Quantitation and IgG subclass distribution of antichromatin autoantibodies in SLE mice

Antinucleosome Antibodies in Patients with Juvenile Systemic Lupus Erythematosus

Our objective was to evaluate the frequency of antinucleosome antibodies (anti-Ncs) in juvenile systemic lupus erythematosus (JSLE) comparing it to that observed for anti-DNA and to correlate the presence of these antibodies with clinical manifestations and disease activity. Anti-Ncs and anti-DNA were detected by ELISA in 74 patients with JSLE and 64 normal controls. Clinical records were reviewed. Disease activity was assessed by SLEDAI score. Anti-Ncs and anti-DNA showed sensitivity of 52.7% and 54% and specificity of 98.4% and 95.3%, respectively. Disagreement between the two assays was found in 25.7% of the cases: isolated positive Anti-Ncs in nine cases (12.2%) and isolated positive anti-DNA in 10 cases (13.5%). Agreement was found in 74.3%: both positive antibodies in 30 cases and both negative in 25. The presence of anti-Ncs was significantly associated with malar erythema, hemolytic anemia, anti-DNA and low complement levels, but not with renal manifestations. The presence of anti-Ncs was associated with a higher SLEDAI median ( P < 0.001) and its titers correlated with the SLEDAI score ( r = 0.504; P < 0.001). The frequency, sensitivity and specificity values were similar between anti-Ncs and anti-DNA antibodies in patients with JSLE. Nevertheless, the discordance of 25.7% between the two assays suggests that both antibodies may have a complementary diagnostic role. The association and correlation between anti-Ncs and several disease activity parameters demonstrated its usufulness in the follow-up of these patients.

Dual-reactive B cells are autoreactive and highly enriched in the plasmablast and memory B cell subsets of autoimmune mice

Dual–light chain–expressing B cells in autoimmune prone mice increase with age, contribute to the memory and plasma cell compartments, and are autoreactive.

Rare dual-reactive B cells expressing two types of Ig light or heavy chains have been shown to participate in immune responses and differentiate into IgG⁺ cells in healthy mice. These cells are generated more often in autoreactive mice, leading us to hypothesize they might be relevant in autoimmunity. Using mice bearing Igk allotypic markers and a wild-type Ig repertoire, we demonstrate that the generation of dual-κ B cells increases with age and disease progression in autoimmune-prone MRL and MRL/lpr mice. These dual-reactive cells express markers of activation and are more frequently autoreactive than single-reactive B cells. Moreover, dual-κ B cells represent up to half of plasmablasts and memory B cells in autoimmune mice, whereas they remain infrequent in healthy mice. Differentiation of dual-κ B cells into plasmablasts is driven by MRL genes, whereas the maintenance of IgG⁺ cells is partly dependent on Fas inactivation. Furthermore, dual-κ B cells that differentiate into plasmablasts retain the capacity to secrete autoantibodies. Overall, our study indicates that dual-reactive B cells significantly contribute to the plasmablast and memory B cell populations of autoimmune-prone mice suggesting a role in autoimmunity.

The MHC haplotype H2b converts two pure nonlupus mouse strains to producers of antinuclear antibodies

Studies of mouse lupus models have linked the MHC H2(b) haplotype with the earlier appearance of antinuclear autoantibodies and the worsening of nephritis. However, it is unknown whether H2(b) by itself, in the context of pure nonlupus strains, is "silent" or sufficient with regard to loss of tolerance to chromatin (nucleosomes). In this study we show that, beginning approximately 6-9 mo of age, H2(b)-congenic BALB/c (denoted BALB.B) mice, unlike BALB/c (H2(d)) and H2(k)-congenic BALB/c (denoted BALB.K) mice, develop strikingly increased serum levels of anti-chromatin Ab dominated by the IgG2a subclass, along with minor increase of Abs to DNA and moderately increased total serum IgG2a. The BALB.B mice did not have glomerulonephritis or an increased mortality rate. H2(b)-congenic C3H/He mice (designated C3.SW mice), unlike C3H/He (H2(k)) mice, showed low but measurable serum levels of chromatin-reactive IgG2a Abs and minor but significant hypergammaglobulinemia. By immunofluorescence, IgG2a of sera from both H2(b)-congenic strains stained HEp-2 cell nuclei, confirming the presence of antinuclear autoantibodies. Thus, in the context of two pure nonlupus genomes, the MHC H2(b) haplotype in homozygous form is sufficient to induce loss of tolerance to chromatin.

