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

CD95 and the MRL-lpr Mouse Model

CD95 (Fas-ligand) is a key mediator of cell death in multiple setting, thus its loss within the MRL-lpr (Fas^lpr) homozygote mice results in spontaneous autoimmunity. This is characterized by the development of arthritis and immune complex glomerulonephrosis making this strain a useful model for studying systemic lupus erythematosus. Herein we describe a method to exploit the heterozygote offspring of this strain in a model to study the effects of a CD95L blocking peptide on lupus-like disease in vivo.

B lymphocytes in systemic lupus erythematosus: lessons from therapy targeting B cells

Systemic lupus erythematosus (SLE) is a complex disease characterizedby numerous autoantibodies and clinical involvement in multiple organ systems. Autoantibodies are usually present in serum for years before the onset of clinical disease. Autoimmunity begins with a limited number of autoantibodiesand evolves to become progressivelymore diverse. Eventually clinical disease ensues. The immunological events triggering the onset of clinical manifestations have not yet been defined. While undoubtedly T cells and dendritic cells appear to play major roles in SLE, a central role for B cells in the pathogenesis of this disease has been brought to the fore in the last few years by work performed both in mice and humans by multiple laboratories.As a result, there is little doubt about the importance of B cells in the development of SLE. Yet much remains to be learned about their role in the ongoing disease process and the merit of targeting B cells for the treatment of SLE. This article will review the role of B cells in human SLE as well as the currently available data on the treatment of SLE by depleting B cells with anti-CD20 (rituximab).

T cells, murine chronic graft-versus-host disease and autoimmunity

The chronic graft-versus-host disease (cGVHD) in mice is characterized by the production of autoantibodies and immunopathology characteristic of systemic lupus erythematosus (lupus). The basic pathogenesis involves the cognate recognition of foreign MHC class II of host B cells by alloreactive CD4 T cells from the donor. CD4 T cells of the host are also necessary for the full maturation of host B cells before the transfer of donor T cells. CD8 T cells play critical roles as well. Donor CD8 T cells that are highly cytotoxic can ablate or prevent the lupus syndrome, in part by killing recipient B cells. Host CD8 T cells can reciprocally downregulate donor CD8 T cells, and thus prevent them from suppressing the autoimmune process. Thus, when the donor inoculum contains both CD4 T cells and CD8 T cells, the resultant syndrome depends on the balance of activities of these various cell populations. For example, in one cGVHD model (DBA/2(C57BL/6xDBA/2)F1, the disease is more severe in females, as it is in several of the spontaneous mouse models of lupus, as well as in human disease. The mechanism of this female skewing of disease appears to depend on the relative inability of CD8 cells of the female host to downregulate the donor CD4 T cells that drive the autoantibody response. In general, then, the abnormal CD4 T cell help and the modulating roles of CD8 T cells seen in cGVHD parallel the participation of T cells in genetic lupus in mice and human lupus, although these spontaneous syndromes are presumably not driven by overt alloreactivity.

B cell maturation antigen deficiency exacerbates lymphoproliferation and autoimmunity in murine lupus

Systemic lupus erythematosus and its preclinical lupus-prone mouse models are autoimmune disorders involving the production of pathogenic autoantibodies. Genetic predisposition to systemic lupus erythematosus results in B cell hyperactivity, survival of self-reactive B cells, and differentiation to autoantibody-secreting plasma cells (PCs). These corrupt B cell responses are, in part, controlled by excess levels of the cytokine BAFF that normally maintains B cell homeostasis and self-tolerance through limited production. B cell maturation Ag (BCMA) is a receptor for BAFF that, under nonautoimmune conditions, is important for sustaining enduring Ab protection by mediating survival of long-lived PCs but is not required for B cell maturation and homeostasis. Through analysis of two different lupus-prone mouse models deficient in BCMA, we identify BCMA as an important factor in regulating peripheral B cell expansion, differentiation, and survival. We demonstrate that a BCMA deficiency combined with the lpr mutation or the murine lupus susceptibility locus Nba2 causes dramatic B cell and PC lymphoproliferation, accelerated autoantibody production, and early lethality. This study unexpectedly reveals that BCMA works to control B cell homeostasis and self-tolerance in systemic autoimmunity.

Homeostatic expansion of autoreactive immunoglobulin-secreting cells in the Rag2 mouse model of Omenn syndrome

Hypomorphic RAG mutations, leading to limited V(D)J rearrangements, cause Omenn syndrome (OS), a peculiar severe combined immunodeficiency associated with autoimmune-like manifestations. Whether B cells play a role in OS pathogenesis is so far unexplored. Here we report the detection of plasma cells in lymphoid organs of OS patients, in which circulating B cells are undetectable. Hypomorphic Rag2^R229Q knock-in mice, which recapitulate OS, revealed, beyond severe B cell developmental arrest, a normal or even enlarged compartment of immunoglobulin-secreting cells (ISC). The size of this ISC compartment correlated with increased expression of Blimp1 and Xbp1, and these ISC were sustained by elevated levels of T cell derived homeostatic and effector cytokines. The detection of high affinity pathogenic autoantibodies toward target organs indicated defaults in B cell selection and tolerance induction. We hypothesize that impaired B cell receptor (BCR) editing and a serum B cell activating factor (BAFF) abundance might contribute toward the development of a pathogenic B cell repertoire in hypomorphic Rag2^R229Q knock-in mice. BAFF-R blockade reduced serum levels of nucleic acid-specific autoantibodies and significantly ameliorated inflammatory tissue damage. These findings highlight a role for B cells in OS pathogenesis.

A perspective on B-cell-targeting therapy for SLE

In recent years, large controlled trials have tested several new agents for systemic lupus erythematosus (SLE). Unfortunately, none of these trials has met its primary outcome. This does not mean progress has not been made. In fact, a great deal has been learned about doing clinical trials in lupus and about the biological and clinical effects of the drugs being tested. Many of these drugs were designed to target B cells directly, e.g., rituximab, belimumab, epratuzumab, and transmembrane activator and calcium modulator and cyclophilin ligand interactor-immunoglobulin (TACI-Ig). The enthusiasm for targeting B cells derives from substantial evidence showing the critical role of B cells in murine models of SLE, as well promising results from multiple open trials with rituximab, a chimeric anti-CD20 monoclonal antibody that specifically depletes B cells (Martin and Chan in Immunity 20(5):517-527, 2004; Sobel et al. in J Exp Med 173:1441-1449, 1991; Silverman and Weisman in Arthritis Rheum 48:1484-1492, 2003; Silverman in Arthritis Rheum 52(4):1342, 2005; Shlomchik et al. in Nat Rev Immunol 1:147-153, 2001; Looney et al. in Arthritis Rheum 50:2580-2589, 2004; Lu et al. in Arthritis Rheum 61(4):482-487, 2009; Saito et al. in Lupus 12(10):798-800, 2003; van Vollenhoven et al. in Scand J Rheumatol 33(6):423-427, 2004; Sfikakis et al. Arthritis Rheum 52(2):501-513, 2005). Why have the controlled trials of B-cell-targeting therapies failed to demonstrate efficacy? Were there flaws in design or execution of these trials? Or, were promising animal studies and open trials misleading, as so often happens? This perspective discusses the current state of B-cell-targeting therapies for human lupus and the future development of these therapies.

