The abnormal lpr double-negative T cell fails to proliferate in vivo

Mice homozygous for the autosomal recessive gene lpr develop marked lymphadenopathy and a systemic autoimmune disease resembling human systemic lupus erythematosus. The enlarged nodes are dominated by T cells with an unusual surface phenotype: dull Thy-1+, dull CD3+, CD4-, CD8-, B220+ (double-negative T cells or DNTs). Despite their massive accumulation in vivo, these cells fail to proliferate in response to conventional T-cell mitogens in vitro. The identification of the lpr mutation as a defect in the Fas apoptosis receptor gene suggests that DNT accumulation may result from abnormal persistence rather than overproliferation. To test in vivo whether DNTs persist abnormally or have a capacity to differentiate into single-positive T cells, we have performed cell transfer experiments between congenic strains of lpr and +/+ mice differentially marked by expression of the Ly-1 or Thy-1 alleles. Although transferred lpr lymph node cells were mostly DNTs at the time of injection, most recovered cells of donor origin were single positive, particularly CD8+, at all time points after transfer. Furthermore, transfer of purified DNTs resulted in recovery of relatively few cells of donor origin. Transfer of lpr T cells enriched for CD8 expression confirmed the preferential survival of this subset. Thus, DNTs are a surprisingly transient population and have little capacity for transformation to single positives. This would suggest that DNTs are constantly being renewed, perhaps from CD4+ and CD8+ precursors.

Greatly reduced lymphoproliferation in lpr mice lacking major histocompatibility complex class I

Mice homozygous for the lpr gene have a defect in fas (CD95), a cell surface receptor that belongs to the tumor necrosis factor receptor family and that mediates apoptosis. This genetic abnormality results in lymphoproliferation characterized by the accumulation of CD4-CD8- (double negative [DN]) T cells, autoantibody production, and background strain-dependent, end-organ disease. Our previous results suggested that major histocompatibility complex (MHC) class I may be involved in the development of DN cells. To test this hypothesis, we derived C57BL/6-lpr/lpr (B6/lpr) mice that were deficient for the beta 2-microglobulin gene (beta 2m lpr) and had no detectable class I expression. At 6 mo of age, compared with B6/lpr littermates with normal class I genes, these mice showed greatly reduced lymphadenopathy, mostly due to a dramatic decrease in the number of DN cells. Significant changes in the percentage of other T cell subsets were noted, but only gamma/delta+ T cells showed a marked increase in both percentage and absolute numbers. Analysis of T cell receptor V beta expression of the remaining DN T cells in beta 2m -lpr mice showed a shift to a CD4-like repertoire from a CD8-like repertoire in control B6/lpr mice, indicating that a small MHC class II selected DN population was unmasked in lpr mice lacking class I. We also found that the production of immunoglobulin G (IgG) autoantibodies (antichromatin and anti-single stranded DNA), total IgG and IgG2a, but not total IgM or IgM rheumatoid factor, was significantly reduced in the beta 2m -lpr mice. This work suggests that >90% of DN T cells in lpr mice are derived from the CD8 lineage and are selected on class I. However, a T cell subset selected on class II and T cells expressing gamma/delta are also affected by the lpr defect and become minor components of the aberrant DN population.

Apoptosis abnormalities of splenic lymphocytes in autoimmune lpr and gld mice

The murine gene lpr encodes an aberrant form of the apoptosis-inducing receptor Fas. The gene gld, which causes an autoimmune syndrome phenotypically identical to that caused by lpr, encodes a mutant Fas ligand. Because the lpr gene must be expressed in both T and B cells to produce autoimmune disease, it might be anticipated that apoptosis abnormalities would be present in both. Therefore, we quantitated apoptosis in T and B cells from lpr, gld, and normal mice in a short-term in vitro culture system. Freshly isolated spleen cells from normal, lpr, or gld mice showed little or no apoptosis as assessed by quantitative DNA flow cytometry. However, after overnight culture, both T and B cells showed substantial spontaneous apoptosis. Such apoptosis increased strikingly with age in normal but not in autoimmune B cells. CD23low B cells, which are prominent in lpr and gld mice, were particularly notable for high levels of programmed cell death in normal mice. The apoptosis caused by the gld defect could not be corrected by coculture with normal spleen cells. The persistence with age of low levels of B cell apoptosis in lpr and gld mice presumably reflects deficient Fas/Fas ligand interactions. The further localization of the B cell apoptosis defect to the unusual CD23low B cells, which accumulate in lpr and gld mice, adds to the evidence that these cells may be of critical importance to autoimmunity.

