Isotypic and allotypic specificity of mouse rheumatoid factors

Protective and pathogenic roles for B cells during systemic autoimmunity in NZB/W F1 mice

Delineating the relative contributions of B lymphocytes during the course of autoimmune disease has been difficult. Therefore, the effects of depleting all mature B cells using a potent CD20 mAb, or of depleting circulating and marginal zone B cells using a ligand-blocking CD22 mAb, were compared in NZB/W F(1) mice, a model for human systemic lupus erythematosus. Single low-dose mAb treatments depleted B cells efficiently in both NZB/W F(1) and C57BL/6 mice. Prophylactic B cell depletion by repeated CD20 mAb treatments prolonged survival during pristane-accelerated lupus in NZB/W F(1) mice, whereas CD22 mAb had little effect. Despite effective B cell depletion, neither mAb treatment prevented autoantibody generation. In addition, CD20, CD22, and control mAb-treated NZB/W F(1) mice developed anti-mouse IgG autoantibodies in contrast to parental NZB and NZW strains, which may have reduced the effectiveness of B cell depletion. Despite this, low-dose CD20 mAb treatment initiated in 12-28-wk-old mice, and administered every 4 wk thereafter, significantly delayed spontaneous disease in NZB/W F(1) mice. By contrast, B cell depletion initiated in 4-wk-old mice hastened disease onset, which paralleled depletion of the IL-10-producing regulatory B cell subset called B10 cells. B10 cells were phenotypically similar in NZB/W F(1) and C57BL/6 mice, but were expanded significantly in young NZB/W F(1) mice. Thus, B cell depletion had significant effects on NZB/W F(1) mouse survival that were dependent on the timing of treatment initiation. Therefore, distinct B cell populations can have opposing protective and pathogenic roles during lupus progression.

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.

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.

Immunogenetic markers as probes for polymorphism, gene regulation and gene transfer in man--the Gm system in perspective

The genetic markers of immunoglobulins (Ig) demonstrable by immunological methods have shown their usefulness as genetic probes. The study of these allotypes originally proved that Ig production is under conventional genetic control and also established that allelic exclusion is valid for the key molecules of the immune response. The codons responsible for the G1m(a) marker and their position in the human genome are precisely known. This knowledge implies that Gm typing may be used as a convenient and reliable means of following the fate of IgG constant gene segments. Anti-Gm's are common in rheumatoid arthritis. They appear early in the disease and may persist throughout life. The stimulus for their appearance has not yet been established. The anti-Gm's in the allegedly autoimmune disease rheumatoid arthritis are commonly and apparently paradoxically specific for Gm gene products of other persons. Another apparent paradox brought to light by Ig allotype research is the occasional appearance of non-nominal allotypes in contradiction to Mendelian laws. It is proposed that a plausible explanation for these two paradoxes is Ig gene transfer between individuals with viral vectors. Reasons for this proposal and some possible consequences of gene transfer in a polymorphic species are delineated. Immunogenetics and DNA technology in combination provide powerful tools to elucidate the fate of genes. A method allowing the assignment of G1m(a+) and G1m(a-) at the gene level by polymerase chain reaction analysis has recently been established and is briefly described.

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.

Monoclonal IgM rheumatoid factor-like anti-globulins enhance the inhibitory effects of Plasmodium falciparum-specific monoclonal antibodies in vitro

Monoclonal IgM rheumatoid factor-like anti-globulins were produced by in vitro stimulation of naive BALB/c spleen cells with lipopolysaccharide, and by hyperimmunization of mice with merozoites of Plasmodium falciparum, followed by fusion of the spleen cells to mouse myelomas. In vitro, these anti-globulins augmented the inhibitory effects of P. falciparum-specific polyclonal mouse sera and monoclonal IgG1 and IgG2b antibodies by binding to Fc fragments of IgG molecules attached to blood-stage parasites. In some instances, the presence of anti-globulins correlated with an increase in the number of schizonts which failed to disperse merozoites. In other cases, parasitaemia remained low in the absence of the schizont inhibition phenomenon, suggesting that anti-globulins contribute to host cell protection not only by agglutinating merozoites, but also by increasing the density of the antibody coat surrounding the parasites, thus interfering with parasite receptor-erythrocyte ligand interactions. The anti-globulins were not inhibitory when added to parasite cultures containing IgG not specific for P. falciparum. These results may help explain the function of IgM anti-globulins found at elevated serum levels in some patients with malaria or other chronic infectious diseases.

