Inhibition of mesangial cell nitric oxide in MRL/lpr mice by prostaglandin J2 and proliferator activation receptor-gamma agonists

MRL/Mp-lpr/lpr (MRL/lpr) mice develop immune complex glomerulonephritis similar to human lupus. Glomerular mesangial cells are key modulators of the inflammatory response in lupus nephritis. When activated, these cells secrete inflammatory mediators including NO and products of cyclooxygenase perpetuating the local inflammatory response. PGJ2, a product of cyclooxygenase, is a potent in vitro inhibitor of macrophage inflammatory functions and is postulated to function as an in vivo inhibitor of macrophage-mediated inflammatory responses. We hypothesized that in lupus, a defect in PGJ2 production allows the inflammatory response to continue unchecked. To test this hypothesis, mesangial cells were isolated from MRL/lpr and BALB/c mice and stimulated with IL-1beta or LPS plus IFN-gamma. In contrast to the 2- to 3-fold increase in PGJ2 production by stimulated BALB/c mesangial cells, supernatant PGJ2 did not increase in MRL/lpr mesangial cell cultures. NO production in stimulated MRL/lpr and BALB/c mesangial cells, was blocked by PGJ2 and pioglitazone. These studies suggest that abnormalities in PGJ2 production are present in MRL/lpr mice and may be linked to the heightened activation state of mesangial cells in these mice.     

Cloning of B cells from autoimmune MRL-lpr/lpr and MRL.xid mice

The relationship between colony formation (cloning) of B cells and their activation in murine autoimmunity was investigated in MRL-lpr/lpr and MRL.xid mice. Cells from MRL-lpr/lpr mice showed similar requirements for in vitro growth as normal CBA/J and BALB/c cells, with maximal colony formation in the presence of the supporting factors lipopolysaccharide and sheep red blood cells. The frequency of colony-forming cells from MRL-lpr/lpr spleens or hapten-specific B-cell preparations was slightly greater than the two normal control strains, with this difference significant only for a comparison of BALB/c and MRL-lpr/lpr spleens. In contrast, MRL-lpr/lpr mice bearing the xid gene for B-cell immunodeficiency (MRL.xid) had markedly reduced B-cell colony formation. These mice nevertheless expressed anti-DNA antibodies, although at levels reduced from that of MRL-lpr/lpr controls. These results indicate that enhanced in vitro colony formation need not accompany B-cell hyperactivity in murine autoimmune disease and that autoantibody production can occur in mice with impairment in this growth property.     

T-cell mediated suppression in the MRL mouse

MRL/lpr mice possess an autosomal recessive gene, lpr, which is associated with lymphoproliferation and acceleration of autoimmune disease. Lymphoproliferation has been ascribed to a single gene defect predominantly affecting the T-lymphocyte component of the immune system. MRL/++ mice do not possess the lpr autosomal recessive mutation and do not develop early lymphadenopathy. T-lymphocyte functional activity was studied in these mice using the polyclonal T-cell mitogens PHA and Con A. Our results indicated a significant suppression of the spleen and lymph node response of MRL/lpr mice to these polyclonal mitogens as compared to the MRL/++ response noted as early as 6 weeks of age. In addition, there was a progressive decline in the MRL/lpr spleen and lymph node cell mitogenic responses with increasing age. Spleen and lymph node cells from 20-week MRL/lpr mice were also relatively unresponsive in the mixed lymphocyte culture reaction as compared to cells from MRL/ ++ or BALB/c mice. The in vitro proliferative response of the MRL mice was further examined with respect to possible accessory cell modulation by both macrophages and T cells. It was found that in 20-week MRL/lpr lymph nodes a significant degree of suppression of lymphocyte proliferation could be mediated by the MRL/lpr T cell. Increased lymphocyte proliferation to a mitogenic signal could only be demonstrated in those MRL/lpr mice 3 weeks of age.     

B cells are required for lupus nephritis in the polygenic, Fas-intact MRL model of systemic autoimmunity.