Apoptosis abnormalities of splenic lymphocytes in autoimmune lpr and gld mice

The murine gene lpr encodes an aberrant form of the apoptosis-inducing receptor Fas. The gene gld, which causes an autoimmune syndrome phenotypically identical to that caused by lpr, encodes a mutant Fas ligand. Because the lpr gene must be expressed in both T and B cells to produce autoimmune disease, it might be anticipated that apoptosis abnormalities would be present in both. Therefore, we quantitated apoptosis in T and B cells from lpr, gld, and normal mice in a short-term in vitro culture system. Freshly isolated spleen cells from normal, lpr, or gld mice showed little or no apoptosis as assessed by quantitative DNA flow cytometry. However, after overnight culture, both T and B cells showed substantial spontaneous apoptosis. Such apoptosis increased strikingly with age in normal but not in autoimmune B cells. CD23low B cells, which are prominent in lpr and gld mice, were particularly notable for high levels of programmed cell death in normal mice. The apoptosis caused by the gld defect could not be corrected by coculture with normal spleen cells. The persistence with age of low levels of B cell apoptosis in lpr and gld mice presumably reflects deficient Fas/Fas ligand interactions. The further localization of the B cell apoptosis defect to the unusual CD23low B cells, which accumulate in lpr and gld mice, adds to the evidence that these cells may be of critical importance to autoimmunity.

Co-infusion of normal bone marrow partially corrects the gld T-cell defect. Evidence for an intrinsic and extrinsic role for Fas ligand

Ipr and gld mice develop systemic autoimmune diseases with nearly indistinguishable manifestations, including the accumulation of massive numbers of CD4-CD8- T lymphocytes. In vivo chimera experiments have shown that the Ipr mutation is functionally expressed in both T and B cells. When lethally irradiated Ipr mice were given a combination of normal and Ipr bone marrow, only Ipr-derived B cells produced autoantibodies and only Ipr-derived T cells hyperproliferated. In contrast, analogous experiments with gld mice showed that the co-infusion of normal bone marrow greatly reduced autoantibody production. These results indicated that the gld B cell defect was extrinsic to those cells producing autoantibodies, in agreement with the recent molecular data showing that the normal gene products of the Ipr and gld loci form an interacting receptor-ligand pair. In the present study, we have extended our functional studies with gld mice using T cell-marked congenic donors. Lymphadenopathy was reduced three- to fourfold in gld mice given a combination of congenic normal and gld bone marrow compared with mice given gld bone marrow alone, and the absolute number of CD4-CD8- T cells was reduced by a factor of 7. Surprisingly, the residual CD4-CD8- T cells present in the mixed chimeras were derived entirely from the gld donor marrow. This suggests that the gld mutation results in both an extrinsic and intrinsic defect in T cells.

In vivo depletion of Thy-1-positive cells originating from normal bone marrow abrogates the suppression of gld disease in normal-gld mixed bone marrow chimeras

Mice homozygous for gld develop an autoimmune syndrome characterized by hypergammaglobulinemia, massive accumulation of abnormal T cells and the production of autoantibodies. Previous studies in our laboratory have shown that reconstitution of lethally irradiated B6/gld recipients with a mixture of normal and gld bone marrow (BM) suppresses the gld-induced syndrome. In this report we extend this observation by demonstrating that the depletion of normal Thy-1+ cells, but not normal B cells, restores gld disease in mixed BM chimeras congenic for Thy-1 and IgH alleles. These results strongly suggest that normal T cells suppress the development of gld-related abnormalities. It is probable that the mechanism by which normal Thy-1+ cells mediate the suppression is Fas ligand dependent.

In vivo depletion of Thy-1-positive cells originating from normal bone marrow abrogates the suppression of gld disease in normal-gld mixed bone marrow chimeras

Mice homozygous for gld develop an autoimmune syndrome characterized by hypergammaglobulinemia, massive accumulation of abnormal T cells and the production of autoantibodies. Previous studies in our laboratory have shown that reconstitution of lethally irradiated B6/gld recipients with a mixture of normal and gld bone marrow (BM) suppresses the gld-induced syndrome. In this report we extend this observation by demonstrating that the depletion of normal Thy-1+ cells, but not normal B cells, restores gld disease in mixed BM chimeras congenic for Thy-1 and IgH alleles. These results strongly suggest that normal T cells suppress the development of gld-related abnormalities. It is probable that the mechanism by which normal Thy-1+ cells mediate the suppression is Fas ligand dependent.

