgM RFs with IgG Fc regions. The propensity of APM to inhibit IgM RF binding was assessed by competitive enzyme immunoassays with solid-phase human IgG. Ten RA serum samples and three purified monoclonal cryoglobulins, all of which had RF activity, were tested in this system. We found that the presence of APM significantly reduced the binding of IgM RFs. The inhibitory propensity of APM with monoclonal RF cryoglobulins was increased by the addition of CaCl(2) to the binding buffer. Similar inhibition of the binding of RA derived RFs to IgG was observed for Asp-Phe and its amidated derivative, indicating that the methyl ester is not required for APM's interaction with IgM antibodies. A human (Mez) IgM known to bind octameric peptides derived from the Fc portion of a human IgG(1) antibody was tested for binding of dipeptides by the Pepscan method of combinatorial chemistry. The relative binding constants of Asp-Phe and Phe-Asp were ranked among the highest values for 400 possible combinations of the 20 most common amino acids. Possible blocking interactions of APM were explored by computer-assisted docking studies with the model of a complex of an RF Fab with the Fc of a human IgG(4) antibody. Modeling of ternary immune complexes revealed a few key residues, which could act as molecular recognition sites for APM. A structural hypothesis is presented to explain the observed interference with RF reactivity by APM. Extrapolations of the current results suggest that APM may inhibit the binding of IgG in a substantial proportion of IgM RFs. Interference of RF reactivity, especially in RA patients, may alleviate the pain and immobility resulting from chronic inflammation of the joints.

Molecular analysis of rheumatoid factor (RF)-negative B cell hybridomas from rheumatoid synovial tissue: evidence for an antigen-induced stimulation with selection of high mutated IgVH and low mutated IgVL/lambda genes

The mutational pattern of IgVH and IgVL genes from synovial tissue B cell hybridomas (n = 8) of patients (n = 4) with rheumatoid arthritis (RA) was analysed, which had been produced by the electrofusion technique without prior in vitro stimulation. The molecular data were correlated with immunohistopathological data and parameters of local disease activity. The IgVH genes of the B cell hybridomas belonged to the VH3 family (DP42; DP47, n = 2; DP53), the VH1 family (DP75), the VH4 family (DP71) and the VH5 family (DP73); 7/7 IgVH genes showed somatic mutations, the R/S ratio (CDR) was > 3 in 4/7 IgVH genes and the mean R/S ratio of all IgVH genes was 9.3 (CDR) and 1.0 (FR), suggesting an antigen-dependent selection. The IgVL/lambda genes belonged to the Vlambda1 family (DPL2, DPL5, DPL8nf), the Vlambda2 family (DPL11, n = 2) and to the Vlambda6 family (IGLV6S1); 6/6 IgVL genes showed somatic mutations, the R/S ratio (CDR) was > 3 in 3/6 IgVL genes and the mean R/S ratio of all IgVL was 3.0 (CDR) and 2.3 (FR), suggesting an antigen-dependent selection. The synovial tissue exhibited germinal centres in the follicles (3/4), with the unique distribution of Ki-M4+ follicular dendritic cells and Ki-67+ proliferating cells and a dominance of IgA+ plasma cells (3/3). All patients were positive for RF in serum and exhibited severe local symptoms (swelling 4/4; warmth 4/4; effusion 2/4), whereas the hybridomas were negative for RF. Since B cell hybridomas showed hypermutation and affinity selection for IgVH and IgVL/lambda genes and the patients exhibited severe local symptoms with germinal centres in synovial tissue, this study indicates that an antigen-driven process is behind the B cell expansion in the synovial tissue of clinically affected joints. These mutated B hybridomas were negative for RF, thus suggesting that antigens different from RF are also involved in the local B cell expansion and in the chronic synovitis of RA.