B cells are required for both the expression of lupus nephritis and spontaneous T cell activation/memory cell accumulation in MRL-Faslpr mice (MRL/lpr). Autoimmunity in the MRL/lpr strain is the result of Fas-deficiency and multiple background genes; however, the precise roles of background genes vs Fas-deficiency have not been fully defined. Fas-deficiency (i.e., the lpr defect) is required in B cells for optimal autoantibody expression, raising the possibility that the central role for B cells in MRL/lpr mice may not extend to MRL/+ mice and, thus, to lupus models that do not depend on Fas-deficiency ("polygenic lupus"). To address this issue, B cell-deficient, Fas-intact MRL/+ mice (JHd-MRL/) were created; and disease was evaluated in aged animals (>9 mo). The JHd-MRL/+ animals did not develop nephritis or vasculitis at a time when the B cell-intact littermates had severe disease. In addition, while activated/memory CD4+ and CD8+ T cells accumulated in B cell-intact mice, such accumulation was substantially inhibited in the absence of B cells. This effect appeared to be restricted to the MRL strain because it was not seen in B cell-deficient BALB/c mice (JHd-BALB) of similar ages. The results indicate that B cells are essential in promoting systemic autoimmunity in a Fas-independent model. Therefore, B cells have an important role in pathogenesis, generalizable to lupus models that depend on multiple genes even when Fas expression is intact. The results provide further rationale for B cell suppression as therapy for systemic lupus erythematosus.     

Lupus associated membrane protein. Changes in the sensitivity of proteases during the life span of mice with lupus

A murine monoclonal anti-DNA antibody, PME77, spontaneously produced in autoimmune B/W mouse, has been shown to react with a protein present at the surface of several cells involved in lupus pathogenesis. We have called this cell-surface protein LAMP (Lupus Associated Membrane Protein). Mild elastase treatment of lymphoid cells from non autoimmune (BALB/c or CBA/ca) mice releases five polypeptides (34, 33, 17, 16 and 14 kDa) recognized by PME77. These polypeptides are not found after treatment of these cells with papain or trypsin. When lymphoid cells from autoimmune mice (MRL/lpr/lpr and B/W) are treated with elastase, trypsin or papain, PME77 detected in all supernatants a single polypeptide of 55 kDa. It is demonstrated in the present work that: (1) this 55 kDa polypeptide is also detected in the elastase supernatant of glomeruli from MRL/lpr/lpr and B/W mice but not from BALB/c and CBA/ca mice. These results suggest that LAMP expressed at the surface of lymphoid and glomerular cells from lupus mice displays altered sensitivity to proteases. (2) The change in sensitivity to proteolytic enzymes appears between 1 and 3 weeks after birth in MRL/lpr/lpr mice. Such modifications might results in the appearance of a non-self antigen and elicit an anti-LAMP immune response.     

Fas/Fas ligand deficiency results in altered localization of anti-double-stranded DNA B cells and dendritic cells

Autoantibodies directed against dsDNA are found in patients with systemic lupus erythematosus as well as in mice functionally deficient in either Fas or Fas ligand (FasL) (lpr/lpr or gld/gld mice). Previously, an IgH chain transgene has been used to track anti-dsDNA B cells in both nonautoimmune BALB/c mice, in which autoreactive B cells are held in check, and MRL-lpr/lpr mice, in which autoantibodies are produced. In this study, we have isolated the Fas/FasL mutations away from the autoimmune-prone MRL background, and we show that anti-dsDNA B cells in Fas/FasL-deficient BALB/c mice are no longer follicularly excluded, and they produce autoantibodies. Strikingly, this is accompanied by alterations in the frequency and localization of dendritic cells as well as a global increase in CD4 T cell activation. Notably, as opposed to MRL-lpr/lpr mice, BALB-lpr/lpr mice show no appreciable kidney pathology. Thus, while some aspects of autoimmune pathology (e.g., nephritis) rely on the interaction of the MRL background with the lpr mutation, mutations in Fas/FasL alone are sufficient to alter the fate of anti-dsDNA B cells, dendritic cells, and T cells.     

