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.     

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.     

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.     

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.     

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.     

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.     

T cell reactivity to MHC class II-bound self peptides in systemic lupus erythematosus-prone MRL/lpr mice

The epitopes recognized by pathogenic T cells in systemic autoimmune disease remain poorly defined. Certain MHC class II-bound self peptides from autoimmune MRL/lpr mice are not found in eluates from class II molecules of MHC-identical C3H mice. Eleven of 16 such peptides elicited lymph node cell and spleen cell T cell proliferation in both MRL/lpr (stimulation index = 2.03-5.01) and C3H mice (stimulation index = 2.03-3.75). IL-2 and IFN-gamma production were detected, but not IL-4. In contrast to what was seen after immunization, four self peptides induced spleen cell proliferation of T cells from naive MRL/lpr, but not from C3H and C57BL/6.H2(k), mice. These peptides were derived from RNA splicing factor SRp20, histone H2A, beta(2)-microglobulin, and MHC class II I-A(k)beta. The first three peptides were isolated from I-E(k) molecules and the last peptide was bound to I-A(k). T cell responses, evident as early as 1 mo of age, depended on MHC class II binding motifs and were inhibited by anti-MHC class II Abs. Thus, although immunization can evoke peripheral self-reactive T cells in normal mice, the presence in MRL/lpr mice of spontaneous T cells reactive to certain MHC-bound self peptides suggests that these T cells actively participate in systemic autoimmunity. Peptides eluted from self MHC class II molecules may yield important clues to T cell epitopes in systemic autoimmunity.     

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.     

Ontogeny and function of B220+ L3T4+ T-cell subset of MRL/Mp-lpr/lpr mice

T-cell-enriched populations obtained from lymph nodes (LNs) of 4-month-old MRL/Mp-lpr/lpr (MRL-lpr), C3H/HeJ-lpr/lpr (C3H-lpr), and C3H/HeJ-gld/gld (C3H-gld) mice were studied for the expression of B220, L3T4, and Lyt 2 antigens. A new B220+ L3T4+ phenotype was demonstrated in T-cell populations of these mice by two-color flow cytometry with phycoerythrin-conjugated monoclonal antibodies (MoAb) to L3T4 and FITC-anti-B220 MoAb. The generation of the T subset was apparently under the influence of the lpr or gld gene, since it could not be demonstrated in T-cell-enriched populations of MRL/Mp- +/+ and normal C3H mice. The expression level of L3T4 antigen on the T subset was lower than that on B220- L3T4+ cells, while the level of B220 antigen was similar to that of B220+ L3T4- or B220+ Lyt 2- cells. The B220+ L3T4+ phenotype appeared in LNs and spleens, but not in thymuses, of MRL-lpr mice as early as 2 months of age. Its proportion to whole LN T cells at this age was equivalent to that observed in 4-month-old mice. Functional studies on FACS-sorted cell populations revealed that the T subset similar to B220+ L3T4- cells possessed deficiencies in the IL-2-IL-2 receptor system. The appearance of the T subset with an intermediate phenotype and its functional defects suggests that lpr and gld genes in these autoimmune mice exert their influences on the ontogeny and function of L3T4+ T cells and contribute to the induction of early lupus.     

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.     

Unique surface phenotype of T cells in lymphoproliferative autoimmune MRL/Mp-lpr/lpr mice

MRL/l mice, which carry the mutant gene lpr, develop massive T cell lymphoproliferation and an autoimmune syndrome. The surface antigen profile of MRL/l lymphocytes was analyzed with rat monoclonal antibodies. They included YE1/9.9, anti-transferrin receptor; YE1/7.1, which reacts with a population of proliferating immature T cells; and YE1/19.1, a newly identified antibody reactive with a surface antigen on EL-4 cells, which consists of two disulfide-bonded polypeptide chains, each of 115,000 m.w. Flow cytometric analysis of lymphocytes from the enlarged lymph nodes of MRL/1 mice showed the majority of them to be Lyt-1+, YE1/7.1+, YE1/19.1+, YE1/9.9-. In contrast, YE1/7.1 and YE1/19.1 antibodies did not significantly react with lymphocytes from the congenic MRL/n mice, which lack the lpr gene and do not develop lymphoproliferation. Lymphocytes from younger MRL/l mice, which have almost normal size lymph nodes, were also YE1/7.1-, YE1/19.1-. A small proportion of mitogen-stimulated MRL/n lymph node cells appeared to express these antigens at low densities, but it is not known whether they represent a unique cell population. Among the several lymphoid cell lines tested, only the T lymphoma line EL-4 had the Lyt-1+, YE1/7.1+, YE1/19.1+ phenotype. These results suggest that the lpr mutation induces the expansion of a unique T cell subset.     

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.     

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.     