Fas expression on antigen-specific T cells has costimulatory, helper, and down-regulatory functions in vivo for cytotoxic T cell responses but not for T cell-dependent B cell responses

Fas-mediated apoptosis is an important contributor to contraction of Ag-driven T cell responses acting only on activated Ag-specific T cells. The effects of targeted Fas deletion on selected cell populations are well described however little is known regarding the consequences of Fas deletion on only activated Ag-specific T cells. We addressed this question using the parent-into-F(1) (P-->F(1)) model of acute or chronic (lupus-like) graft-vs-host disease (GVHD) as a model of either a CTL-mediated or T-dependent B cell-mediated response, respectively. By transferring Fas-deficient lpr donor T cells into Fas-intact F(1) hosts, the in vivo role of Ag-specific T cell Fas can be determined. Our results demonstrate a novel dichotomy of Ag-specific T cell Fas function in that: 1) Fas expression on Ag-activated T cells has costimulatory, helper, and down-regulatory roles in vivo and 2) these roles were observed only in a CTL response (acute GVHD) and not in a T-dependent B cell response (chronic GVHD). Specifically, CD4 T cell Fas expression is important for optimal CD4 initial expansion and absolutely required for help for CD8 effector CTL. Donor CD8 T cell Fas expression played an important but not exclusive role in apoptosis and down-regulation. By contrast, CD4 Fas expression played no detectable role in modulating chronic GVHD induction or disease expression. These results demonstrate a novel role for Ag-specific T cell Fas expression in in vivo CTL responses and support a review of the paradigm by which Fas deficiency accelerates lupus in MRL/lpr lupus-prone mice.

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.

B cell depletion with anti-CD79 mAbs ameliorates autoimmune disease in MRL/lpr mice

MRL/lpr mice develop a spontaneous systemic lupus erythematosus-like autoimmune syndrome due to a dysfunctional Fas receptor, with contributions from other less well-defined genetic loci. The removal of B cells by genetic manipulation not only prevents autoantibody formation, but it also results in substantially reduced T cell activation and kidney inflammation. To determine whether B cell depletion by administration of Abs is effective in lupus mice with an intact immune system and established disease, we screened several B cell-specific mAbs and found that a combination of anti-CD79alpha and anti-CD79beta Abs was most effective at depleting B cells in vivo. Anti-CD79 therapy started at 4-5 mo of age in MRL/lpr mice significantly decreased B cells (B220(+)CD19(+)) in peripheral blood, bone marrow, and spleens. Treated mice also had a significant increase in the number of both double-negative T cells and naive CD4(+) T cells, and a decreased relative abundance of CD4(+) memory cells. Serum anti-chromatin IgG levels were significantly decreased compared with controls, whereas serum anti-dsDNA IgG, total IgG, or total IgM were unaffected. Overall, survival was improved with lower mean skin scores and significantly fewer focal inflammatory infiltrates in submandibular salivary glands and kidneys. Anti-CD79 mAbs show promise as a potential treatment for systemic lupus erythematosus and as a model for B cell depletion in vivo.

CD19 hyperexpression augments Sle1-induced humoral autoimmunity but not clinical nephritis

OBJECTIVE

B cell hyperactivity is a common denominator in murine and human systemic lupus erythematosus. Some susceptibility genes in lupus are associated with B cell hyperactivity, but others are clearly not. While the Sle1 lupus susceptibility locus of NZM2410/NZW origin leads to chromatin-focused autoimmunity, genetically engineered overexpression of CD19 leads to "generalized" B cell hyperactivity. We undertook this study to determine the degree to which generalized B cell hyperactivity can amplify lupus pathogenesis.

METHODS

To elucidate the impact of generalized B cell hyperactivity on Sle1-triggered autoimmunity, B6 mice bearing the human CD19 transgene were rendered congenic for the Sle1(z) genetic locus and phenotyped for serologic, cellular, and pathologic evidence of lupus.

RESULTS

As expected, B6.Sle1.hCD19(Tg/Tg) mice, homozygous at Sle1 and bearing the hCD19 transgene, exhibited high levels of IgM and IgG anti-DNA/antiglomerular autoantibodies, skewed B cell subsets, and profoundly activated B and T cells. Despite exhibiting glomerular IgM, IgG, and complement deposits, these mice did not exhibit accelerated mortality or any clinical evidence of renal dysfunction.

CONCLUSION

Generalized B cell hyperactivity may augment humoral autoimmunity, but this may not suffice to engender end-organ disease in lupus. These findings allude to the presence of an additional distal checkpoint that dissociates pathogenic autoantibody formation and renal immunoglobulin deposition from the progression to clinical nephritis in lupus.

Interaction between antigen presenting cells and autoreactive T cells derived from BXSB mice with murine lupus

Systemic lupus erythematosus (SLE) is a typical autoimmune disease involving multiple systems and organs. Ample evidence suggests that autoreactive T cells play a pivotal role in the development of this autoimmune disorder. This study was undertaken to investigate the mechanisms of interaction between antigen presenting cells (APCs) and an autoreactive T cell (ATL1) clone obtained from lupus-prone BXSB mice. ATL1 cells, either before or after gamma-ray irradiation, were able to activate naive B cells, as determined by B cell proliferation assays. Macrophages from BXSB mice were able to stimulate the proliferation of resting ATL1 cells at a responder/stimulator (R/S) ratio of 1/2.5. Dendritic cells (DCs) were much more powerful stimulators for ATL1 cells on a per cell basis. The T cell stimulating ability of macrophages and B cells, but not DCs, was sensitive to gamma-ray irradiation. Monoclonal antibodies against mouse MHC-II and CD4 were able to block DC-mediated stimulation of ATL1 proliferation, indicating cognate recognition between ATL1 and APCs. Our data suggest that positive feedback loops involving macrophages, B cells and autoreactive T cells may play a pivotal role in keeping the momentum of autoimmune responses leading to autoimmune diseases.

Spontaneous B cell hyperactivity in autoimmune-prone MRL mice

The MRL-lpr/lpr mouse strain is a commonly used model of the human autoimmune disease systemic lupus erythematosus (SLE). Although much is known about the contribution of the lpr Fas mutation to B cell tolerance breakdown, the role of the genetic background of the MRL strain itself is less well explored. In this study, we use the MD4 anti-hen egg lysozyme Ig (IgHEL) transgenic system to explore B cell function in MRL+/+ and non-autoimmune mice. We demonstrate that MRL IgHEL B cells show spontaneous hyperactivity in the absence of self-antigen, which is associated with low total B cell numbers but an expansion of the marginal zone B cell population. However, B cell anergy is normal in the presence of soluble lysozyme [soluble hen egg lysozyme (sHEL)], and MRL IgHEL B cells undergo normal elimination in the presence of sHEL when competing with a polyclonal C57BL/6 B cell repertoire. We conclude that B cell hyperactivity may contribute to the autoimmune phenotype of MRL+/+ and MRL-lpr/lpr strains when it initiates antibody responses to rare or sequestered antigens that are below the threshold for tolerance induction, but that there is no B cell intrinsic defect in anergy in MRL mice.