Elicitation of experimental allergic encephalomyelitis (EAE) in mice with the aid of pertussigen

Seeking common abnormalities in mice genetically predisposed to lupus-like autoimmune disease, we investigated (1) the ontogeny of Ia antigens (I-A/I-E) on the surfaces of resident peritoneal macrophages (rpM phi) of lupus and normal mice, (2) spontaneous and lectin-induced in vitro production of M phi-stimulating factors (interferon, IFN; M phi-activating factor, MAF; M phi-Ia-inducing/recruiting factor, MIRF), and (3) responses of rpM phi from such animals to Ia-inducing signals. Indirect immunofluorescence techniques showed that Ia+ rpM phi increased numerically during the life spans of MRL/Mp lpr/lpr, while no such increase was observed in age-matched non-lpr MRL/Mp +/+ or (MRL/Mp lpr/lpr X MRL/Mp +/+)F1 hybrid mice. However, neonatal thymectomy, which prevents lymphoproliferation and autoimmune disease in MRL/Mp lpr/lpr mice, had no effect on this enhanced M phi I-A/I-E expression. NZB mice developed a similar increase with age, whereas BXSB and (NZB X NZW)F1 lupus mice, like immunologically normal controls, had low numbers of I-A/I-E+ rpM phi. Cultured splenocytes of lupus mice, including those with high percentages of I-A/I-E+ rpM phi, did not spontaneously (in the absence of mitogens) elaborate MIRF, MAF, or IFN activity. Furthermore, concanavalin A-stimulated splenocytes from lupus mice, particularly strains with early autoimmune disease manifestations [MRL/Mp lpr/lpr, male BXSB, and female (NZB X NZW)F1] produced levels of these lymphokines that were lower than normal controls. MRL/Mp lpr/lpr and NZB rpM phi, when stimulated in vitro with the supernatant of a MIRF-producing T cell hybridoma, did not hyperrespond. Our study shows that increased I-A/I-E+ rpM phi occur in some, but not all, lupus mice and this increase does not correlate with increased spontaneous or mitogen-induced production of M phi-stimulating lymphokines nor with hyperresponsiveness to Ia-inducing signals.     

Decreased expression of the Ets family transcription factor Fli-1 markedly prolongs survival and significantly reduces renal disease in MRL/lpr mice

Increased Fli-1 mRNA is present in PBLs from systemic lupus erythematosus patients, and transgenic overexpression of Fli-1 in normal mice leads to a lupus-like disease. We report in this study that MRL/lpr mice, an animal model of systemic lupus erythematosus, have increased splenic expression of Fli-1 protein compared with BALB/c mice. Using mice with targeted gene disruption, we examined the effect of reduced Fli-1 expression on disease development in MRL/lpr mice. Complete knockout of Fli-1 is lethal in utero. Fli-1 protein expression in heterozygous MRL/lpr (Fli-1(+/-)) mice was reduced by 50% compared with wild-type MRL/lpr (Fli-1(+/+)) mice. Fli-1(+/-) MRL/lpr mice had significantly decreased serum levels of total IgG and anti-dsDNA Abs as disease progressed. Fli-1(+/-) MRL/lpr mice had significantly increased splenic CD8(+) and naive T cells compared with Fli-1(+/+) MRL/lpr mice. Both in vivo and in vitro production of MCP-1 were significantly decreased in Fli-1(+/-) MRL/lpr mice. The Fli-1(+/-) mice had markedly decreased proteinuria and significantly lower pathologic renal scores. At 48 wk of age, survival was significantly increased in the Fli-1(+/-) MRL/lpr mice, as 100% of Fli-1(+/-) MRL/lpr mice were alive, in contrast to only 27% of Fli-1(+/+) mice. These findings indicate that Fli-1 expression is important in lupus-like disease development, and that modulation of Fli-1 expression profoundly decreases renal disease and improves survival in MRL/lpr mice.     

