Activities of dipeptidyl peptidases in BXSB mice and MRL/lpr mice with lupus erythematosus-like syndrome

Activities of peptidases were examined in tissues of male BXSB and male MRL/Mp-lpr/lpr (MRL/lpr) mice which are animal models of human systemic lupus erythematosus. Female BXSB and male MRL/+ + mice without histopathological changes were used as controls. Activity of DPP II in the spleen, kidney, and liver showed an increase at 13 and 20 weeks of age, while that of DPP IV was decreased at 20 weeks of age, as compared to control mice. The ratio of DPP II/DPP IV activities in the tissues was significantly increased and these findings agree with our previous results in the tissues of NZB mice and in the serum of patients with lupus erythematosus, underscoring the importance of hydrolytic enzymes in the pathogenesis of autoimmune diseases.     

Responses of B cells from autoimmune mice to IL-5

Three strains of mice (NZB/W F1 X NZW (NZB/W), BXSB, and MRL/Mp-lpr/lpr (MRL/lpr] develop an autoimmune disease that is clinically and immunologically similar to human SLE. A characteristic of these mice is polyclonal B cell hyperactivity. To explore whether this may be related to hyper-responsiveness to B cell stimulatory factors, we investigated the proliferative and secretory responses of B cells from these mice to semi-purified natural and rIL-5, a major regulator of B cell development in the mouse. As this lymphokine stimulates growth and differentiation of activated B cells, attention was focused on in vivo-activated B cell populations, obtained from the interface of 50/65% Percoll density gradients, from normal or autoimmune mice. This cell population from NZB/W mice secreted IgM and incorporated [3H]TdR at significantly higher levels in response to IL-5, and was more sensitive to IL-5, than a comparable population from several normal murine strains. NZB/W female and male mice displayed heightened responses to IL-5, indicating that this is characteristic of the strain in general and is not associated with the accelerated severe disease of the females. Small resting B cells from NZB/W and normal mice were insensitive to IL-5 stimulation. In contrast to NZB/W mice, no difference was observed in the magnitude of either proliferative or Ig secretory responses between in vivo-activated B cell populations from autoimmune BXSB and MRL/lpr or normal mice. Thus, B cell hyper-responsiveness to IL-5 is a characteristic of NZB/W mice but not of two other lupus-prone murine strains. As one unique feature of NZB/W mouse B cells compared to normal and other autoimmune B cells is an elevated proportion of Ly-1+ B cells, the possibility of IL-5 hyper-responsiveness being associated with this B cell subpopulation was investigated. Fluorescence-activated cell sorter sorted Ly-1+ and Ly-1- B cells both responded to IL-5, however Ly-1+ B cells consistently showed a higher stimulation index in both proliferative and Ig secretory responses to this lymphokine.     

Defective B cell tolerance induction in New Zealand black mice. I. Macrophage independence and comparison with other autoimmune strains

B cell unresponsiveness was examined in vitro by using spleen cells from autoimmune NZB, BXSB/Mp male, MRL/Mp-Ipr/Ipr (MRL/l), and control mice, and the tolerogen trinitrophenyl human gamma-globulin (TNP-HGG). The B cell subset responsive to TNP-Brucella abortus in each autoimmune and control strain that was tested was highly susceptible to tolerance induction with the use of high epitope density conjugates (TNP30HGG and TNP32HGG). When a tolerogen with a lower epitope density was used (TNP7HGG), several control strains were all rendered tolerant in a thymic-independent and hapten-specific manner. NZB B cells were resistant to all concentrations of TNP7HGG tested, whereas B cells from BXSB/Mp male and MRL/1 mice were resistant to low concentrations of this tolerogen. NZB mice were resistant in addition to tolerance induction with TNP9HGG, TNP10HGG, and TNP12.7HGG. Experiments were performed to determine whether splenic macrophages played a role in resistance to tolerance in NZB mice. The mixing of NZB and control DBA/2J T cell-depleted splenocytes revealed no modulatory effects by the accessory cells in culture. Moreover, B cells rigorously depleted of macrophages by double Sephadex G-10 column passage exhibited characteristic patterns of resistance or susceptibility in NZB and control strains, respectively. These findings support the conclusion that resistance to tolerance in NZB mice is determined at the B cell level and are consistent with the hypothesis that diverse immunoregulatory disturbances contribute in varying degrees to the development of systemic lupus erythematosus in different inbred strains of mice.     

