Regulation of B cell apoptosis by Bcl-2 and Bcl-XL and its role in the development of autoimmune diseases (Review)

Cell death is a common event during B cell development. The demise of developing B cells is a regulated process that serves to select cell populations bearing functional receptors and to remove cells that are no longer needed or potentially autoreactive. Bcl-2 and Bcl-XL, two members of the bcl-2 gene family of programmed cell death regulators with anti-apoptotic activity, are expressed in a highly regulated pattern during B cell maturation. Overexpression of Bcl-2 in developing B cells of transgenic mice, in the presence of T cell dependent costimulatory signals, results in the generation of a modified B cell repertoire and in the production of pathogenic autoantibodies. While disregulation of programmed cell death in B cells may cause autoimmune manifestations in mice, the involvement of such alterations in the pathogenesis of autoimmune diseases in humans merits further investigation.

Increase in Bcl-2 level promoted by CD40 ligation correlates with inhibition of B cell apoptosis induced by vacuolar type H(+)-ATPase inhibitor

We have previously demonstrated that cell death of WEHI-231 cells induced by specific inhibitors of vacuolar type H(+)-ATPase (V-ATPase) occurs through apoptosis. CD40 is involved in regulating activation, differentiation, and apoptosis of B cells. Here we show that the CD40 ligation rescues WEHI-231 cells from apoptotic cell death induced by a specific V-ATPase inhibitor, concanamycin A. CD40 signaling with anti-CD40 antibody resulted in the induction of Bcl-2 and Bcl-XL proteins in WEHI-231 cells. Constitutive expression of Bcl-2 but not Bcl-XL inhibited concanamycin A-induced apoptosis. These findings suggest that the expression of Bcl-2 mediated through CD40 signaling rescues the apoptotic cell death induced by blockade of V-ATPase. Interestingly, the acidification of intracellular acidic compartments was completely inhibited when WEHI-231 cells were cultured with concanamycin A, even in the presence of anti-CD40 antibody. In addition, apoptosis in WEHI-231 cells induced by concanamycin A was strongly suppressed when cultured with imidazole, a cell-permeable base, suggesting that apoptosis induced by concanamycin A is preceded by intraacidification.

Difficulty walking. A presentation of idiopathic juvenile osteoporosis

Idiopathic juvenile osteoporosis is a rare condition that may present as difficulty walking. Difficulty walking represents a challenging differential diagnosis in pediatrics. Diagnostic studies are usually oriented to rule out neuromuscular etiologies or, once organic causes have been reasonably discarded, conversion disorders. We describe 2 patients who presented with difficulty or inability to walk due to idiopathic juvenile osteoporosis, a rare disease unfamiliar to most physicians. However, early diagnosis in patients can avoid extensive testing and prolonged hospitalizations.

[Public Health Nursing in Spain and Navarra throughout the present century]

The evolution of humanity over the course of history, political reforms and the reforms of the health services have brought the different professions related with health to take part in this evolution. The professionals of nursing have not remained outside this evolution, changing both their functions and their formation. With respect to the field of public health, it seems that the task developed by these professionals is sometimes overlooked and lost, which is why this article attempts to present the work realised by community nurses throughout this century, paying special attention to their development in Navarra and a proposal for the future.

A1 demonstrates restricted tissue distribution during embryonic development and functions to protect against cell death

Members of the bcl-2 gene family are essential regulators of cell survival in a wide range of biological processes. A1, a member of the family, is known to be expressed in certain adult tissues. However, the precise tissue distribution and function of A1 remains poorly understood. We show here that A1 is expressed in multiple tissues during murine embryonic development. In the embryo, A1 was detected first at embryonic day 11.5 in liver, brain, and limbs. At day 13.5 of gestation, A1 expression was observed in the central nervous system, liver, perichondrium, and digital zones of developing limbs in a pattern different from that of bcl-X. In the central nervous system of 15.5-day embryos, A1 was expressed at high levels in the ventricular zone and cortical plate of brain cortex. Significantly, the interdigital zones of limbs and the intermediate region of the developing brain cortex, two sites associated with extensive cell death, were devoid of A1 and bcl-X. The expression of A1 was retained in many adult tissues. To assess the ability of A1 to modulate cell death, stable transfectants expressing different amounts of A1 protein were generated in K562 cells. Expression of A1 was associated with retardation of apoptotic cell death induced by actinomycin D and cycloheximide as well as by okadaic acid. Confocal microscopy showed that the A1 protein was localized to the cytoplasm in a pattern similar to that of Bcl-2. These results demonstrate that the expression of A1 is wider than previously reported in adult tissues. Furthermore, its distribution in multiple tissues of the embryo suggests that A1 plays a role in the regulation of physiological cell death during embryonic development.

