Autoreactive T cells in MRL/Mpr-lpr/lpr mice. Characterization of the lymphokines produced and analysis of antigen-presenting cells required

Lymph node cells from 4-wk-old MRL/Mp-lpr/lpr mice, but not from MRL/Mp-+/+ mice, when cultured in vitro for 5 to 7 days, will spontaneously proliferate and produce IL-2. We examined the expression of several cell surface Ag on lymph node cells from MRL/Mp-lpr/lpr mice before and after in vitro culture. There is an increase in the expression of Thy-1, L3T4, IL-2R, T cell activating protein, T cell receptor, and T3 complex on the surface of cultured cells. Cultured cells produced IL-3, IFN-gamma, and small but detectable amounts of IL-1 in addition to IL-2. Gamma irradiation of APC from young MRL/Mp-lpr/lpr mice or treatment of APC with a mAb (J11D) and C, completely abrogated their stimulatory capacity. These experiments suggest that B cells are the predominant APC responsible in the activation of autoreactive T cells in MRL/Mp-lpr/lpr mice. Lymph node cells from C57BL/6-lpr/lpr or C3H-lpr/lpr mice were unable to spontaneously proliferate or produce IL-2. Lymph node cells from (MRL/Mp-lpr/lpr x C57BL/6-lpr/lpr) F1 mice or (C3H-lpr/lpr x MRL/Mp-lpr/lpr) F1 mice did proliferate and produced IL-2 after in vitro culture. Using T cells from these F1 animals and APC from each parental haplotype, we found that APC from MRL/Mp-lpr/lpr mice induced more proliferation and greater amounts of IL-2, when compared to APC from F1 animals. APC from C57BL6-lpr/lpr mice or C3H-lpr/lpr were unable to induce spontaneous proliferation and IL-2 production. Therefore, B cells from MRL/Mp-lpr/lpr mice appear to possess unique features that enable them to activate autoreactive T cells more effectively than B cells from other mice bearing the lpr/lpr gene.     

Influence of the Ig H chain locus on autoantibody production in autoimmune mice.

Autoimmune disease is influenced by multiple genes. In this study, we investigated the role of one genetic locus, Ig H chain. IgG2a antichromatin, anti-ssDNA, and antihistone autoantibodies (autoAb) from (MRL/Mp-lpr/lpr x C57BL/6-lpr/lpr), (Ighj/b); (C57BL/6-lpr/lpr x C57BL/6-lpr/lpr-Igha), (Ighb/a); and (MRL/Mp-lpr/lpr x MRL/Mp-lpr/lpr-Ighb), (Ighj/b) mice were determined using allotype-specific ELISA. Strikingly, antichromatin and antihistone antibodies (Ab) were comprised of significantly more b allotype than either a or j allotype in all cohorts of F1 mice examined. In mice that produced anti-Sm Ab, the b allotype was used preferentially for these autoAb as well. However, no allotype skewing was observed in IgG2a Ab directed against TNP or DNA, or for total IgG2a. An Igh recombinant locus was utilized to examine the genetic control of b allotype skewing in lpr mice and in chronic graft vs host disease. In both models, the VH region did not appear to be responsible for the preferential use of b allotype. These results indicate a contribution to autoimmunity by the Igh locus and raise the possibility that Ig allotype may influence autoimmune disease by its effect on the production of certain autoAb.     

Autoantibody in MRL/Mp-lpr/lpr mice. A monoclonal antibody specific for the abnormal T cells from mice bearing the lpr/lpr gene

We generated mAb from an unimmunized autoimmune MRL/Mp-lpr/lpr mouse. One of these mAb A108, reacted with cell surface Ag present on abnormal T cells from MRL/Mp-lpr/lpr, C3H-lpr/lpr, and C57BL/6-lpr/lpr mice. We failed to detect significant numbers of A108 bearing cells in the lymph nodes of MRL-Mp/+/+, normal C3H or normal C57BL/6 mice. Therefore, the expression of A108 correlates with the presence of the lpr/lpr gene. A108 binds to a variety of murine T cell tumor lines (e.g., EL4, BW5147, and YAC-1) and human T cell tumor lines (e.g., MOLT-3, Sup T1, and Jurkat). A108 does not bind to normal human PBL. Immunoprecipitation of surface iodinated EL-4 and BW5147 with A108 identified one major protein with a Mr of about 17.5-kDa. The significance of these findings with respect to the development of lymphoid proliferation and autoimmune disease in mice bearing the lpr/lpr gene will be discussed.     