Quantitative analysis of peripheral allergen-specific B lymphocytes in asthma

We have recently shown that the number of peripheral allergen-specific T cells can, in part, predict, together with methacholine hyperresponsiveness, the bronchial response to inhaled allergen in asthmatic patients. This study was designed to explore the role of blood B cells committed to produce allergen-specific IgE in asthma. Twenty-three asthmatic patients sensitized to Dermatophagoides pteronyssinus and 11 control subjects were studied. Peripheral blood B cells, committed to produce allergen-specific IgE, were enumerated by limiting dilution microcultures of Epstein-Barr virus (EBV)-transformed B cells. An allergen inhalation challenge was performed in all asthmatic subjects. No difference was found in the frequency of B cells committed to produce allergen-specific IgE either between asthmatic patients and controls or between asthmatic patients with or without late-phase bronchial response to allergen. No correlation was found between the frequency of B cells committed to produce allergen-specific IgE and the bronchial response to the allergen inhalation challenge. We conclude that, in quantitative terms, peripheral allergen-specific B cells are not as relevant as T cells to the development of the asthmatic response in the model of provoked asthma.

Complement activating properties of monoreactive and polyreactive IgM rheumatoid factors

OBJECTIVES

To estimate the complement activating properties of monoclonal, monoreactive, and polyreactive IgM rheumatoid factors derived from Epstein-Barr virus transformed B cells isolated from peripheral blood and synovial tissue of patients with rheumatoid arthritis (RA).

METHODS

An enzyme linked immunosorbent assay (ELISA) was used to measure the activation of the classical pathway of complement by monoclonal IgM rheumatoid factor. Monoclonal IgM rheumatoid factor was bound to IgG Fc adsorbed onto microtitre plates and then reacted with diluted normal human serum as a source of complement. The activation and binding of C4 were measured with F(ab')2 antibody to human C4. The complement activating property of IgM rheumatoid factor bound to IgG Fc was tentatively expressed as the ratio of the amount of bound C4 to the amount of bound IgM rheumatoid factor.

RESULTS

The complement activating property of monoreactive IgM rheumatoid factor was shown to be about three times higher than that of polyreactive IgM rheumatoid factor.

CONCLUSIONS

Monoreactive IgM rheumatoid factor with the higher complement activating property would result in a greater degree of complement dependent inflammation and might have a more important pathogenic role in RA than polyreactive IgM rheumatoid factor.

The B cell repertoire of patients with rheumatoid arthritis. Frequencies and specificities of peripheral blood B cells reacting with human IgG, human collagens, a mycobacterial heat shock protein and other antigens

Using a potent in vitro limiting dilution culture system, we have activated human peripheral blood B cells to proliferate and to differentiate into antibody-secreting cells (ASC). Under these conditions 25-100% of B cells are clonally expanded and produce IgM, IgG or IgA. Culture supernatants were tested for antibodies binding to human IgG-Fc fragments (RF), the 65-kD heat shock protein of Mycobacterium bovis (hsp60), human collagens type I, II, IV, V, transferrin, lactoferrin, albumins, and gelatine. All blood samples contained precursors of ASC (p-ASC) able to produce IgM binding to these antigens in frequencies above 0.03% of B cells. Most interestingly, a significant difference exists between rheumatoid arthritis (RA) patients and controls, concerning the relative frequencies of p-ASC able to produce monospecific or multireactive RF. Whereas most p-ASC(RF) in RA patients are monospecific (mean ratio 3.7), most p-ASC(RF) in healthy control persons are cross-reactive with at least one of five other antigens tested (mean ratio 0.2). The data suggest a disease-specific expansion of p-ASC committed to the production of monospecific rheumatoid factors.

Rheumatoid factors

Rheumatoid factors (RFs) have been studied for over 50 years and are probably the most written about of any antibody. Nevertheless, the etiology of these RFs and the precise role they play in the pathogenesis of rheumatoid arthritis (RA) and juvenile rheumatoid arthritis (JRA) remain a major interest. When RFs participate in the generation of inflammation in RA and JRA, they probably do so by forming immune complexes (IC) or are themselves able to bring about the inflammatory response. Their presence has been associated with more severe disease, vasculitis, and systemic symptoms. The present review summarises the literature over the last few years on new and interesting findings on RF. This review covers an update on RF assays, RF cross-reactivity, specificity studies, immune complex formation, RF lymphocyte studies, and RF binding.