The effect of thymectomy on lupus-prone mice

The effect of neonatal thymectomy on the induction and/or modification of murine SLE disease was examined in several representative groups of mice with early-life SLE (MRL/Mp-lpr/lpr females, BXSB males, (NZB X W)F1 females, (NZW X BXSB)F1 males and females), late-life SLE (MRL/Mp-+/+ and BXSB females), and normal strains (BALB/c and C57BL/6 females). Our results indicated that thymectomy prevented disease only in the MRL/Mp-lpr/lpr SLE mice, and that this effect diminished as thymectomy was delayed beyond 3 wk post-natally. In the other SLE mice studied, neonatal thymectomy did not modify disease symptoms to any significant degree. Moreover, depletion of mature T cells from donor BXSB male bone marrow did not affect the expression of early-life SLE in thymectomized BXSB female recipients. Neonatal thymectomy did not induce SLE in normal mice. Of note, neonatal thymectomy did not completely deplete the Thy-1.2+ cell population, i.e., 10 to 15% remained in the spleens of the thymectomized mice. This incomplete T cell depletion, together with the previously demonstrated dependence on and hyperresponsiveness of BXSB and (NZB X W)F1 B cells to T helper cell-derived accessory signals, cast doubts on earlier conclusions that B cells from some SLE mice can autonomously proliferate and differentiate to autoantibody-secreting cells. It seems more appropriate to conclude that B cells from the various SLE mice vary in their degree of response to, and production of, T cell-derived helper signals, and thus in their expression of B cell hyperactivity and disease.     

Altered expression of self-reactive T cell receptor V beta regions in autoimmune mice.

Intrathymic tolerance results in elimination of T cells bearing self-reactive TCR V beta regions in mice expressing certain combinations of I-E and minor lymphocyte stimulatory (Mls) phenotypes. To determine if autoimmune strains of mice have a defect in intrathymic deletion of self-reactive TCR V beta regions, expression of V beta 3, V beta 6, V beta 8.1, and V beta 11 were examined in lpr/lpr and +/+ strains of mice; MRL/MpJ(H-2K, I-E+, Mlsb,), C57BL/6J(H-2b, I-E-, Mlsb,), C3H/HeJ(H-2k, I-E+, Mlsc), AKR/J(H-2k, I-E+, Mlsa); and in autoimmune NZB/N(H-2d, I-E+, Mlsa) and BXSB(H-2b, I-E-, Mlsb) mice. The results suggest that, during intrathymic development, self-reactive T cells are deleted in autoimmune strains of mice as found in normal control strains of mice. However, the TCR V beta repertoire is skewed in autoimmune strains compared to normal strains of mice. For example, MRL-lpr/lpr mice, but not other lpr/lpr strains, had increased expression of V beta 6 relative to expression in control MRL(-)+/+ mice, which is associated with collagen-induced arthritis. These data are consistent with a model of normal affinity for negative selection of self-reactive T cells in the thymus of autoimmune strains of mice followed by expansion of autoreactive T cell clones in the peripheral lymphoid organs. The peripheral lymphoid organs of lpr/lpr mice contain an expanded population of abnormal CD4-, CD8-, 6B2+ T cells. Elimination of self-reactive peripheral T cells suggests that these abnormal cells are derived from a CD4+ subpopulation in the thymus. Flow cytometry analysis of peripheral lymph node T cells from MRL-lpr/lpr mice reveal three populations of CD4+ T cells expressing low, intermediate and high intensity of B220 (6B2). This supports the hypothesis that in lpr/lpr mice, self-reactive CD4+ T cells are eliminated in the thymus, and that these cells lose expression of CD4 and acquire expression of 6B2 in the periphery.     