B cells in health and disease

B cells play a key role in regulating the immune system by producing antibodies, acting as antigen-presenting cells, providing support to other mononuclear cells, and contributing directly to Inflammatory pathways. Accumulating evidence points to disruption of these tightly regulated processes in the pathogenesis of autoimmune disorders. Although the exact mechanisms involved remain to be elucidated, a fundamental feature of many autoimmune disorders is a loss of B-cell tolerance and the inappropriate production of autoantibodies. Dysfunctional immune responses resulting from genetic mutations that cause intrinsic B-cell abnormalities and induction of autoimmunity in the T-cell compartment by B cells that have broken tolerance may also contribute to these disorders. These findings provide the rationale for B-cell depletion as a potential therapeutic strategy in autoimmune disorders and other disease states characterized by inappropriate immune responses. Preliminary results with the CD20-targeted monoclonal antibody rituximab indicate that rituximab can improve symptoms in a number of autoimmune and neurologic disorders (including rheumatoid arthritis, systemic lupus erythematosus, and paraneoplastic neurologic syndromes). Additional studies are warranted to further characterize the role of B cells in autoimmune diseases and the therapeutic utility of B-cell depletion.

B Cell Tolerance Checkpoints That Restrict Pathways of Antigen-Driven Differentiation

Autoreactive B cells can be regulated by deletion, receptor editing, or anergy. Rheumatoid factor (RF)-expressing B lymphocytes in normal mice are not controlled by these mechanisms, but they do not secrete autoantibody and were presumed to ignore self-Ag. Surprisingly, we now find that these B cells are not quiescent, but instead are constitutively and specifically activated by self-Ag. In BALB/c mice, RF B cells form germinal centers (GCs) but few Ab-forming cells (AFCs). In contrast, autoimmune mice that express the autoantigen readily generate RF AFCs. Most interestingly, autoantigen-specific RF GCs in BALB/c mice appear defective. B cells in such GCs neither expand nor are selected as efficiently as equivalent cells in autoimmune mice. Thus, our data establish two novel checkpoints of autoreactive B cell regulation that are engaged only after initial autoreactive B cell activation: one that allows GCs but prevents AFC formation and one that impairs selection in the GC. Both of these checkpoints fail in autoimmunity.

Autoreactive responses to environmental factors: 3. Mouse strain-specific differences in induction and regulation of anti-DNA antibody responses due to phthalate-isomers

Little is known of the role of specific environmental factors in promoting autoimmune disorders such as systemic lupus erythematosus (SLE). This study addresses how exposure to phthalates, common environmental factors in foods, and biomedical devices could affect the immune functions of resistant and autoimmune-prone mice. We have previously shown that immunization with ortho-phthalate evokes anti-DNA antibody in BALB/c and NZB/W F1 mice, but only the latter suffer from nephritis and high mortality. BALB/c mice, in contrast, develop idiotype-specific CD8+ suppressor T cells downregulating autoreactive B cells. Here we report that all phthalate-isomers (ortho-, meta- and para-) are capable of inducing anti-DNA antibody responses and SLE-like syndromes. Kidney pathology worsens in NZB/W F1 and to a degree, in C57BL/6 mice after repeated exposure to phthalates. Only BALB/c and DBA/2 overcome adverse autoreactivity by induction of Ts cells; but in vivo depletion of these T cells renders these strains susceptible to autoreactivity. Anti-DNA antibodies in affected NZB/W F1 are largely IgG2a-type, while in BALB/c, DBA/2, and C57BL/6 mice IgG1-type. This is further corroborated by cytokine analyses that imply corresponding Th1/Th2 involvement. In summary, the commonly used phthalates appear harmful to susceptible strains, while BALB/c and DBA/2 are spared due to induction of Ts cells.

Genetic Dissection of Systemic Lupus Erythematosus Pathogenesis: Partial Functional Complementation betweenSle1andSle3/5Demonstrates Requirement for Intracellular Coexpression for Full Phenotypic Expression of Lupus

Sle1 on chromosome 1 and Sle3/5 on chromosome 7 are two of the most critical lupus susceptibility loci of the New Zealand Black/White-derived NZM2410 mouse strain. In contrast to C57BL/6 mice congenic for either Sle1 (B6.Sle1) or Sle3/5 (B6.Sle3/5), strains that express only a modest lupus-related phenotype, the bicongenic B6.Sle1.Sle3/5 strain has a robust phenotype, suggesting a critical role for epistatic interactions in lupus pathogenesis. Mixed chimera experiments indicated that the two loci are functionally expressed by different cell populations and predicted that phenotypic expression of the phenotypic features of the B6.Sle1.Sle3/5 strain could be fully reproduced with a combination of B6.Sle1 and B6.Sle3/5 bone marrow. Contrary to our expectations, there was only a partial functional complementation in these mixed chimeras. Spleen enlargement, CD4:CD8 ratio elevation, and epitope spreading of autoantibodies were fully developed in B6+B6.Sle1.Sle3/5 but not in B6.Sle1+B6.Sle3/5 mixed chimeras. This study is the first to present evidence that the pathways mediated by two critical lupus susceptibility loci derived from the New Zealand White strain must be integrated intracellularly for epistatic interactions to occur. Our mixed chimera approach continues to provide novel insights into the functional genetic pathways underlying this important murine model of systemic autoimmunity.

p53 is required for spontaneous autoantibody production in B6/lpr lupus mice

The p53 tumor suppressor molecule triggers a key pathway of apoptosis in injured cells, in part through induction of Fas. The importance of Fas as a receptor mediating apoptosis is highlighted by the lupus-like systemic autoimmunity seen in animals and humans with nonfunctional Fas molecules. We set out to see if the absence of p53, superimposed on the Fas defect of lpr mice, might further accelerate or exacerbate their systemic autoimmunity. We generated double mutant mice (p53(-/-) lpr) having defects in both p53- and Fas-dependent pathways, hypothesizing that animals with lesions in both Fas- and p53-dependent pathways would show reduced ability to delete autoreactive or injured cells, thereby producing more severe autoimmune disease. Surprisingly, these mice have lower autoantibody levels than the single mutant lpr mice. These studies suggest an unanticipated role for p53 in the progression of autoimmunity and the production of autoantibodies.

Human innate B cells: a link between host defense and autoimmunity?

B cells play a variety of immunoregulatory roles through their antigen-presentation ability and through cytokine and chemokine production. Innate immune activation of B cells may play a beneficial role through the generation of natural cross-reactive antibodies, by maintaining B cell memory and by exercising immunomodulatory functions that may provide protection against autoimmunity. In this article, we review human B cell populations and their functional properties, with a particular focus on a population of inherently autoreactive B cells, which seem to play an important physiological role in innate immunity, but which, if selected into adaptive immune responses, appear to become pathogenic agents in systemic lupus erythematosus.