Bax can antagonize Bcl-XL during etoposide and cisplatin-induced cell death independently of its heterodimerization with Bcl-XL

Bax, a member of the Bcl-2 family of proteins, has been shown to promote apoptosis while other members of the family, including Bcl-XL and Bcl-2, inhibit cell death induced by a variety of stimuli. The mechanism by which Bax promotes cell death is poorly understood. In the present report, we assessed the ability of Bax to antagonize the death repressor activity of Bcl-XL during chemotherapy-induced apoptosis in the lymphoid cell line, FL5.12. Expression of wild-type Bax countered the repressor activity of Bcl-XL against cell death mediated by VP-16 and cisplatin. We performed site-directed mutagenesis of the BH1, BH2, and BH3 homology regions in Bax to determine the ability of wild-type and mutant Bax to heterodimerize with Bcl-XL and to antagonize the protective effect of Bcl-XL against chemotherapy-induced apoptosis. Bax proteins expressing alanine substitutions of the highly conserved amino acids glycine 108 in BH1, tryptophan 151 and 158 in BH2, and glycine 67 and aspartic acid 68 in BH3 retained their ability to promote chemotherapy-induced cell death that was inhibited by Bcl-XL and to form heterodimers with Bcl-XL. Bax proteins containing deletions of the most highly conserved amino acids in BH1 (Delta102-112) and BH2 (Delta151-159) maintained the ability of Bax to antagonize the death repressor activity of Bcl-XL and to associate with Bcl-XL. However, Bax with BH3 deleted did not form heterodimers with Bcl-XL, but retained its ability to counter the death repressor activity of Bcl-XL. These results demonstrate that the conserved BH3, but not BH1 or BH2, homology region of Bax is necessary for its interaction with Bcl-XL in mammalian cells. Furthermore, our results indicate that Bax does not require BH1, BH2, BH3, or heterodimerization with Bcl-XL to counter the death repressor activity of Bcl-XL. Therefore, Bax can antagonize Bcl-XL during VP-16 and, in a lesser degree, during cisplatin-induced cell death independent of its heterodimerization with Bcl-XL.

Constitutive expression of bcl-2 in B cells causes a lethal form of lupuslike autoimmune disease after induction of neonatal tolerance to H-2b alloantigens

The bcl-2 protooncogene has been shown to provide a survival signal to self-reactive B cells, but it fails to override their developmental arrest after encounter with antigen. Furthermore, constitutive expression of bcl-2 in B cells does not promote the development of autoimmune disease in most strains of mice, indicating that signals other than those conferred by bcl-2 are required for long-term survival and differentiation of self-reactive B cells in vivo. To further examine the factors that are required for the pathogenesis of autoimmune disease, we have assessed the effect of bcl-2 overexpression on the development of host-versus-graft disease, a self-limited model of systemic autoimmune disease. In this model, injection of spleen cells from (C57BL/6 x BALB/c)F1 hybrid mice into BALB/c newborn parental mice induces immunological tolerance to donor tissues and activation of autoreactive F1 donor B cells through interactions provided by allogeneic host CD4+ T cells. BALB/c newborns injected with spleen cells from (C57BL/6 x BALB/c)F1 mice expressing a bcl-2 transgene in B cells developed high levels of anti-single-stranded DNA and a wide range of pathogenic autoantibodies that were not or barely detectable in mice injected with nontransgenic spleen cells. In mice injected with transgenic B cells, the levels of pathogenic autoantibodies remained high during the course of the study and were associated with long-term persistence of donor B cells, development of a severe autoimmune disease, and accelerated mortality. These results demonstrate that bcl-2 can provide survival signals for the maintenance and differentiation of autoreactive B cells, and suggest that both increased B cell survival and T cell help play critical roles in the development of certain forms of systemic autoimmune disease.