The Upregulation of Genomic Imprinted DLK1-Dio3 miRNAs in Murine Lupus Is Associated with Global DNA Hypomethylation

Epigenetic factors such as DNA methylation and microRNAs (miRNAs) are now increasingly recognized as vital contributors to lupus etiology. In this study, we investigated the potential interaction of these two epigenetic factors in lupus-prone MRL-lpr mice. We recently reported dysregulated expression of miRNAs in splenocytes of MRL-lpr mice. Here, we report that a majority of the upregulated miRNAs in MRL-lpr mice is located at the genomic imprinted DLK1-Dio3 domain. Further, we show a differential magnitude of upregulation of DLK1-Dio3 miRNA cluster in purified splenic CD4⁺ T, CD19⁺ B, and splenic CD4^-CD19^- cells from MRL-lpr lupus mice when compared to control MRL mice. MRL-lpr splenocytes (especially CD19⁺ and CD4^-CD19^- subsets) were hypomethylated compared to cells from control, MRL mice. We further show that deliberate demethylation of splenocytes from control MRL mice, but not from MRL-lpr lupus mice, with specific DNA methylation inhibitor 5-Aza-2’-deoxycytidine significantly augmented DLK1-Dio3 miRNAs expression. These findings strongly indicate that the upregulation of DLK1-Dio3 miRNAs in lupus splenic cell subsets is associated with reduced global DNA methylation levels in lupus cells. There was a differential upregulation of DLK-Dio3 miRNAs among various demethylated splenic cell subsets, which implies varied sensitivity of DLK1-Dio3 miRNA cluster in these cell subsets to DNA hypomethylation. Finally, inhibition of select DLK1-Dio3 miRNA such as miR-154, miR-379 and miR-300 with specific antagomirs significantly reduced the production of lupus-relevant IFNγ, IL-1β, IL-6, and IL-10 in lipopolysaccharide (LPS) activated splenocytes from MRL-lpr mice. Our study is the first to show that DNA methylation regulates genomic imprinted DLK1-Dio3 miRNAs in autoimmune lupus, which suggests a connection of DNA methylation, miRNA and genomic imprinting in lupus pathogenesis.     

Effects of Arsenic Trioxide on INF-gamma Gene Expression in MRL/lpr Mice and Human Lupus

Arsenic trioxide (As2O3; ATO), a traditional Chinese medicine, is used to treat patients with acute promye-locytic leukemia, while its application for treatment of systemic lupus erythematosus (SLE) is still under evaluation. The high expression of INF-gamma (INF-γ) is a primary pathogenic factor in SLE. It is found that ATO can reduce INF-γ expression levels in lupus-prone mice, whereas it is not clear whether ATO has the same effect on SLE patients. Therefore, this study was to investigate the underlying mechanism of the effects of ATO on the expression of INF-γ in splenocytes of MRL/lpr mice and PBMCs of human lupus. The mRNA and protein expression levels of INF-γ were assessed by real-time RT-PCR and ELISA, respectively. The histone acetylation status of the INF-γ promoter and the binding of RNA polymerase II (RNA Pol II) to the INF-γ promoter were detected using a chromatin immunoprecipitation (ChIP) technique. The mRNA and protein expression levels of INF-γ decreased in both splenocytes of MRL/lpr mice and PBMCs of SLE patients with ATO treatment, which were accompanied by reduced histone H4 and H3 acetylation in INF-γ promoter and decreased combination of RNA Pol II to the INF-γ promoter. Therefore, ATO may reduce the expression level of the INF-γ by altering the levels of INF-γ promoter acetylation and the combination of RNA Pol II to the INF-γ promoter in splenocytes of MRL/lpr mice and PBMCs of SLE patients.     

Mesenchymal stem cell transplantation inhibits abnormal activation of Akt/GSK3β signaling pathway in T cells from systemic lupus erythematosus mice

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by activation and proliferation of autoreactive T cells and B cells. We examined changes in cell cycle progression of T cells from MRL/lpr mice with or without allogenic bone marrow mesenchymal stem cells (BMMSCs) treatment and analyzed the expression of cell cycle associated proteins. In addition, the Akt/GSK3β protein kinase cascade was studied. We demonstrated that high-dose MSCs transplantation effectively ameliorated disease activity in MRL/lpr mice. BMMSCs treatment inhibited G1/S transition of the abnormal lupus T lymphocytes. Moreover, it increased the expression of p21(WAF1/CIP1) and p27(Kip1) and decreased the expression of CDK2. Furthermore, high-dose MSCs inhibited abnormal activation of the Akt/GSK3β signaling pathway of T cells from MRL/lpr mice. Our results suggest that high-dose BMMSCs transplantation successfully treated MRL/lpr lupus mice by inhibiting abnormal activation of Akt/GSK3β signaling pathway of T cells.     