The autoimmune mouse MRL/Mp-lpr/lpr contains cells with spontaneous cytotoxic activity against target cells bearing self-determinants

Spontaneously cytotoxic cells possessing specificity and having a complex pattern of reactivity directed at least partly against self-determinants develop by the age of 10 weeks in the autoimmune mouse strain MRL/Mp-lpr/lpr (MRL-lpr) and by the age of 6 months in C57BL/6-lprl/lpr. Similar effector cells do not develop in either MRL/Mp-+/+(MRL-+/+) or normal C57BL/6 mice up to 6 months old. Freshly prepared suspensions of both lymph node and bone marrow cells from individual MRL-lpr mice could kill Con A- or LPS-induced blast cells and fresh thymocytes from MRL-+/+ and other mouse strains with strong preference for strains carrying (self)-H-2k determinants in a 4-hr51Cr release assay. These results imply that self-reactive cells are generated as part of the lpr gene defect.     

A role for the Cr2 gene in modifying autoantibody production in systemic lupus erythematosus

Systemic lupus erythematosus is an autoimmune disease characterized by autoantibody production against nuclear Ags. Recent studies suggest that the Cr2 gene, which encodes for complement receptor (CR)1 and CR2, is important in disease susceptibility. Because the precise disease phenotype related to this gene, in isolation or in relation to other genetic loci, is not known, we analyzed C57BL/6 mice with a targeted mutation in Cr2 (C57BL/6.Cr2(-/-)) with or without a concomitant mutation in Fas (C57BL/6.lpr Cr2(-/-)). The Cr2(null) mutation in a C57BL/6.lpr background markedly increases the serum concentrations of IgG1 and IgG2b and the levels of antinuclear and anti-dsDNA Abs as compared with C57BL/6.lpr controls. There is also a trend for higher concentrations of IgG2a and IgG3. In contrast, isolated deficiencies in either these CRs or Fas have a limited effect in the production of anti-dsDNA Abs. Moreover, the Cr2(null) mutation does not affect other disease manifestations. These findings demonstrate that abnormalities in CR1 and CR2 may be linked to the production of autoantibodies by modifying the effect of other systemic lupus erythematosus susceptibility genes. Phenotypic expression of other disease manifestations need additional Cr2-independent genetic factors.     

Accelerated ischemia/reperfusion-induced injury in autoimmunity-prone mice

Natural Abs have been implicated in initiating mesenteric ischemia/reperfusion (I/R)-induced tissue injury. Autoantibodies have affinity and self-Ag recognition patterns similar to natural Abs. We considered that autoimmunity-prone mice that express high titers of autoantibodies should have enhanced I/R-induced injury. Five-month-old B6.MRL/lpr mice displayed accelerated and enhanced intestinal I/R-induced damage compared with 2-mo-old B6.MRL/lpr and age-matched C57BL/6 mice. Similarly, older autoimmune mice had accelerated remote organ (lung) damage. Infusion of serum IgG derived from 5-mo-old but not 2-mo-old B6.MRL/lpr into I/R resistant Rag-1-/- mice rendered them susceptible to local and remote organ injury. Injection of monoclonal IgG anti-DNA and anti-histone Abs into Rag-1-/- mice effectively reconstituted tissue injury. These data show that like natural Abs, autoantibodies, such as anti-dsDNA and anti-histone Abs, can instigate I/R injury and suggest that they are involved in the development of tissue damage in patients with systemic lupus erythematosus.     

Programmed death ligand 1 regulates a critical checkpoint for autoimmune myocarditis and pneumonitis in MRL mice

MRL/MpJ-Fas(lpr) (MRL-Fas(lpr)) mice develop a spontaneous T cell and macrophage-dependent autoimmune disease that shares features with human lupus. Interactions via the programmed death 1/programmed death ligand 1 (PD-1/PD-L1) pathway down-regulate immune responses and provide a negative regulatory checkpoint in mediating tolerance and autoimmune disease. Therefore, we tested the hypothesis that the PD-1/PD-L1 pathway suppresses lupus nephritis and the systemic illness in MRL-Fas(lpr) mice. For this purpose, we compared kidney and systemic illness (lymph nodes, spleen, skin, lung, glands) in PD-L1 null (-/-) and PD-L1 intact (wild type, WT) MRL-Fas(lpr) mice. Unexpectedly, PD-L1(-/-);MRL-Fas(lpr) mice died as a result of autoimmune myocarditis and pneumonitis before developing renal disease or the systemic illness. Dense infiltrates, consisting of macrophage and T cells (CD8(+) > CD4(+)), were prominent throughout the heart (atria and ventricles) and localized specifically around vessels in the lung. In addition, once disease was evident, we detected heart specific autoantibodies in PD-L1(-/-);MRL-Fas(lpr) mice. This unique phenotype is dependent on MRL-specific background genes as PD-L1(-/-);MRL(+/+) mice lacking the Fas(lpr) mutation developed autoimmune myocarditis and pneumonitis. Notably, the transfer of PD-L1(-/-);MRL(+/+) bone marrow cells induced myocarditis and pneumonitis in WT;MRL(+/+) mice, despite a dramatic up-regulation of PD-L1 expression on endothelial cells in the heart and lung of WT;MRL(+/+) mice. Taken together, we suggest that PD-L1 expression is central to autoimmune heart and lung disease in lupus-susceptible (MRL) mice.     

