The MRL Model: A Valuable Tool in Studies of Autoimmunity-Brain Interactions

The link between systemic autoimmunity, brain pathology, and aberrant behavior is still a largely unexplored field of biomedical science. Accumulating evidence points to causal relationships between immune factors, neurodegeneration, and neuropsychiatric manifestations. By documenting autoimmunity-associated neuronal degeneration and cytotoxicity of the cerebrospinal fluid from disease-affected subjects, the murine MRL model had shown high validity in revealing principal pathogenic circuits. In addition, unlike any other autoimmune strain, MRL mice produce antibodies commonly found in patients suffering from lupus and other autoimmune disorders. This review highlights importance of the MRL model as a useful preparation in understanding the links between immune system and brain function.

Anti-chromatin antibodies drive in vivo antigen-specific activation and somatic hypermutation of rheumatoid factor B cells at extrafollicular sites

A dominant type of spontaneous autoreactive B cell activation in murine lupus is the extrafollicular generation of plasmablasts. The factors governing such activation have been difficult to identify due to the stochastic onset and chronic nature of the response. Thus, the ability to induce a similar autoreactive B cell response with a known autoantigen in vivo would be a powerful tool in deciphering how autoimmune responses are initiated. We report here the establishment and characterization of a system to initiate autoreactive extrafollicular B cell responses, using IgG anti-chromatin antibodies, that closely mirrors the spontaneous response. We demonstrate that exogenously administered anti-chromatin antibody, presumably by forming immune complexes with released nuclear material, drives activation of rheumatoid factor B cells in AM14 Tg mice. Anti-chromatin elicits autoreactive B cell activation and development into antibody-forming cells at the T zone/red pulp border. Plasmablast generation occurs equally in BALB/c, MRL/+ and MRL/lpr mice, indicating that an autoimmune-prone genetic background is not required for the induced response. Importantly, infused IgG anti-chromatin induces somatic hypermutation in the absence of a GC response, thus proving the extrafollicular somatic hypermutation pathway. This system provides a window on the initiation of an autoantibody response and reveals authentic initiators of it.

The characteristics of hematopoietic stem cells from autoimmune-prone mice and the role of neural cell adhesion molecules in abnormal proliferation of these cells in MRL/lpr mice

BACKGROUND AND OBJECTIVES

Using various animal models for autoimmune diseases, we have previously shown that such diseases are stem cell disorders.1 In order to understand how autoimmune diseases develop, we investigated the distinct qualitative differences between hematopoietic stem cells (HSC) from normal and autoimmune-prone mice.

DESIGN AND METHODS

We studied the major histocompatibility complex (MHC) restriction between HSC and stromal cells in vitro and in vivo. We also examined the ability of HSC to adhere to a stromal cell line and, using flow cytometry, analyzed the expression of various adhesion molecules in HSC before and after the onset of autoimmune disease. In addition, the effect of antibodies to anti-adhesion molecules on the proliferation of HSC was investigated.

RESULTS

The abnormal HSC of MRL/lpr mice showed no MHC restriction (or preference) with stromal cells either in vitro or in vivo, although there was MHC restriction between normal HSC and stromal cells, as we previously reported.2,3 The abnormal HSC of MRL/lpr mice exhibited enhanced adhesion to stromal cells in vitro and expressed a higher amount of adhesion molecules such as neural cell adhesion molecule (NCAM). Interestingly, the proliferation of HSC in MRL/lpr mice was significantly suppressed by anti-NCAM monoclonaal antibodies.

INTERPRETATION AND CONCLUSIONS

Abnormal HSC of MRL/lpr mice are more resilient than normal HSC. Furthermore, among various adhesion molecules, only NCAM shows increased expression on HSC of MRL/lpr mice after the onset of autoimmune diseases, and these molecules contribute to the enhanced proliferation capacity of abnormal HSC in MRL/lpr mice. The present findings suggest that there are intrinsic qualitative differences between HSC from normal and autoimmune-prone MRL/lpr mice.