The B cell repertoire in patients with systemic autoimmune diseases: analysis of Epstein-Barr virus (EBV)-inducible circulating precursors that produce autoantibodies against nuclear ribonucleoprotein (nRNP)

Peripheral blood B cells from patients with systemic autoimmune disease and healthy volunteers were immortalized using EBV and the frequencies of B cell precursors that produced immunoglobulin class-specific antibodies against anti-nRNP, a specific marker for mixed connective tissue disease, were assessed using limiting dilution analysis. The frequencies of EBV-induced B cell precursors that produced IgG anti-nRNP were correlated closely with the serum titres of the corresponding autoantibodies, which indicates that B cell precursors that produced potentially pathogenic autoantibodies could be immortalized from the peripheral blood of the patients by EBV. In contrast, the frequency of EBV-induced B cell precursors that produced IgM anti-nRNP in patients with systemic autoimmune disease was comparable to that in healthy volunteers and greater than those that produced IgG and IgA anti-nRNP. Moreover, many of the clones that produced IgM antibodies against nRNP reacted with other autoantigens, such as double-stranded DNA, single-stranded DNA and rabbit IgG. These polyreactive IgM antibodies are believed to belong to the 'natural antibodies', to be coded by the germline immunoglobulin V genes, and to react with evolutionarily conserved structural cellular components, including nRNP. Our finding that nRNP is one of the target antigens for this polyreactive autoantibody may lead to the elucidation of the origin of the pathogenic IgG and IgA anti-nRNP antibodies found in sera from patients with systemic autoimmune diseases.

Immunophenotypic subclassification of chronic lymphocytic leukaemia (CLL)

To determine the significance of the immunophenotypic heterogeneity of B-cell chronic lymphocytic leukaemia (CLL), surface immunoglobulins (SIgs), mouse rosette assays (MR), and a panel of monoclonal antibodies for B cells, T cells and myeloid cells were performed on peripheral blood samples from 61 newly diagnosed cases. Four groups were observed: group I (SIg+, MR+, CD19/20+, CD5+, T antigen (Ag)-; 27 cases); group II (SIg+, MR+, CD19/20+, CD5+, T Ag+; 17 cases); group III (SIg+, MR+ CD19/20+, CD5-, T AG-; 12 cases); and group IV (SIg-, MR+, CD19/20+, Cd5+, T Ag-; 5 cases). Groups were compared according to French-American-British Cooperative Group subtypes, clinical and laboratory features, Rai staging, and survival. Typical CLL morphology (greater than 90% small lymphocytes) was present in 20/20 (100%) of group I cases and 23/27 (85%) group II, III and IV cases (P = 0.09). Expression of a myeloid antigen was seen in 5/27 group I cases (18%) and 1/16 group II cases (6%), but was not predictive of survival (P = 0.36). The CD5- group III had a lower haemoglobin level (P less than 0.0001), higher Rai stage (P less than 0.002), and poorer survival at 5 years (P less than 0.02) than the other groups. We conclude that at least four distinct immunophenotypic subgroups of B-cell CLL can be determined. Expression of myeloid or T-cell antigens does not appear to predict for patient survival; however, lack of CD5 antigen may be associated with more advanced stage of disease and poor patient survival.

Analysis of monoclonal rheumatoid factors obtained from the B-cell repertoire in rheumatoid arthritis

We have sought to determine whether rheumatoid factors (RF) produced in rheumatoid arthritis (RA) were different from physiological RF produced in normal, healthy adults. RF-secreting clones were established following Epstein-Barr virus (EBV) stimulation of peripheral blood lymphocytes. Ten RF-secreting clones were established from seven RA patients and 16 from six healthy controls. All monoclonal RF (MRF), except two in each group, were monoreactive and ten of these were shown to have low to medium affinity for IgG,Fc, irrespective of their origin. A majority (74%) of the MRF bound to protein A, indicating that genes of the VHIII family were preferentially used for synthesizing these autoantibodies. The expression of cross-reactive idiotypes (CRI) by the MRF did not allow distinction between those derived from RA patients and controls. The VHI-associated CRI G8 and VHIII-associated CRID12 were expressed at low frequency in both panels of RF. These CRI have been shown to be expressed at high frequency in RF paraproteins. However, the idRQ idiotype was expressed within both panels of RF. A possible distinction between polyreactive and monoreactive MRF appeared to be light chain usage since all (four) polyreactive RF used lambda chains while the normal kappa/lambda ratio was observed for monoreactive RF. The frequency of EBV-activated cells secreting IgM bearing CRI or secreting RF was determined and showed that CRI expression occurred with a higher frequency than did RF, suggesting a dissociation between CRI expression and RF activity.