Prominent dominant negative effect of a mutant Fas molecule lacking death domain on cell-mediated induction of apoptosis

Using a panel of transfectant B lymphoma cells expressing varying amounts of the mutant Fas together with the endogenous wild type Fas, semi-quantitative studies on the dominant negative effect of a murine mutant Fas molecule lacking death domain were carried out. In anti-Fas antibody-mediated induction of apoptosis, the mutant molecules exerted significant dominant-negative effect only when their expression level was comparable to or higher than that of wild type molecules, or when exposed to low amounts of the antibody. The inhibitory effect was accompanied by the failure in DISC formation in spite of Fas aggregation. When they were subjected to T cell-mediated Fas-based induction of apoptosis, however, the dominant negative effect was prominent such that the expression of even a small amount of the mutant molecules resulted in significant inhibition. Such a strong inhibitory effect explains the dominant phenotype of this type of mutant Fas molecules in ALPS heterozygous patients and also implies that the physiological effectors for Fas in vivo are cells, i.e., FasL-expressing activated T cells.

T-helper cell intrinsic defects in lupus that break peripheral tolerance to nuclear autoantigens

Special populations of T helper cells drive B cells to produce IgG class switched, pathogenic autoantibodies in lupus. The major source of antigenic determinants (epitopes) that trigger interactions between lupus T and B cells is nucleosomes of apoptotic cells. These epitopes can be used for antigen-specific therapy of lupus. Secondly, the autoimmune T cells of lupus are sustained because they resist anergy and activation-induced programmed cell death by markedly upregulating cyclooxygenase (COX) 2 along with the antiapoptotic molecule c-FLIP. Only certain COX-2 inhibitors block pathogenic anti-DNA autoantibody production in lupus by causing death of autoimmune T helper cells. Hence COX-2 inhibitors may work independently of their ability to block the enzymatic function of COX-2, and structural peculiarities of these select inhibitors may lead to better drug discovery and design.

Negative role of colony-stimulating factor-1 in macrophage, T cell, and B cell mediated autoimmune disease in MRL-Fas(lpr) mice

Inflammation in the kidney and other tissues (lung, and salivary and lacrimal glands) is characteristic of MRL-Fas(lpr) mice with features of lupus. Macrophages (Mphi) are prominent in these tissues. Given that 1) Mphi survival, recruitment, proliferation, and activation during inflammation is dependent on CSF-1, 2) Mphi mediate renal resident cell apoptosis, and 3) CSF-1 is up-regulated in MRL-Fas(lpr) mice before, and during nephritis, we hypothesized that CSF-1-deficient MRL-Fas(lpr) mice would be protected from Mphi-mediated nephritis, and the systemic illness. To test this hypothesis, we compared CSF-1-deficient MRL-Fas(lpr) with wild-type strains. Renal pathology is suppressed and function improved in CSF-1-deficient MRL-Fas(lpr) mice. There are far fewer intrarenal Mphi and T cells in CSF-1-deficient MRL-Fas(lpr) vs wild-type kidneys. This leukocytic reduction results from suppressed infiltration, and intrarenal proliferation, but not enhanced apoptosis. The CSF-1-deficient MRL-Fas(lpr) kidneys remain preserved as indicated by greatly reduced indices of injury (nephritogenic cytokines, tubular apoptosis, and proliferation). The renal protective mechanism in CSF-1-deficient mice is not limited to reduced intrarenal leukocytes; circulating Igs and autoantibodies, and renal Ig deposits are decreased. This may result from enhanced B cell apoptosis and fewer B cells in CSF-1-deficient MRL-Fas(lpr) mice. Furthermore, the systemic illness including, skin, lung, and lacrimal and salivary glands pathology, lymphadenopathy, and splenomegaly are dramatically suppressed in CSF-1-deficient MRL-Fas(lpr) as compared with wild-type mice. These results indicate that CSF-1 is an attractive therapeutic target to combat Mphi-, T cell-, and B cell-mediated autoimmune lupus.

B cell depletion as a novel treatment for systemic lupus erythematosus: a phase I/II dose-escalation trial of rituximab

OBJECTIVE

Safer and more effective therapies are needed for the treatment of systemic lupus erythematosus (SLE). B lymphocytes have been shown to play fundamental pathogenic roles in SLE, and therefore, elimination of B cells with the use of rituximab may represent a new therapy for SLE.

METHODS

A phase I/II dose-escalation trial of rituximab added to ongoing therapy in SLE was conducted. Rituximab was administered as a single infusion of 100 mg/m2 (low dose), a single infusion of 375 mg/m2 (intermediate dose), or as 4 infusions (1 week apart) of 375 mg/m2 (high dose). CD19+ lymphocytes were measured to determine the effectiveness of B cell depletion. The Systemic Lupus Activity Measure (SLAM) score was used as the primary outcome for clinical efficacy.

RESULTS

Rituximab was well tolerated in this patient population, with most experiencing no significant adverse effects. Only 3 serious adverse events, which were thought to be unrelated to rituximab administration, were noted. A majority of patients (11 of 17) had profound B cell depletion (to <5 CD19+ B cells/microl). In these patients, the SLAM score was significantly improved at 2 and 3 months compared with baseline (P = 0.0016 and P = 0.0022, respectively, by paired t-test). This improvement persisted for 12 months, despite the absence of a significant change in anti-double-stranded DNA antibody and complement levels. Six patients developed human antichimeric antibodies (HACAs) at a level > or =100 ng/ml. These HACA titers were associated with African American ancestry, higher baseline SLAM scores, reduced B cell depletion, and lower levels of rituximab at 2 months after initial infusion.

CONCLUSION

Rituximab therapy appears to be safe for the treatment of SLE and holds significant therapeutic promise, at least for the majority of patients experiencing profound B cell depletion. Based on these results, controlled trials of rituximab appear to be warranted.

Separation of the New Zealand Black genetic contribution to lupus from New Zealand Black determined expansions of marginal zone B and B1a cells

The F(1) hybrid of New Zealand Black (NZB) and New Zealand White (NZW) mice develop an autoimmune disease similar to human systemic lupus erythematosus. Because NZB and (NZB x NZW)F(1) mice manifest expansions of marginal zone (MZ) B and B1a cells, it has been postulated that these B cell abnormalities are central to the NZB genetic contribution to lupus. Our previous studies have shown that a major NZB contribution comes from the Nba2 locus on chromosome 1. C57BL/6 (B6) mice congenic for Nba2 produce antinuclear Abs, and (B6.Nba2 x NZW)F(1) mice develop elevated autoantibodies and nephritis similar to (NZB x NZW)F(1) mice. We studied B cell populations of B6.Nba2 mice to better understand the mechanism by which Nba2 leads to disease. The results showed evidence of B cell activation early in life, including increased levels of serum IgM, CD69(+) B cells, and spontaneous IgM production in culture. However, B6.Nba2 compared with B6 mice had a decreased percentage of MZ B cells in spleen, and no increase of B1a cells in the spleen or peritoneum. Expansions of these B cell subsets were also absent in (B6.Nba2 x NZW)F(1) mice. Among the strains studied, B cell expression of beta(1) integrin correlated with differences in MZ B cell development. These results show that expansions of MZ B and B1a cells are not necessary for the NZB contribution to lupus and argue against a major role for these subsets in disease pathogenesis. The data also provide additional insight into how Nba2 contributes to lupus.