Membranous glomerulonephritis development with Th2-type immune deviations in MRL/lpr mice deficient for IL-27 receptor (WSX-1)

MRL/lpr mice develop spontaneous glomerulonephritis that is essentially identical with diffuse proliferative glomerulonephritis (World Health Organization class IV) in human lupus nephritis. Lupus nephritis is one of the most serious complications of systemic lupus erythematosus. Diffuse proliferative glomerulonephritis is associated with autoimmune responses dominated by Th1 cells producing high levels of IFN-gamma. The initial mounting of Th1 responses depends on the function of the WSX-1 gene, which encodes a subunit of the IL-27R with homology to IL-12R. In mice deficient for the WSX-1 gene, proper Th1 differentiation was impaired and abnormal Th2 skewing was observed during infection with some intracellular pathogens. Disruption of the WSX-1 gene dramatically changed the pathophysiology of glomerulonephritis developing in MRL/lpr mice. WSX-1-/- MRL/lpr mice developed disease resembling human membranous glomerulonephritis (World Health Organization class V) with a predominance of IgG1 in glomerular deposits, accompanied by increased IgG1 and IgE in the sera. T cells in WSX-1-/- MRL/lpr mice displayed significantly reduced IFN-gamma production along with elevated IL-4 expression. Loss of WSX-1 thus favors Th2-type autoimmune responses, suggesting that the Th1/Th2 balance may be a pivotal determinant of human lupus nephritis development.

B lymphocytes mediate Fas-dependent cytotoxicity in MRL/lpr mice

The Fas/Fas ligand (FasL) pathway is one of the two major effector mechanisms of T cell-mediated cytotoxicity. To prevent nonspecific killing by lymphoid cells, FasL expression on the cell surface of immune effector cells is strictly regulated. However, MRL/lpr autoimmune-prone mice massively overexpress FasL on their T lymphocytes, which render them able to kill Fas+ targets in vitro and in vivo. It is surprising that we show in the present work that B lymphocytes purified from MRL/lpr spleen cells express FasL to the same extent as T cells at the mRNA and protein level. These B cells are potent cytotoxic effectors against Fas+ but not Fas- targets. The B lymphocyte effectors were used ex vivo without any in vitro activation by B cell stimuli. Furthermore, we found that MRL/lpr B lymphocytes have the same cytotoxic potential as natural killer cells, which have been characterized as potent, Fas-mediated, cytotoxic effectors. The level of membrane-anchored FasL increases with the size of the B cell and cell-surface activation marker CD69 expression, indicating that the expression of FasL is up-regulated in parallel with the activation state of the B cell. The activated B cell population contained the major cytotoxic activity, and a minor part was associated with CD138/Syndecan-1+ plasma cells.

MRL/Mp CD4+,CD25- T cells show reduced sensitivity to suppression by CD4+,CD25+ regulatory T cells in vitro: a novel defect of T cell regulation in systemic lupus erythematosus

OBJECTIVE

To investigate the hypothesis that loss of suppression mediated by peripheral CD4+,CD25+ regulatory T cells is a hallmark of systemic lupus erythematosus (SLE).

METHODS

Mice of the MRL/Mp strain were studied as a polygenic model of SLE. Following immunomagnetic selection, peripheral lymphoid CD25+ and CD25- CD4+ T cells were cultured independently or together in the presence of anti-CD3/CD28 monoclonal antibody-coated beads. Proliferation was assessed by measuring the incorporation of tritiated thymidine.

RESULTS

While MRL/Mp CD4+,CD25+ regulatory T cells showed only subtle abnormalities of regulatory function in vitro, syngeneic CD4+,CD25- T cells showed significantly reduced sensitivity to suppression, as determined by crossover experiments in which MRL/Mp CD4+,CD25- T cells were cultured with H-2-matched CBA/Ca CD4+,CD25+ regulatory T cells in the presence of a polyclonal stimulus.

CONCLUSION

Our findings highlight a novel defect of peripheral tolerance in SLE. Identification of this defect could open new opportunities for therapeutic intervention.

T-bet as a possible therapeutic target in autoimmune disease

The prominent role of pro-inflammatory cytokines produced by T helper-1 (T(H1)) cells in regulating autoimmune responses in vitro and in vivo has been demonstrated. Recent observations of T cell polarisation by regulatory transcription factors--especially T-bet (T-box expressed in T cells)--raise the question of their influence in controlling autoimmune diseases. Here, the authors summarise recent observations of the role of T-bet in controlling chronic inflammatory and autoimmune diseases and discuss the implications of these findings for future therapeutic approaches.