Monoclonal IgGs from an autoimmune MRL/Mp-lpr/lpr mouse induce an interleukin-3-dependent myeloid cell line to produce tumor necrosis factor alpha and interleukin-6.

We previously reported that two IgG mAbs, 1D11 and 1G10, derived from an autoimmune MRL/Mp-lpr/lpr(MRL/l) mouse, induced IL-3 synthesis in the IL-3-dependent myeloid cell line, FDC-P2/185-4. In this study, we found that these mAbs induced TNF-alpha and IL-6 production in FDC-P2/185-4 cells. Both TNF-alpha and IL-6 were secreted rapidly within 1 hr after the addition of mAb to the cells. Increases of TNF-alpha and IL-6 mRNA were also observed in FDC-P2/185-4 cells stimulated with MRL/l-derived mAb. The anti-Fc gamma RII mAb 2.4G2 suppressed TNF-alpha and IL-6 production induced by these mAbs. Our results suggest that some IgGs of MRL/l mice may have the capacity to induce cytokine synthesis in Fc gamma R-bearing cells.     

Immunoregulation in MRL/Mp-lpr/lpr mice: evidence for decreased helper-T-cell and increased suppressor-T-cell function with age

In vivo and in vitro plaque-forming cell (PFC) responsiveness to sheep erythrocytes (SRBC) was used to assess immunoregulatory function in the autoimmune MRL mouse strain. MRL/Mp-lpr/lpr (MRL/l) mice had good primary and secondary IgM and IgG responses in vivo compared to MRL/Mp-+/+ (MRL/n) mice when young, but with age the MRL/l responses declined markedly. In vitro primary SRBC-specific PFC responses in MRL/l mice declined at the same time as in vivo responses, indicating that the in vivo autoimmune environment could not account for cellular dysfunction. When varied mixtures of T and B cells from MRL/l and MRL/n mice were cultured, abnormalities in MRL/l T-cell function became apparent. T-helper-cell (T_H) function declined rapidly with age, beginning by 2 to $\text{2}\text{1}\text{2}$ months of age. T cells from MRL/l mice 2 months of age and older also had increased suppressor activity when cultured with B cells and MRL/n T cells. The degree of suppressor activity increased with age. The correlation of these findings with results of previous studies by others and with autoimmune disease is discussed.     

Suppressive effect of interferon-beta-activated natural killer cells on lipopolysaccharide-induced B cell differentiation of MRL/Mp-lpr/lpr mice

The suppressive effects of mouse recombinant interferon-beta (IFN-beta) on B cell differentiation of MRL/Mp-lpr/lpr (MRL/1) mouse, a model of autoimmune diseases, and C3H/H2 mice, a normal situation, were investigated. Spleen mononuclear cells were cultured in the presence of lipopolysaccharide (LPS), and the suppressive effect of IFN-beta was examined on differentiation of B cells to plaque-forming cells (PFCs) by highly sensitive reversed hemolytic plaque assay. IFN-beta (5,000-10,000 units/ml) suppressed more than 50% of PFCs of both MRL/1 and C3H/H2 mice. This suppressive activity as well as the cytotoxicity of natural killer (NK) cells enhanced by IFN-beta was abrogated by treatment of the spleen cells with anti-asialo GM1 antibody in the presence of complement. This suppressive activity was also abrogated by intravenous administration of 20 microliter/mouse of anti-asialo GM1 12 hr before cultivation of spleen cells. These results suggest that NK cells activated by IFN might be responsible for the immunoregulation in autoimmune diseases.     

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.     

T cell autoimmunity in Ig transgenic mice.

Autoantibodies directed at a diverse group of proteins of the U1/Sm ribonucleoprotein (snRNP) are characteristic of systemic lupus erythematosus and are found in the MRL murine model of this disease. This study examines the role of transgenic B lymphocytes in the regulation of autoreactive T cells to the snRNP autoantigen. Transgenic mice were developed bearing an Ig heavy chain gene specific for the D protein component of murine snRNP. B lymphocytes in these mice are neither deleted nor anergic and are of an immature (heat-stable Aghigh) phenotype. T lymphocytes from anti-snRNP transgenic mice were examined using a recombinant form of the D protein of the murine snRNP complex. Our results revealed that transgenic anti-snRNP B cell APCs stimulated CD4 T cells from wild-type C57BL/6 and MRL lpr/lpr mice, while nonspecific APCs failed to stimulate CD4 T cells. This study demonstrates that autoreactive T cells are not deleted from wild-type mice, although their activation is facilitated by autoantigen-specific APCs. The snRNP-reactive T cells in C57BL/6 transgenic mice are tolerized, in contrast to those T cells from MRL lpr/lpr transgenic mice. These studies implicate a role for autoreactive B lymphocytes in the in vivo activation and/or diversification of autoreactive T cells.