Imbalance towards Th1 predominance is associated with acceleration of lupus-like autoimmune syndrome in MRL mice

To investigate the respective roles of Th1 and Th2 cells in the pathogenesis of lupus-like autoimmune disease, we have analyzed the spontaneous and antigen-induced productions of IgG1 vs IgG2a and IgG3 subclasses in relation to the mRNA expression of INF-gamma (Th1 cytokine promoting IgG2a and IgG3 production), IL-4 (Th2 cytokine promoting IgG1 production), and IL-10 (Th2 cytokine) in CD4+ T cells from lupus-prone MRL mice. For this purpose, two paired sets of MRL mice were chosen for the comparison of these parameters: (a) MRL-lpr/lpr (lpr for lymphoproliferation) and its recently described substrain with a prolonged survival, termed MRL-lpr/lpr.ll (ll for long lived) and (b) MRL male mice bearing the Yaa (Y-linked autoimmune acceleration) gene (MRL.Yaa) with an accelerated disease and their male counterparts lacking the Yaa gene. We demonstrate herein that the accelerated development of lupus-like autoimmune disease in MRL-lpr/lpr and MRL.Yaa mice, as compared with MRL-lpr/lpr.ll and MRL-+/+ mice, respectively, was correlated with an enhanced expression of IFN-gamma vs IL-4 and IL-10 mRNA in CD4+ T cells, which paralleled with an increase of spontaneous and foreign T cell-dependent antigen-induced productions of IgG2a and IgG3 vs IgG1 antibodies. These data suggest that an imbalance towards Th1 predominance may play a significant role in the acceleration of lupus-like autoimmune disease in MRL mice.

bcl-x exhibits regulated expression during B cell development and activation and modulates lymphocyte survival in transgenic mice

We have assessed during B cell development, the regulation and function of bcl-x, a member of the bcl-2 family of apoptosis regulatory genes. Here we show that Bcl-xL, a product of bcl-x, is expressed in pre-B cells but downregulated at the immature and mature stages of B cell development. Bcl-xL but not Bcl-2 is rapidly induced in peripheral B cells upon surface immunoglobulin M (IgM) cross-linking, CD40 signaling, or LPS stimulation. Transgenic mice that overexpressed Bcl-xL within the B cell lineage exhibited marked accumulation of peripheral B cells in lymphoid organs and enhanced survival of developing and mature B cells. B cell survival was further increased by simultaneous expression of bcl-xL and bcl-2 transgenes. These studies demonstrate that Bcl-2 and Bcl-xL are regulated differentially during B cell development and activation of mature B cells. Induction of Bcl-xL after signaling through surface IgM and CD40 appears to provide mature B cells with an additional protective mechanism against apoptotic signals associated with antigen-induced activation and proliferation.

Age-dependent injury in human umbilical vein endothelial cells: relationship to apoptosis and correlation with a lack of A20 expression

BACKGROUND

It has recently been shown that human umbilical vein endothelial cells (HUVEC) become increasingly sensitive to growth factor deprivation, resulting in cell death, as a function of age in culture. The overall goal of the present study was to investigate the mechanism of lethal injury in these cells and compare the injury process to other known mechanisms of injury in the same cells.

EXPERIMENTAL DESIGN

HUVEC were established in culture and maintained for four passages. Injury to first-passage cells and fourth-passage cells were examined for injury in the presence of agents that are known to confer resistance to apoptosis. Ultrastructural features of injury and DNA fragmentation patterns were assessed. Expression of factors that are known to be associated with resistance to apoptosis in other models were assessed.

RESULTS

Fourth-passage HUVEC undergoing injury exhibited morphologic features characteristic of apoptosis and DNA fragmentation. Agents known to inhibit apoptotic cell injury in other models inhibited injury. A20 expression was correlated with resistance to injury in fourth-passage HUVEC, but there was no correlation between bcl-2 and bcl-x expression and resistance to injury.

CONCLUSIONS

HUVEC injury resulting from growth factor deprivation increases as a function of age in vitro and appears to be a form of apoptosis. A20 expression may confer resistance to cell injury through this pathway.

