Serum-serum interactions in autoimmune mice

Autoantibodies in rheumatoid arthritis and their clinical significance

Autoantibodies are proven useful diagnostic tools for a variety of rheumatic and non-rheumatic autoimmune disorders. However, a highly specific marker autoantibody for rheumatoid arthritis (RA) has not yet been determined. The presence of rheumatoid factors is currently used as a marker for RA. However, rheumatoid factors have modest specificity (~70%) for the disease. In recent years, several newly characterized autoantibodies have become promising candidates as diagnostic indicators for RA. Antikeratin, anticitrullinated peptides, anti-RA33, anti-Sa, and anti-p68 autoantibodies have been shown to have >90% specificity for RA. These autoantibodies are reviewed and the potential role of the autoantibodies in the pathogenesis of RA is briefly discussed.

Further characterization of the autoantibody response of Palmerston North mice

PN mice spontaneously develop, with age, a lupus-like disease. The present study further evaluated autoantibody production in female PN mice. As early as 1 month of age, all PN mice had detectable IgM antibodies to dsDNA and ssDNA and two-thirds produced IgM anticardiolipin antibodies. By 3 months of age, all PN mice exhibited evidence of isotype switch in their autoantibody response; 88-100% had serum IgG antibodies to ssDNA and dsDNA, respectively. By 6-12 months of age, essentially all female PN mice had IgG antibodies to ssDNA, dsDNA, cardiolipin and other phospholipids (PS, PC, PI, and PG), and IgG and 63% produced IgG anti-mouse erythrocyte antibodies. In addition, 50-100% produced IgA antibodies to dsDNA and ssDNA, and one-third produced IgA anti-IgG antibodies. Antibodies to U1RNP and Sm were present in 81% of 6- to 12-month-old PN mice and 39-94% had IgG or IgM antibodies to mouse thymocytes. Although all four IgG isotypes were represented in the anti-dsDNA response, IgG1 antibodies dominated the IgG anticardiolipin response. The presence of IgA autoantibodies and the predominance of IgG1 in the IgG anticardiolipin response suggest that IL-4 and either IL-5 and/or TGF-beta serve as B cell stimulatory cytokines for autoreactive B cells in PN mice.

Induction of "wire-loop" lesions by murine monoclonal IgG3 cryoglobulins

We have recently demonstrated that an IgG3 rheumatoid factor (RF) monoclonal antibody (mAb), clone 6-19, derived from unmanipulated autoimmune MRL/MpJ-lpr/lpr mice, is able to generate cryoglobulins via a non-immunological IgG3 Fc interaction, and to induce an acute glomerulonephritis associated with cryoglobulinemia. Using this experimental model, we have characterized the glomerular lesions induced by the 6-19 RF monoclonal cryoglobulin, in particular the ultrastructural localization of the cryoglobulin deposits. Although their initial localization was confined to the mesangium, the 6-19 cryoglobulins were progressively accumulated in the subendothelial spaces of glomerular capillary walls, leading to the formation of glomerular lesions resembling the "wire-loop" lesion characteristically described for lupus nephritis. In addition, we have found that identical glomerular "wire-loop" lesions were induced by the 6-19-J558 hybrid antibody, composed of the 6-19 gamma 3 heavy chain and J558 lambda 1 light chain, which loses the RF activity, but retains the cryoglobulin activity. These results strongly suggest that the direct deposition of IgG3 cryoglobulins by itself, without involvement of immune complex formation, results in the generation of the classical "wire-loop" lesion characteristic of lupus nephritis. In addition, we have found that similar "wire-loop" lesions were generated by one anti-DNA mAb derived from (NZB x NZW)F1 hybrid mice, and two of four IgG3 mAb of unknown specificities, derived from MRL/MpJ-lpr/lpr mice. The absence of significant glomerular lesions, in spite of large amounts of cryoglobulins, in mice receiving two IgG3 mAb suggests the importance of physicochemical property of cryoglobulins to provoke glomerular lesions.

The oral mucosa of the MRL/I mouse: a synoptic picture of systemic autoimmune disorders

The oral manifestations of systemic autoimmunity were investigated in a kinetic study of the MRL/1 mouse. Lesions in the epithelium, connective tissue and minor salivary glands were characterized in serial sections of the soft palate and the cheeks with respect to 1) the type of inflammatory cells present, 2) the presence and type of vasculitis, 3) the presence of necrosis, 4) the occurrence of deposits. By the age of 16 wk, 100% of our animals had developed mild to severe lesions in at least one compartment of the mucosa. Between 16 and 32 wk of age, pathologic manifestations affected the epithelial and subepithelial tissues, the striated muscle tissue, the vascular system and, much less frequently, the minor salivary gland network.