An indirect asymmetrical sandwich ELISA using anti-allotype antibodies for the specific and quantitative measurement of mouse IgG2a of Igh-1b allotype

We recently described an indirect double sandwich ELISA (Klein-Schneegans et al., J. Immunol. Methods (1989) 119, 117) which permits the specific and quantitative measurement of mouse IgM, IgA and IgG subclasses with one major exception: IgG2a of the b allotype (Igh-1b in mouse strains such as C57BL/6) could not be reliably quantitated even by a very specific and sensitive asymmetrical sandwich ELISA (using two different anti-IgG2a isotype antibodies for capture and for detection). We now describe a similar method based on the use of two different anti-IgG2a allotype antibodies for the capture and detection of IgG2a in the serum of Igh-1b mouse strains.

Genetic control of inflammatory arthritis in congenic lpr mice

To determine the genetic requirements for the development of inflammatory arthritis in MRL-lpr/lpr mice, clinical, serologic, and pathologic features of lpr/lpr and +/+ mice of MRL, B6, C3H, and AKR strains were studied. Arthritis was evaluated by histopathologic examination of the knee joint, while sera were tested for the presence of rheumatoid factor (RF) and anti-DNA activity by ELISA. Of the strains tested to age 7 months, only the MRL-lpr/lpr mice developed histologic evidence of arthritis. All lpr mice, however, produced both IgM RF and IgG RF, although amounts varied among strains. These results indicate that the lpr gene as well as another gene(s) in the MRL background are necessary for the development of inflammatory arthritis and that this lesion may be independent of RF production.

Isolation of self-recognizing IgG2a monoclonal rheumatoid factors

Hybridoma cell lines were produced by fusing spleen cells from 11 mice that expressed the lpr mutation to nonsecreting SP2/0 myeloma cells. Five to 20% of the hybridoma cell lines so derived were found to secrete antibodies that recognized autologous IgG2a. Out of 168 anti-IgG2a clones tested, 4 clones produced anti-IgG2a rheumatoid factor (RF) that was itself IgG2a. Two clones recognized self IgG2a while the other two clones each recognized a nonself IgG2a allotypic determinant. These findings indicate that self-recognizing antibodies are a component, albeit a minor one, of the RF repertoire of lpr/lpr mice.

Heterogeneity in rheumatoid factor isotypes and specificities in MRL mice

MRL/lpr mice spontaneously develop an arthritis which, in several respects, is similar to human rheumatoid arthritis, including joint inflammation and circulating rheumatoid factors. In human disease, circulating IgM rheumatoid factor (RF) predominates but, surprisingly, in these mice we have detected much more IgA rheumatoid factor. This IgA rheumatoid factor has a major specificity for IgG2a, but heterogeneity in binding specificity was seen between different mice. IgG rheumatoid factors were determined in a heterologous mouse IgG assay, in which each subclass of rheumatoid factor was tested for its ability to bind to the remaining IgG subclasses. Rheumatoid factor activity was detected in all the IgG subclasses, but particularly elevated levels were seen in IgG3 and IgG1. Both the levels and specificities of IgG rheumatoid factors were markedly different between each mouse.

A new assay uses monoclonal anti-Rh(D) antibodies to determine rheumatoid factor specificity: reactivity to a monoclonal antibody of the Gm allotype G3m(21) is more frequent in rheumatoid patients negative for G3m(21)

A new method has been developed to determine the specificities of polyclonal rheumatoid factors (naturally occurring antibodies which react with human Fc gamma) (RF) found in sera from patients with rheumatoid arthritis. In this method, monoclonal anti-Rh(D) antibodies of known IgG isotype and allotype are bound to erythrocytes and then act as the target IgG antigen for RF in a direct haemagglutination test. Using two monoclonal anti-D antibodies of the IgG3 isotype and G3m(21) allotype, which were cloned from different donors, we found that a large number of rheumatoid sera reacted with both these G3m(21) proteins. In contrast reactivity of rheumatoid sera with polyclonal anti-D of the G3m(21) allotype in the direct haemagglutination test was rare. A strong correlation was found between reactivities to both G3m(21) monoclonal anti-D antibodies but not with a monoclonal anti-D antibody carrying the alternative allele, namely G3m(5). Haemagglutination inhibition experiments using human paraproteins of known IgG isotype and allotype provided some additional evidence that this method can detect RF with specificity for the G3m(21) allotypic determinant or a related allotypic determinant in polyclonal rheumatoid sera. When each patient's autoantibody response was related to their Gm phenotype, we found that the frequency of reactivity for G3m(21) monoclonal anti-D antibodies was significantly greater in patients negative for G3m(21) than in patients positive for the G3m(21) allotype. IgM preparations from patients' sera were dissociated at acid pH but no 'hidden' antibodies were found. We suggest trans-placental sensitization as one of several possible interpretations of this finding.