Bcl-XL displays restricted distribution during T cell development and inhibits multiple forms of apoptosis but not clonal deletion in transgenic mice

The survival of T lymphocytes is tightly controlled during development. Here, we show that Bcl-xL, a protein homologue of Bcl-2, is highly regulated in the thymus in a pattern different than that of Bcl-2. The maximum expression was in CD4+CD8+ thymocytes, a developmental stage where Bcl-2 is downregulated. To assess the role of Bcl-xL in thymocyte apoptosis, we generated mice overexpressing an E mu-bcl-x transgene within the T cell compartment. Constitutive expression of Bcl-xL resulted in accumulation of thymocytes and mature T cells in lymphoid organs. Thymocytes overexpressing Bcl-xL exhibited increased viability in vitro and were resistant to apoptosis induced by different signals, including glucocorticoid, gamma irradiation, calcium ionophore, and CD3 cross-linking. However, Bcl-xL was unable to block clonal deletion of thymocytes reactive with self-superantigens or H-Y antigen. These studies demonstrate that Bcl-2 and Bcl-xL, two functionally related proteins, are regulated independently during T cell development. In contrast to Bcl-2, which has been implicated in the maintenance of mature T cells, Bcl-xL appears to provide a survival signal for the maintenance of more immature CD4+CD8+ thymocytes before positive selection.

Modulation of anti-IgM-induced B cell apoptosis by Bcl-xL and CD40 in WEHI-231 cells. Dissociation from cell cycle arrest and dependence on the avidity of the antibody-IgM receptor interaction

The demise of B cell progenitors expressing functional IgM receptors for self appears to be the main mechanism by which B cell tolerance is accomplished. The genetic mechanisms that regulate the death process during this critical step of B cell development are still poorly understood. We have studied the regulation of apoptosis in WEHI-231 lymphoma cells after treatment with a panel of anti-IgM mAbs as an in vitro model of clonal B cell deletion. We showed that a product of bcl-x, Bcl-xL, can inhibit anti-IgM-induced apoptosis but not cell cycle arrest in a dose-dependent manner. Bcl-xL was efficient in protecting B cells from low but not high avidity anti-IgM mAbs. In contrast to that observed with Bcl-xL, CD40 stimulation was efficient in inhibiting both cell cycle arrest and apoptosis after IgM cross-linking regardless of the binding avidity of the anti-IgM Ab. Moreover, activation through IgM receptors but not CD40 induced up-regulation followed by rapid down-modulation of Bcl-xL. Thus, the capacity of Bcl-xL to modulate anti-IgM-induced apoptosis in WEHI-231 cells is highly dependent on the avidity of the Ab-IgM receptor interaction.

Modulation of anti-IgM-induced B cell apoptosis by Bcl-xL and CD40 in WEHI-231 cells. Dissociation from cell cycle arrest and dependence on the avidity of the antibody-IgM receptor interaction

The demise of B cell progenitors expressing functional IgM receptors for self appears to be the main mechanism by which B cell tolerance is accomplished. The genetic mechanisms that regulate the death process during this critical step of B cell development are still poorly understood. We have studied the regulation of apoptosis in WEHI-231 lymphoma cells after treatment with a panel of anti-IgM mAbs as an in vitro model of clonal B cell deletion. We showed that a product of bcl-x, Bcl-xL, can inhibit anti-IgM-induced apoptosis but not cell cycle arrest in a dose-dependent manner. Bcl-xL was efficient in protecting B cells from low but not high avidity anti-IgM mAbs. In contrast to that observed with Bcl-xL, CD40 stimulation was efficient in inhibiting both cell cycle arrest and apoptosis after IgM cross-linking regardless of the binding avidity of the anti-IgM Ab. Moreover, activation through IgM receptors but not CD40 induced up-regulation followed by rapid down-modulation of Bcl-xL. Thus, the capacity of Bcl-xL to modulate anti-IgM-induced apoptosis in WEHI-231 cells is highly dependent on the avidity of the Ab-IgM receptor interaction.

