Serological and histological characterization of the new mutant strain of lpr mice, CBA/KlJms-lprcg/lprcg

Experimental use of mouse models of systemic lupus erythematosus

Mouse models of lupus have for many years provided accessible and reliable research systems for the pathogenesis and therapy of systemic autoimmune disease, spanning a spectrum of inbred strains that develop spontaneous disease to experimentally induced, sometimes genetically manipulated animals. Nearly all the models share in common the development of glomerulonephritis and autoantibodies, including antinuclear and DNA specificities, the most common endpoints examined in experimental studies, but exhibit specific differences in the incidence of other end-organ manifestations such as hemolytic anemia, arthritis, dermatitis, and vasculitis. This chapter contrasts the clinical characteristics of these various models, providing an outline for their use and analysis.

Sjögren's syndrome in mice carrying the Ipr(cg) gene and the therapeutic efficacy of an immunosuppressive agent FK506

The influence of the Ipr(cg) gene on the development of Sjögren's syndrome was followed up to 5 months of age in male and female mice of MRL, CBA and C3H strains. In MRL-Ipr(cg) mice, focal mononuclear cell infiltration started at 2 months and became conspicuous after 3 months of age in the lacrimal and submandibular glands but was minimal in the parotid and sublingual glands, even at 5 months of age, without any apparent sex effects found. In CBA and C3H mice carrying the Ipr(cg) gene, this manifestation of Sjögren's syndrome was much less prominent, indicating that the participation of some genes of the MRL strain may be indispensable for the development of Sjögren's syndrome in mice carrying this gene. In MRL-Ipr(cg) mice, an immunosuppressive agent, FK506, improved the serological abnormalities (decreased levels of anti-double-stranded DNA antibody of IgG2a and IgG3 subclasses) and proteinuria. It also reduced the manifestations of Sjögren's syndrome when it was intraperitoneally administered three times weekly at a dose of 2 mg/kg from 6 weeks (before disease onset) until 5 months of age (the termination of the experiment). Although VP8.2+ T cells have been demonstrated to be responsible for causing several autoimmune diseases, the selective deletion of Vp8.2+ T cells with the superantigen encoded by mouse mammary tumor virus did not affect the disease severity at all, suggesting that this T cell repertoire may not play a crucial role in induction of Sjögren's syndrome.

The TNF-ligand and receptor superfamilies: controllers of immunity and the Trojan horses of autoimmune disease?

This review is concerned with the tumour necrosis factor receptor and ligand superfamilies, with particular reference to their roles in the immunopathogenesis of Systemic Lupus Erythematosus (SLE). The tumour necrosis factor receptor and ligand superfamilies are well characterized as the molecular controllers of the immune system, acting as 'judges', 'juries', and, where necessary, 'executioners' to determine the fate of immune cells during development, proliferation and differentiation. However, these molecules exert extreme immunopathological effects when unregulated, or dysfunctional. The importance of these molecules in the pathogenesis of autoimmunity is now apparent, and has been considered in detail. Finally, specific consideration has been given to their clinical significance and potential diagnostic and therapeutic applications.

A substrain of NZB mouse as an animal model of autoimmune inner ear disease

A substrain of an autoimmune-prone mouse, NZB/kl, was found to show spontaneous elevation of the auditory brainstem response (ABR) threshold with age. Morphological examination of the inner ear in NZB/kl mice with high ABR thresholds revealed pathological changes confined to the stria vascularis, including marked thickening of the capillary basement membrane which contained many foamy structures, and vacuolar degeneration of the intermediate cells. Circular or granular IgM deposits and some IgG deposits were found in the stria vascularis in the mice with high ABR thresholds, suggesting that deposits of immune complexes (mainly IgM antibodies) could cause strial damage that resulted in the ABR threshold elevation. Another substrain of NZB mice, NZB/san, showed lower levels of IgM immune complexes and anti-ss DNA antibodies, and did not develop either inner ear morphological changes or a high ABR threshold. NZB/kl mice may provide a useful animal model for studying the mechanism of autoimmune inner ear disease.