Co-infusion of normal bone marrow partially corrects the gld T-cell defect. Evidence for an intrinsic and extrinsic role for Fas ligand

Ipr and gld mice develop systemic autoimmune diseases with nearly indistinguishable manifestations, including the accumulation of massive numbers of CD4-CD8- T lymphocytes. In vivo chimera experiments have shown that the Ipr mutation is functionally expressed in both T and B cells. When lethally irradiated Ipr mice were given a combination of normal and Ipr bone marrow, only Ipr-derived B cells produced autoantibodies and only Ipr-derived T cells hyperproliferated. In contrast, analogous experiments with gld mice showed that the co-infusion of normal bone marrow greatly reduced autoantibody production. These results indicated that the gld B cell defect was extrinsic to those cells producing autoantibodies, in agreement with the recent molecular data showing that the normal gene products of the Ipr and gld loci form an interacting receptor-ligand pair. In the present study, we have extended our functional studies with gld mice using T cell-marked congenic donors. Lymphadenopathy was reduced three- to fourfold in gld mice given a combination of congenic normal and gld bone marrow compared with mice given gld bone marrow alone, and the absolute number of CD4-CD8- T cells was reduced by a factor of 7. Surprisingly, the residual CD4-CD8- T cells present in the mixed chimeras were derived entirely from the gld donor marrow. This suggests that the gld mutation results in both an extrinsic and intrinsic defect in T cells.

Characterization of the Su antigen, a macromolecular complex of 100/102 and 200-kDa proteins recognized by autoantibodies in systemic rheumatic diseases

The Su autoantigen was characterized biochemically using human and murine autoimmune sera and the clinical significance of anti-Su antibodies was studied in 236 Japanese and 160 American patients with systemic rheumatic diseases. Anti-Su in immunodiffusion (ID) was strongly associated with immunoprecipitation of one or more 100- to 102-kDa proteins by MRL/lpr mouse sera (27/32 of ID positive vs 4/20 of ID negative, P = 0.000016), and all four human anti-Su reference sera immunoprecipitated the 100/102-kDa protein(s). In addition, all sera immunoprecipitated a less efficiently labeled approximately 200-kDa protein that comigrated on sucrose density gradients with the 100/102-kDa proteins. Based on these data, a complex of the 100/102-kDa and 200-kDa proteins is likely to be the main target of anti-Su antibodies. Three of four anti-Su monospecific sera were negative for immunofluorescent antinuclear antibodies (ANA), suggesting anti-Su antibodies may be associated with a negative ANA in some cases. Autoantibodies to Su were detected frequently by immunoprecipitation in systemic lupus erythematosus (17-21%), scleroderma (13-20%), and overlap syndrome (22-40%) and were associated with autoantibodies to Ku.

T-B collaboration for autoantibody production in lpr mice is cognate and MHC-restricted

A central question in autoimmunity is the mechanism of T cell help for autoantibody production. For responses to exogenous Ag, T-B collaboration is restricted by MHC class II molecules. To determine whether T cell help that leads to autoantibodies in murine SLE is also MHC-restricted, we have constructed bone marrow chimeras with Ig heavy chain (lgh) allotype- and I-A-congenic donor B6/lpr mice and I-A-congenic recipients. Developing T cells were thus positively selected in the host thymus to interact with B cells bearing I-A of one haplotype or the other. Additional control host mice were heterozygous for I-A expression, allowing T helper cell selection for both I-A haplotypes. Five months after reconstitution, serum total IgG2a, IgM, IgG2a antichromatin, and IgM rheumatoid factor were quantitated by allotype-specific ELISA. Data showed that whereas substantial numbers of B cells were present from both donor strains in all mice, autoantibody production was overwhelmingly from those donor B cells expressing the same I-A haplotype as the host. Sera from the I-A heterozygous control recipient group had roughly equal quantities of autoantibodies of both allotypes, as expected. The finding of MHC class II restriction implies that the T cell help that drives autoantibody production in lpr mice is delivered through cognate (cell-to-cell) interactions and not by soluble factors alone.