Oligoclonality of rheumatoid factors arising spontaneously in lpr/lpr mice

Rheumatoid factors (RF) from individual mice of the MRL/lpr and C3H/lpr strains were examined with regard to target specificity and heavy chain class expression. It was found that MRL/lpr-derived RF preferentially recognize IgG2a target antibodies while C3H/lpr-derived RF exhibit a broader range of cross-reactivity. IgM RF represent only a minor proportion of the RF response in both strains. The IgG2a-specific RF produced by the lpr strains were found to consist of relatively equal proportions of IgG1, IgG2b, IgG3, and IgA antibodies. However, most of the RF produced by a single individual expressed the same heavy chain class and antigen-binding specificity. These results indicate that within an individual lpr mouse, circulating RF are derived from extensive expansion of a limited number of antigen-activated precursors.

Rheumatoid factors in natural retrovirus infections of the cat and cattle

The occurrence of IgM-rheumatoid factors (RFs) was investigated in natural retrovirus infection of cats with feline leukaemia virus and of cattle with bovine leukaemia virus. IgM-RFs of polyclonal character were detected. No significant differences were observed between the amounts of IgM-RFs in the retrovirus-infected animals and their respective controls.

Autoantibodies to anti-DNA with anti-allotypic and anti-idiotypic specificities in (NZB X NZW)F1 mice

The monoclonal A52 (IgG2b, kappa) anti-DNA autoantibody represents a major cross-reactive idiotype in the murine and human autoimmune response to DNA. Examination of sera and purified IgG derived from (NZB X NZW)F1 mice showed that these mice develop an age-dependent binding reactivity with the pure anti-DNA IgG. Three monoclonal antibodies possessing this reactivity were prepared from unprimed female (NZB X NZW)F1 mice. One of these monoclonal antibodies appeared to be directed against allotypic determinants present in the NZB IgG2b; the other two antibodies exhibited a marked preference for idiotypic determinants of the A52 IgG. The IgG anti-allotype and anti-idiotype activities in (NZB X NZW)F1 mice may, therefore, represent the products of a deregulated immune system and/or constitute the normal elements of a functional immune regulation system.

Isotypically restricted activation of B lymphocytes by lactic dehydrogenase virus

Lactic dehydrogenase elevating virus (LDV) was found to selectively stimulate IgG2a synthesis in infected mice. Within one week after infection, the production of IgG2a increased nearly 50-fold whereas that of IgM, IgA, IgG1 and IgG3 remained virtually unchanged. IgG2b synthesis was also enhanced but to a lesser extent. Several observations suggested that this stimulation of IgG2 production resulted from a polyclonal B cell activation: (a) the isoelectric focusing patterns of IgG2a before and after LDV infection were exactly the same, (b) the frequency of clones with anti-LDV activity in hybridoma collections derived from infected mice was extremely low (less than 4/1000) and (c) the proliferative response elicited by LDV in unsensitized animals was comparable with that induced by lipopolysaccharide. The effect of LDV on immunoglobulin synthesis was drastically reduced in nude mice but was not affected by the X-linked B lymphocyte defect of animals carrying the xid mutation.

Binding of in vivo formed immune complexes by monoclonal mouse rheumatoid factors

Mouse rheumatoid factors (RF) have previously been shown to bind immune complexes formed in vitro with greater affinity than monomeric IgG. The present report extends this observation and shows that this property of mouse RF is retained with immune complexes formed in vivo. This observation strengthens the idea that the interaction of RF with immune complexes could play a physiological role.