Biased expression of variable region gene families of the immunoglobulin heavy chain in autoimmune-prone mice

We have examined usage of variable region gene families of the immunoglobulin heavy chain (VH gene family) in spleens of MRL/MpJ-1pr/lpr (MRL/lpr), (NZB x NZW)F1, and BXSB mice by Northern analysis using various VH probes, including the VHPAR gene which we cloned and identified as a gene encoding the heavy-chain variable region of antipoly(ADP-ribose) antibody. The amount of VHS107 family mRNA was almost constant for the same amount of splenic crude RNA in autoimmune-prone and normal mice, while concentrations of other family mRNAs were elevated in autoimmune-prone mice. For example, per splenic RNA the VHPAR family was expressed in MRL/lpr mice 10 times more than in their normal counterpart, MRL/MpJ-+/+ (MRL/+) mice. These results indicate the bias of VH gene usage in autoimmune-prone mice. Expression of the VHS107 family was depressed from an early life stage of MRL/lpr and male BXSB mice. Furthermore, the expression of IL-4 and IL-5 were quantitatively compared, as B cell differentiation factor was thought to be produced by abnormally proliferative T cells in lymph nodes of MRL/lpr mice. We could not, however, observe overproduction of IL-4 and IL-5 mRNA in the lymph nodes.     

Treatment of murine lupus with monoclonal anti-T cell antibody

Three strains of autoimmune mice (MRL/lpr, NZB/NZW, and BXSB) were treated with repeated injections of rat monoclonal anti-T cell antibody (anti-Thy-1.2) in order to determine 1) the extent and duration of target cell depletion, 2) the effect of T cell depletion on the course of autoimmunity, and 3) the magnitude and consequences of the host immune response to the monoclonal antibody. Mice were treated with 6 mg of anti-Thy-1.2 every 2 wk beginning early in their disease. Treatment produced a substantial reduction in circulating T cells in all three strains. Therapy was beneficial in MRL/lpr mice. It reduced lymphadenopathy, lowered autoantibody concentrations, retarded renal disease, and prolonged life. In contrast, treatment did not improve autoimmunity in NZB/NZW mice, and it caused fatal anaphylaxis in BXSB mice. These findings demonstrate that monoclonal antilymphocyte antibodies can serve as specific probes to examine the cells that contribute to autoimmunity. Moreover, they illustrate the potential therapeutic value of monoclonal antilymphocyte antibodies when a pathogeneic cell subset can be identified. However, the same antibody may have a broad range of effects, from efficacy to severe toxicity, even in diseases that share clinical features.     

Protection of murine lupus by the Ead transgene is MHC haplotype-dependent

A high-level expression of a transgene, Ead, encoding the I-Ed alpha-chain is very effective in protection against murine lupus. To investigate the specific contribution of select H-2 haplotypes on the Ead transgene-mediated disease-suppressing effect, we generated H-2 congenic (NZB x BXSB)F1 hybrid mice bearing either H-2b/b, H-2d/b, or H-2d/d haplotype, and compared the transgene-mediated protective effect on the clinical development (autoantibody production and glomerulonephritis) of lupus in these F1 hybrids. The level of protection was most remarkable in mice bearing the I-E- H-2b/b haplotype but was only minimal in I-E+ H-2d/d F1 hybrids. Additional analysis demonstrated a marked suppression of lupus in I-E+ H-2k/k (MRL x BXSB)F1 hybrid mice, indicating that the transgene is able to suppress autoimmune responses even in mice already expressing I-E molecules at a homozygous level. Our results indicate that the level of the transgene-mediated protection is dependent on the host H-2 haplotype. This suggests that the autoimmune suppressive activity of the Ead transgene is likely to be determined through the interaction of the transgene product with the host MHC class II molecules, providing new insight into the role of MHC in lupus-like autoimmunity.     

Increased spontaneous polyclonal activation of B lymphocytes in mice with spontaneous autoimmune disease.

Early in life, mice of four kinds [NZB, (NZB X NZW)F1, MRL/1, and male BXSB] with autoimmune disease spontaneously produced far more (greater than 3 S.D.) anti-hapten antibody-forming cells in spleens and greater concentrations of anti-hapten antibodies in sera than immunologically normal strains of mice (AKR, BALB/c, C57BL/6, DBA/1-J, DBA/2J, LG/J, 129, NZW, and female BXSB). This increased nonspecific antibody production by the abnormal animals' B cells correlated well with the spontaneous development of anti-single-stranded DNA antibodies, but not with serum levels of the viral envelope glycoprotein, gp70. These results suggest that the spontaneous formation of autoantibodies in mice whose immunologic disorder is manifested by a lupus-like disease may result from polyclonal activation of B cells by endogenous or exogenous B cell activators.     