Binding of circulating SLE autoantibodies to oxygen free radical damaged chromatin

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disease characterized by various immunologic disorders, including production of autoantibodies, formation of immune complexes, decreased serum complement levels, and lymphocytopenia. One of the hallmarks of this disease is the loss of tolerance to nuclear antigens. The dominant presence of antibodies against the exposed conformational epitopes on chromatin strongly suggests that the pathogenic immune response in lupus is driven by chromatin. In the present study, the binding of SLE autoantibodies with native chromatin and oxygen free radical damaged chromatin was studied. As assessed by direct binding and inhibition ELISA, circulating SLE autoantibodies exhibited a high degree of specificity towards the reactive oxygen species (ROS)-modified chromatin in comparison to native chromatin and this binding specificity was reiterated visually by gel retardation assay. The data suggested possible role of modified chromatin in the induction of SLE autoantibodies and higher recognition of oxidatively damaged chromatin by antibodies in sera of SLE patients. It is indicated that free radical modified chromatin or nucleosomes might be the antigen for the production of circulating autoantibodies in SLE.

Generation of monoclonal antibodies against highly conserved antigens

Background

Therapeutic antibody development is one of the fastest growing areas of the pharmaceutical industry. Generating high-quality monoclonal antibodies against a given therapeutic target is very crucial for the success of the drug development. However, due to immune tolerance, some proteins that are highly conserved between mice and humans are not very immunogenic in mice, making it difficult to generate antibodies using a conventional approach.

Methodology/Principal Findings

In this report, the impaired immune tolerance of NZB/W mice was exploited to generate monoclonal antibodies against highly conserved or self-antigens. Using two highly conserved human antigens (MIF and HMGB1) and one mouse self-antigen (TNF-alpha) as examples, we demonstrate here that multiple clones of high affinity, highly specific antibodies with desired biological activities can be generated, using the NZB/W mouse as the immunization host and a T cell-specific tag fused to a recombinant antigen to stimulate the immune system.

Conclusions/Significance

We developed an efficient and universal method for generating surrogate or therapeutic antibodies against “difficult antigens” to facilitate the development of therapeutic antibodies.

Spontaneous autoimmunity in mice that carry an IghV partial transgene: a required arginine in VHCDR3

We describe a unique spontaneous mouse model of autoimmunity, which occurs on a non-autoimmune-prone SWR genetic background. In this model, SWR mice carry an IghV partial transgene (pTg) encoding only the heavy chain variable domain of an antibody directed against chromatin. Autoimmune disease in pTg mice was manifested by some of the features of systemic lupus erythematosus (SLE), including the presence of serum anti-nuclear antibodies, splenomegaly, skin lesions and a moderate degree of kidney pathology, in various combinations among individuals. Autoimmunity was observed in three independent transgenic lines, but not in three control lines carrying a nearly identical pTg, in which a VHCDR3 codon for Arg was replaced by one for Ser to ablate chromatin reactivity. Various features of disease were often but not always accompanied by anti-chromatin antibodies. Unexpectedly, the anti-chromatin antibodies detected in seropositive animals were not encoded by the pTg. These observations strongly implicate a role for the transgene product in disease initiation but not necessarily for end-state pathology, and they raise the possibility that autoreactive B cells may play a previously unappreciated role in initiating the development of systemic autoimmunity.

T cell-independent spontaneous loss of tolerance by anti-double-stranded DNA B cells in C57BL/6 mice

Systemic lupus erythematosus is characterized by loss of tolerance to DNA and other nuclear Ags. To understand the role of T cells in the breaking of tolerance, an anti-DNA site-specific transgenic model of spontaneous lupus, B6x56R, was studied. T cells were eliminated by crossing B6x56R with CD4(-/)(-) or TCRbeta(-/-)delta(-/-) mice, and the effects on anti-dsDNA serum levels, numbers of anti-dsDNA Ab-secreting cells, and isotypes of anti-dsDNA were analyzed. In addition, the development and activation of B cells in these mice were examined. Surprisingly, the presence of T cells made little difference in the development and character of the serum anti-dsDNA Ab in B6x56R mice. At 1 mo of age, anti-dsDNA Abs were somewhat lower in mice deficient in alphabeta and gammadelta T cells. Levels of Abs later were not affected by T cells, nor was autoantibody class switching. B cell activation was somewhat diminished in T cell-deficient mice. Thus, in the B6 background, the presence of an anti-dsDNA transgene led the production of autoantibodies with a specificity and isotype characteristic of murine systemic lupus erythematosus with little influence from T cells. TLR9 also did not appear to play a role. Although we do not yet understand the mechanism of this failure of immunoregulation, these results suggest that similar processes may influence autoimmunity associated with clinical disease.