Unexpected autoantibody production in membrane Ig-mu-deficient/lpr mice

In the B lymphocyte lineage, Fas-mediated cell death is important in controlling activated mature cells, but little is known about possible functions at earlier developmental stages. In this study we found that in mice lacking the IgM transmembrane tail exons (muMT mice), in which B cell development is blocked at the pro-B stage, the absence of Fas or Fas ligand allows significant B cell development and maturation, resulting in high serum Ig levels. These B cells demonstrate Ig heavy chain isotype switching and autoimmune reactivity, suggesting that lack of functional Fas allows maturation of defective and/or self-reactive B cells in muMT/lpr mice. Possible mechanisms that may allow maturation of these B cells are discussed.

Nucleolin as the earliest target molecule of autoantibodies produced in MRL/lpr lupus-prone mice

To elucidate the autoantigen against which autoantibodies are produced in the earliest phase of the disease process of systemic lupus erythematosus (SLE), serum samples were collected individually and serially from 10 NZB/NZW F1 and 10 MRL/lpr mice. Using immunoblots with mouse thymoma cell (EL-4) lysates as substrates, all mice were found to generate autoantibody against an either 150-kDa, 110-kDa, 75-kDa, or 55-kDa molecule in as early as 4 weeks. Anti-DNA antibodies occurred almost at the same time or after those against these four molecules. The number of antigens reactive with autoantibodies in immunoblots increased gradually with age. Antibodies against histone molecules were produced after 8 weeks of age. Among the four antigens, the 110-kDa molecule was identified as nucleolin, which is an abundant nucleolar phosphoprotein. Nucleolin binds DNA, RNA, and nucleic acid-binding proteins such as histone H1. Nucleolin is a target of granzyme A of cytotoxic T cells, and autoantibodies against it are found in sera from patients with SLE as well as from those with various viral infections. These results indicate that nucleolin is one of the immunodominant molecules that break down self-tolerance and initiate autoantibody-spreading in a mouse model of SLE.

Autoantibody responses and pathology regulated by B7-1 and B7-2 costimulation in MRL/lpr lupus

The activation of T lymphocytes requires both Ag-mediated signaling through the TCR as well as costimulatory signals transmitted through B7-1 and/or B7-2 with CD28. The interference of B7-mediated costimulatory signals has been proposed as one immunotherapeutic intervention for the prevention autoimmune disease. This study has examined autoantibody responses and autoimmune pathology in a murine model of human systemic lupus erythematosus (SLE), the MRL-lpr/lpr mouse, genetically deficient in B7-1 or B7-2, or in mice treated with B7-1/B7-2 blocking Abs. In contrast to other studies of murine models of SLE, MRL-lpr/lpr mice treated with B7 blocking Abs exhibit strong anti-small nuclear ribonucleoprotein (snRNP) and anti-DNA autoantibody responses with some changes in isotype switching as compared with untreated animals. All MRL-lpr/lpr mice deficient in B7-1 or B7-2 produce anti-snRNP and anti-DNA titers with isotypes virtually identical with wild-type animals. However, the absence of B7-2 costimulation did interfere with the spontaneous activation and the accumulation of memory CD4+ or CD8+ T lymphocytes characteristic of wild-type MRL-lpr/lpr mice. IgG and C3 complement deposition was less pronounced in the kidneys of B7-2 deficient MRL-lpr/lpr mice, reflecting their lessor degree of glomerulonephritis. By comparison, B7-1-deficient MRL-lpr/lpr mice had more severe IgG and C3 deposits in glomeruli.

Improved generation of catalytic antibodies by MRL/MPJ-lpr/lpr autoimmune mice

To compare the abilities of different strains of mice to elicit catalytic antibodies (Abs), we determined the occurrence of esterolytic Abs in BALB/c (normal strain) and MRL/MPJ-lpr/lpr (MRL/lpr, autoimmune) mice after immunization with the transition state analog (TSA) 1. Hybridoma supernatants elicited against TSA 1 were screened by ELISA for binding to the BSA-conjugated TSA 1 (=3b), and then screened for binding to the BSA-linked short TSA 2 (=4). We obtained eight times more positives from MRL/lpr mice than from BALB/c mice by these screening steps. The monoclonal antibodies (mAbs) obtained here were examined for binding and catalytic activity. Fifteen of 25 mAbs from MRL/lpr had esterolytic activity, compared with only two of 21 mAbs from BALB/c. These results demonstrated that the occurrence of catalytic Abs was much higher in MRL/lpr mice than in BALB/c mice, which is in good agreement with the previous report by Tawfik et al. [Tawfik, D.S., Chap, R., Green, B.S., Sela, M., Eshhar, Z., 1995. Proc. Natl. Acad. Sci. U.S.A. 92, 2145-2149] using a different kind of TSA. Thus, these studies strongly suggest that using the appropriate strain can be a key factor in the efficient production of catalytic Abs. Furthermore, these mAbs were characterized to elucidate the mechanism of strain difference, and determine whether MRL/lpr mice can be used with other TSAs for the efficient production of catalytic Abs.