Studies of consomic mice bearing the Y chromosome of the BXSB mouse

Previous studies have demonstrated that the Y chromosome of the BXSB mouse can lead to accelerated autoimmunity in inbred BXSB mice and in F1 hybrids. To additionally study the effects of the BXSB-Y, we have studied three sets of Y-consomic mice, NZB.BXSB-Y, NZW.BXSB-Y, and CBA/J.BXSB-Y, each consisting of background genes from the non-BXSB parent and the Y chromosome from the BXSB mouse. The effect of the BXSB-Y on autoantibody production, immunopathology, and survival was assessed. We found that the CBA/J.BXSB-Y mice showed few differences from control CBA/J males. In contrast, NZW.BXSB-Y males had accelerated renal and cardiac disease and early death, resembling that previously reported for (NZW X BXSB)F1 mice. NZB.BXSB-Y males had accelerated anti-erythrocyte autoantibodies but not accelerated anti-DNA. They lived almost as long as NZB mice. The presence of the BXSB-Y in all of the consomic mice was confirmed by crossing the consomic mice with BXSB females and demonstrating accelerated disease in the male offspring. This study demonstrates that the BXSB-Y chromosome autoimmune accelerating factor does not act alone but operates through other genes, and that the effects on different genetic backgrounds are different. The studies have implications for human lupus; they also provide a basis for future molecular biology studies of the BXSB-Y and the genes upon which it acts.     

Proliferative activity of autoimmune MRL mouse serum IgG to interleukin 3-dependent cell line through autocrine mechanism

Serum of an autoimmune MRL/Mp-lpr/lpr (MRL/l) mouse supported the proliferation of interleukin 3 (IL-3)-dependent cell line, FDC-P2. This IL-3-like activity initially appeared at 1 month of age and increased with age. Females showed higher titers than did males. MRL/Mp-+/+ mouse sera also exhibited such activity, though somewhat later in life only in female. Other autoimmune mice, NZB, NZB/NZW F1, and BXSB, demonstrated no such activity in either males or females, young and old. The active component of MRL/l sera was shown to be IgG. F(ab')2 or Fc fragments of MRL/l-IgG lost such activity. Not all IL-3-dependent cell lines, however, responded to MRL/l-IgG. We subcloned MRL-IgG responding and nonresponding clones from FDC-P2 cells and both were still dependent to IL-3. Such nonresponding IL-3-dependent cell lines, however, could be stimulated by the culture supernatant of the responding cell line, FDC-P2/185-4, after being stimulated with MRL/l-IgG. In this culture supernatant, IL-3 was found, thus the existence of an autocrine system was suggested in the IL-3-dependent MRL/l-IgG responding cell line.     

C1q deficiency and autoimmunity: the effects of genetic background on disease expression

Gene-targeted C1q-deficient mice have been shown to develop a syndrome reminiscent of human systemic lupus erythematosus with antinuclear Abs and proliferative glomerulonephritis. Initial phenotypic analysis conducted in (129 x C57BL/6) hybrid mice showed that background genes were a significant factor for the full expression of the autoimmune disease. To assess the contribution of background genes in the expression of the autoimmune phenotype, the disrupted C1qa gene was backcrossed for seven generations onto C57BL/6 and MRL/Mp(+/+) strains. These were intercrossed with C57BL/6.lpr/lpr and MRL/Mp-lpr/lpr strains to generate C1q-deficient substrains. In C1q-deficient C57BL/6 mice, no evidence of an autoimmune phenotype was found, and C1q deficiency in both the C57BL/6.lpr/lpr and MRL/Mp-lpr/lpr strains did not modify the autoimmune phenotype observed in wild-type controls. However, in C1q-deficient MRL/Mp(+/+) animals an acceleration of both the onset and the severity of antinuclear Abs and glomerulonephritis was seen. Disease was particularly pronounced in females, which developed severe crescentic glomerulonephritis accompanied by heavy proteinuria. In addition, the C1q-deficient MRL/Mp(+/+) mice had an impairment in the phagocytic clearance of apoptotic cells in vivo. These data demonstrate that the expression of autoimmunity in C1q-deficient mice is strongly influenced by other background genes. The work also highlights the potential value of the C1q-deficient MRL/Mp(+/+) strain as a tool with which to dissect further the underlying mechanisms of the autoimmune syndrome associated with C1q deficiency.     