Autoimmunity in mice bearing lprcg: a novel mutant gene

A novel mutation at the lpr (lymphoproliferation)(Fas) locus, lprcg, that can complement gld (generalized lymphoproliferative disease) in induction of lymphadenopathy was discovered in CBA/K1Jms mice. The lpr and lprcg mutations are a defective allele of the Fas locus that encodes an apoptosis-mediating receptor. The former does not express the receptor and the latter expresses the point-mutated nonfunctional receptor. The gld locus is hypothesized to encode a ligand for the receptor and the gld mutation to have a defect that leads to incompetent expression of the ligand. The absence and non-functioning of the receptor in lpr/lpr and lprcg/lprcg mice, respectively, and the lack of the ligand in gld/gld mice may arrest apoptosis of lymphoid cells in the thymus, resulting in the same type of lymphadenopathy characterized by expansion of unusual CD4-CD8- (DN) T cells. Less severe lymphadenopathy induced by complementarity between lprcg and gld may be explained by less efficient apoptosis resulting from competition for the ligand between the functional and nonfunctional receptors. Phenotypically, lpr and lprcg are different from gld in the function at bone marrow (BM) and lymph node (LN) levels: lpr/lpr and lprcg/lprcg BM cause atrophy but gld/gld BM hyperplasia of wild-type (+/+) LNs, and lpr/lpr and lprcg/lprcg LNs but not gld/gld LNs allow the homing of lpr- and lprcg-induced DN T cells. Lymphadenopathy is equally prominent in CBA-lprcg/lprcg and MRL-lprcg/lprcg mice. Hypergammaglobulinemia, autoantibodies and circulating immune complexes are detectable at significant levels in both lprcg/lprcg mice but at higher levels on the MRL background. Pathological signs like glomerulonephritis and vasculitis are clinically unimportant in CBA-lprcg/lprcg but strikingly severe in MRL-lprcg/lprcg mice. Noticeably, clinically significant glomerulonephritis and vasculitis also develop with slight but significant serological aberrations in MRL-lprcg/+ heterozygotes. Graft-vs.-host disease-like syndrome in the lprcg/lprcg BM-->+/+ chimera is minimal on the CBA but as severe as life-threatening on the MRL background as in the MRL-lpr/lpr BM-->MRL(-)+/+ chimera. Thus, autoimmune diseases induced by the lpr, lprcg and gld genes are actually indistinguishable in the clinical, serological and pathological aspects on the same strain background and the disease caused by the interaction between lprcg and gld is less severe in all the aspects, consistent with the receptor-ligand theory. The lprcg/lprcg mice with different strain backgrounds together with lpr/lpr and gld/gld mice will serve as a powerful tool for elucidation of the mechanism of development of single-gene autoimmune diseases at a molecular biological level.

Mechanisms of hearing disturbance in an autoimmune model mouse NZB/kl

A subline of the NZB mouse, NZB/kl, was found to develop severe hearing disturbances at high frequency sound at the age of 4 to 6 months. Deposition of IgG was observed on the capillary wall of the stria vascularis of the mice, but the concentration of circulating immune complex did not seem to be correlated to the deposition. Electron microscopic examination revealed that the capillaries had a thick basement membrane, and in severe cases the membrane contained foamy structures of various size. In some cases the base membrane was so thick that the capillary lumen was narrowed, and the intermediate cells seemed to be damaged. No pathological findings were found in other inner ear tissues. These results suggest that the changes in the stria vascularis were possibly caused by an autoimmune mechanism which resulted in hearing disturbance.

Novel monoclonal antibodies to double stranded DNA that require Ca2+ or Mg2+ for their binding

Murine monoclonal antibody (MoAb) 2B5 (IgG2aK) was obtained by its binding on a solid phase to double-stranded (ds) DNA from one of the mutant CBA/K1(CBA/K1Jms-1prcg/1prcg) mice which were recently found, in our institute, to develop lymphadenopathy associated with the production of anti-double-stranded (ds) antibodies. MoAb 2B5 was highly specific for dsDNA, as shown by enzyme-linked immunosorbent assay (ELISA). The dsDNA binding of 2B5 was decreased dose-dependently by the chelating agent EDTA, being lost completely with 2.5-5.0 mM EDTA, whereas dsDNA on the solid phase remained intact after incubation with EDTA. Addition of Ca2+ or Mg2+ to antibody in culture supernatant that had lost dsDNA binding activity by dialysis against Ca2+ and Mg(2+)-free buffer restored its binding with dsDNA to the original level, indicating that MoAb 2B5 requires Ca2+ or Mg2+ for its binding with dsDNA. It is unknown whether MoAb 2B5 recognizes new conformational epitopes created in the presence of Ca2+ or Mg2+, but this MoAb should be useful in studies on the modes of interaction of DNA with antibodies and DNA-binding proteins.