T-B collaboration for autoantibody production in lpr mice is cognate and MHC-restricted

A central question in autoimmunity is the mechanism of T cell help for autoantibody production. For responses to exogenous Ag, T-B collaboration is restricted by MHC class II molecules. To determine whether T cell help that leads to autoantibodies in murine SLE is also MHC-restricted, we have constructed bone marrow chimeras with Ig heavy chain (lgh) allotype- and I-A-congenic donor B6/lpr mice and I-A-congenic recipients. Developing T cells were thus positively selected in the host thymus to interact with B cells bearing I-A of one haplotype or the other. Additional control host mice were heterozygous for I-A expression, allowing T helper cell selection for both I-A haplotypes. Five months after reconstitution, serum total IgG2a, IgM, IgG2a antichromatin, and IgM rheumatoid factor were quantitated by allotype-specific ELISA. Data showed that whereas substantial numbers of B cells were present from both donor strains in all mice, autoantibody production was overwhelmingly from those donor B cells expressing the same I-A haplotype as the host. Sera from the I-A heterozygous control recipient group had roughly equal quantities of autoantibodies of both allotypes, as expected. The finding of MHC class II restriction implies that the T cell help that drives autoantibody production in lpr mice is delivered through cognate (cell-to-cell) interactions and not by soluble factors alone.

Chronic graft versus host disease-associated autoimmune manifestations are independently regulated by different MHC class II loci

Murine chronic graft vs host disease (GVHD) resembles human SLE in autoantibody specificities and glomerulonephritis. Chronic GVHD is induced by donor T cell recognition of recipient Ia Ag. This study compared the role of the two murine class II loci by inducing GVHD in donor/recipient combinations differing at the I-A, I-E, or both I-A and I-E loci. Serum autoantibody levels were mostly higher in I-E-induced GVHD, compared with I-A GVHD, and anti-Sm and anti-dsDNA were produced only in the I-E groups. When the GVHD was induced by differences at both I-A and I-E loci, autoantibody levels and specificities were generally comparable to the I-E group. Only anti-DPP-IV and IgG2bb-specific IgM rheumatoid factor were expressed at higher levels in the I-A and the I-A/E groups, but both autoantibodies were also present in the I-E group. Renal disease, in contrast to autoantibody production, was significantly greater in I-A-induced GVHD. Proteinuria was detected in both the I-A and I-A/E groups, but not in the I-E group. Histopathologic data also showed substantial glomerulonephritis in the I-A and I-A/E groups, but little in the I-E group. IgM deposits were detected in the mesangial region of all groups, but were more marked in the I-A and I-A/E groups. IgG deposits were far more prevalent in the I-A and I-A/E groups and were located predominantly in the capillary walls. These results show a direct relationship between the recognition of specific foreign Ia molecules and the autoimmunity observed: I-E resulted in elevated autoantibody production; I-A resulted in glomerulonephritis; whereas both I-A and I-E resulted in additive autoimmune manifestations. These results also showed an apparent disparity between the presence of commonly measured autoantibodies and the development of renal disease. This work provides a model to delineate further the regulatory role of the MHC class II loci in the development of autoimmunity.

Chronic graft versus host disease-associated autoimmune manifestations are independently regulated by different MHC class II loci

Murine chronic graft vs host disease (GVHD) resembles human SLE in autoantibody specificities and glomerulonephritis. Chronic GVHD is induced by donor T cell recognition of recipient Ia Ag. This study compared the role of the two murine class II loci by inducing GVHD in donor/recipient combinations differing at the I-A, I-E, or both I-A and I-E loci. Serum autoantibody levels were mostly higher in I-E-induced GVHD, compared with I-A GVHD, and anti-Sm and anti-dsDNA were produced only in the I-E groups. When the GVHD was induced by differences at both I-A and I-E loci, autoantibody levels and specificities were generally comparable to the I-E group. Only anti-DPP-IV and IgG2bb-specific IgM rheumatoid factor were expressed at higher levels in the I-A and the I-A/E groups, but both autoantibodies were also present in the I-E group. Renal disease, in contrast to autoantibody production, was significantly greater in I-A-induced GVHD. Proteinuria was detected in both the I-A and I-A/E groups, but not in the I-E group. Histopathologic data also showed substantial glomerulonephritis in the I-A and I-A/E groups, but little in the I-E group. IgM deposits were detected in the mesangial region of all groups, but were more marked in the I-A and I-A/E groups. IgG deposits were far more prevalent in the I-A and I-A/E groups and were located predominantly in the capillary walls. These results show a direct relationship between the recognition of specific foreign Ia molecules and the autoimmunity observed: I-E resulted in elevated autoantibody production; I-A resulted in glomerulonephritis; whereas both I-A and I-E resulted in additive autoimmune manifestations. These results also showed an apparent disparity between the presence of commonly measured autoantibodies and the development of renal disease. This work provides a model to delineate further the regulatory role of the MHC class II loci in the development of autoimmunity.