Selective modulation of CD4+ T cells from lupus patients by a promiscuous, protective peptide analog

A peptide encompassing residues 131-151 of the spliceosomal U1-70K protein and its analog phosphorylated at Ser140 were synthesized as potential candidates for the treatment of patients with lupus. Studies in the MRL/lpr and (NZB x NZW)F1 lupus models have demonstrated that these sequences contain a CD4+ T cell epitope but administration of the phosphorylated peptide only ameliorates the clinical manifestations of treated MRL/lpr mice. Binding assays with soluble HLA class II molecules and molecular modeling experiments indicate that both peptides behave as promiscuous epitopes and bind to a large panel of human DR molecules. In contrast to normal T cells and T cells from non-lupus autoimmune patients, we found that PBMCs from 40% of lupus patients selected randomly and CFSE-labeled CD4+ T cells proliferate in response to peptide 131-151. Remarkably, however, we observed that phosphorylation of Ser140 prevents CD4+ T cells proliferation but not secretion of regulatory cytokines, suggesting a striking immunomodulatory effect of phosphorylated analog on lupus CD4+ T cells that was unique to patients. The analog might act as an activator of regulatory T cells or as a partial agonist of TCR.     

Autoimmune CD4+ T cells interfere with immune tolerance to a thymic-independent antigen

The ability of autoimmune T cell subsets to interfere with tolerization of B cells can be studied by using thymic-independent Ag. We have defined an abnormality within the CD4+ T cell compartment in young NZB and MRL-lpr/lpr mice by studying tolerance of spleen and B cells to the thymic independent Ag, fluorescein-Brucella abortus. Tolerization of spleen cells is defective in MRL-lpr/lpr mice, but not MRL-+/+ or C3H.lpr mice, suggesting that the defect requires both the autosomal MRL background and the lpr gene to be present. T enriched cells from NZB mice and from MRL-lpr/lpr mice (but not MRL-+/+ or C3H.lpr mice) reverse tolerance in spleen cells from [NZB X DBA/2]F1 and C3H/HeJ mice, respectively. This interference is removed by treatment with anti-CD4 antibody and C. Supernatants from cultured T cells of NZB and MRL-lpr/lpr mice also prevent tolerance in spleen cells of [NZB X DBA/2]F1 and MRL-+/+ mice, respectively, unless CD4+ cells are removed prior to T cell culture. Removal of T cells from NZB and MRL-lpr/lpr spleen cells allows normal tolerization of B cells, which is abrogated by the addition of syngeneic T cells or cultured T cell supernatants. This effect also depends on the presence of CD4+ T cells. These studies show that in MRL-lpr/lpr mice, through interaction of the lpr and MRL background genes in a T cell subset, and in NZB mice, CD4+ T cells interfere with B cell tolerance to a thymic-independent Ag.     

Comparison of immunological effects of cholera toxin on autoimmune MRL/lpr and BXSB mice.

MRL/lpr and BXSB mice were treated weekly or biweekly with cholera toxin (CT) in intravenous dose of 2 micrograms/mouse. CT treatment notably alleviated proteinuria in MRL/lpr mice, but did not influence the course of lupus nephritis in BXSB male mice. Flow cytometric analysis showed that anomalous B220+ T cells in spleen and thymus were reduced in CT-treated MRL/lpr mice while no significant change in lymphocyte populations was induced in BXSB male mice by this treatment. The suppressive effect of CT treatment on Con A response and the augmentative action on LPS response were observed in MRL/lpr mice. The latter may reflect increased B cells in relative number in the peripheral lymphoid organs. Mitogenic responses in CT-treated BXSB male mice remained unchanged in comparison with those of untreated group. Increased production of IL-6 by spleen cells was demonstrated in MRL/lpr mice treated with CT while in BXSB mice the level of IL-6 was not changed by the treatment with CT. Production of IFN gamma was suppressed by CT treatment in both strains of mice. This may be attributed to the inhibitory effect of CT on IFN gamma-producing Th1 cells as reported previously (Munoz et al, J. Exp. Med. 172: 95-103, 1990). However, CT treatment did not inhibit anti-DNA antibody production in BXSB mice, whereas the autoantibodies were markedly decreased in MRL/lpr mice treated with CT.     