Nephritogenicity of the lprcg gene on the MRL background

The novel lymphoproliferative and autoimmune lprcg gene, originally discovered in the CBA/K1Jms (CBA) strain of mice, was transferred onto the MRL/MpJ (MRL) strain background, and the resultant partially congenic MRL-lprcg/lprcg carrying 93% or more MRL genomes on average were examined for immune-complex glomerulonephritis and serological aberrations. Ordinary histological studies revealed that MRL-lprcg/lprcg mice developed glomerulonephritis histologically indistinguishable from that in MRL-lpr/lpr but at a lower frequency than in MRL-lpr/lpr mice. Glomerular immune complex deposition was almost the same in MRL-lprcg/lprcg and MRL-lpr/lpr mice. The levels of serum Ig, circulating immune complexes and autoantibodies in MRL-lprcg/lprcg were comparable to or even higher than those in MRL-lpr/lpr mice. Comparison of the serological abnormalities between MRL-lprcg/lprcg with glomerulonephritis and CBA-lprcg/lprcg without it evidenced the enhanced class switch from IgM to IgG responses in both class-specific autoantibody responses and serum Ig levels in MRL-lprcg/lprcg as in MRL-lpr/lpr mice. These results taken together indicate that the lprcg gene functions in much the same manner as lpr in induction of glomerulonephritis and serological abnormalities on the MRL background as expected from the allelism between the two mutant genes.

A crucial role of the thymus in induction by the lprcg gene of lymphadenopathy with autoimmunity in the mouse

The new mutation at the lpr locus, lprcg, induces massive lymphoproliferation characterized by the selective expansion of CD4-, CD8-, B220+, Thy-1+ cells or double-negative T lymphocytes and production of autoantibodies as does lpr. The thymus is necessary for the induction of anomalous double-negative T lymphocytes and autoimmune symptoms by lpr. To determine whether or not the thymus is also indispensable to expression of the function of lrpcg, lprcg homozygous athymic nude mice (lprcg/lprcg nu/nu; lprcg nudes) were constructed by crossing CBA/KlJms-lprcg/lprcg (CBA-lprcg) and DDD/l-nu/nu mice and observed for lymphoid organ hyperplasia and autoantibody production with or without thymus grafts from various strains of mice including CBA-lprcg. Neither lymphoproliferation nor significantly increased production of autoantibodies was observed in unmanipulated lprcg nudes. In contrast, thymus grafts of both +/+ and lprcg/lprcg genotypes caused lymphoid organ hyperplasia composed of anomalous double-negative T lymphocytes and significantly augmented the production of antibodies against single-stranded DNA (ssDNA). Interestingly, serum Ig and anti-ssDNA antibody levels rose in response to thymus grafts only in IgG but not in IgM classes. These results indicate that the thymus plays a crucial role in the induction of abnormal T-cell differentiation by lprcg and that thymic genotype is irrelevant.

Cell electrophoretic characterization of abnormally expanded lymphocytes in autoimmune lprcg, lpr, gld and Yaa mice, and of thymocyte subsets

Autoimmune mice carrying the lprcg/lprcg(lprcg),lpr/lpr(lpr),gld/gld(gld) and Yaa genes exhibit massive lymphoproliferation and a systemic lupus erythematosus-like syndrome. The surface markers of abnormally expanded lymphocytes used were Thy-1+, CD4-CD8- (double negative, DN) and CD45+ for lprcg, lpr, gld and (lprcg X gld) hybrid (F1-lprcg-gld) mice, and Ig+ for Yaa mice. To characterize the cell surface properties and differentiation pathway of lymphocytes in autoimmune mice, the cell electrophoretic mobility (EPM) was determined for the lymph node (LN), spleen and thymus cells. The EPM of lymphocytes derived from swollen LN was of the T cell type in lprcg, lpr, gld and F1-lprcg-gld mice, but of the B cell type in Yaa mice, indicating that the EPM of abnormally proliferated lymphocytes in autoimmune mice reflects their origin, and that the surface properties detected as a net negative charge were the same in abnormal and normal lymphocytes. The electrophoretic behavior of whole thymocytes was also the same in autoimmune and normal mice. The DN, and CD4+CD8- and CD4-CD8+ (single positive, SP) thymocytes from normal mice exhibited high EPM, while CD4+CD8+ (double positive, DP) thymocytes exhibited low EPM. According to the recent concept of intrathymic T cell differentiation (Schwartz, R. H., Cell. 1989, 57, 1073-1081), it is suggested that EPM of thymocytes may change with maturation in the following manner: DN thymocytes with high EPM----DP thymocytes with low EPM----SP thymocytes and autoimmune DN T cells with high EPM.