The ability of B cells to participate in allogeneic cognate T-B cell interactions in vitro depends on the presence of CD4+ T cells during their development

We have assessed in vitro whether the absence of T cells in the natural environment of F1 hybrid mice influences the ability of their B cells to participate in an allogeneic interaction with CD4+ cells from parental mice. For this purpose, B cells from athymic CB6F1 nu/nu mice or from CB6F1 mice depleted in different T cell subsets were incubated in vitro with purified CD4+ BALB/c cells. Here, we show that B cells from CB6F1 nu/nu mice or from euthymic CB6F1 mice depleted from birth of CD4+ cells were unable to respond to allogeneic stimulation with BALB/c CD4+ T cells, which produce normal levels of cytokines. The addition of dendritic cells from euthymic CB6F1 mice did not revert this defect. B cells from CB6F1 mice lacking CD4+ T cells showed a selective reduction in the expression of CD23. We found a complete restoration of both the CD23 expression and the ability of CB6F1 nu/nu B cells to respond in vitro to an allogeneic stimulation by CD4+ cells in two instances: (1) after neonatal engraftment of a syngeneic thymus into CB6F1 nu/nu mice, which partially reconstitutes the mature T cell populations; and (2) after preincubation of B cells from CB6F1 nu/nu mice with high concentrations of rIL-4. However, the addition of an anti-CD23 mAb did not interfere with the polyclonal activation of CB6F1 B cells in this system. These results indicate that CD4+ cells play an important role in the functional maturation of B cells by promoting their ability to participate in allogeneic cognate T-B cell interactions.

The ability of B cells to participate in allogeneic cognate T-B cell interactions in vitro depends on the presence of CD4+ T cells during their development

We have assessed in vitro whether the absence of T cells in the natural environment of F1 hybrid mice influences the ability of their B cells to participate in an allogeneic interaction with CD4+ cells from parental mice. For this purpose, B cells from athymic CB6F1 nu/nu mice or from CB6F1 mice depleted in different T cell subsets were incubated in vitro with purified CD4+ BALB/c cells. Here, we show that B cells from CB6F1 nu/nu mice or from euthymic CB6F1 mice depleted from birth of CD4+ cells were unable to respond to allogeneic stimulation with BALB/c CD4+ T cells, which produce normal levels of cytokines. The addition of dendritic cells from euthymic CB6F1 mice did not revert this defect. B cells from CB6F1 mice lacking CD4+ T cells showed a selective reduction in the expression of CD23. We found a complete restoration of both the CD23 expression and the ability of CB6F1 nu/nu B cells to respond in vitro to an allogeneic stimulation by CD4+ cells in two instances: (1) after neonatal engraftment of a syngeneic thymus into CB6F1 nu/nu mice, which partially reconstitutes the mature T cell populations; and (2) after preincubation of B cells from CB6F1 nu/nu mice with high concentrations of rIL-4. However, the addition of an anti-CD23 mAb did not interfere with the polyclonal activation of CB6F1 B cells in this system. These results indicate that CD4+ cells play an important role in the functional maturation of B cells by promoting their ability to participate in allogeneic cognate T-B cell interactions.

Menstrual disorders in girls with systemic lupus erythematosus treated with cyclophosphamide

To study the ovarian toxicity associated with cyclophosphamide in girls with systemic lupus erythematosus (SLE), we retrospectively reviewed the charts of 30 SLE girls aged 16 yr or younger at diagnosis, followed at three university hospitals. Gynaecological history was extracted from the charts or obtained prospectively. Ten had not received cyclophosphamide therapy, six were treated with daily oral cyclophosphamide, 10 with intravenous pulses and four with daily oral and intravenous pulses. Median oral cyclophosphamide dose was 38 g (inter-quartile range 75) and median intravenous dose 12.95 g (inter-quartile range 6.2). Six girls had oligomenorrhoea (20%) and one amenorrhoea (3%). Two treated with oral cyclophosphamide had oligomenorrhoea (33%) and one amenorrhoea (17%), two treated with both oral and intravenous pulses had oligomenorrhoea (50%), and none of those treated with intravenous pulses alone had menstrual disturbances (50% oral vs 0% intravenous pulses; P = 0.016). Girls who had menstrual disturbances had received higher doses of cyclophosphamide than those who did not (medians: 63 vs 15 g; P < 0.05). In summary, menstrual disturbances in SLE girls treated with cyclophosphamide are related to the total dose and perhaps to the administration method.