Autoreactivity accelerates the development of autoimmunity and lymphoproliferation in MRL/Mp-lpr/lpr mice

Lymph node T cells from autoimmune MRL/Mp-lpr/lpr mice, but not from congeneic MRL/Mp-+/+ mice, spontaneously proliferate and produce IL 2 when cultured in vitro for 5 to 7 days. This autologous activation depends critically on the length of in vitro culture and the initial culture density, indicating that cell to cell interaction may be essential. Phenotypic characterization of cultured cells suggests that both L3T4+ and Lyt-2+ T cells proliferate. However, only L3T4+ T cells produce IL 2. Mixing experiments reveal that the inability of freshly isolated lymph node cells from MRL/Mp-lpr/lpr mice to proliferate is not due to the presence of suppressor cells. Supernatant from 7-day cultures failed to induce freshly isolated cells to proliferate. Thus, the failure of freshly isolated cells to spontaneously proliferate and secrete IL 2 is not due to the inability of the cells to produce soluble mediators. Similar to the inactivation of normal T lymphocytes, in vitro addition of monoclonal anti-L3T4 or anti-IL 2 receptor antibody significantly inhibits the activation of these cultured lymphocytes. Spontaneous proliferation and IL 2 production can be blocked by the addition of monoclonal anti-I-Ak but not by monoclonal anti-I-Ad. Spontaneous proliferation and IL 2 production can be detected in young (4-wk-old) MRL/Mp-lpr/lpr mice at a time when their lymphocyte composition and physiology appear to be normal. More interestingly, spontaneous proliferation and IL 2 production cannot be detected in C57BL/6J mice bearing the lpr/lpr gene. These experiments support the notion that aberrant syngeneic autoreactivity may act as an accelerating factor in the pathogenesis of lymphoproliferation and autoimmunity in MRL/Mp-lpr/lpr mice.     

Anti-CD4 monoclonal antibody therapy suppresses autoimmune disease in MRL/Mp-lpr/lpr mice.

MRL/Mp-lpr/lpr (MRL/lpr) mice spontaneously develop systemic autoimmune disease, characterized by vasculitis, lymphadenopathy, glomerulonephritis, and autoantibody formation. The target organ inflammatory lesions are composed largely of CD4+ "helper" T cells, while the massively enlarged lymph nodes are composed primarily of CD3+ CD4- CD8- TCR alpha/beta + "double-negative" T cells. In this study we investigated the effect of treatment of MRL/lpr mice with anti-CD4 monoclonal antibody (mAb); control groups consisted of animals treated with normal saline or rat immunoglobulin (Ig). Anti-CD4 mAb treatment, which was started at 4 weeks and continued through 20 weeks of age, resulted in a dramatic reduction of both the frequency and severity of the autoimmune disease, as demonstrated histologically and serologically. Anti-CD4 mAb therapy markedly reduced the frequency of glomerulonephritis and eliminated vasculitis of the major renal arterial branches. Glomerulonephritis was detected in 9 of 9 saline-treated, 9 of 9 rat Ig-treated, but in only 1 of 9 anti-CD4 mAb-treated mice; vasculitis was detected in 6 of 9 saline-treated, 7 of 9 rat Ig-treated, but in none of 9 anti-CD4 mAb-treated mice. The frequency of antinuclear antibodies, titer of anti-dsDNA antibodies, and total Ig levels were all significantly reduced by anti-CD4 mAb therapy. These data support the hypothesis that CD4+ T cells play a central role in the disease process in this autoimmune strain.     