Modulation of autoimmunity by TLR9 in the chronic graft-vs-host model of systemic lupus erythematosus

Chronic graft-vs-host (cGVH) disease is induced in nonautoimmune mice by the transfer of alloreactive T cells that recognize foreign MHC class II. It closely resembles systemic lupus erythematosus, with antinuclear Abs and immune-mediated nephritis. Recent work has implicated TLRs, particularly TLR9, in the recognition of certain autoantigens in vitro and in vivo. To explore further the role of TLR9 in systemic autoimmunity, we induced cGVH disease in C57BL/6 (B6) mice lacking TLR9, including B6 mice expressing the anti-DNA-encoding IgH transgenes 3H9 or 56R (B6.3H9.TLR9(-/-), B6.56R.TLR9(-/-)). We found that cGVH disease caused breakdown of B cell tolerance to chromatin and DNA in TLR9(-/-) recipients of alloreactive cells, yet that nephritis was less severe and that some autoantibody titers were lower compared with B6-cGVH controls. Spleen lymphocyte analysis showed that cGVH disease strikingly depleted marginal zone B cells in B6 mice, but did not influence T cell subsets in either B6 or B6-TLR9(-/-) hosts. B6.56R.TLR9(-/-) mice had less spontaneous production of autoantibodies than B6.56R mice, but there were no significant differences between B6.56R and B6.56R.TLR9(-/-) postinduction of cGVH disease. Taken together, these results suggested that TLR9 may worsen some aspects of systemic autoimmunity while alleviating others.

The effect of the phytoestrogen coumestrol on the NZB/W F1 murine model of systemic lupus

Coumestrol is a naturally occurring plant estrogen. As estrogen influences cellular and humoral immunity, and has known effects on murine models of lupus, we investigated the effect of coumestrol on disease expression in the NZB/W F1 mouse. Female NZB/W F1 mice were fed a "standard" rodent diet including soy proteins, a non-soy diet, or a non-soy diet with 0.01% coumestrol. Outcome measures included survival, autoantibody expression, immunoglobulin levels, proteinuria, renal histology and B cell immunohistochemistry, and renal mRNA expression. At 24 weeks, the treatment group had decreased prevalence of autoantibodies detected by immunofluorescence and less splenomegaly. At 39 weeks, the prevalence of autoantibodies was similar but the treatment group had less proteinuria. Overall, there was little effect of treatment on renal mRNA levels as assessed by gene array analysis, but functional ontology mapping revealed that genes encoding proteins involved in the immune response were most often affected. These results suggest that treatment with coumestrol may ameliorate some aspects of disease progression in this model of systemic autoimmunity.

Activation and tolerance in CD4(+) T cells reactive to an immunoglobulin variable region

Antibody diversity creates an immunoregulatory challenge for T cells that must cooperate with B cells, yet discriminate between self and nonself. To examine the consequences of T cell reactions to the B cell receptor (BCR), we generated a transgenic (Tg) line of mice expressing a T cell receptor (TCR) specific for a κ variable region peptide in monoclonal antibody (mAb) 36-71. The κ epitope was originally generated by a pair of somatic mutations that arose naturally during an immune response. By crossing this TCR Tg mouse with mice expressing the κ chain of mAb 36-71, we found that κ-specific T cells were centrally deleted in thymi of progeny that inherited the κTg. Maternally derived κTg antibody also induced central deletion. In marked contrast, adoptive transfer of TCR Tg T cells into κTg recipients resulted in T and B cell activation, lymphadenopathy, splenomegaly, and the production of IgG antichromatin antibodies by day 14. In most recipients, autoantibody levels increased with time, Tg T cells persisted for months, and a state of lupus nephritis developed. Despite this, Tg T cells appeared to be tolerant as assessed by severely diminished proliferative responses to the Vκ peptide. These results reveal the importance of attaining central and peripheral T cell tolerance to BCR V regions. They suggest that nondeletional forms of T tolerance in BCR-reactive T cells may be insufficient to preclude helper activity for chromatin-reactive B cells.

