I-E-linked control of spontaneous rheumatoid factor production in normal mice

Agonistic antibodies to Fas induce a breach in the endothelial lining of the liver and a breakdown in B cell tolerance

Liver disease can be associated with a breakdown in self-tolerance and the production of autoantibodies such as rheumatoid factors (RF), which bind to IgG. Here we investigated whether primary, non-infectious liver damage was sufficient to induce autoantibody production. We established a model of targeted liver damage induced by weekly sublethal injections of pro-apoptotic anti-Fas (CD95) antibodies. Liver damage, monitored by measurements of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels, was minimal 1 week after anti-Fas injection. However, the sublethal Fas stimulation was sufficient to trigger significant haemorrhage in the liver, as assessed by Evans Blue dye leakage into the organ 5 h after anti-Fas antibody injection. We observed an induction of RF in response to the weekly injections of sublethal anti-Fas antibodies but not of isotype control antibodies, indicating a breakdown of self-tolerance induced by Fas engagement. RF induction was unlikely to be due to direct activation of B cells, as splenocytes stimulated with anti-Fas antibodies in vitro did not produce RF. These studies show that sublethal damage to the liver by Fas engagement leads to liver haemorrhage and is sufficient to trigger the breakdown of self-tolerance.

Rheumatoid factor induction in murine models of liver injury

Alcoholic liver disease and hepatitis C are associated with the production of autoantibodies such as rheumatoid factors (RF), which bind to IgG and can aid in host defence, but are also associated with pathological conditions such as rheumatoid arthritis. Because little is known about the role of RF in liver disease, we characterized the RF production that either occurred spontaneously in response to alcohol consumption or was induced by injection of an Escherichia coli glycolipoprotein in C57Bl/6 mice. Whereas severe liver damage was induced by carbon tetrachloride (CCl(4)), minimal damage was caused by chronic alcohol consumption. Liver damage was monitored by measurements of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Circulating RF was induced in response to chronic alcohol consumption; the latter probably involved Toll-like receptor ligation. In contrast, CCl(4)-induced damage was not associated with RF induction. However, concurrent treatment with an E. coli glycolipoprotein macromolecule that induced RF, protected against CCL(4)-induced liver damage as measured by a highly significant decrease (P = 0.008) at 4 weeks in AST and ALT. RF induced by E. coli glycolipoprotein correlated with 'protection' from liver damage, indicating that the RF autoimmune response does not necessarily exacerbate liver disease.

Rheumatoid Factors: Good or Bad for You?

BACKGROUND

Rheumatoid factors (RFs) are autoantibodies associated with rheumatoid arthritis. They can be detected in normal individuals, although transiently. This dichotomy has led to questions about the origins and types of RFs. Recently it has been shown that B cells that produce RFs only do so when activated by two signals, one from engagement of the B-cell receptor and the other from recognition of a pathogen-associated molecular pattern through a Toll-like receptor (TLR). These autoantibodies thus link the innate and acquired immune responses.

OBJECTIVE

Through a review of the literature, an examination of the current knowledge of RF induction is presented. The focus is on a discussion of a beneficial or detrimental role for RFs in normal individuals and in those with chronic disease.

RESULTS

What makes RF 'good' in some cases and 'bad' in others may reflect the type of RF produced. Low-affinity polyreactive IgM RFs are probably beneficial as they aid in the clearance of immune complexes that are more efficiently cleared, and the RF B cell can act as an antigen-presenting cell and stimulate host defense. However, large amounts of high-affinity RFs found in patients with chronic disease may be harmful by participation in a vicious cycle of autoantibody production by stimulation of self lymphocytes, and/or deposition in blood vessels thus causing vasculitis.

CONCLUSIONS

Whether RFs are beneficial or detrimental depends on the context in which they are expressed, the type and amount of RF produced, whether the response is perpetuated by TLR ligation and whether other cells are stimulated either directly or indirectly by RF-positive B cells.

Rheumatoid factors: host resistance or autoimmunity?

Rheumatoid factors (RFs), autoantibodies that bind to the Fc portion of IgG, are important in the immune response. RF-committed B-cells exist in the circulating lymphocyte pool in a high frequency (approximately 1-2 %) in normal individuals and in patients with pathological conditions associated with the sustained levels of circulating RF, such as rheumatoid arthritis (RA), Sjogren's syndrome (SS), and mixed cryoglobulinemia, associated with hepatitis C virus infection. RFs are induced by many infectious entities (viruses, bacteria, parasites) as a consequence of a secondary immune response to the pathogen, but usually the response is transient. It is likely that RFs play an important role in the host's defense against infection, both at the cellular level, where the RF B-cell can be an antigen presenting cell which can promote the antipathogen response, and at the humoral level, where RFs can contribute to the mopping up of the IgG antipathogen antibodies by contributing to immune complex formation and clearance. There has been much research on RFs in chronic pathological conditions, and the literature pertaining to their origin, structure, binding specificities, and possible roles in disease are discussed. The importance of the host defense, sometimes at the expense of an autoimmune response, is a balance that needs to be considered in light of a possible outcome of health or disease.