Enhanced activation of dendritic cells by autologous apoptotic microvesicles in MRL/lpr mice

IntroductionSystemic lupus erythematosus is associated with a persistent circulation of modified autoantigen-containing apoptotic debris that might be capable of breaking tolerance. We aimed to evaluate apoptotic microvesicles obtained from lupus or control mice for the presence of apoptosis-associated chromatin modifications and for their capacity to stimulate dendritic cells (DC) from lupus and control mice.MethodApoptotic microvesicles were in vitro generated from splenocytes, and ex vivo isolated from plasma of both MRL/lpr lupus mice and normal BALB/c mice. Microvesicles were analyzed using flow cytometry. Bone marrow-derived (BM)-DC cultured from MRL/lpr or BALB/c mice were incubated with microvesicles and CD40 expression and cytokine production were determined as measure of activation.ResultsMicrovesicles derived from apoptotic splenocytes or plasma of MRL/lpr mice contained more modified chromatin compared to microvesicles of BALB/c mice, and showed enhanced activation of DC, either from MRL/lpr or BALB/c mice, and consecutively an enhanced DC-mediated activation of splenocytes. The content of apoptosis-modified chromatin in microvesicles of apoptotic splenocytes correlated with their potency to induce interleukin-6 (IL-6) production by DC. Microvesicle-activated MRL/lpr DC showed a significant higher production of IL-6 and tumor growth factor-β (TGF-β) compared to BALB/c DC, and were more potent in the activation of splenocytes.ConclusionApoptotic microvesicles from MRL/lpr mice are more potent activators of DC, and DC from MRL/lpr mice appear relatively more sensitive to activation by apoptotic microvesicles. Our findings indicate that aberrations at the level of apoptotic microvesicles and possibly DC contribute to the autoimmune response against chromatin in MRL/lpr mice.     

Effects of calorie restriction on immunologic functions and development of autoimmune disease in NZB mice.

Chronic energy (calorie) intake restriction (CEIR) prolonged life, inhibited autoimmune disease, and influenced immunologic and hematologic parameters in NZB mice. Abnormalities in numbers and proportions of T and B cells populations were corrected. Deficient responses to phytomitogens, mixed lymphocyte reactions, formation of plaque-forming cells to sheep red blood cells in vitro, production of cytotoxic T lymphocytes after in vitro stimulation, and interleukin 2 production were also corrected. CEIR prevented the extreme splenomegaly that normally occurs with age in NZB mice. This influence was associated with reduction of a greatly expanded non-T, non-B lymphoid cell population. Calorie restriction also prevented in NZB mice the rapid decrease in total numbers of colony-forming B cells in bone marrow that is also characteristic of mice of this strain. The influences of CEIR on immune parameters and hematopoiesis were generally less marked in non-autoimmune-prone DBA/2 mice than in autoimmune-prone NZB mice. CEIR has been shown to produce profound influences on several strains of autoimmune-prone mice (NZB x NZW)F1, MRL/lpr, BXSB, and NZB herein). In each of these strains, the pathogenesis and manifestations of autoimmune disease are dissimilar. Therefore, it seems likely that calorie restriction acts on an as yet elusive mechanism that operates to foster development of the diseases associated with aging common to each of these autoimmune strains as well as autoimmune-resistant mice and rats. Further investigation of the molecular and cellular bases of the benefits of CEIR seems urgent.     