Roles of I-E molecule and CD28 costimulation in induction of suppression by staphylococcal enterotoxin B in vivo.

Exposure to bacterial superantigens leads to the induction of a subsequent state of immune hyporesponsiveness. Using a transwell coculture system, a previous report demonstrated that splenocytes from staphylococcal enterotoxin B (SEB)-injected BALB/c mice secreted soluble mediators to suppress the proliferative response of naive syngeneic splenocytes to SEB stimulation. We show in the present study that, in contrast to the suppressive effect induced by SEB in BALB/c (H-2(d) haplotype), MRL(+/+), and MRL-lpr/lpr (H-2(k)) mice, SEB-primed splenocytes from I-E(-) strains such as B6, B10, A.BY (H-2(b)), and A.SW (H-2(s)) mice failed to inhibit the CD25 expression and the proliferative activity of their syngeneic naive responder splenocytes. Further results revealed that the SEB-primed cells from BALB/c, but not B6, mice inhibited the CD25 expression and proliferation of naive responder cells from either BALB/c or B6 mice, indicating the critical regulatory role of the effector cells. Unlike SEB, staphylococcal enterotoxin A induced profound suppression in both BALB/c and B6 mice. Moreover, the suppressive competence of SEB-primed splenocytes was diminished in CD28-deficient BALB/c mice. Taken together, our results indicate that when SEB is used as a stimulator in vivo, both the I-E molecule and CD28 costimulation are required for the induction of regulatory cells bearing suppressive activity.     

Enrichment of anti-glomerular antigen antibody-producing cells in the kidneys of MRL/MpJ-Fas(lpr) mice

Lupus nephritis is characterized by immune complex deposition and infiltration of inflammatory cells into the kidney including Ab-producing cells (AbPCs). Although AbPCs play a central role in the pathogenesis of immune complex glomerulonephritis in lupus, the specificity and pathogenic role of AbPCs infiltrating into the kidneys in lupus are poorly understood. To characterize AbPCs present in lupus kidneys, we isolated AbPCs from diseased MRL/MpJ-Faslpr (MRL/lpr) mouse kidneys. ELISPOT assays, using glomerular Ag (GA) extracts as Ag, demonstrated significant enhancement of anti-GA AbPCs in the kidneys as compared in peripheral blood or spleen of the same mouse. We isolated hybridomas with anti-GA specificity from MRL/lpr mouse kidneys. All the anti-GA mAbs had polyreactive binding to ssDNA, dsDNA, and IgG (i.e., rheumatoid factor), but not to histones or Sm. Sequence analysis of anti-GA Abs suggested the occurrence of somatic mutations and amino acid replacement in complementarity-determining regions with a high replacement to silent ratio resulting in charged amino acids. Intravenous administration of the monoclonal anti-GA Abs into BALB/c mice resulted in graded deposition in glomeruli paralleling their ELISA anti-GA reactivity. These results suggest that AbPCs infiltrating the kidneys in MRL/lpr mice accumulate as a result of Ag selection and likely play a pathologic role in lupus nephritis.     

Molecular evolution of catalytic antibodies in autoimmune mice.