Development of the T cell receptor repertoire in lpr mice

The development of double-negative (DN; CD4-, CD8-) T cells and their relationship with other T cell subsets in lpr mice remain poorly understood. Based on studies identifying lpr as a mutation in the fas gene, it has been hypothesized that defective apoptosis in the thymus abnormally affects T cell development and results in the lpr phenotype. A review of studies of T cell receptor repertoires in lpr mice, however, suggests that thymic events are mostly normal in lpr mice. Thus, a global defect in negative selection is not apparent in any T cell population, and positive selection of CD4+ and CD8+ subsets appears to be normal. Surprisingly, repertoire studies also suggest that the majority of DN T cells are positively selected on class I, but not class II, MHC molecules. Furthermore, the expansion of the DN T cell population appears to be driven by abnormal peripheral events. Together, these results provide new insights into the role of fas in T cell development and the aberrant T cell lymphoproliferation in lpr mice.

The role of B cell abnormalities in the systemic autoimmune syndromes of lpr and gld mice

B cell abnormalities play a central role in the systemic autoimmune syndromes of lpr and gld mice. In the lpr model, autoantibody production requires the intrinsic expression of the lpr gene in B cells, while in the gld mouse the genetic defect is extrinsic, yet probably results in a similar failure of B cell tolerance. Despite their abnormality, lpr B cells require lpr (abnormal) T cells in order to produce autoantibodies.

Regulation of anti-Sm autoantibodies by the immunoglobulin heavy chain locus

Anti-Sm antibodies are specific markers for systemic lupus erythematosus in MRL mice and in humans. The prevalence of anti-Sm positivity in inbred MRL/Mp-lpr/lpr(MRL/lpr) mice is consistently about 25% at 5 mo of age, when the disease is at its peak. The control of the development of anti-Sm in individual MRL/lpr mice has been shown to be the result of stochastic factors, and previous research has indicated that the immunoglobulin heavy chain (IgH) b allotype may be more amenable to the production of anti-Sm. We have now further investigated the influence of the IgH genetic locus on the production of anti-Sm and other autoantibodies in an allotype congenic MRL strain, the MRL/Mp-Ipr/Ipr-IgHb (MRL/lpr-IgHb). Strikingly, 78% of MRL/lpr-IgHb mice produced anti-Sm, compared with 27% of contemporaneous MRL/lpr (IgHj) mice. Of those mice that were positive for anti-Sm, the MRL/lpr-IgHb strain produced significantly higher levels of anti-Sm than did the anti-Sm positive MRL/lpr mice. No differences were observed between the conventional MRL/lpr and the MRL/lpr-IgHb levels of antichromatin, anti-ssDNA, antiribosomal P, or anti-Su. In addition, kidney function, which was assessed by measuring serum urea nitrogen levels, was similar in the two strains. These results support the notion that the control of anti-Sm production in MRL/lpr mice operates through the IgH locus.