Immunosusceptibility genes in rheumatoid arthritis

The polygenic predisposition to RA is conferred particularly by disease susceptibility sequences in the HVR3 of HLA DRB1 present in those subtypes of DR4 and DR1 that are associated with RA. The aim of this study was to examine predisposing interactions between genes encoding HLA and immunoglobulin molecules. Accordingly, we compared the genetic background of 114 Australian patients with RA with that of Australian controls of similar ethnic background. We identified HLA-A, B, and DR phenotypes serologically, HLA-DR, DQ alleles, and subtypes of DR4 by DNA typing, and Gm allogenotypes and immunoglobulin switch region polymorphisms by RFLP. For the subjects with RA, we confirmed previously reported observations that included an excess of females, 71%, a high frequency of HLA types DR4 or DR1 of 77% versus controls 47%, and a high frequency of the HVR3 susceptibility sequences of 76%, with 24% homozygous, and 52% heterozygous for the sequences. We observed other genetic correlations in RA that included increases in frequencies of DR4 in males, DR1 in females, the class I specificity HLA-B27 overall but more particularly in females, 24% in females, versus 5% of controls, HLA-DQB1*0302 (DQ8) in DR4*0401-positive patients, and the Gm allogenotype 1,2,3;23 +/- ; 5,10, 15% of patients versus 4% of controls. Examination of switch region genes gave no evidence of differences in the polymorphisms distributions. Thus, the major genetic risks for RA that are conferred by female gender and the HVR3 of HLA DRB1 are modulated by interactions between gender and HLA class I and class II alleles, and the Gm allogenotype.

Activation of effector functions by immune complexes of mouse IgG2a with isotype-specific autoantibodies

Analysis of five monoclonal autoantibodies, rheumatoid factors produced by hybridomas generated from spleen cells of BALB/c mice repeatedly infected with A/PR/8/34 human influenza A virus, revealed that they recognized distinct but spatially related epitopes. The differing isoallotypic specificity of the IgM and IgA monoclonal antibodies correlated with the presence of Ile258 and Ala305, respectively. Although these data suggest that the epitopes recognized are within the CH2 domain, all antibodies failed to inhibit IgG antigen reactivity with Staphylococcus aureus protein A (SpA), C1q, mouse C3, human Fc gamma RI or mouse Fc gamma RII, activities known to be predominantly determined by CH2 domain structures. Reactivity of the IgA antibody, Z34, with IgG2b allowed further specificity studies using a panel of 26 mutant IgG2b proteins, each having single amino acid replacements over the surface of the CH2 domain. The only substitution that affected Z34 reactivity was Asn/Ala297, which destroyed the glycosylation sequon, resulting in secretion of an aglycosylated IgG molecule. The epitope recognized by Z34 therefore seems to be located outside of the Fc gamma R and C1q binding sites, but to be dependent on the presence of carbohydrate for expression. In contrast to the binding studies, complement activation by aggregated IgG2a, through classical or alternative pathways, was inhibited by the presence of autoantibodies. The functional significance of isotype-specific autoantibody in immune regulation is discussed.

Selective induction of rheumatoid factors by superantigens and human helper T cells

Production of autoantibodies specific for the Fc region of autologous IgG, called rheumatoid factors (RF), is a characteristic finding in patients with rheumatoid arthritis (RA). To study the requirements regulating the synthesis of these autoantibodies, we have cloned human helper T cells and co-cultured them with purified B cells. To mimic cognate T-B cell interaction, we have used bacterial superantigens that function by cross-linking HLA molecules on the B cell with selected T cell receptor (TCR) molecules expressing a particular polymorphism of the V beta gene segment. Data presented here demonstrate that the staphylococcal enterotoxin D (SE D), but not other bacterial superantigens, exhibits an ability to induce IgM, IgG, and especially RF production, in B cells from RA patients and normal individuals. Comparison with the polyclonal antibody production in B cell cultures driven by anti-CD3-stimulated T cell clones confirmed that SE D shifted the repertoire of secreted antibodies toward immunoglobulins with Fc binding specificity, suggesting that SE D preferentially stimulates RF+ B lymphocytes. B cells with the potential to secrete RF were highly frequent in RA patients, requiring as few as 150 peripheral B cells/culture to detect RF in the culture supernatants. SE D-induced RF synthesis was strictly dependent on the presence of selected CD4+T helper cells and required a direct membrane contact between B cells and T helper cells. Here, we propose a model that SE D selectively induces RF production depending on the availability of SE D responsive T cells in the TCR repertoire of the responder.