Autoreactive responses to an environmental factor. 2. Phthalate-induced anti-DNA specificity is downregulated by autoreactive cytotoxic T cells

An environmental factor (phthalate) was shown, in our previous study, to induce serum anti-DNA responses in BALB/c, NZB and lupus-prone NZB/W F1 mice. Out of such anti-phthalate responses, cross-reactive populations were identified that strongly bind phthalate, DNA, or both. A phthalate-specific BALB/c monoclonal antibody, 2C3-Ig (gamma1,kappa), showed considerable affinity for DNA and had extensive sequence homology with the heavy and light chain variable regions of a known anti-DNA immunoglobulin, BV04-01, from lupus-prone NZB/W F1 mice. This study was initiated to address how BALB/c mice, but not NZB/W F1 mice, are protected from these adverse autoreactive B cells. Using 2C3 hybridoma cells as the prototype autoreactive BALB/c B cell, we determined whether its DNA-binding monoclonal antibody would induce any regulatory cell-mediated immune responses. Synthetic idiopeptides corresponding to the heavy and light chain variable regions of 2C3-Ig were found to be effective at inducing specific effector cells in BALB/c mice, but not in lupus-prone F1 mice. The splenocytes from BALB/c mice incubated in vitro with the idiopeptides, particularly the complementarity-determining region 1 (VL1) of the 2C3-Ig light chain, showed significant proliferative and cytolytic responses. A CD8+ cytotoxic T-lymphocyte (CTL) response was elicited that recognized the VL1 peptide presented by the Kd allele, and affected the growth of 2C3 cells. In vivo depletion of CD8+ T cells in BALB/c mice significantly decreased this CTL activity but increased the anti-DNA humoral response. These results suggest that autoreactive CTLs are induced in non-autoimmune prone mice as a mechanism to downregulate self-reactive B cells.

Mechanisms of autoimmunity

Autoimmunity results from the failure of self-tolerance of the adaptive immune system. The reactivity of antibodies and T cells against endogenous antigens frequently causes organ damage, and consequent autoimmune disease. Systemic lupus erythematosus (SLE) is an extreme example of such a breakdown of tolerance. Our studies with spontaneous genetic mouse models of SLE and an experimentally induced model have elucidated many of the underlying cellular and genetic mechanisms of this immune dysregulation. We find that the B cell plays a key central role in this process and represents an attractive target for therapeutic intervention.

Studies of murine systemic autoimmunity

Systemic autoimmunity is an important clinical problem, offering a window into fundamental questions of self-nonself tolerance. We have used cellular immunology, serology, and immunopathology to approach several spontaneous mouse models. Although much remains to be done, a picture is emerging of pathological antigen-driven immune responses to self nuclear antigens, highly dependent on multiple genes, and susceptible to abnormalities of apoptosis.

Autoreactive responses to an environmental factor: 1. phthalate induces antibodies exhibiting anti-DNA specificity

Environmental factors have been implicated in the induction of autoimmune disorders. We report here that a common chemical, phthalate, used widely in synthetic polymers and cosmetics induces serum anti-self DNA antibodies in BALB/c, NZB and autoimmune-prone NZB/W F1 mice. The latter group experiences a high mortality, and significantly higher anti-DNA antibody levels along with nephritis and other histopathologic changes in kidney. Comparison of amino acid sequences of an anti-phthalate BALB/c B-cell hybrid, 2C3 with the known database at the National Center for Biotechnology Information reveals a striking homology between the variable regions of 2C3-Ig (gamma1, kappa) and an anti-DNA antibody, BV04-01 (gamma2b,kappa) isolated from the lupus-prone NZB/W F1 mice. The homology is 98% for kappa light chain and 70% for gamma heavy chain. Like 2C3-Ig, BV04-01 also has specificity for d(pT)4. Furthermore, the light chains of both 2C3-Ig and BV04-01 are products of Vkappa1 gene. To understand the nature of anti-phthalate responses in general, hybridomas generated from phthalate-keyhole limpet haemocyanin-primed BALB/c splenocytes were characterized. The study identifies cross-reactive populations that strongly bind phthalate, DNA, or both. Of the 14 hybridomas evaluated, six express the same Vkappa1 gene-derived light chain as 2C3, and bind both phthalate and ds and ss-DNA. They specifically recognize the oligonucleotides, d(pT)4, and d(pT)10. Additionally, when antisera raised against idiopeptides corresponding to 2C3-Ig hypervariable regions are allowed to react with 2C3-Ig, their binding is blocked specifically by both d(pT)4 and phthalate. This study clearly demonstrates that phthalate exposure leads to activation of a significant number of autoreactive B-cells, with the consequence of a significant pathogenic progression in susceptible NZB/W F1 mice but not in non-autoimmune-prone BALB/c.

Activation of natural killer T cells in NZB/W mice induces Th1-type immune responses exacerbating lupus

In vivo treatment of mice with the natural killer T (NKT) cell ligand, alpha-galactosylceramide (alphaGalCer), ameliorates autoimmune diabetes and experimental autoimmune encephalomyelitis (EAE) by shifting pathogenic Th1-type immune responses to nonpathogenic Th2-type responses. In the current study, in vivo activation of NKT cells in adult NZB/W mice by multiple injections of alphaGalCer induced an abnormal Th1-type immune response as compared with the Th2-type response observed in nonautoimmune C57BL/6 mice. This resulted in decreased serum levels of IgE, increased levels of IgG2a and IgG2a anti-double-stranded DNA (anti-dsDNA) Ab's, and exacerbated lupus. Conversely, treatment of NZB/W mice with blocking anti-CD1d mAb augmented Th2-type responses, increased serum levels of IgE, decreased levels of IgG2a and IgG2a anti-dsDNA Ab's, and ameliorated lupus. While total CD4+ T cells markedly augmented in vitro IgM anti-dsDNA Ab secretion by splenic B cells, the non-CD1d-reactive (CD1d-alphaGalCer tetramer-negative) CD4+ T cells (accounting for 95% of all CD4+ T cells) failed to augment Ab secretion. The CD1d-reactive tetramer-positive CD4+ T cells augmented anti-dsDNA Ab secretion about tenfold. In conclusion, activation of NKT cells augments Th1-type immune responses and autoantibody secretion that contribute to lupus development in adult NZB/W mice, and anti-CD1d mAb might be useful for treating lupus.