Delayed apoptotic cell clearance and lupus-like autoimmunity in mice lacking the c-mer membrane tyrosine kinase

Mice lacking the membrane tyrosine kinase c-mer have been shown to have altered macro-phage cytokine production and defective phagocytosis of apoptotic cells despite normal phagocytosis of other particles. We show here that c-mer-deficient mice have impaired clearance of infused apoptotic cells and that they develop progressive lupus-like autoimmunity, with antibodies to chromatin, DNA, and IgG. The autoimmunity appears to be driven by endogenous antigens, with little polyclonal B cell activation. These mice should be an excellent model for studying the role of apoptotic debris as an immunogenic stimulus for systemic autoimmunity.

Glomerular deposition of immune complexes made with IgG2a monoclonal antibodies

The factors that determine whether immune complexes (IC) are cleared safely from the circulation or are deposited in vulnerable tissues such as glomeruli are not well defined. To better understand how IC are handled, the present study examined the fate in vivo of three model IC preparations with different immunochemical characteristics. Radiolabeled IC were constructed with murine IgG1, IgG2a, or IgG3 anti-DNP mAbs bound to DNP-BSA, designated IgG1 IC, IgG2a IC, and IgG3 IC, respectively. The IC were infused i.v. into BALB/c mice, and clearance and tissue localization of the three IC probes were compared. The results indicate that the major portion of each IC preparation was cleared from the circulation by the liver. However, compared with the other two probes, IgG2a IC were preferentially deposited in the kidney. Histologic examination revealed the presence of IgG2a IC in glomeruli. The enhanced renal uptake of IgG2a IC could not be attributed solely to such characteristics as IC size, Ag/Ab ratio, Ab charge, or affinity. However, the preferential renal deposition of IgG2a IC was abrogated by complement depletion. Thus, enhanced renal uptake in normal mice was complement dependent. These data suggest that interactions between IC and the complement system can influence the propensity of IC to deposit in tissues susceptible to IC-mediated injury.

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.

The Role of Host (Endogenous) T Cells in Chronic Graft-Versus-Host Autoimmune Disease

Chronic graft-vs-host (cGVH) disease induced by the transfer of Ia-incompatible spleen cells from one normal mouse strain (such as B6.C-H2bm12/KhEg (bm12)) to another (such as C57BL/6) causes an autoimmune syndrome resembling systemic lupus erythematosus (SLE). The role of host-derived T cells in this response is not obvious. Previous reports suggested that host T cells might serve to down-regulate the autoimmune syndrome. To address this issue more definitively, we used CD4 knockout (KO) or CD8KO C57BL/6 (B6) mice as recipients in the bm12→C57B6 cGVH model. CD4KO B6 mice injected with allogeneic bm12 spleen cells (bm12→CD4KO group) showed no evidence of cGVH disease. They made no detectable autoantibodies, including anti-chromatin, anti-dsDNA, anti-ssDNA, and rheumatoid factor. They survived at least 20 wks after induction of cGVH disease; and they did not develop nephritis, based on the absence of detectable levels of proteinuria and normal renal histology at the time of sacrifice. By contrast, CD8KO B6 mice (bm12→CD8KO group) and normal B6 mice (bm12→B6 group) injected with bm12 spleen cells generally showed similar levels of mortality, nephritis, and autoantibodies, although the autoantibody titers declined somewhat after week 8 in the bm12→CD8KO group. Control groups of recipients injected with B6 spleen cells showed no induction of autoantibodies. A surprising finding, however, was that the B6→CD8KO group developed severe histologic glomerulonephritis in the absence of autoantibodies and with decreased immune deposits. These results indicate that endogenous (host) CD4+ T cells play an essential role in the cGVH autoimmune syndrome.