Regulation of antibody production mediated by Fc gamma receptors, IgG binding factors, and IgG Fc-binding autoantibodies

Fc receptors (FcRs) are immunoglobulin-binding structures that enable antibodies to perform a variety of functions by forming connections between specific recognition and effector cells. Besides eliciting cytotoxicity, inducing secretion of mediators and endocytosis of opsonized particles, FcRs are involved in the regulation of antibody production, both as integral membrane proteins and as soluble molecules released from the cell surface. Most FcRs belong to the same family of proteins as their ligands (immunoglobulin superfamily). This review contains recent data obtained by use of monoclonal antibodies and cloning studies on FcRs and FcR-like molecules. The importance of fine specificity of receptor binding site(s)--that of the conformation of FcRs and their ligands in triggering signaling mechanisms--is analyzed. The regulatory function of membrane-bound and -released FcRs; the correlation between cell cycle, FcR expression, and release; as well as the possible mechanisms of these phenomena are discussed.

The contribution of non-MHC genes to susceptibility to autoimmune diseases

Genetic studies of experimental models of autoimmune diseases, including systemic lupus-like syndromes and organ-specific autoimmunity, provide major information on genetic control of autoimmune diseases. In addition to genes known to be linked to the major histocompatibility complex (MHC), these studies point to multiple genes located outside the MHC that influence the onset and the progression of autoimmune diseases. Identification of these genes and of their interrelationships is now a major task that will be facilitated by recent progress in molecular biology and gene mapping. Among candidate genes, antigen-receptor genes (i.e., immunoglobulin- and T-cell receptor genes) most likely contribute an important part of the autoimmune susceptibility in several of these animal models. Available linkage data suggest a similar involvement of these antigen-receptor genes in several human autoimmune diseases. In addition to a better understanding of pathogenic mechanisms associated with autoimmunity, the knowledge of these disease-predisposing genes is expected to permit a better classification of often complex syndromes as well as the design of new treatments.

Stimulation of B and T cells by in vivo high dose immunoglobulin administration in normal mice

Adult BALB/c mice were injected intravenously with a preparation of pooled normal murine IgG (400 mg/kg/day, on five consecutive days) and studied 8, 15, and 60 days later. High dose IgG administration increased the total numbers of splenic activated B and CD4+ (but not CD8+) T cells, as well as the numbers of splenic Ig-secreting cells, particularly in the IgG isotypes. Reactivities to some autoantigens, but not to bacterial or other heteroantigens, were selectively amplified amongst IgM-secreting cells. IgG administration did not alter the specific primary immune response to heterologous erythrocytes or bacterial dextran. No cellular alterations were detected in the lymph nodes or peritoneal cavity of treated animals. Most of these effects subsided with time, but some autoantibody reactivities remained elevated 60 days later. The present results suggest that the therapeutic effects of high dose IgG administration which have been reported in human diseases might be associated with the immunostimulatory activities of such treatment.

Treatment with IL2/vaccinia recombinant virus leads to serologic, histologic and phenotypic normalization of autoimmune MRL/lpr-lpr mice

We have analyzed the effect of IL2 administered in vivo on both the lymphoproliferation and autoimmune disease progression of MRL/lpr mice. Human IL2 was delivered by infecting MRL/lpr mice with vaccinia virus recombinants at different stages of lpr disease. The results reported here showed that treatment of lpr mice with IL2 mediated: (1) restored normal thymic differentiation illustrated by an expansion of the double positive population accompanied by increased numbers of mature thymocytes; (2) depletion of the peripheral CD3+ CD4- CD8- (DN) T-cell population; (3) normalization in the pattern of TcRV beta gene expression displayed by mature T cells; (4) decreased urine-protein levels and immune complex deposition in the kidney, with a resultant absence of glomerulonephritis; and (5) an increased longevity (from 195 to more than 400 days). We speculate that the dramatic reduction in the abnormally expanded CD3+ DN T-cell population following IL2 therapy might be directly related to the amelioration and/or prevention of autoimmune disease in these mice. Collectively, these results suggest that diseases showing a selective expansion of DN cells should be envisaged as possible targets for the treatment described here.

Isolation and characterization of IgG2a-reactive autoantibodies from influenza virus-infected BALB/c mice

Repeated influenza virus infection induces the production of dominantly IgG2a-type virus-specific antibodies as well as the appearance of IgG2a-reactive autoantibodies in BALB/c mice characterized by low spontaneous rheumatoid factor-type autoantibody production. IgG2a-reactive autoantibody-producing hybridomas could be isolated from the spleen of influenza virus-infected BALB/c mice. The mAb produced by these clones represent not only IgM but also IgG and IgA isotypes and show strong isotype or isoallotype specificity. The common functional property of these autoantibodies is their preferential- and high-affinity binding to complexed, solid-phase-bound or heat-aggregated IgG2a when compared to native soluble or cell-bound IgG2a. The mechanism of induction and the possible biological function of these autoantibodies are discussed in the light of their fine specificity and functional properties.