Activation of natural killer T cells in NZB/W mice induces Th1-type immune responses exacerbating lupus

In vivo treatment of mice with the natural killer T (NKT) cell ligand, alpha-galactosylceramide (alphaGalCer), ameliorates autoimmune diabetes and experimental autoimmune encephalomyelitis (EAE) by shifting pathogenic Th1-type immune responses to nonpathogenic Th2-type responses. In the current study, in vivo activation of NKT cells in adult NZB/W mice by multiple injections of alphaGalCer induced an abnormal Th1-type immune response as compared with the Th2-type response observed in nonautoimmune C57BL/6 mice. This resulted in decreased serum levels of IgE, increased levels of IgG2a and IgG2a anti-double-stranded DNA (anti-dsDNA) Ab's, and exacerbated lupus. Conversely, treatment of NZB/W mice with blocking anti-CD1d mAb augmented Th2-type responses, increased serum levels of IgE, decreased levels of IgG2a and IgG2a anti-dsDNA Ab's, and ameliorated lupus. While total CD4+ T cells markedly augmented in vitro IgM anti-dsDNA Ab secretion by splenic B cells, the non-CD1d-reactive (CD1d-alphaGalCer tetramer-negative) CD4+ T cells (accounting for 95% of all CD4+ T cells) failed to augment Ab secretion. The CD1d-reactive tetramer-positive CD4+ T cells augmented anti-dsDNA Ab secretion about tenfold. In conclusion, activation of NKT cells augments Th1-type immune responses and autoantibody secretion that contribute to lupus development in adult NZB/W mice, and anti-CD1d mAb might be useful for treating lupus.

Biology of FasL

FasL (CD95L) is a well-known and well-characterized death-inducing ligand. Spontaneous mutations in FasL and its cognate receptor Fas (CD95) have helped understand the role of these molecules in the disease. Once thought to be mainly involved in the homeostasis of immune system, the territory of FasL regulation has been expanded to angiogenesis and tumor progression. Here, we review what is currently known about the role of FasL in many areas of biology.

Effect of genetic deficiency of terminal deoxynucleotidyl transferase on autoantibody production and renal disease in MRL/lpr mice

Terminal deoxynucleotidyl transferase (TdT) places non-template-coded nucleotides (N additions) in the VH CDR3 of T cell receptors and immunoglobulins. Amino acids coded for by N additions are important in autoantibody binding of dsDNA in lupus. We hypothesized that a genetic lack of TdT would modulate disease in lupus-prone mice. To test this hypothesis, we derived TdT-deficient MRL/lpr mice. Serum levels of anti-dsDNA antibodies and anti-dsDNA producing splenocytes were significantly lower in the TdT(-) versus TdT(+) littermates. Albuminuria, glomerular IgG deposition, and pathologic renal disease were significantly reduced in the TdT(-) mice. Sequence analysis of anti-dsDNA hybridomas derived from TdT(-) mice revealed a lack of N additions, short VH CDR3 segments, yet the presence of VH CDR3 arginines. Thus, the genetic absence of TdT reduces autoantibody production and clinical disease in MRL/lpr mice, confirming the importance of N additions in the autoimmune response in these mice.

Activation of rheumatoid factor (RF) B cells and somatic hypermutation outside of germinal centers in autoimmune-prone MRL/lpr mice

Two critical questions need to be answered concerning the origins of autoreactive B cells in autoimmunity. First, how are autoreactive B cells regulated in normal situations? Second, how do such B cells escape tolerance mechanisms during autoimmunity? To address these questions, an Ig transgenic (Tg) mouse system based on the rheumatoid factor (RF) specificity has been developed. Tg mice express either the H or both H and L chains from AM14, an MRL/lpr-derived RF. Using this system, it was first shown that RF B cells are neither tolerized nor activated in a normal mouse. New insights into the timing and sites of initial RF B cell activation in MRL/lpr mice have been gained recently. RF B cells are activated. It was found, unexpectedly, that RF B cell activation, somatic hypermutation, and selection take place outside of the germinal center. We discuss the implications of this for the regulation of autoreactive B cells as well as for the regulation of hypermutation.

IL-12 deficiency in MRL-Fas(lpr) mice delays nephritis and intrarenal IFN-gamma expression, and diminishes systemic pathology

Autoimmune disease in MRL-Fas(lpr) mice is characterized by fatal nephritis, systemic pathology, and autoantibodies, mimicking human lupus. We previously reported that 1) intrarenal IL-12 elicits nephritis by fostering the accumulation of intrarenal IFN-gamma-secreting T cells, and 2) MRL-Fas(lpr) mice deficient in the IFN-gamma receptor were spared from nephritis. Therefore, we hypothesized that eliminating IL-12 in MRL-Fas(lpr) mice reduces IFN-gamma-secreting cells and thereby prevents systemic pathology. For this purpose, we constructed an IL-12p40-deficient MRL-Fas(lpr)(IL-12(-/-)) strain. We determined that glomerular and interstitial, but not perivascular, renal pathology were decreased in IL-12(-/-) mice vs the wild-type (WT) strain (5 mo of age). Similarly, systemic pathology (lung, lacrimal and salivary glands, skin, and lymphadenopathy) was diminished. The intrarenal accumulation of T cells (CD4(+), CD8(+), CD4(-)CD8(-)B220(+)) and macrophages was dramatically reduced in IL-12(-/-) MRL-Fas(lpr) kidneys. We determined that there were fewer IFN-gamma transcripts (>70%) in the IL-12(-/-) protected kidneys compared with the WT kidneys. Similarly, cells propagated from IL-12(-/-) MRL-Fas(lpr) kidneys generated substantially less IFN-gamma when stimulated with IL-12 and IL-18 compared with those from WT kidneys, and we detected fewer CD8 and B220 T cells producing IFN-gamma in these IL-12(-/-) MRL-Fas(lpr) kidneys. Of note, survival was modestly extended in the IL-12(-/-) MRL-Fas(lpr) mice. While lung and lacrimal and salivary gland pathology remained reduced in moribund IL-12(-/-) MRL-Fas(lpr) mice, renal pathology and IFN-gamma expression were equivalent to those in the WT strain. Thus, we suggest that IL-12 is a therapeutic target for multiple tissues in lupus; however blocking IL-12 alone is not sufficient to confer enduring protection from lupus nephritis.

NF-kappa B is required for surface Ig-induced Fas resistance in B cells

The susceptibility of primary murine B cells to Fas-mediated apoptosis is regulated in a receptor-specific fashion. Whereas CD40 engagement produces marked sensitivity to Fas killing, engagement of the B cell Ag receptor blocks Fas signaling for cell death in otherwise Fas-sensitive, CD40-stimulated targets and thus induces Fas resistance. The signaling pathway that leads from B cell Ag receptor to Fas resistance has not been fully characterized, but has been shown to depend on new gene expression. NF-kappa B is activated following B cell Ag receptor engagement and is associated with antiapoptosis; thus, it would seem a likely candidate to mediate transcriptional activation for inducible Fas resistance. Inhibition of B cell Ag receptor signaling for NF-kappa B activation completely blocked induction of Fas resistance by anti-Ig, and this same phenotype was observed both with chemical inhibitors such as lactacystin and pyrrolidinedithiocarbamate as well as with an I kappa B alpha dominant negative TAT fusion protein. Antiapoptotic, NF-kappa B-responsive transcripts include two gene products previously implicated in mediating anti-Ig-induced Fas resistance, Bcl-x(L) and FLIP. B cell Ag receptor-induced up-regulation of both these gene products was blocked by NF-kappa B inhibition, suggesting a mechanism by which the loss of nuclear NF-kappa B alters the sensitivity of B cell Ag receptor-stimulated B cells to Fas-mediated apoptosis. These results indicate that activation of NF-kappa B plays a key role in mediating Fas resistance produced by B cell Ag receptor engagement.