Autoimmune glomerulonephritis induced in congenic mouse strain carrying telomeric region of chromosome 1 derived from MRL/MpJ

In lupus erythematosus-prone mice, including the BXSB, NZW and NZB strains, telomeric regions of chromosome 1 (Chr.1) contain major glomerulonephritis susceptibility loci such as Bxs3, Sle1, and Nba2. To assess whether strain MRL, a model for lupus erythematosus, had glomerulonephritis susceptibility loci on Chr.1, we created B6.MRLc1(82-100) congenic mice carrying MRL/MpJ Chr.1 (82-100 cM) based on the C57BL/6 background and investigated renal pathology. From 6 months of age, B6.MRLc1 (82-100) showed the onset of diseases such as splenomegaly due to proliferation of CD3- or B220-positive cells, glomerular damage, and an increased serum anti-dsDNA antibody concentration, and these were earlier and severer in females. The score for glomerular damage was higher in B6.MRLc1(82-100) mice over 12 months old than in C57BL/6 or even in wild-type MRL/MpJ. Immune-complex depositions were demonstrated on glomerular basement membrane in B6.MRLc1(82-100) by immunohistochemistry and electron microscopy. For the percentage of IgG1-positive glomeruli, B6.MRLc1 (82-100) had significantly higher values than C57BL/6. In evaluations of clinical parameters, serum levels of blood urea nitrogen and the anti-dsDNA antibody in B6.MRLc1(82-100) were significantly higher than those in C57BL/6. In conclusion, B6.MRLc1(82-100) clearly developed autoimmune-mediated glomerulonephritis, and we demonstrated that MRL Chr.1 contained a novel glomerulonephritis susceptibility locus. We named this locus Mag (MRL autoimmune glomerulonephritis) and it provided new insights into the genetic basis and pathogenesis of lupus nephritis.     

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.     

IgG3 production in MRL/lpr mice is responsible for development of lupus nephritis

MRL/Mp-lpr/lpr (MRL/lpr) mice spontaneously develop lethal glomerulonephritis (GN) similar to human lupus nephritis, associated with the expression of lymphoproliferation gene lpr. To examine whether a particular IgG subclass is responsible for development of GN in these mice, first quantitative analysis of IgG subclasses in serum and in kidney eluates was performed. Although IgG2a was the dominant subclass in serum throughout the lifespan of mice, the IgG3 level in kidney eluates was three times higher than that of IgG2a at the 16 wk of age, which is the time of onset of development of severe GN. In sera of the 12-wk-old mice, half of the IgG3 was in immune complex form, whereas IgG2a in this form was only 17% of the total amount. Second, cyclosporin A, which ameliorates GN in MRL/lpr mice despite autoantibody production, was found to reduce serum IgG3 and mRNA levels, associated with the revision of cationic shift of the serum IgG3 spectrotype seen in isoelectric focusing. Third, among the hybrid mice with non-autoimmune-prone C3H/HeJ-lpr/lpr (C3H/lpr) mice, MRL/lpr x (MRL/lpr x C3H/lpr) F1, in which the genetic background for GN is likely segregated, the mRNA level for IgG3 correlated well with the degree of glomerular lesion. These findings indicate that production of IgG3 in MRL/lpr mice is one of the major factors responsible for development of GN in these mice, and that this is due to the genetic background of the MRL strain.     

Treatment of autoimmune MRL/Ipr mice with monoclonal antibody to Thy-1.2: a single injection has sustained effects on lymphoproliferation and renal disease

MRL/Mp-lpr/lpr (MRL/lpr) mice spontaneously develop an autoimmune disease characterized by anti-DNA antibodies, immune-complex glomerulonephritis, and massive proliferation of a distinct population of T cells. The proliferating T cells have the phenotype Thy-1.2+, T200+, Lyt-1+,2-,3-, but Thy-1.2 and Lyt-1 are expressed in abnormally low density. These cells appear to function as helper cells, and neonatal thymectomy prevents both lymphoproliferation and autoimmunity, which suggests that autoimmunity in MRL/lpr mice is secondary to T cell proliferation. We therefore attempted to reduce lymphoproliferation by treating MRL/lpr mice with a single injection of rat monoclonal antibody (MAb) to Thy-1.2 (30-H12, IgG2b). Mice were treated at 8 wk, before the onset of overt disease. We found that MRL/lpr mice were resistant to depletion of circulating T cells (CTC) by anti-Thy-1.2; 0.6 mg of antibody totally depleted CTC from normal mice, but had little or no effect on CTC in MRL/lpr mice. However, treatment with 6 mg of MAb against Thy-1.2 reduced CTC in MRL/lpr mice by over 70%. Moreover, this single treatment markedly reduced the proliferation of CTC over the ensuing 3 mo, despite clearance of the anti-Thy-1.2 from the circulation within 3 wk. Treated mice maintained better renal function than untreated controls, as assessed by levels of blood urea nitrogen (BUN), although anti-DNA antibodies were not significantly reduced. The effect of anti-Thy-1.2 was specific; treatment with rat MAb to the common leukocyte antigen T200 produced only a transient effect on circulating lymphocytes and did not reduce renal disease. The prolonged effects of a single injection of anti-Thy-1.2 suggest that the MAb produces a sustained alteration in immune regulation. The improvement in renal disease is in accord with evidence that autoimmune disease in MRL/lpr mice is T cell dependent. Monoclonal anti-lymphocyte antibodies may be useful in the treatment of autoimmunity.     