Conventional B cells, not B1 cells, are the source of autoantibodies in chronic graft-versus-host disease

B1 (CD5+) B cells have been implicated as a source of certain autoantibodies in several murine and human studies. We have previously shown in the lpr model of autoimmunity, however, that conventional B cells, not B1 cells, were the source of autoantibodies directed at chromatin, ssDNA, and IgG. In the current study, we have investigated the origin of autoantibodies in chronic graft-versus-host (GVH) disease, induced in nonautoimmune mice by transferring la-incompatible spleen cells. GVH mice develop multiple autoantibodies and significant kidney damage. Therefore, this model allowed us to examine the B cell subset involved in both autoantibody production and tissue injury. We used two protocols to establish B cell chimeras that possessed immunoglobulin heavy chain (lgh) allotype-marked peritoneal (B1-cell source) cells and bone marrow-derived (conventional B cell source) cells from nonautoimmune C57BL/6kh (B6) congenic mice. In both types of chimera, chronic GVH was induced by giving mice alloreactive T cells i.p. All of the subsequent anti-chromatin, RF, and anti-ssDNA autoantibodies were produced by the conventional B cells and not by B1 cells. In addition, glomerular immune complex deposits of both IgM and IgG originated from the conventional B cells and not from B1 cells. These findings thus parallel those from our previous work on autoantibodies in lpr, and extend those findings by demonstrating that antibodies within pathogenic immune complexes in the kidneys are also exclusively of conventional B cell origin.

Regulation of anti-Sm autoantibodies by the immunoglobulin heavy chain locus

Anti-Sm antibodies are specific markers for systemic lupus erythematosus in MRL mice and in humans. The prevalence of anti-Sm positivity in inbred MRL/Mp-lpr/lpr(MRL/lpr) mice is consistently about 25% at 5 mo of age, when the disease is at its peak. The control of the development of anti-Sm in individual MRL/lpr mice has been shown to be the result of stochastic factors, and previous research has indicated that the immunoglobulin heavy chain (IgH) b allotype may be more amenable to the production of anti-Sm. We have now further investigated the influence of the IgH genetic locus on the production of anti-Sm and other autoantibodies in an allotype congenic MRL strain, the MRL/Mp-Ipr/Ipr-IgHb (MRL/lpr-IgHb). Strikingly, 78% of MRL/lpr-IgHb mice produced anti-Sm, compared with 27% of contemporaneous MRL/lpr (IgHj) mice. Of those mice that were positive for anti-Sm, the MRL/lpr-IgHb strain produced significantly higher levels of anti-Sm than did the anti-Sm positive MRL/lpr mice. No differences were observed between the conventional MRL/lpr and the MRL/lpr-IgHb levels of antichromatin, anti-ssDNA, antiribosomal P, or anti-Su. In addition, kidney function, which was assessed by measuring serum urea nitrogen levels, was similar in the two strains. These results support the notion that the control of anti-Sm production in MRL/lpr mice operates through the IgH locus.

Conventional B cells, not B1 cells, are the source of autoantibodies in chronic graft-versus-host disease

B1 (CD5+) B cells have been implicated as a source of certain autoantibodies in several murine and human studies. We have previously shown in the lpr model of autoimmunity, however, that conventional B cells, not B1 cells, were the source of autoantibodies directed at chromatin, ssDNA, and IgG. In the current study, we have investigated the origin of autoantibodies in chronic graft-versus-host (GVH) disease, induced in nonautoimmune mice by transferring la-incompatible spleen cells. GVH mice develop multiple autoantibodies and significant kidney damage. Therefore, this model allowed us to examine the B cell subset involved in both autoantibody production and tissue injury. We used two protocols to establish B cell chimeras that possessed immunoglobulin heavy chain (lgh) allotype-marked peritoneal (B1-cell source) cells and bone marrow-derived (conventional B cell source) cells from nonautoimmune C57BL/6kh (B6) congenic mice. In both types of chimera, chronic GVH was induced by giving mice alloreactive T cells i.p. All of the subsequent anti-chromatin, RF, and anti-ssDNA autoantibodies were produced by the conventional B cells and not by B1 cells. In addition, glomerular immune complex deposits of both IgM and IgG originated from the conventional B cells and not from B1 cells. These findings thus parallel those from our previous work on autoantibodies in lpr, and extend those findings by demonstrating that antibodies within pathogenic immune complexes in the kidneys are also exclusively of conventional B cell origin.