SLE - Rituximab in lupus

B cells are essential to the development of systemic lupus erythematosus (SLE). The chimeric monoclonal antibody rituximab depletes B cells by targeting the pan-B-cell surface marker CD20. Preliminary experience with this agent in SLE and other autoimmune diseases has been encouraging. Controlled trials in SLE will be necessary to determine whether rituximab is useful therapy in this disease, and will teach us more about the roles of B cells in its pathogenesis.

Genetic dissection of systemic lupus erythematosus pathogenesis: evidence for functional expression of Sle3/5 by non-T cells

On the non-autoimmune C57BL/6 (B6) background, the chromosome 7-derived lupus susceptibility loci Sle3 and Sle5 have been shown to mediate an elevated CD4:CD8 ratio with an increase in activated CD4(+) T cells, decreased susceptibility to apoptosis, and a break in humoral tolerance. Development of subcongenic strains has subsequently shown that the elevated CD4:CD8 ratio is due to Sle3 but that both loci contribute to the development of autoantibodies. To elucidate the functional expression patterns of these loci, adoptive transfer experiments were conducted. All possible combinations of bone marrow reconstitution, including syngenic, were conducted between the congenic B6 and B6.Sle3/5 strains. It was found that the Sle3/5 locus was functionally expressed by bone marrow-derived cells, but not by host cells, and that the elevated CD4:CD8 phenotype could be reconstituted in radiation chimeras. Using Ly5-marked congenic strains and B6 host mice, additional experiments surprisingly demonstrated that the elevated CD4:CD8 ratio was neither an intrinsic property of the T cells nor of single positive thymocytes. Allotype-marked chimeras indicated that autoantibody production by B cells was also an extrinsic property, as shown by the fact that B cells without the Sle3/5 interval contributed to autoantibody production. These experiments strongly suggest that a gene within the B6.Sle3/5 interval was expressed by a bone marrow-derived, nonlymphocyte population in the thymus and periphery and was affecting T cell selection and/or survival.

Immunoglobulin and autoantibody responses in MRL/lpr mice treated with 'toxic oils'

The toxic oil syndrome (TOS) occurred in Spain in 1981 as a result of ingestion of oil mixtures containing aniline-denatured rapeseed oil. The disease afflicted almost 20000 people, resulted in more than 400 deaths, and mimicked an autoimmune disease in all patients. Phenilamine-propanediol (PAP) has been implicated as a possible etiologic agent of TOS but absence of an acceptable animal model to evaluate the autoimmune potential of the 'case oil' has hindered identification of the actual etiologic agent(s). The purpose of this study was twofold; (1) to develop an animal model of human disease to investigate the immunological etiology and pathogenesis of TOS and (2) to determine if the 'case oil' responsible for TOS and/or two synthesized oils either induced or exacerbated the systemic autoimmune disease that occurs spontaneously in the MRL/lpr mouse. The oils tested were a denatured rapeseed oil collected from a family (case oil) who were affected by the TOS (CO756), a rapeseed oil denatured with 2% aniline and enriched with a mixture of diesters of PAP (RSD), and a rapeseed oil denatured with 2% aniline but contained no diesters of PAP (RSA). Female MRL/lpr mice, 7 weeks of age, received orally either an undiluted (neat) or a 1:10 diluted dose of each test oil, canola oil (oil control), water (nai;ve control), or 50-ppm mercury (positive control). Half of each group was sacrificed after 5 weeks of exposure and the remaining mice after 10 weeks of exposure. Serum IgG1, IgG2a, IgE isotypes and antinuclear (ANA), collagen type II, histone, single-stranded DNA (ssDNA), double-stranded DNA (dsDNA) and Sm autoantibody concentrations were determined after 5 and 10 weeks of exposure. The oils did not significantly affect the concentrations of the serum immunoglobulins, although a shift in the IgG1:IgG2a ratio towards IgG1 was noted from 12 to 17 weeks of age (5-10 weeks of treatment). The oils did however stimulate the systemic autoimmune response. The RSD neat treatment resulted in a nonsignificant but noted increase in autoantibodies to collagen (10 weeks), histone (10 weeks) and dsDNA (5 and 10 weeks). CO756 neat increased the serum levels of ANA (5 weeks), collagen (5 weeks) and dsDNA (5 and 10 weeks). The RSA 1:10 dilution increased ssDNA and dsDNA autoantibodies at 5 weeks. The results suggest that PAP is an active principle of these noted responses. These data, coupled with the toxicology and pathology data from this study (Toxicol. Path. 29 (2001) 630), revealed that the three oils incited induction of the lymphoproliferative syndrome and that the two oils containing PAP induced and enhanced the systemic autoimmune response that develops spontaneously at an early age in the MRL/lpr mouse. There was also a positive correlation noted between serum autoantibody concentrations and progression of the idiopathic autoimmune syndrome in the MRL/lpr mouse.

Isolation and functional analysis of autoreactive T cells from BXSB mice with murine lupus

CD4(+) T helper cells play a pivotal role in the pathogenesis of SLE, although the mechanism is still unclear. The present study was designed to isolate and characterize autoreactive T lymphocytes from BXSB mice, a mouse model for human SLE. Splenocytes from 6-month-old male BXSB mice with murine lupus were repeatedly stimulated in vitro with irradiated syngeneic B cells in the presence of recombinant IL-2, resulting in six autoreactive T-cell lines and two T-cell clones. TCR analysis showed that, one of the T-cell lines, ATL1, was almost clonal, as a Vbeta2.1-Jbeta2, a Valpha5.1-Jalpha15 and a Valpha10.1-Jalpha15 chains were predominantly expressed in this line. The two clones derived from ATL1 turned out to be sister clones, using the TCR Vbeta2.1-Jbeta2 and Valpha10.1-Jalpha15 chains. ATL1 cells proliferated in response to stimulation of syngeneic and H-2-matched allogeneic B cells and secreted IFN-gamma. Monoclonal Ab against CD4 and CD28 inhibited the proliferative response of ATL1 for syngeneic B cells. Interestingly, ATL1 did not respond to BXSB spleen or peritoneal macrophages, suggesting that B cells were able to either express accessory molecules necessary for T-cell triggering or present cryptic epitopes recognized by the autoreactive T cells. Moreover, ATL1 was able to help BXSB, but not C57BL/6, B cells producing IgG and IgM Abs against dsDNA and histone in vitro. Passive transfer of viable ATL1 cells into young female BXSB mice significantly accelerated the production of autoantibodies. Possible mechanisms of interaction between ATL1 and lupus B cells are further discussed.