Abnormal IgG galactosylation and arthritis in MRL-Fas(lpr) or MRL-FasL(gld) mice are under the control of the MRL genetic background.

MRL mice bearing the lpr (Fas) or gld (Fas ligand) mutation, MRL-Fas(lpr) or MRL-FasL(gld), respectively, develop arthritis similar to rheumatoid arthritis, but C3H and C57BL/6 mice bearing such mutations do not. In MRL-Fas(lpr) mice, agalactosylated oligosaccharides in serum IgG increase significantly in comparison to MRL-+/+ mice without arthritis. In this study, an increased level of agalactosylation in IgG, as compared to MRL-+/+, was found in both MRL-Fas(lpr) and MRL-FasL(gld) mice. In contrast, the incidence of IgG without galactose was comparable among C3H-Fas(lpr), C3H-FasL(gld), and C3H-+/+ mice as well as between C57BL/6-Fas(lpr) and C57BL/6-+/+ mice. These results suggest that the increase in agalactosylated IgG and the development of arthritis in MRL-Fas(lpr) and MRL-FasL(gld) mice are controlled by the MRL genetic background.     

Abrogation of lupus nephritis in activation-induced deaminase-deficient MRL/lpr mice

We generated MRL/lpr mice deficient in activation-induced deaminase (AID). Because AID is required for Ig hypermutation and class switch recombination, these mice lack hypermutated IgG Abs. Unlike their AID wild-type littermates, AID-deficient MRL/lpr mice not only lacked autoreactive IgG Abs but also experienced a dramatic increase in the levels of autoreactive IgM. This phenotype in AID-deficient mice translated into a significant reduction in glomerulonephritis, minimal mononuclear cell infiltration in the kidney, and a dramatic increase in survival to levels comparable to those previously reported for MRL/lpr mice completely lacking B cells and well below those of mice lacking secreted Abs. Therefore, this study wherein littermates with either high levels of autoreactive IgM or autoreactive IgG were directly examined proves that autoreactive IgM Abs alone are not sufficient to promote kidney disease in MRL/lpr mice. In addition, the substantial decrease in mortality combined with a dramatic increase in autoreactive IgM Abs in AID-deficient MRL/lpr mice suggest that autoreactive IgM Abs might not only fail to promote nephritis but may also provide a protective role in MRL/lpr mice. This novel mouse model containing high levels of autoreactive, unmutated IgM Abs will help delineate the contribution of autoreactive IgM to autoimmunity.     

Spontaneous autoimmunity in 129 and C57BL/6 mice-implications for autoimmunity described in gene-targeted mice

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disorder in which complex genetic factors play an important role. Several strains of gene-targeted mice have been reported to develop SLE, implicating the null genes in the causation of disease. However, hybrid strains between 129 and C57BL/6 mice, widely used in the generation of gene-targeted mice, develop spontaneous autoimmunity. Furthermore, the genetic background markedly influences the autoimmune phenotype of SLE in gene-targeted mice. This suggests an important role in the expression of autoimmunity of as-yet-uncharacterised background genes originating from these parental mouse strains. Using genome-wide linkage analysis, we identified several susceptibility loci, derived from 129 and C57BL/6 mice, mapped in the lupus-prone hybrid (129 × C57BL/6) model. By creating a C57BL/6 congenic strain carrying a 129-derived Chromosome 1 segment, we found that this 129 interval was sufficient to mediate the loss of tolerance to nuclear antigens, which had previously been attributed to a disrupted gene. These results demonstrate important epistatic modifiers of autoimmunity in 129 and C57BL/6 mouse strains, widely used in gene targeting. These background gene influences may account for some, or even all, of the autoimmune traits described in some gene-targeted models of SLE.     