Factors involved in the pathogenesis of neutrophilic vasculitis in MRL/Mp-lpr/lpr mice: a model for human microscopic angiitis

Anti-neutrophil cytoplasm antibodies (ANCA) directed against myeloperoxidase (MPO) are detected in patients with microscopic angiitis. Human MPO autoantibodies stimulate neutrophil degranulation in vitro and are thought to be pathogenic. We have previously shown that MRL-lpr mice with MPO autoantibodies have a higher incidence of vasculitis than their seronegative littermates. The aim of the present study is to determine the relationship between MPO autoantibodies and microscopic angiitis. The neutrophil binding properties of anti-MPO monoclonal antibodies (mAbs) from MRL-lpr mice were tested using murine heterophils (neutrophils) present in blood and induced peritoneal exudates. MRL anti-MPO mAbs selectively bind activated neutrophils which express MPO in vitro. The pathogenicity of an IgG2b anti-MPO mAb, C6, was investigated in vivo. Anti-MPO mAb, C6 was administered to young MRL mice which had been primed with exogenous TNF alpha to induce neutrophil activation and expression of MPO. Neutrophilic vasculitis similar to microscopic angiitis occurred in 33% of MRL mice which had been treated with anti-MPO mAb. The lesions were mainly restricted to sites of previous endothelial insult which suggests an active role for injured endothelium in this pathology.

Efficient peripheral clonal elimination of B lymphocytes in MRL/lpr mice bearing autoantibody transgenes

Peripheral B cell tolerance was studied in mice of the autoimmune-prone, Fas-deficient MRL/ lpr.H-2(d) genetic background by introducing a transgene that directs expression of membrane-bound H-2Kb antigen to liver and kidney (MT-Kb) and a second transgene encoding antibody reactive with this antigen (3-83mu delta, anti-Kk,b). Control immunoglobulin transgenic (Ig-Tg) MRL/lpr.H-2(d) mice lacking the Kb antigen had large numbers of splenic and lymph node B cells bearing the transgene-encoded specificity, whereas B cells of the double transgenic (Dbl-Tg) MRL/lpr.H-2(d) mice were deleted as efficiently as in Dbl-Tg mice of a nonautoimmune B10.D2 genetic background. In spite of the severely restricted peripheral B cell repertoire of the Ig-Tg MRL/lpr.H-2(d) mice, and notwithstanding deletion of the autospecific B cell population in the Dbl-Tg MRL/lpr.H-2(d) mice, both types of mice developed lymphoproliferation and exhibited elevated levels of IgG anti-chromatin autoantibodies. Interestingly, Dbl-Tg MRL/lpr.H-2(d) mice had a shorter lifespan than Ig-Tg MRL/lpr.H-2(d) mice, apparently as an indirect result of their relative B cell lymphopenia. These data suggest that in MRL/lpr mice peripheral B cell tolerance is not globally defective, but that certain B cells with receptors specific for nuclear antigens are regulated differently than are cells reactive to membrane autoantigens.

IFN-gamma receptor signaling is essential for the initiation, acceleration, and destruction of autoimmune kidney disease in MRL-Fas(lpr) mice