Correction of gld autoimmunity by co-infusion of normal bone marrow suggests that gld is a mutation of the Fas ligand gene

lpr and gld mice develop phenotypically indistinguishable systemic autoimmune diseases and marked lymphadenopathy dominated by CD4-CD8- T cells. In vivo chimera experiments have demonstrated that both lpr T and lpr B cells are intrinsically defective. Analogous experiments were conducted using gld mice. Lethally irradiated gld mice were given mixtures of congenic gld and normal (+/+) bone marrow differentially marked by Ig heavy chain allotype. In sharp contrast to lpr-(+)/+ mixed chimeras, gld-(+)/+ chimeras had little autoantibody production at 5 months and minimal adenopathy at 6 months, indicating that the normal marrow-derived cells corrected the gld defect. Thus, aberrant autoantibody production is due to a defect extrinsic to the gld B cell and lymphoproliferation is due to a defect extrinsic to the gld T cell. These data support the hypothesis that gld mice lack an apoptosis-inducing ligand. The receptor for this ligand may be the Fas molecule, which is defective in lpr mice.

Selection of the T cell receptor repertoire in Lpr mice

The development of double-negative (CD4-, CD8-) T cells and other T cells subsets in lymphoproliferation (lpr) mice continues to be poorly defined. Recent studies indicate that lpr is a mutation of a receptor mediating apoptosis. It has thus been hypothesized that T cell development in the thymus should be abnormally affected. In this study, we analyzed the TCR V beta repertoire of double-negative T cells as well as CD4+ and CD8+ single-positive subsets in various lpr and matched non-lpr strains. Particular comparisons were made to determine the influence of different class I and class II molecules on repertoire formation. The data demonstrate that positive and negative selection of the CD4+ and CD8+ subsets are normal in lpr mice when compared with non-lpr congenic mice. Surprisingly, the result also suggest that double-negative T cells are mostly selected on class I MHC molecules in a pattern similar to the CD8+ population, and that T cells positively selected on class II MHC antigens may be absent from the double-negative population. In all lpr strains, we also found an increased percentage of double-negative V beta 8.3+ cells out of proportion to levels in the CD4+ or CD8+ subsets. Longitudinal studies and studies in thymectomized animals showed that this increase reflects a peripheral process selectively affecting V beta 8.3+ double-negative T cells. Together, these repertoire data provide new insight into the effect of the lpr genetic defect on T cell development and the derivation of double-negative T cells. Despite the role of Fas in apoptosis and the abnormal expression of this gene in lpr mice, the present results support the hypothesis that thymic events are relatively normal in lpr mice, and that the double-negative T cells are mostly class I MHC selected and expanded by abnormal peripheral processes.

Selection of the T cell receptor repertoire in Lpr mice

The development of double-negative (CD4-, CD8-) T cells and other T cells subsets in lymphoproliferation (lpr) mice continues to be poorly defined. Recent studies indicate that lpr is a mutation of a receptor mediating apoptosis. It has thus been hypothesized that T cell development in the thymus should be abnormally affected. In this study, we analyzed the TCR V beta repertoire of double-negative T cells as well as CD4+ and CD8+ single-positive subsets in various lpr and matched non-lpr strains. Particular comparisons were made to determine the influence of different class I and class II molecules on repertoire formation. The data demonstrate that positive and negative selection of the CD4+ and CD8+ subsets are normal in lpr mice when compared with non-lpr congenic mice. Surprisingly, the result also suggest that double-negative T cells are mostly selected on class I MHC molecules in a pattern similar to the CD8+ population, and that T cells positively selected on class II MHC antigens may be absent from the double-negative population. In all lpr strains, we also found an increased percentage of double-negative V beta 8.3+ cells out of proportion to levels in the CD4+ or CD8+ subsets. Longitudinal studies and studies in thymectomized animals showed that this increase reflects a peripheral process selectively affecting V beta 8.3+ double-negative T cells. Together, these repertoire data provide new insight into the effect of the lpr genetic defect on T cell development and the derivation of double-negative T cells. Despite the role of Fas in apoptosis and the abnormal expression of this gene in lpr mice, the present results support the hypothesis that thymic events are relatively normal in lpr mice, and that the double-negative T cells are mostly class I MHC selected and expanded by abnormal peripheral processes.