Local IgA and IgM rheumatoid factor production in autoimmune MRL/lpr mice

Spontaneous local immunoglobulin (IgA, IgG, IgM) as well as IgA and IgM rheumatoid factor (RF) production in salivary glands, lymph nodes, and spleen was analyzed at various ages in autoimmune MRL/Mp-lpr/lpr (MRL/lpr) mice by using an ELISPOT assay. The longitudinal design of the study permitted correlations with severity of disease in salivary glands (sialadenitis). Local production of immunoglobulins in salivary glands and lymph nodes occurred with a pattern of IgG much greater than IgM greater than IgA. This isotype pattern differed from that simultaneously observed in spleen where IgG did not predominate to the same extent. Moreover, the spleen was the major site of IgM production. Rheumatoid factors constituted a significant fraction of local IgA and IgM in involved salivary glands. The pattern of IgA RF isotype expression in salivary glands contrasted with that observed in spleen. While the number of IgA and IgG secreting cells increase at an early age, the peak of RF production in salivary glands occurs in older mice. Furthermore, the level of immunoglobulin secretion was positively correlated with disease severity in salivary glands. The results suggest that local RF production is a secondary event in salivary gland inflammation in MRL/1pr mice rather than an initiating factor in this process.

Cryoglobulinemia induced by a murine IgG3 rheumatoid factor: skin vasculitis and glomerulonephritis arise from distinct pathogenic mechanisms

MRL-lpr/lpr mice spontaneously develop a lupus-like syndrome characterized by immunopathological manifestations such as necrotizing vascular lesions of ear tips and severe glomerulonephritis. Similar skin vascular and glomerular lesions associated with cryoglobulinemia can be induced in normal mice by injection of a monoclonal antibody (mAb)--6-19 (gamma 3 heavy chain and kappa light chain), exhibiting both cryoglobulin and anti-IgG2a rheumatoid factor (RF) activities--derived from the MRL-lpr/lpr autoimmune mouse. To determine the role of RF and/or IgG3 Fc fragment-associated cryoglobulin activities in 6-19 mAb-induced tissue lesions, a 6-19-J558L hybrid mAb (gamma 3 heavy chain and lambda 1 light chain) was produced by fusion between the 6-19 hybridoma and the J558L myeloma. Here we report that the 6-19-J558L hybrid mAb, which loses the RF activity but retains the cryoglobulin activity, fails to induce skin vascular lesions. However, it is still able to provoke glomerular lesions identical to those caused by the 6-19 mAb. Further, we have observed that the depletion of the corresponding autoantigen, IgG2a, in mice by treatment with anti-IgM antisera from birth also prevents the development of skin but not glomerular lesions. Our results indicate that both RF and cryoglobulin activities of the 6-19 mAb are required for the development of skin vasculitis, but its cryoglobulin activity alone is sufficient to cause glomerular lesions. In addition, cDNA cloning and sequencing of the 6-19 mAb has revealed that the 6-19 kappa light chain variable region amino acid sequence is encoded in a germ-line configuration, suggesting that immunoglobulin variable region germ-line genes could contribute to the generation of pathogenic autoantibodies.

Polyarthritis in MRL-lpr/lpr mice: mouse type II collagen is antigenic but not arthritogenic

In addition to a lupus-like syndrome and massive T cell proliferation, MRL-lpr/lpr(MRL/l) mice develop an arthritic process very similar serologically and histologically to human rheumatoid arthritis (RA). Recently, we have developed in DBA/1 mice an experimental model of autoimmune arthritis (EAA) which shares clinical features with RA, by injecting homologous type II collagen (CII). In order to investigate the possible relationship between the spontaneous polyarthritis of MRL/l mice and collagen induced EAA, we immunized MRL/l mice with mouse (M) CII. Our findings revealed that the injection of 100 micrograms M-CII in young or old MRL/l mice did not modify the articular pathology which spontaneously develops in non-injected mice. Circulating autoantibodies to native M-CII were found in the sera of immunized young mice but were not detected in non injected or immunized old mice. Conversely, denatured alpha 1 (II) chains or CB peptides derived from M-CII were recognized by most of the MRL/l sera whether mice had been immunized or not. The incidence of positive sera as well as the intensity of the response evaluated by Western blot analysis increased with the age of the mice. Taken together, our data suggest that, even if the injection of homologous CII in MRL/l mice may accelerate the onset of joint pathology, the spontaneous disease arises independently of an autoimmune response against native CII.

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.