CSF-1 and TNF-alpha in the kidney of MRL-Fas(lpr) mice are proximal events that precede and promote autoimmune lupus nephritis, while apoptosis of renal parenchymal cells is a feature of advanced human lupus nephritis. In the MRL-Fas(lpr) kidney, infiltrating T cells that secrete IFN-gamma are a hallmark of disease. To examine the impact of IFN-gamma on renal injury in MRL-Fas(lpr) mice, we constructed a IFN-gamma R-deficient strain. In MRL-Fas(lpr) mice lacking IFN-gamma R, circulating and intrarenal CSF-1 were absent, TNF-alpha was markedly reduced, survival was extended, lymphadenopathy and splenomegaly were prevented, and the kidneys remained protected from destruction. Mesangial cells (MC) that were signaled through the IFN-gamma R induced CSF-1 and TNF-alpha in MRL-Fas(lpr) mice. We detected a large number of apoptotic renal parenchymal cells in advanced nephritis and determined that signaling via the IFN-gamma R induces apoptosis of tubular epithelial cells (TEC), but not MC. By comparison, TNF-alpha induces apoptosis in MC, but not TEC, of the MRL-Fas(lpr) strain. Thus, IFN-gamma is directly and indirectly responsible for apoptosis of TEC and MC in MRL-Fas(lpr) mice, respectively. In conclusion, IFN-gamma R signaling is essential for the initiation (CSF-1), acceleration (CSF-1 and TNF-alpha), and apoptotic destruction of renal parenchymal cells in MRL-Fas(lpr) autoimmune kidney disease.

Enhanced lymphoproliferation and diminished autoimmunity in CD4-deficient MRL/lpr mice

MRL/lpr mice spontaneously develop an autoimmune disease with features of systemic lupus erythematosus. They also develop a lymphoproliferative disorder characterized by a massive accumulation of double-negative (DN) T cells that lack both CD4 and CD8. To clarify the role of CD4 in autoimmunity and lymphoproliferation in these mice, CD4-deficient MRL/lpr mice were generated. CD4-deficient MRL/lpr mice developed massive expansion of DN T cells in the blood, spleen, and lymph nodes, which significantly exceeded the degree of lymphoproliferation in CD4-expressing control MRL/lpr mice. Despite this lymphoproliferation, CD4-deficient MRL/lpr mice produced little, if any, antibodies to double-stranded DNA, and they had prolonged survival relative to CD4-expressing littermates. However, they eventually developed moderately severe nephritis, characterized by immunoglobulin and complement deposition in glomeruli, vasculitis, and renal infiltration by CD8+ T cells. These findings indicate that (1) lymphoproliferation in MRL/lpr mice does not require the expression of CD4; (2) autoantibody production in MRL/lpr mice is dependent on the expression of CD4 and not on the accumulation of DN T cells; and (3) the development of nephritis in MRL/lpr mice involves both CD4-dependent and CD4-independent mechanisms.

The primary site of CD4- 8- B220+ alphabeta T cells in lpr mice: the appendix in normal mice

There have been no reports on an abundance of CD4- 8- B220+ alphabeta T cells, seen in autoimmune mice carrying the lpr gene (abnormal Fas gene), in any immune organs of normal mice. We herein report, however, that such alphabeta T cells were abundant at intraepithelial sites of the appendix in normal mice. They lacked the expression of NK1.1 Ags (C57BL/6 mice), but had the morphology of granular lymphocytes and contained forbidden T cell clones in the minor lymphocyte-stimulating antigen (Mls) system (C3H/He mice with Mls-1b2a). In other words, many properties of intraepithelial T cells in the appendix resembled those ascribed to abnormal alphabeta T cells, which expand in the lymph nodes and spleen of lpr mice. In the case of lpr mice, CD4- 8- B220+ alphabeta T cells first expanded in the appendix and then extended to other organs. CD4- 8- B220+ alphabeta T cells seemed to originate in situ from c-kit+ stem cells in the appendix. These results suggest that the appendix is one of the primary sites in which CD4- 8- B220+ alphabeta T cells exist, and that these cells carry many primordial properties as prototype T cells.

Characterization of a unique anti-DNA hybridoma

We have previously described the isolation and in vitro binding properties of eight anti-DNA monoclonal antibodies (MAbs) from an MRL-lpr mouse. In light of recent reports that have indicated it is possible to isolate multiple MAbs from a single hybridoma, our pathogenic hybridoma, 11F8, was examined for evidence of similar phenomena. Chromosome counting suggested that 11F8 cells are unusual and might indeed be expressing multiple heavy and/or light chains. PCR, cloning, and sequencing of immunoglobulin heavy and light chains indicate that 11F8 displays expression of both gamma 2a and gamma 3 heavy chains at the DNA level. Flow cytometry and amino acid sequencing reveals that expression of multiple isotypes also occurs at the protein level but only a single heavy- and light-chain sequence is able to bind DNA. Based on these results, we conclude that 11F8 is an unusual hybridoma that secretes two distinct heavy and at least one light chain from a single cell, and may represent a trioma, a stable three-cell fusion.