Low-affinity anti-Smith antigen B cells are regulated by anergy as opposed to developmental arrest or differentiation to B-1

Understanding the regulation of B lymphocytes specific for self-Ags targeted in human and murine systemic lupus erythematosus, such as the ribonucleoprotein Smith Ag (Sm), is crucial to understanding the etiology of this autoimmune disease. To address the role of B cell receptor affinity in the regulation of anti-Sm B cells, we generated low-affinity anti-Sm transgenic mice by combining the anti-Sm 2-12H transgene with a V(kappa)8 transgene. In contrast to 2-12H transgenic mice, in which anti-Sm B cells are predominantly splenic transitional, and peritoneal B-1, low-affinity anti-Sm B cells are long-lived B-2 cells and are found in the spleen, lymph nodes, and peritoneum. However, they are unresponsive to LPS in vitro, indicating that they are anergic, although they do not down-regulate IgM and are not excluded from follicles even in the presence of nonautoreactive B cells. Thus, low-affinity anti-Sm B cells appear to have a partial form of anergy. Interestingly, these cells have elevated levels of MHC class II and CD95, but not CD40, CD80, or CD86, suggesting that they are poised to undergo deletion rather than activation upon T cell encounter. These data identify anergy as a mechanism involved in anti-Sm B cell regulation.

Evidence for an interferon-inducible gene, Ifi202, in the susceptibility to systemic lupus

The Nba2 locus is a major genetic contribution to disease susceptibility in the (NZB x NZW)F(1) mouse model of systemic lupus. We generated C57BL/6 mice congenic for this NZB locus, and these mice produced antinuclear autoantibodies characteristic of lupus. F(1) offspring of congenic and NZW mice developed high autoantibody levels and severe lupus nephritis similar to (NZB x NZW)F(1) mice. Expression profiling with oligonucleotide microarrays revealed only two differentially expressed genes, interferon-inducible genes Ifi202 and Ifi203, in congenic versus control mice, and both were within the Nba2 interval. Quantitative PCR localized increased Ifi202 expression to splenic B cells and non-T/non-B cells. These results, together with analyses of promoter region polymorphisms, strain distribution of expression, and effects on cell proliferation and apoptosis, implicate Ifi202 as a candidate gene for lupus.

Inhibition of NF-kappaB in T cells blocks lymphoproliferation and partially rescues autoimmune disease in gld/gld mice

The Fas ligand (FasL)/Fas pathway is crucial for the maintenance of homeostasis of the peripheral immune system. Its importance is illustrated by the spontaneous mouse mutants gld andlpr which lack functional FasL and Fas receptor, respectively. These animals develop lymphadenopathy, splenomegaly, increased serum Ig and autoantibodies, leading to an autoimmune syndromeand premature death. The Rel/NF-kappaB family of transcription factors plays an important role in peripheral lymphocyte proliferation and survival. In this report, we studied the consequences of T cell-specific inhibition of NF-kappaB on the development of the gld phenotype. Transgenic gld/gld mice expressing a non-degradable form of IkappaBalpha under the control of T cell-specific regulatory elements show dramatically reduced lymphadenopathy, splenomegaly, and an almost complete elimination of Thy-1(+)B220(+)CD4(-)CD8(-) abnormal T cells, correlating with reduced proliferative responses and increased apoptosis of peripheral T cells upon TCR triggering. Interestingly, the B cell abnormalities that are characteristic of gld/gld mice, such as the production of autoantibodies, high levels of serum Ig, and the development of glomerulonephritis, are partially corrected. These results suggest that the T cell-specific inhibition of NF-kappaB opens apoptotic pathways distinct from FasL/Fas which, along with a diminished proliferative response, blocks splenomegaly and lymphadenopathy and partially rescues autoimmune disease in gld/gld mice.

Autoimmune disease: why and where it occurs

Autoimmune disease is controlled by genetic and environmental factors. Both of these affect susceptibility to autoimmunity at three levels: the overall reactivity of the immune system, the specific antigen and its presentation, and the target issue.

Anti-Sm B cell differentiation in Ig transgenic MRL/Mp-lpr/lpr mice: altered differentiation and an accelerated response

To determine the regulation of B cells specific for the ribonucleoprotein Sm, a target of the immune system in human and mouse lupus, we have generated mice carrying an anti-Sm H chain transgene (2-12H). Anti-Sm B cells in nonautoimmune 2-12H-transgenic (Tg) mice are functional, but, in the absence of immunization, circulating anti-Sm Ab levels are not different from those of non-Tg mice. In this report, we compare the regulation of anti-Sm B cells in nonautoimmune and autoimmune MRL/Mp-lpr/lpr (MRL/lpr) and bcl-2-22-Tg mice. Activation markers are elevated on splenic and peritoneal anti-Sm B cells of both nonautoimmune and autoimmune genetic backgrounds indicating Ag encounter. Although tolerance to Sm is maintained in 2-12H/bcl-2-22-Tg mice, it is lost in 2-12H-Tg MRL/lpr mice, as the transgene accelerates and increases the prevalence of the anti-Sm response. The 2-12H-Tg MRL/lpr mice have transitional anti-Sm B cells in the spleen similar to nonautoimmune mice. However, in contrast to nonautoimmune mice, there are few if any peritoneal anti-Sm B-1 cells. These data suggest that a defect in B-1 differentiation may be a factor in the loss of tolerance to Sm and provide insight into the low prevalence of the anti-Sm response in lupus.

Early cellular events in systemic autoimmunity driven by chromatin-reactive T cells

In vivo exposure of the thymus of normal mice to procainamide-hydroxylamine, a lupus-inducing drug, causes development of chromatin-reactive T cells. Autoantibodies subsequently appear, but their origin and significance are unknown. The current studies were undertaken to determine the specificities of B cells that respond to chromatin-reactive T cells at the initiation of this autoimmune process. Three days after adoptive transfer of 6 x 10(6) chromatin-reactive T cells, B cells with the capacity to secrete IgM anti-chromatin antibodies were detected in 1/10(6) splenocytes, and these became 10- to 50-fold more numerous if either the donor T cells or the recipient had defective Fas due to the lpr allele. Five days later these mice developed IgG anti-chromatin-secreting B cells at a precursor frequency of 3-6 x 10(-5). B cells with dDNA-binding activity isolated from mice primed in vivo to a complex of methylated pigeon cytochrome c and dDNA could stimulate naive, cytochrome c-reactive T cells in vitro, demonstrating that B cells can internalize dDNA-bound proteins through their dDNA immunoblobulin receptor and can functionally present a T cell epitope. However, no capacity of chromatin for binding anti-dDNA antibodies was detected, and IgM dDNA-specific B cells did not expand when challenged with chromatin-reactive T cells in vivo. The rapid and robust expansion of anti-chromatin-secreting B cells indicates that the normal immune repertoire includes nontolerant autoreactive B cells that respond to strong T cell drive and are readily manifested if Fas-mediated activation-induced cell death is inhibited.