The MRL-lpr/lpr mouse. A model for the study of rheumatoid arthritis

Autoimmune MRL-lpr/lpr mice develop a spontaneous destructive arthropathy sharing some features with rheumatoid arthritis including synovial cell proliferation, pannus formation, rheumatoid nodule-like lesions and circulating rheumatoid factors. Rheumatoid factors elaborated by MRL-lpr/lpr mice exhibit binding characteristics similar to those found in the sera of patients with rheumatoid arthritis; however, these autoantibodies do not appear to be essential for the induction of arthritis in MRL-lpr/lpr mice. Molecular studies, indicating that VH genes from several VH families are capable of encoding these rheumatoid factors, argue against the existence of unique "autoantibody genes" in the germline of MRL-lpr/lpr mice. Although the mechanisms underlying cartilage injury in MRL-lpr/lpr mice have not been elucidated, available evidence suggests that invading synovial cells play an important role. Delineation of the cellular and molecular mechanisms responsible for articular destruction in MRL-lpr/lpr mice may provide important insights concerning the pathogenesis of rheumatoid arthritis.

Hormone control of autoantibodies to calf thymus nuclear extract (CTE) and DNA in MRL-lpr and MRL-+/+ mice

Because hormonal influences on autoimmune disease in MRL-lpr and MRL-+/+ mice have not been defined completely, we examined animals which had been castrated and implanted with the opposite sex hormone. Antibodies directed at non-DNA antigens in a calf thymus nuclear extract (designated CTE) and specific anti-DNA antibodies were increased in estrogen-treated males, testosterone-treated females, and sham-operated female controls compared to sham-operated males. Analysis by sucrose gradient ultracentrifugation revealed that gonadal hormones exerted marked differences in the distribution and nature of circulating IgM anti-CTE antibodies. Although 19 S IgM was the predominant form of anti-CTE antibodies in experimental groups showing elevated anti-CTE responses, estrogen-treated male MRL-lpr mice expressed a large additional population of anti-CTE IgM antibody released by acid dissociation of apparently cryptic complexes. An unexpected additional finding was the presence of cryptic anti-CTE IgG (7 S) in all groups of MRL-lpr and MRL-+/+ mice, revealed only in sucrose gradient analysis under acid conditions. It is suggested that sex-related factors may account, in part, for apparent differences in levels of circulating autoantibodies observed in MRL mice by influencing the degree to which autoantibody populations exist in circulating complexes.

Mycoplasma pulmonis arthritis in mice: microbiological and immunological features

Mycoplasma pulmonis m53 was inoculated intraarticularly in the bilateral hind footpads and bilateral knee joints of BALB/c mice. Mycoplasmas were recovered from the affected joints over 20 weeks accompanying acute or subacute inflammation. Intensive deposition of immunoglobulins, a complement (C3) and mycoplasma cell antigens occurred in synovial and adjacent connective tissues. The histopathologically intact kidneys, brain, and lungs showed deposition of IgG and the complement on the endothelial cells of blood vessels. An IgG-rheumatoid factor like substance (RFLS) was detected in the serum of the mice by an enzyme-linked immunoabsorbent assay. Persistence of mycoplasma cells and immune complexes in the articular tissues might cause the prolongation of inflammatory responses in murine mycoplasmal arthritis.

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.

Solid-phase enzyme-linked immunospot (ELISPOT) assay for enumeration of IgG rheumatoid factor-secreting cells

Although IgG rheumatoid factor may play an essential role in the pathogenesis of rheumatoid arthritis, there is no precise method for its specific detection at the cellular level. A modification of the recently developed enzyme-linked immunospot assay has been devised for enumeration of cells secreting IgG rheumatoid factor (IgG RF) and simultaneous quantitation of the IgG RF secreted. Specific, sensitive and simple, this new assay should provide a valuable tool for study of isotype-specific RF secretion by single cells.

IgG rheumatoid factors and cryoglobulins in mice bearing the mutant gene lpr (lymphoproliferation)

The autosomal recessive mutant gene, lpr (lymphoproliferation), produces a massive proliferation of T cells in autoimmune MRL mice. Since the MRL strain bearing the lpr mutation is the only strain that spontaneously develops high titers of rheumatoid factors (RF), we have investigated whether non-autoimmune mice (C57BL/6, C3H/HeJ and AKR) bearing the lpr gene could produce RF. Serum levels of RF activity were assessed by a new radioimmunoassay, in which serum samples pretreated with acetate buffer were incubated with 125I-mouse IgG and precipitated with 7% polyethylene glycol. The majority of serum from 4- to 6-month-old non-autoimmune strains of mice bearing the lpr gene exhibited significant RF activity, as did MRL-lpr/lpr mice. Sucrose density-gradient analysis has revealed that all the IgG RF activity was present in a form of immune complexes, sedimenting in the intermediate position (7-19S) and fully dissociable into 7S IgG under an acid condition. This indicates that the production of IgG RF does not require a particular background genome of the MRL strain. In addition, mice bearing the lpr mutation developed extremely large amounts of cryoglobulins, which paralleled the production of RF. Analysis of components of their cryoglobulins revealed a marked enrichment of IgG3 subclass as compared to other IgG subclasses and IgM. These results suggest that IgG3-containing immune complexes represent the major source of cryoglobulins occurring in mice bearing the lpr gene.