A new role for B cells in systemic autoimmunity: B cells promote spontaneous T cell activation in MRL-lpr/lpr mice

A conventional view of the pathogenesis of systemic lupus erythematosus has emerged. The role of B cells is to secrete pathogenic autoantibodies, while the role of T cells is to provide help for autoantibody-producing B cells. A problem with this view is that spontaneous T cell activation as well as T cell infiltration of organs such as kidney and skin are prominent features in systemic lupus erythematosus patients and murine models of lupus. The identification of T cell infiltrates, in particular, suggests that autoantibody-mediated damage may be only part of the story and that T cells could also play a primary role in immune-mediated pathology. To test the role of B cells directly, we previously generated autoimmune-prone MRL-lpr/lpr mice that lack B cells. The complete absence of T cell infiltrates in these mice was surprising, and it prompted us to examine whether a key role of B cells in disease evolution is to prime autoreactive T cells. Here we demonstrate, by comparing B cell-deficient and control mice, that the expansion of activated and memory T cells in the MRL-lpr/lpr mouse is indeed highly dependent on B cells. These results suggest a novel role for B cells in autoimmune disregulation.

Hypogammaglobulinaemia occurs in Fas-deficient MRL-lpr mice following deletion of MHC class II molecules

Fas (CD95)-mediated apoptosis in B and T cells is deficient in both human autoimmune lymphoproliferative syndrome and in MRL-lpr mice, a model for systemic lupus erythematosis (SLE). Autoimmune disease in these mice is associated with polyclonal B cell activation, increased serum immunoglobulin and autoantibodies. In non-autoimmune mice MHC class II is not required for normal serum immunoglobulin expression, and previously we have shown using MHC class II-deficient MRL-lpr mice (MRL-lpr Ab-/-) that generation of specific antibodies to DNA requires MHC class II-directed T cell help. In contrast, in the present study we demonstrate that MRL-lpr Ab-/- mice also have a profound reduction of total serum immunoglobulin levels, suggesting abnormal polyclonal regulation of B cells by MHC class II-directed T cells occurs in the autoimmune MRL-lpr strain. This abrogation of immunoglobulin production does not occur in MHC class II-deficient non-obese diabetic (NOD) mice, nor in MHC class I-deficient NOD or MRL-lpr mice. Reduced immunoglobulin levels in MRL-lpr Ab-/- mice were not due to a lack of B cells or to an increased loss of circulating immunoglobulin, but were associated with reduced numbers of surface IgG-positive B cells. These results define a general abnormal regulation of B cells in MRL-lpr mice through a process requiring MHC class II, and suggest that Fas deficiency may allow expansion of totally T-dependent B cells.

Effects of sialadenitis after cellular transfer in autoimmune MRL/lpr mice

The MRL/Mp mice bearing a lymphoproliferative gene, lpr (MRL/Mp-lpr/lpr), provide an appropriate model for the study of autoimmune mechanisms leading to the destruction of salivary and lacrimal gland tissue in Sjögren's syndrome. By 7-8 weeks of age, progressive focal inflammatory cell infiltrates are observed in salivary glands. We examined the possibility of transferring this disorder into syngeneic, young animals. Spleen cells and infiltrating mononuclear cells (MNC) enzymatically eluted from salivary glands were used. The results showed that sialadenitis could be transferred in vivo to young MRL/lpr mice by splenic and salivary gland MNC. The most striking finding was observed in male recipients where the highest incidence of sialadenitis (5/5) was seen in the group injected intravenously with a small dose (1 x 10(6) of salivary gland MNC, CD8+ splenic cells alone were not able to transfer disease. On the other hand, CD4+ splenic cells induced a more severe sialadenitis compared to the control animals. The transfer of pooled cells from salivary glands resulted in the most severe and accelerating sialadenitis (P < 0.05) in female recipients compared with the control animals. Overall, the highest sialadenitis scores (> 0.10) were obtained only after transfer of CD4+ spleen cells and infiltrating salivary gland MNC. These findings indicate that sialadenitis in MRL/lpr mice is mediated by cellular mechanisms and suggest that the infiltrating MNC have the ability to accelerate autoimmune disease in the salivary glands.