MHC class II-bound self peptides from autoimmune MRL/lpr mice reveal potential T cell epitopes for autoantibody production in murine systemic lupus erythematosus

The systemic lupus erythematosus-like syndrome in MRL/lpr mice involves high-titered IgG autoantibodies, particularly antinuclear Abs that target histones, DNA, and RNA particles. Although T cell help is required for the generation of antinuclear Abs, the epitopes recognized by such helper T cells are unknown. To address this question, we isolated and sequenced self peptides bound by MHC class II molecules from MRL/lpr mice. We identified a number of peptides that are not seen in similar preparations from nonautoimmune C3H animals. The "abnormal" peptide donors include histone, a protein component of a small nuclear ribonucleoprotein, ribosomal proteins, and RNA processing enzymes. We postulate that the peptides from these donors are T cell epitopes required for the generation of the most frequent antinuclear Abs specificities seen in MRL/lpr mice.     

Defective T cell response to presented antigen in autoimmune mice

The effect of the single autosomal recessive gene lpr on antigen presentation was studied. MRL/Mp-lpr/lpr, C3H/HeJ-lpr/lpr, C57BL/6J-lpr/lpr, and their normal congenic partners were investigated. Mice bearing the lpr gene were unable to respond to TNP-KLH when presented by syngeneic antigen-presenting cells. The congenic normal partners gave a brisk response. Mixing experiments demonstrated that the defect resided with the lpr responding T cell and not with the lpr antigen-presenting cell. Antigen-presenting cells from lpr mice were capable of inducing T cell proliferation in normal congenic partners, whereas antigen-presenting cells from normal mice failed to stimulate lpr T cells. This defect was intrinsic to an Lyt-1+2- cell. Pharmacologic restoration was attempted by in vivo and in vitro administration of interleukin 2. However, cells from lpr mice remained unaffected. The relationship of these findings to autoimmunity is discussed.     

Spontaneous Autoimmunity in 129 and C57BL/6 Mice—Implications for Autoimmunity Described in Gene-Targeted Mice

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disorder in which complex genetic factors play an important role. Several strains of gene-targeted mice have been reported to develop SLE, implicating the null genes in the causation of disease. However, hybrid strains between 129 and C57BL/6 mice, widely used in the generation of gene-targeted mice, develop spontaneous autoimmunity. Furthermore, the genetic background markedly influences the autoimmune phenotype of SLE in gene-targeted mice. This suggests an important role in the expression of autoimmunity of as-yet-uncharacterised background genes originating from these parental mouse strains. Using genome-wide linkage analysis, we identified several susceptibility loci, derived from 129 and C57BL/6 mice, mapped in the lupus-prone hybrid (129 × C57BL/6) model. By creating a C57BL/6 congenic strain carrying a 129-derived Chromosome 1 segment, we found that this 129 interval was sufficient to mediate the loss of tolerance to nuclear antigens, which had previously been attributed to a disrupted gene. These results demonstrate important epistatic modifiers of autoimmunity in 129 and C57BL/6 mouse strains, widely used in gene targeting. These background gene influences may account for some, or even all, of the autoimmune traits described in some gene-targeted models of SLE.     

Expression of a bone marrow-associated Ly-6 determinant on the T cell population expanding in the lymph nodes of the autoimmune mouse strain MRL/Mp-lpr/lpr

In this report we describe the reactivity patterns of two monoclonal anti-Ly-6.2 antibodies toward lymph node (LN) cells of the autoimmune MRL/Mp-lpr/lpr (lpr) and the normal congenic MRL/Mp-+/+ (+/+) mouse strains. The monoclonal antibody 34-11-3, which has previously been found to detect a LN-associated Ly-6.2 antigen, reacted with both lpr and +/+ LN cells. Another monoclonal antibody, 34-10-7, which has been demonstrated to detect a bone marrow- (BM) associated determinant, was found to react with a small proportion of +/+ LN cells and unexpectedly with a high percentage of lpr LN cells. The expression of this BM determinant found in the LN of lpr mice was age dependent, and its presence on Thy-1.2+ cells increased with the expansion of a subset of Lyt-1+2- cells. In contrast, dual labeling experiments showed that in +/+ and young lpr mice a small subset of Lyt-1+2+ cells express this BM-associated Ly6.2 determinant. Therefore these findings demonstrate that the lpr gene-dependent T cell expansion in the LN results in both aberrant expression and association of lymphocyte cell surface markers.