Interleukin 6 dependence of anti-DNA antibody production: evidence for two pathways of autoantibody formation in pristane-induced lupus

Pristane induces a lupus-like syndrome in nonautoimmune mice characterized by the development of glomerulonephritis and lupus-associated autoantibodies. This is accompanied by overproduction of interleukin (IL)-6, a cytokine linked with autoimmune phenomena. The goal of this study was to evaluate the role of IL-6 in autoantibody production in pristane-induced lupus. BALB/cAn IL-6-deficient (-/-) and -intact (+/+) mice were treated with pristane or phosphate-buffered saline, and autoantibody production was evaluated. Pristane induced high levels of immunoglobulin (Ig)G anti-single-stranded DNA, -double-stranded (ds)DNA, and -chromatin antibodies in IL-6(+/+), but not IL-6(-/-) mice by enzyme-linked immunosorbent assay. High titer IgG anti-dsDNA antibodies also were detected in sera from +/+, but not -/-, mice by Crithidia luciliae kinetoplast staining. The onset of IgG anti-dsDNA antibody production in +/+ mice occurred >5 mo after pristane treatment, well after the onset of nephritis, suggesting that these antibodies are not directly responsible for inducing renal disease. In contrast to anti-DNA, the frequencies of anti-nRNP/Sm and anti-Su antibodies were similar in pristane-treated IL-6(-/-) and IL-6(+/+) mice. However, levels were higher in the +/+ group. These results suggest that IgG anti-DNA and chromatin antibodies in pristane-treated mice are strictly IL-6 dependent, whereas induction of anti-nRNP/Sm and Su autoantibodies is IL-6 independent. The IL-6 dependence of anti-DNA, but not anti-nRNP/Sm, may have implications for understanding the patterns of autoantibody production in lupus. Anti-DNA antibodies are produced transiently, mainly during periods of disease activity, whereas anti-nRNP/Sm antibody levels are relatively insensitive to disease activity. This may reflect the differential IL-6 dependence of the two responses.

Affinity isolation of neuron-reactive antibodies in MRL/lpr mice

Autoantibodies from the MRL/lpr mice react with numerous proteins on neuronal cell surfaces. The purpose of this study was to isolate and characterize a population of autoantibodies reactive preferentially or exclusively with nervous system tissue. Using a purified plasma membrane preparation from brain cortex of balb/c mice coupled to diaminopropylamine agarose gel, we affinity-isolated antineuronal antibodies from pooled MRL/lpr immunoglobulins. The isolated immunoglobulins reacted with brain cortex plasma membranes and neuroblastoma cells (but not liver, kidney, or fibroblasts) by Western blot and indirect immunofluorescence with confocal microscopy. By Western blot, the epitopes in the brain cortex were proteins of apparent molecular weights 101, 63, 53, 43, 39, and 33, kd; the epitopes in the neuroblastoma cells were 63, 57, and 53 kd. Lectin column isolation revealed that the 101 and 63 kd epitopes were glycosylated. Indirect immunofluorescence revealed that the antibodies bound to the cell soma more intensely than to the cell processes of viable cultured neuroblastoma cells. The cell surface localization of this binding was confirmed by confocal microscopy. Within the central nervous system the antibodies bound more intensely to primary cultures of isolated neurons from fetal cortex than to hippocampal or neostriatal cells. With these antibodies we can begin studies of their potential pathogenic effects.

Antigen nonspecific effect of major histocompatibility complex haplotype on autoantibody levels in systemic lupus erythematosus-prone lpr mice

MHC-linked genes strongly influence susceptibility to autoimmune diseases and also regulate responses to exogenous antigens. To begin to understand the mechanism of this MHC effect on disease, we have investigated MHC-congenic mouse strains that develop spontaneous autoimmunity because of the lpr gene. C57BL6/lpr (B6/lpr) mice (H-2b) are known to have substantial levels of autoantibodies to chromatin, single stranded DNA (ssDNA3), and IgG of different murine subclasses (rheumatoid factor). We have crossed the H-2d and the H-2bm12 (la mutant) haplotypes onto the B6/lpr background. Surprisingly, levels of all the autoantibodies were markedly lower in B6/lpr.H-2d, but levels in B6/lpr.H-2bm12 were no different from those in B6/lpr mice. The downregulating influence of the H-2d allele was dominant, and there was no effect on autoantibody fine specificities. The genetics of the H-2d effect and its diffuse influence on multiple autoantibody specificities, in addition to the lack of effect of the bm12 mutation, which modifies the peptide-binding groove of I-A, together raise the question of whether MHC-linked genes other than classical (IR) genes may be responsible for MHC disease associations in this model.