Autoimmune-prone mice share a promoter haplotype associated with reduced expression and function of the Fc receptor FcgammaRII

Human autoimmune diseases thought to arise from the combined effects of multiple susceptibility genes include systemic lupus erythematosus (SLE) and autoimmune diabetes. Well-characterised polygenic mouse models closely resembling each of these diseases exist, and genetic evidence links receptors for the Fc portion of immunoglobulin G (FcR) with their pathogenesis in mice and humans [1] [2] [3]. FcRs may be activatory or inhibitory and regulate a variety of immune and inflammatory processes [4] [5]. FcgammaRII (CD32) negatively regulates activation of cells including B cells and macrophages [6]. FcgammaRII-deficient mice are prone to immune-mediated disease [7] [8] [9]. The gene encoding FcgammaRII, Fcgr2, is contained in genetic susceptibility intervals in mouse models of SLE such as the New Zealand Black (NZB) contribution to the (NZB x New Zealand White (NZW)) F1 strain [1] [10] [11] and the BXSB strain [12], and in human SLE [1] [2] [3]. We therefore sequenced Fcgr2 and identified a haplotype defined by deletions in the Fcgr2 promoter region that is present in major SLE-prone mouse strains (NZB, BXSB, SB/Le, MRL, 129 [13]) and non-obese diabetic (NOD) mice but absent in control strains (BALB/c, C57BL/6, DBA/2, C57BL/10) and NZW mice. The autoimmune haplotype was associated with reduced cell-surface expression of FcgammaRII on macrophages and activated B cells and with hyperactive macrophages resembling those of FcgammaRII-deficient mice, and is therefore likely to play an important role in the pathogenesis of SLE and possibly diabetes.     

A single monoclonal anti-Ia antibody inhibits antigen-specific T cell proliferation controlled by distinct Ir genes mapping in different H-2 I subregions

A xenogeneic rat anti-mouse Ia monoclonal antibody, M5/114 (gamma 2b, kappa), was studied for its effects in vitro on T cell proliferative responses. Strain distribution studies revealed that M5/114 could inhibit I-A subregion-restricted T cell responses of the H-2b,d,q,u but not the H-2f,k,s haplotypes, indicating that this xenoantibody recognizes a polymorphic determinant on mouse Ia molecules. This same monoclonal antibody was found to inhibit BALB/c (H-2d) T cell proliferation to both G60A30T10 and G58L38 phi 4. The Ir genes regulating responses to these antigens map to either the I-A subregion (GAT), or the I-A and I-E subregions (GL phi), raising the possibility that M5/114 recognizes both I-A and I-E subregion-encoded Ia glycoproteins. It could be shown, using appropriate F1 responding cells, that M5/114 does in fact affect GAT and GL phi responses by interaction with both the I-A and the I-E subregion products, and not by any nonspecific effect resulting from binding to the I-A subregion product alone. These results are consistent with genetic and biochemical studies directly demonstrating that M5/114 recognizes A alpha A beta and E alpha E beta molecular complexes. The existence of a shared epitope on I-A and I-E subregion products suggests the possibility that these molecules arose by gene duplication. Finally, the precise correlation between the Ia molecules recognized by M5/114 and the ability of this antibody to block T cell responses under Ir gene control strengthens the hypothesis that Ia antigens are Ir gene products.     

A signal adaptor SLAM-associated protein regulates spontaneous autoimmunity and Fas-dependent lymphoproliferation in MRL-Faslpr lupus mice

Autoantibody production and lymphadenopathy are common features of systemic autoimmune disease. Targeted or spontaneous mutations in the mouse germline have generated many autoimmune models with these features. Importantly, the models have provided evidence for the gene function in prevention of autoimmunity, suggesting an indispensable role for the gene in normal immune response and homeostasis. We describe here pathological and genetic characterizations of a new mutant strain of mice, the mutation of which spontaneously occurred in the Fas-deficient strain, MRL/Mp.Faslpr (MRL/lpr). MRL/lpr is known to stably exhibit systemic lupus erythematosus-like diseases. However, the mutant mice barely displayed autoimmune phenotypes, though the original defect in Fas expression was unchanged. Linkage analysis using (mutant MRL/lpr x C3H/lpr)F2 mice demonstrated a nucleotide insertion that caused loss of expression of small adaptor protein, signaling lymphocyte activation molecule (SLAM)-associated protein (SAP). SAP is known to be a downstream molecule of SLAM family receptors and to mediate the activation signal for tyrosine kinase Fyn. Recent studies have shown pleiotropic roles of SAP in T, B, and NK cell activations and NKT cell development. The present study will provide evidence for an essential role for SAP in the development of autoimmune diseases, autoantibodies, and lymphadenopathy in MRL/lpr lupus mice.