The Fas-deficient SCID mouse exhibits the development of T cells in the thymus

The Fas Ag is a cell surface protein that mediates apoptosis and is highly expressed on thymocytes. However, the role of the Fas system in the thymus is unclear. To study the role of the Fas system in the thymus, we established a novel SCID mouse bearing the lpr (lymphoproliferation) mutation. Thymocytes from these mice differentiated into CD4+ CD8+ T cells and then underwent further differentiation into CD4+ CD8- or CD4- CD8+ single-positive T cells with a low surface expression of CD3, whereas B cell development remained unrescued. These TCR-positive T cells can proliferate in response to stimulation with PMA plus ionomycin, but not with third-party spleen cells. Furthermore, thymocytes from scid/lpr mice had a great variety of TCR Vbeta repertoires. These results suggest that the Fas system plays an essential role in regulating the development of intrathymic T cells as well as peripheral T cells.

Linomide administration to mice attenuates the induction of nitric oxide synthase elicited by lipopolysaccharide-activated macrophages and prevents nephritis in MRL/Mp-lpr/lpr mice

Nitric oxide is involved as a messenger molecule in a large number of physiologic and pathologic responses. Local generation of high nitric oxide output through the expression of the calcium-independent, cytokine-inducible form of nitric oxide synthase (iNOS) can result in either protective or damaging effects. The development of drugs that specifically suppress iNOS expression or inhibit its activity may therefore provide an excellent therapeutic tool for treatment of a diverse set of dysfunctions, including asthma, inflammatory processes, and autoimmune disease. We show compelling evidence that linomide, an immunomodulator known to ameliorate autoimmune diseases, prevents accumulation in the macrophages of mRNA encoding iNOS in mice injected with LPS. This effect is partially mediated by the blocking of TNF-alpha and IL-beta production by activated macrophages. Here, we also present evidence that kidneys from MRL/Mp-lpr/lpr mice express high iNOS levels when the mice develop glomerulonephritis. The administration of linomide to MRL/Mp-lpr/lpr mice significantly decreases iNOS mRNA levels and prevents the development of glomerulonephritis, extending the half-life of mice of this strain. This linomide effect is compatible with its role in preventing the development of autoimmune disease and extends its possible use to other pathologic manifestations associated with iNOS expression, such as the systemic lupus erythematosus-associated glomerulonephritis present in MRL/Mp-lpr/lpr mice.

Fas (CD95) expression and death-mediating function are induced by CD4 cross-linking on CD4+ T cells

The CD4 receptor contributes to T-cell activation by coligating major histocompatibility complex class II on antigen presenting cells with the T-cell receptor (TCR)/CD3 complex, and triggering a cascade of signaling events including tyrosine phosphorylation of intracellular proteins. Paradoxically, CD3 cross-linking prior to TCR stimulation results in apoptotic cell death, as does injection of anti-CD4 antibodies in vivo of CD4 ligation by HIV glycoprotein (gp) 120. In this report we investigate the mechanism by which CD4 cross-linking induces cell death. We have found that CD4 cross-linking results in a small but rapid increase in levels of cell surface Fas, a member of the tumor necrosis factor receptor family implicated in apoptotic death and maintenance of immune homeostasis. Importantly, CD4 cross-linking triggered the ability of Fas to function as a death molecule. Subsequent to CD4 cross-linking, CD4+ splenocytes cultured overnight became sensitive to Fas-mediated death. Death was Fas-dependent, as demonstrated by cell survival in the absence of plate-bound anti-Fas antibody, and by the lack of CD4-induced death in cells from Fas-defective lymphoproliferative (lpr) mice. We demonstrate here that CD4 regulates the ability of Fas to induce cell death in Cd4+ T cells.

Effect of mizoribine on pulmonary lesions in MRL/lpr/lpr mice

The present study was made to investigate the effect of mizoribine (MZR), an imidazole nucleoside immunosuppressant, on pulmonary lesions and immunological mode of action of MRL/lpr/lpr mice. Four-week-old female MRL/lpr/lpr mice were injected subcutaneously with 20 mg/kg body weight of MZR every other day. For control, mice were given phosphate-buffered saline (PBS) every other day. MZR caused the delay in the histological development of peribronchial and perivascular lymphocytic infiltrations in the lungs of MRL/lpr/lpr (MRL/lpr) mice. And then, MZR suppressed the number of immunoglobulin (Ig) (IgG and IgM) secreting B cells and anti-DNA-secreting B cells in the spleen of MRL/lpr/lpr mice. The above data indicate that MZR could be useful for the treatment of pulmonary lesions associated with autoimmune disorders such as systemic lupus erythematosus (SLE).