Genesis and evolution of antichromatin autoantibodies in murine lupus implicates T-dependent immunization with self antigen

Autoantibodies reacting with chromatin and its components, histones and DNA, are characteristic of the human autoimmune disease SLE and drug-induced lupus, but the mechanisms of their induction remain unknown. Serial serum samples collected over short intervals from lupus-prone MRL/MP-lpr/lpr and BXSB mice were tested by ELISA on chromatin and its substructures to characterize the initial autoimmune response to these antigens. Direct binding studies demonstrated that the early autoantibodies recognized discontinuous epitopes on native chromatin and the (H2A-H2B)-DNA subnucleosome. As the immune response progressed, native DNA and other chromatin constituents generally became antigenic. Based on adsorption studies and IgG subclass restriction, antibodies to native DNA were more related to chromatin than to denatured DNA. The kinetics of autoantibody appearance and the Ig class distribution were similar to the kinetics and distribution seen in antibodies induced by immunization with an exogenous T-dependent antigen. These results are most consistent with the view that autoantibodies reacting with chromatin are generated by autoimmunization with chromatin, and antibodies to native DNA are a subset of the wide spectrum of antichromatin autoantibodies.

Evidence for bound antineuronal antibodies in brains of NZB/W mice

Antibodies reactive with neuronal tissue are present in the sera of the murine models of systemic lupus erythematosus (SLE). Access of these antibodies to the central nervous system is an important prerequisite to the hypothesis that these antibodies affect neuronal function. In this study, we isolated antibodies from neutral and acid washes of brain parenchyma of NZB/W F1 mice. Antibody could be eluted from the brains of NZB/W F1 but not control mice. The immunoglobulin was predominantly IgG1; the binding characteristics of the brain eluted antibody were narrower than those of antibody from sera and eluted from visceral organ.

An intrinsic B cell defect is required for the production of autoantibodies in the lpr model of murine systemic autoimmunity

Mice homozygous for the gene lpr develop marked lymphadenopathy and a spectrum of autoantibodies closely resembling that of human systemic lupus erythematosus. The unusual T cell phenotype of the expanded lymphocyte population and the T-dependence of several antibodies in this strain have suggested that primary T cell abnormalities underlie the autoimmune syndrome. Using double chimeras, we now show that expression of the lpr gene in B cells is absolutely necessary for autoantibody production. Combinations of anti-Thy 1.2 + C' treated bone marrow from congenic strains of C57BL/6 mice, differing only at the immunoglobulin heavy chain (Igh) and lpr loci, were transferred into lethally irradiated B6/lpr mice. Double chimerism was documented by allotype-specific surface IgD and IgM immunofluorescence assay of peripheral blood and by allotype-specific enzyme-linked immunosorbent assay for total IgM in serum. Despite the presence of both +/+ and lpr B cells, IgM and IgG2a anti-chromatin as well as IgM anti-IgG were entirely the products of lpr B cells. Total serum IgG2a and IgG1 were also dominated by the lpr phenotype but not to the same extent. A similar experiment using B6/lpr-Igha recipients confirmed these findings. Additional experiments in which B6/lpr recipients were infused with ratios of donor bone marrow favoring B6.C20 +/+ over B6/lpr showed that even though +/+ B cells were overrepresented, autoantibodies were only of the lpr allotype. In addition, in the presence of lpr B cells, normal B cells showed little response to an exogenous, T cell-dependent antigen. The data thus indicate that lpr B cells manifest an intrinsic abnormality which is essential for autoantibody production in the lpr model.

Immunoglobulin binding to neuronal cell surface epitopes in murine systemic lupus erythematosus

Screening serum by enzyme-linked immunosorbent assay (ELISA) to paraformaldehyde-fixed neuroblastoma cells revealed spontaneous neuron-reactive antibodies in three strains of autoimmune mice not present in comparable studies of BALB/c mice. Immunoglobulin isolation from pooled sera by either ammonium sulfate precipitation or passage over a protein G column enabled quantitative binding by (1) ELISA to neuroblastoma cells and (2) Western blots of plasma membrane preparations of brain cortex and neuroblastoma cells. The antibodies recognized proteins of apparent molecular weights 101,000, 68,000, 63,000, 57,000, 53,000, 43,000, 39,000, and 31,000 Da on the brain cortex and 63,000, 57,000, and 43,000 Da on the neuroblastoma cell membranes. The class of antibody binding was predominantly IgG in the MRL/lpr and IgM in the NZB/W. Differences between MRL/lpr, NZB/W and BXSB mice were observed although it is not yet apparent if this represents a difference in autoantibody production between the strains.