Antigen nonspecific effect of major histocompatibility complex haplotype on autoantibody levels in systemic lupus erythematosus-prone lpr mice

MHC-linked genes strongly influence susceptibility to autoimmune diseases and also regulate responses to exogenous antigens. To begin to understand the mechanism of this MHC effect on disease, we have investigated MHC-congenic mouse strains that develop spontaneous autoimmunity because of the lpr gene. C57BL6/lpr (B6/lpr) mice (H-2b) are known to have substantial levels of autoantibodies to chromatin, single stranded DNA (ssDNA3), and IgG of different murine subclasses (rheumatoid factor). We have crossed the H-2d and the H-2bm12 (la mutant) haplotypes onto the B6/lpr background. Surprisingly, levels of all the autoantibodies were markedly lower in B6/lpr.H-2d, but levels in B6/lpr.H-2bm12 were no different from those in B6/lpr mice. The downregulating influence of the H-2d allele was dominant, and there was no effect on autoantibody fine specificities. The genetics of the H-2d effect and its diffuse influence on multiple autoantibody specificities, in addition to the lack of effect of the bm12 mutation, which modifies the peptide-binding groove of I-A, together raise the question of whether MHC-linked genes other than classical (IR) genes may be responsible for MHC disease associations in this model.

lpr T cells are necessary for autoantibody production in lpr mice

Mice homozygous for the gene Ipr develop a spectrum of autoantibodies closely resembling that of human SLE. Previous work has shown that the lpr defect must be expressed in the T cells that hyperproliferate and in the B cells that produce autoantibodies. Although autoantibody production in lpr mice requires T cells, it is not known whether these need to be lpr T cells. To ask whether normal (+/+) T cells can help lpr B cells produce autoantibodies, we have constructed chimeras containing mixtures of lpr-derived and normal-derived lymphoid cells, and have selectively eliminated the lpr-derived T cells by in vivo treatment with monoclonal anti-Thy-1 of the appropriate allotype. A mixture of T cell-depleted bone marrow from congenic strains of normal and lpr mice differentially marked by Ig H chain allotype and Thy-1 alleles was transferred into lethally irradiated lpr mice. The mice received weekly injections of either anti-Thy-1.2 to deplete specifically lpr T cells or an isotype-matched irrelevant control mAb. Absence of lpr-derived T cells in the experimental group was documented by immunofluorescence. In mice treated with control antibody, autoantibodies of Ipr origin were present in high titers, as determined by allotype-specific ELISA. In contrast, mice depleted of lpr-derived T cells had greatly reduced titers of antichromatin and rheumatoid factor. These mice also had increased levels of serum total IgM and IgG2a of +/+ origin. Parallel experiments were performed using a combination of two lpr marrow sources, also differentially marked by Ig H chain allotype and Thy-1 expression. Mice depleted of Thy-1.2-bearing T cells produced autoantibodies of both allotypes due to the presence of Thy-1.1-bearing T cells of Ipr origin. These data indicate that autoantibody production in lpr mice requires expression of the lpr gene in those T cells that provide help.

lpr T cells are necessary for autoantibody production in lpr mice

Mice homozygous for the gene Ipr develop a spectrum of autoantibodies closely resembling that of human SLE. Previous work has shown that the lpr defect must be expressed in the T cells that hyperproliferate and in the B cells that produce autoantibodies. Although autoantibody production in lpr mice requires T cells, it is not known whether these need to be lpr T cells. To ask whether normal (+/+) T cells can help lpr B cells produce autoantibodies, we have constructed chimeras containing mixtures of lpr-derived and normal-derived lymphoid cells, and have selectively eliminated the lpr-derived T cells by in vivo treatment with monoclonal anti-Thy-1 of the appropriate allotype. A mixture of T cell-depleted bone marrow from congenic strains of normal and lpr mice differentially marked by Ig H chain allotype and Thy-1 alleles was transferred into lethally irradiated lpr mice. The mice received weekly injections of either anti-Thy-1.2 to deplete specifically lpr T cells or an isotype-matched irrelevant control mAb. Absence of lpr-derived T cells in the experimental group was documented by immunofluorescence. In mice treated with control antibody, autoantibodies of Ipr origin were present in high titers, as determined by allotype-specific ELISA. In contrast, mice depleted of lpr-derived T cells had greatly reduced titers of antichromatin and rheumatoid factor. These mice also had increased levels of serum total IgM and IgG2a of +/+ origin. Parallel experiments were performed using a combination of two lpr marrow sources, also differentially marked by Ig H chain allotype and Thy-1 expression. Mice depleted of Thy-1.2-bearing T cells produced autoantibodies of both allotypes due to the presence of Thy-1.1-bearing T cells of Ipr origin. These data indicate that autoantibody production in lpr mice requires expression of the lpr gene in those T cells that provide help.