Serum IgG from CBA/K1Jms-lprcg/lprcg mice induces interleukin 3 in an interleukin-3-dependent cell line--possible correlation with lymphadenopathy

Serum IgG of CBA-K1Jms-lprcg/lprcg (lprcg/lprcg) mice with spontaneous systemic lymphadenopathy supported the proliferation of an IL-3-dependent cell line, FDC-P2/185-4. The lprcg/lprcg IgG induced IL-3 synthesis in FDC-P2/185-4 cells, and cells grew by an autocrine mechanism. There was virtually no time lag between the appearance of lymphadenopathy and an increase of IL-3-inducing activity in the sera. We have previously shown that serum IgG from other autoimmune mice with lymphadenopathy, MRL/Mp-lpr/lpr(MRL/lpr) and C3H/HeJ-gld/gld(C3H/gld), also induces IL-3 synthesis and cell growth in FDC-P2/185-4 cells. Furthermore, neither F1 (lprcg/+) mice between lprcg/lprcg and CBA(-)+/+ nor those (lpr-gld) between C3H-lpr/lpr and C3H/gld showed such IL-3-inducing activity, while those (lprcg-gld) between lprcg/lprcg and C3H/gld showed activity much lower than that of their parental strains but significantly higher than that of normal CBA(-)+/+ mice. This result is consistent with the incidence and degree of lymphadenopathy in these F1 mice. Our results suggest that expression of IgG(s) with cytokine-inducing activity might be controlled by these mutant genes, lpr, gld, and lprcg, and might be related to lymphadenopathy in these mice.

Characterization of lymphoproliferation induced by interactions between lprcg and gld genes

The lprcg gene is the novel mutation at the lpr locus characterized by its complementary to the gld gene in induction of lymphoproliferation in the mouse. Because of the potential usefulness of mice with this mutation in studies on the interrelationship between lpr and gld, we were urged to characterize the lymphoproliferative disease developing in (CBA/K1Jms-lprcg/lprcg x C3H/HeJ-gld/gld) F1 hybrid (lprcg-gld) mice. Despite the milder lymphadenopathy in the lprcg-gld mice, the expanding lymph node cells showed the same surface marker pattern as that in C3H/HeJ-lpr/lpr, C3H/HeJ-gld/gld, and CBA/K1Jms-lprcg/lprcg mice, characterized by the positivity for Thy-1, B220, Ly-6, and Ly-24, and the negativity for L3T4, Lyt-2 (hence designated double-negative cells), and sIg. Furthermore, these cells proved to be of a T-cell lineage based on the rearrangement of the TCR beta-chain gene, the same as the already known double-negative cells. Noticeably, in lprcg-gld mice, serum IgG and autoantibodies of the IgG class were not elevated at an early age but were slightly elevated at an advanced age despite early elevation of the serum IgM and IgM autoantibodies. These results suggest that the lymphoproliferative mice carrying lprcg and gld genes in a heterozygous state will serve as a new tool for inquiring into the interrelationship among lpr, gld, and lprcg.

Role of bone marrow cells in autoantibody production and lymphoproliferation in the novel mutant strain of mice, CBA/KlJms-lprcg/lprcg

The novel mutant gene, lprcg, is allelic with lpr, but complements the gld gene in induction of lymphoproliferation. Mice with this autosomal recessive mutation, CBA/KlJms-lprcg/lprcg (CBA-lprcg), served in this study to analyze the abnormalities of bone marrow (BM) stem cells responsible for autoantibody production and lymphoproliferation by BM transfer experiments. Transferred CBA-lprcg BM cells might have differentiated into so-called double-negative, anomalous lymphoid cells and caused production of autoantibodies such as anti-DNA antibodies in the environment of normal CBA/KlJms-(+)/+ (CBA-(+)) mice. Macroscopic graft-vs.-host-like disease as reported in lpr----non-lpr BM transfer was not observed in these recipients. In this BM chimera, however, lymphoproliferation did not ensue and the host's lymph nodes became atrophic. The lymphoproliferation required the coexistence of lprcg BM cells and lprcg lymph nodes in CBA-(+) mice. The results indicate that the functions of the lprcg gene are expressed at both BM and lymph node levels. Thus, this mutant strain of mice should provide an excellent model for analyzing aberrant lymphocyte differentiation from the BM cells leading to autoimmunity and lymphoproliferative disorder.