Experimental induction of systemic lupus erythematosus by recognition of foreign Ia

A chronic GVH reaction induced in normal mice results in a syndrome that closely resembles SLE. In this study, we compared the autoimmune GVH syndrome induced in parent (C57BL/6Kh [B6] and B6.C-H-2bm12 [bm12]) and F1 [( B6 x bm12]F1) mice by transfer of parental spleen cells. A majority of the mice in all groups developed autoantibodies to chromatin and erythrocytes, and some of the mice also produced anti-dsDNA antibodies. The predominant isotype of the anti-chromatin autoantibodies was found to be IgG2a, although high levels of IgG2b antibodies were also present. Autoantibody production was in general more intense and more prevalent in parent----F1 hybrid combinations, compared to parent----parent infusions. No influence of host or graft gender was observed. These studies show that a chronic GVH reaction can be induced by both parent----parent and parent----hybrid combinations.

Autoantibodies in chronic graft versus host result from cognate T-B interactions

A chronic graft-versus-host reaction (GVH) induced in nonautoimmune mice causes a syndrome that closely resembles SLE. In this model, donor T cells react against incompatible host Ia structures and generate excessive help, which activates a subpopulation of self-reactive B cells. We have studied whether these self-reactive B cells are activated by direct interaction with alloreactive T cells or by nonspecific bystander effects. Two types of chimeras were made: double-parental chimeras, differing at both Ia and Igh allotype [B6.C20 + bm12----(B6.C20 x bm12)F1]; and control chimeras [(B6.C20 x bm12)F1----(B6.C20 x bm12)F1]. A chronic GVH syndrome was induced in the chimeras by infusion of B6 or bm12 spleen cells. Coombs and antichromatin autoantibodies were measured using Igh allotype-specific immunoassays. The double-parental chimeras that received bm12 cells made autoantibodies principally of the Igha allotype, indicating that the bm12 T cells interacted only with the Iab-bearing host B cells. Conversely, double-parental chimeras that received B6 cells made mostly Ighb autoantibodies, indicating direct cognate interaction with the Iabm12-bearing host B cells. The control chimeras made autoantibodies of both allotypes. These results indicate that autoantibodies in chronic GVH result from direct T-B interactions and not from nonspecific T cell-derived factors.

Immunological effects of recombinant interferon gamma in vivo in normal mice: failure to induce autoantibodies

We have investigated the effects on the immune system, and especially on the induction of autoimmunity, of treatment of mice with recombinant IFN-gamma in vivo by several protocols. Neither antichromatin nor Coombs autoantibody was observed. The spleens of the treated animals enlarged two fold, despite a dramatic decrease in numbers of Thy-1+ spleen cells and a smaller decrease in surface Ig+ spleen cells. This was correlated with a markedly diminished Con A response and moderately reduced LPS response. On the other hand, the numbers of IgG secreting cells were augmented in the spleens of treated mice. In addition, IFN-gamma-injected mice lost weight and became anemic. This study shows that, although IFN-gamma-injected in vivo leads to severe changes in the murine immune system, it is not responsible by itself for the induction of autoimmunity.

Regulation of the anti-Sm autoantibody response in systemic lupus erythematosus mice by monoclonal anti-Sm antibodies

The administration of certain monoclonal anti-Sm antibodies (2G7, 7.13) induced most MRL/lpr mice to become anti-Sm positive by 5 mo of age, although other anti-Sm monoclonals (Y2, Y12) suppressed the spontaneous response. Positive anti-Sm antibody enhancement occurred efficiently only in MRL/lpr mice and not in other systemic lupus erythematosus mice that have little spontaneous anti-Sm production. The enhancement by anti-Sm antibodies was specific for the anti-Sm response. The mechanism of the passive antibody enhancement was apparently not isotype- or idiotype-related. The fine specificity of the anti-Sm monoclonal antibody may be essential to its enhancing or suppressing effects, since both enhancing monoclonals recognized only the D Sm polypeptide, whereas both suppressing monoclonals saw the D and the B polypeptides. Furthermore, analysis of serial bleeds from unmanipulated MRL mice that developed anti-Sm positivity showed that the D specificity almost always appeared first. We hypothesize, therefore, that those animals in which an anti-Sm response is initiated by D-specific B-cell clones can become serologically positive with the aid of a positive feedback loop. In contrast, animals in which the initial specificity is for both B and D peptides would be prevented from developing a full anti-Sm response.