Catalytic Abs (catAbs) preferentially evolved in autoimmune MRL/MPJ-lpr/lpr (MRL/lpr) mice upon immunization with the phosphonate transition-state analogue (TSA), but this did not happen in normal BALB/c mice. The majority of the catAbs from MRL/lpr mice were from several independent clones of the same family. Most of them had a lysine at position 95 in the heavy chain (H95), which is at the junctional region. This residue, which interacts with the phosphonate moiety of the TSA and presumably is involved in the catalytic activity, was not changed even after expansive evolution following multiple mutations. By contrast, the majority that arose from BALB/c mice were the non-catAbs, which were quite different in the sequence from the catAbs from MRL/lpr mice, but they were clonally related to one another, so most of them were originated from a single clone. In the MRL/lpr mice, the catalytic subsets that existed in the initial repertoire were effectively captured by the phosphonyl oxygens in the TSA by interacting with the lysine at H95. In the BALB/c mice, however, another noncatalytic subset with only the binding capability directed to a moiety other than the phosphonate moiety was alternatively evolved, because of the lowest abundance or elimination of the catalytic subsets.     

Interferon Regulatory Factor-5 Deficiency Ameliorates Disease Severity in the MRL/lpr Mouse Model of Lupus in the Absence of a Mutation in DOCK2

Interferon regulatory factor 5 (IRF5) polymorphisms are strongly associated with an increased risk of developing the autoimmune disease systemic lupus erythematosus. In mouse lupus models, IRF5-deficiency was shown to reduce disease severity consistent with an important role for IRF5 in disease pathogenesis. However these mouse studies were confounded by the recent demonstration that the IRF5 knockout mouse line contained a loss-of-function mutation in the dedicator of cytokinesis 2 (DOCK2) gene. As DOCK2 regulates lymphocyte trafficking and Toll-like receptor signaling, this raised the possibility that some of the protective effects attributed to IRF5 deficiency in the mouse lupus models may instead have been due to DOCK2 deficiency. We have therefore here evaluated the effect of IRF5-deficiency in the MRL/lpr mouse lupus model in the absence of the DOCK2 mutation. We find that IRF5-deficient (IRF5^−/−) MRL/lpr mice develop much less severe disease than their IRF5-sufficient (IRF5^+/+) littermates. Despite markedly lower serum levels of anti-nuclear autoantibodies and reduced total splenocyte and CD4⁺ T cell numbers, IRF5^−/− MRL/lpr mice have similar numbers of all splenic B cell subsets compared to IRF5^+/+ MRL/lpr mice, suggesting that IRF5 is not involved in B cell development up to the mature B cell stage. However, IRF5^−/− MRL/lpr mice have greatly reduced numbers of spleen plasmablasts and bone marrow plasma cells. Serum levels of B lymphocyte stimulator (BLyS) were markedly elevated in the MRL/lpr mice but no effect of IRF5 on serum BLyS levels was seen. Overall our data demonstrate that IRF5 contributes to disease pathogenesis in the MRL/lpr lupus model and that this is due, at least in part, to the role of IRF5 in plasma cell formation. Our data also suggest that combined therapy targeting both IRF5 and BLyS might be a particularly effective therapeutic approach in lupus.     

Fas and Fas ligand mutations inhibit autoantibody production in pristane-induced lupus

Mutations of Fas (lpr) or Fas ligand (gld) cause a limited lupus-like syndrome in B6 mice by interfering with the deletion of autoreactive B and/or T cells. A more generalized lupus syndrome reminiscent of that of MRL mice can be induced in nonautoimmune strains by pristane, which causes a nonspecific inflammatory response in the peritoneal cavity. We hypothesized that, as in MRL mice, the lpr and gld mutations might accelerate lupus in pristane-treated mice. Pristane-treated B6 mice developed anti-nRNP/Sm, Su, and ribosomal P Abs, but little anti-ssDNA or chromatin. In contrast, B6/lpr and B6/gld mice spontaneously developed anti-ssDNA/chromatin Abs, but not anti-nRNP/Sm/Su/ribosomal P. Unexpectedly, B6/lpr and B6/gld mice were highly resistant to the induction by pristane of IgM anti-ssDNA (2 wk) and IgG anti-nRNP/Sm/Su/ribosomal P autoantibodies (6 mo), suggesting that intact Fas signaling is necessary. Interestingly, pristane did not enhance IgG chromatin Ab production in B6/lpr or B6/gld mice, suggesting that it did not influence the production of autoantibodies that develop spontaneously in the setting of Fas deficiency. Pristane treatment also decreased lymphoproliferation in B6/lpr mice. Increased production of IL-12 was associated consistently with the production of anti-nRNP/Sm/Su/ribosomal P as well as anti-DNA/chromatin. In contrast, production of anti-DNA/chromatin Abs was associated with IL-6 overproduction in pristane-treated mice, but not in lpr mice. The data strongly support the idea that different subsets of autoantibodies are regulated differentially by cytokine stimulation and/or Fas signaling.     