Self-associating IgG rheumatoid factors in MRL/l autoimmune mice

Previous work has shown that the intermediate complexes isolated from the plasma of patients with rheumatoid arthritis are composed of self-associating IgG rheumatoid factors. Mice of the MRL/l strain develop spontaneous autoimmune disease with arthritis that is pathologically similar to human rheumatoid arthritis. Also, the sera of MRL/l mice contain autoantibodies to nuclear antigens as well as IgM and IgG rheumatoid factors. The present studies were done to determine if the IgG rheumatoid factors isolated from these mice undergo self-association. MRL/l mouse sera were categorized into groups A and B based on serum-serum precipitin interactions. Thirteen of 13 MRL/l mice sera examined contained intermediate complexes sedimenting between the 6.6S and 19S components of normal serum by sedimentation velocity ultracentrifugation. There were no differences in the level of intermediate complexes between groups A and B. IgG rheumatoid factors were isolated from the sera of 9 other mice. Upon sedimentation equilibrium ultracentrifugation, these rheumatoid factors underwent concentration-dependent self-association similar to that described for human self-associating IgG rheumatoid factors, although the precise stoichiometry of self-association could not be determined. The IgG rheumatoid factors from group B had higher energies of self-interaction than those from group A. These studies provide additional evidence that MRL/l mice may be the best available animal model for the study of human rheumatoid arthritis.

Rheumatoid factors and secondary immune responses in the mouse. I. Frequent occurrence of hybridomas secreting IgM anti-IgG1 autoantibodies after immunization with protein antigens

The involvement of rheumatoid factor (RF)-secreting cells in normal immune responses was examined by screening hybridomas derived from 129/Sv mice during primary and secondary immune responses against foreign proteins. No RF-secreting cells were detected during primary responses, but up to 10% of the total number of clones obtained during secondary responses produced IgM with anti-IgG activity. Like typical mouse RF, these anti-IgG autoantibodies had a strict isotypic specificity, mostly for IgG1, and a much stronger avidity for immune complexes than for native IgG. The selective activation of IgG1-specific RF during these secondary immune reactions was not due to fortuitous antigenic similarities between mouse IgG1 and the antigens used for immunization, nor did it result from the use of adjuvants for priming, or from contamination of antigen preparations with lipopolysaccharide. It is therefore concluded that, in the 129/Sv mouse, RF production during secondary immune responses is a physiological phenomenon.

Determinants recognized by murine rheumatoid factors: molecular localization using a panel of mouse myeloma variant immunoglobulins

The structures recognized by monoclonal anti-IgG1 rheumatoid factors (RF) were localized by testing their reactivity with mutant immunoglobulins carrying gamma 1 chains that lacked either the CH1 or the CH3 domains. While optimal binding was observed in the absence of CH1, deletion of CH3 completely abolished the reactivity of all but one of the 71 monoclonal RF tested. Similar experiments were carried out with IgG2a- and IgG2b-specific RF by using variant immunoglobulins carrying various hybrid gamma 2a-gamma 2b heavy chains. It was found that both the polyclonal RF produced by autoimmune strains, MRL/MpJ-lpr and NZB/BinJ, and most of the monoclonal RF derived from normal strains, BALB/c, C57Bl/6, and 129/Sv, were directed against determinants located in a segment spanning the C-terminal 8 residues of the CH2 domain and the complete CH3 domain.

Rheumatoid factors and secondary immune responses in the mouse. II. Incidence, kinetics and induction mechanisms

Production of IgM rheumatoid factor (RF) during secondary immune responses was studied in normal mouse strains by measuring RF synthesis in spleen cell cultures. A considerable, although transient, RF response was observed in BALB/c and C57BL/6 mice immunized and i.v. boosted with various protein antigens and with sheep erythrocytes. With most antigens, RF production equalled or exceeded that of antigen-specific IgM, but it peaked and subsided earlier. No RF production was detected when either priming or boosting was omitted. The isotypic specificity of RF depended upon the antigens used for immunization: all proteins tested stimulated the synthesis of RF specific for IgG1, whereas sheep erythrocytes induced both IgG1- and IgG2a-specific RF. Reconstitution experiments of irradiated naïve C57BL/6 mice with various combinations of syngeneic antibody against human transferrin and primed or unprimed spleen cells indicated that important RF responses could be induced only when antigen was injected into mice that had received both antibody and immune spleen cells.