Serum concentrations of IgM, IgG1, IgG2b, IgG3 and IgA in C57BL/6 mice and their congenics at the lpr (lymphoproliferation) locus

The serum concentrations of IgM, IgG1, IgG2b, IgG3 and IgA were determined in mice of C57BL/6 background, from weaning to one year of age, by quantitative isotype-specific, indirect double sandwich enzyme-linked immunosorbent assays (ELISAs). Only limited data could be obtained for the IgG2a isotype in the present study. The mean serum Ig levels found for 6-month-old B6 mice were 0.22 mg/ml for IgM, 0.28 mg/ml for IgG1, 1.22 mg/ml for IgG2b, 0.18 mg/ml for IgG3, 0.075 mg/ml for IgA and about 0.7 mg/ml for IgG2a. In comparison with mice of the wild strain, C57BL/6 mice homozygous at the lpr (lymphoproliferation) locus showed very high increases in serum Ig levels when older than 20 weeks. With 6-month-old B6 lpr mice, increases in concentration were found for all tested heavy chain isotypes: 6 to 6.5-fold for IgA (0.45 mg/ml) and IgG1 (1.82 mg/ml), 9-fold for IgG3 (1.6 mg/ml), 11 to 11.5-fold for IgM (2.44 mg/ml) and IgG2b (13.8 mg/ml) and about 8-fold for IgG2a (5.5 mg/ml). Therefore homozygosity at the lpr locus provides the conditions for generalized, poly-isotypic rather than isotype-specific restricted Ig enhancement. This observation may be more compatible with hyperinducibility of all B-cell subclasses than with excessive production of T-cell-derived factors whose activity would be expected to be restricted to some T-dependent subclasses, and at least to affect IgM-committed B cells to a lesser extent than other B-cell classes.

Rheumatoid factor and Fc signaling: a tale of two Cinderellas

Signaling to lymphocytes depends not only upon the interaction of receptors with specific antigen, but also upon antigen nonspecific receptors which receive input from two classes of molecules, immunologically specific end products and lymphokines. These represent the central elements in the physiologic stimulation of immune responses to both self and foreign antigens. This review is dedicated primarily to describing the function of physiologically active receptors for end product which are central to end product feedback in normal immune responses. The emergence of autoimmunity as a pathologic process resultant from a defective end product signaling mechanism is described.

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.

Cellular interactions for the in vitro production of anti-chromatin autoantibodies in MRL/Mp-lpr/lpr mice

Anti-chromatin autoantibodies are spontaneously produced by autoimmune but not by normal mice. An in vitro system was developed to study the cellular mechanisms of anti-chromatin production in MRL/Mp-lpr/lpr (MRL/lpr) mice. In such cultures, spleen cells from MRL/lpr mice with active autoimmune disease generated substantial amounts of anti-chromatin, as measured by ELISA of culture supernatants and by ELISA spot assay of anti-chromatin-producing cells. In vitro production of anti-chromatin autoantibodies was independent of T cells, even when spleen cells from animals as young as 1 month were examined. In contrast, anti-Sm production under the same conditions was highly T cell dependent. Macrophages and/or macrophage-derived factors were necessary for the in vitro production of anti-chromatin autoantibodies. The lack of anti-chromatin production by cells from nonautoimmune mice could not be ascribed to the presence of suppressor cells. These studies indicate that individual autoantibodies may arise through distinct cellular mechanisms in systemic lupus erythematosus mice. MRL/lpr mice develop global T lymphocyte deficiency along with their autoimmunity. The progressive increase in relatively thymus independent antibodies such as anti-chromatin is consistent with the lack of functional T lymphocytes in aging MRL/lpr mice.