Modulation of renal disease in MRL/lpr mice genetically deficient in the alternative complement pathway factor B

In systemic lupus erythematosus, the renal deposition of complement-containing immune complexes initiates an inflammatory cascade resulting in glomerulonephritis. Activation of the classical complement pathway with deposition of C3 is pathogenic in lupus nephritis. Although the alternative complement pathway is activated in lupus nephritis, its role in disease pathogenesis is unknown. To determine the role of the alternative pathway in lupus nephritis, complement factor B-deficient mice were backcrossed to MRL/lpr mice. MRL/lpr mice develop a spontaneous lupus-like disease characterized by immune complex glomerulonephritis. We derived complement factor B wild-type (B+/+), homozygous knockout (B-/-), and heterozygous (B+/-) MRL/lpr mice. Compared with B+/- or B+/+ mice, MRL/lpr B-/- mice developed significantly less proteinuria, less glomerular IgG deposition, and decreased renal scores as well as lower IgG3 cryoglobulin production and vasculitis. Serum C3 levels were normal in the B-/- mice compared with significantly decreased levels in the other two groups. These results suggest that: 1) factor B plays an important role in the pathogenesis of glomerulonephritis and vasculitis in MRL/lpr mice; and 2) activation of the alternative pathway, either by the amplification loop or by IgA immune complexes, has a prominent effect on serum C3 levels in this lupus model.     

Differences in spermatogenesis in cryptorchid testes among various strains of mice

The purpose of the study reported here was to define strain differences in spermatogenesis in cryptorchid testes in mice. Mice of strains A/J, BALB/c, CBA/N, C3H/He, C57BL/6 (B6), ddY and ICR were found to be sensitive to heat stress attributable to experimentally induced cryptorchidism. In contrast, mice of strains AKR/N (AKR), MRL/MpJ-+/+ (M+) and MRL/MpJ-lpr/lpr (lpr) were resistant to heat stress. Relative increases of apoptotic cells were detected in the sensitive group, but not in the resistant group. A decrease of proliferating cell nuclear antigen-immunoreactive cells after experimentally induced cryptorchidism was observed only in the sensitive group. These results suggested that heat stress-resistant germ cells were present in MRL and AKR strains, possibly originating from the genetic background.     

Functional consequences of the developmental arrest and follicular exclusion of anti-double-stranded DNA B cells

Anti-dsDNA B cells are actively tolerized in nonautoimmune BALB/c mice, as manifested by their developmental arrest, follicular exclusion, and rapid turnover rate. Previously, we have documented changes in the maturation status and follicular localization of anti-dsDNA B cells in autoimmune-prone MRL (+/+ and lpr/lpr) mice. To determine whether these differences in developmental status and follicular localization affect the functional capacity of anti-dsDNA B cells, we have now compared their in vivo life spans and their responses to in vitro stimuli. Our study shows that although anti-dsDNA B cells from both BALB/c and MRL-+/+ mice are localized to the T/B interface, only those in BALB/c mice have a rapid turnover rate. Therefore, the immature status and not the exclusion from the B cell follicle correlates with a shortened life span. Interestingly, apoptotic anti-dsDNA B cells were not detected at the T/B interface in BALB/c mice, suggesting that they are not dying there. This study also demonstrates that anti-dsDNA B cells, regardless of maturation status or follicular localization, are able to proliferate and up-regulate the costimulatory molecule B7-2 in response to CD40 ligand and IL-4. Therefore, one of the critical in vivo differences between anti-dsDNA B cells in BALB/c and MRL-+/+ mice compared with MRL-lpr/lpr mice may be the availability of T cell help.