Monoclonal IgM rheumatoid factors derived from arthritic MRL/Mp-lpr/lpr mice

MRL/lpr/lpr (MRL/l) mice develop a lupus-like syndrome and a disease histologically and serologically similar to human rheumatoid arthritis. Their sera contain polyclonal IgM rheumatoid factors (RF) reactive with all murine IgG subclasses (frequently strongest with IgG2a) and several heterologous IgG. To examine the repertoire and epitopic specificities of these RF, we fused splenocytes from 3.5-mo-old seropositive MRL/l mice with appropriate myeloma partners and derived 1,723 hybridomas of which 23 secreted IgMRF. These monoclonal IgMRF bound to murine IgG only, not to other murine isotypes. Eight murine IgG subclass-specific clonotypes were identified. Most clones reacted with either multiple IgG subclasses or with IgG2a alone. A few clones reacted solely with IgG2b but none reacted exclusively with IgG1 or IgG3. Monoclonal IgMRF with exclusively anti-IgG2a activity exhibited allotypic specificity, reacting, with few exceptions, with a, c, and e, but not b, d, or j IgG2a allotypes. Four clonotypes could be distinguished by cross-reactivity with IgG from species other than mice. Monoclonals possessing activity against several murine subclasses cross-reacted extensively with heterologous IgG, including all human IgG subclasses without allotypic restrictions. Monoclonal IgMRF specific for murine IgG2a or 2b did not cross-react with heterologous IgG. Based on the absence of cross-reactions by IgG2a-specific monoclonal autoantibodies, certain peptides of the IgG CH2 and CH3 domains appear to generate the antigenic determinants of the anti-IgG2a RF in MRL/l mice. All of the monoclonal RF bound to Fc and, with one exception, not to Fab fragments of murine IgG. Binding of the monoclonal RF to substrate IgG was not inhibited by Clq, thus excluding the Clq-binding site at the CH2 domain as one of the responsible epitopes in the induction of MRL/l RF. mIgMRF could be categorized as strongly, weakly, or noninhibitable by protein A, which interacts with IgG molecules at or near the CH2-CH3 junction. Inhibition appears to be caused by conformational changes and/or steric shielding of certain IgG areas distant from this junction and not by identical binding sites between protein A and RF. Certain of the mIgMRF that were weakly or not at all inhibitable by protein A were found to cross-react equally well with human Fc (CH2-CH3 domains) and pFc' (CH3 domain) fragments, indicating that the binding site for these monoclonals is at the CH3 domain. Monoclonal RF were devoid of anti-double-strand DNA, anticollagen, or antipeptidoglycan pentapeptide cross-reactivity, but one of the monoclonals cross-reacted with histones, four with single-strand DNA, and one with both histones and single-strand DNA.

Genetic control of rheumatoid factor production in the mouse. Role of genes linked to the immunoglobulin heavy chain locus and to the major histocompatibility complex

The influence of Igh-1 and H-2 linked genes on the production of IgG2a-specific rheumatoid factors (RF) by 129/Sv mice was examined. Heterozygous animals carrying the 129 alleles, H-2b and Igh-1a, and either H-2k, H-2a, or Igh-1b (but not Igh-1d or Igh-1e) had considerably reduced RF levels. In contrast, Igh-1b linked genes failed to suppress RF production by MRL/MpJ-lpr mice. This lack of suppression was linked to the lymphoproliferation trait characteristic of these animals.

A spontaneous rheumatoid arthritis-like disease in MRL/l mice

MRL/l mice spontaneously develop an arthritis very similar in many respects to human rheumatoid arthritis. A detailed morphologic and serologic analysis of this disease revealed the following: (a) a 75% incidence of synovial and periarticular inflammation, very similar to human rheumatoid arthritis, in 5-6 mo-old females, (b) close associations between presence of joint inflammation and subsynovial and/or periarticular vasculitis, and (c) a close correlation between presence of circulating IgM rheumatoid factor (RF) and demonstrable synovial and/or joint pathology, i.e., 95% of mice with significant levels of IgMRF had synovitis and/or arthritis.

Studies of murine complement. Correlation of hypocomplementemia with other disease parameters in individual NZB/W mice and demonstration of anti-complementary material

We have utilized a new assay for murine complement components to explore the relationship of complement titers to other parameters of disease activity in individual NZB/W female mice. Titers had fallen significantly by 6 months of age, concomitantly with the appearance of antiDNA in serum and of C3 and immunoglobulin in renal glomeruli. The period of hypocomplementemia antedating proteinuria was extremely variable. Heat stable anti-complementary material was found in serum from older NZB/W mice.