CD4+ T cells determine the ability of spleen cells from F1 hybrid mice to induce neonatal tolerance to alloantigens and autoimmunity in parental mice

Spleen cells from F1 hybrid mice injected into newborn parental mice induce a state of cytolytic unresponsiveness to the corresponding alloantigens. However, these mice develop a transient autoimmune syndrome characterized by the production of multiple autoantibodies and glomerulonephritis. Previous reports indicated that the depletion of F1 donor T cells, shortly prior the injection into parental mice, does not interfere with any of these events. Here, we have explored whether the continuous absence of T cells in F1 mice influences the ability of their spleen cells to induce neonatal tolerance to alloantigens and the associated autoimmune manifestations. Our results revealed that spleen cells from athymic (BALB/c x C57BL/6) F1 hybrid (CB6F1) nu/nu mice or from euthymic CB6F1 mice depleted from birth of CD4+ T cells, but not of CD8+ T cells, are unable to induce neonatal tolerance to alloantigens and autoimmune manifestations. By contrast, the partial reconstitution of T cells in CB6F1 nu/nu mice, after the neonatal graft of a syngeneic thymus, restored the capacity of spleen cells from these mice to induce tolerance and autoimmunity when injected into newborn BALB/c mice. These results demonstrate that the functional defect of spleen cells from athymic CB6F1 nu/nu mice to induce neonatal tolerance to alloantigens is directly related to the long-term absence of mature CD4+ T cells. Interestingly, a new increase in the titers of anti-DNA Ab was observed when spleen cells from athymic CB6F1 nu/nu mice were injected into adult BALB/c mice that had been tolerized at birth with normal CB6F1 spleen cells. This finding indicates that B cells from CB6F1 nu/nu mice recover their capacity to interact with alloreactive Th2 cells when they are placed into mice having functional CD4+ T cells. These data indicate that the continuous absence of CD4+ T cells causes a reversible functional defect in F1 spleen cells that determines their inability to induce neonatal tolerance and autoimmunity.

Relapsing focal myositis: a case report

We present a 9 year old boy with a focal myositis presenting as a pseudotumor on the right calf. Other smaller masses were present in the thigh and pretibial area on the same leg. The principal lesion recurred after two surgical excisions. Corticosteroid treatment was unsuccessful. However, methotrexate therapy resulted in a progressive regression of the lesions.

Therapeutic effect of early thymic irradiation in (NZB x NZW)F1 mice, associated with a selective decrease in the levels of IgG3 and gp70-anti-gp70 immune complexes

The lupus-prone (NZB x NZW)F1 female mice (NZB/W) develop an autoimmune disease characterized by production of autoAb and fatal glomerulonephritis. Since it has been previously shown that total lymphoid irradiation has a beneficial effect in this model, we have analyzed whether early thymic irradiation (ETI) could improve the course of the lupus-like syndrome in these mice. NZB/W mice received thymic irradiation (4500 rads) beginning at 10 weeks of age, prior to the onset of autoimmune manifestations. Then, they were evaluated for survival, renal histology, and serological markers of autoimmunity, in comparison to nonirradiated NZB/W females. The treatment with ETI improved nephritis and survival in NZB/W mice: 50% mortality was observed at 12 months in irradiated mice and at 9 months in untreated mice. This improved survival could not be attributed to a reduction in the titers of anti-dsDNA Ab nor in the levels of total immune complexes which were essentially identical in both groups. By contrast, this improvement was related to a selective normalization in the serum levels of IgG3 and gp70-anti-gp70 immune complexes (gp70IC) in ETI NZB/W female mice as compared to that seen in nonirradiated NZB/W females. These data show the therapeutical effect of ETI and support the pathogenic role of IgG3 and gp70IC in the development of glomerulonephritis in NZB/W mice.

Effect of long-term anti-CD4 or anti-CD8 treatment on the development of lpr CD4- CD8- double negative T cells and of the autoimmune syndrome in MRL-lpr/lpr mice

We have determined the effect of anti-CD4 or anti-CD8 monoclonal antibody (mAb) treatment from birth on the generation of the lpr CD4- CD8- double-negative (DN) T cell subset and on the development of lupus-like autoimmune syndrome in MRL-lpr/lpr mice. Both anti-CD4 and anti-CD8 mAb treatments resulted in a marked inhibition of lymph-adenopathy, whereas the development of the lpr DN T cells and of the lupus-like autoimmune syndrome strikingly differed in these two groups of mice. The treatment with anti-CD8 mAb almost completely blocked the appearance of the lpr DN T cells without any significant effect on the development of lupus-like autoimmune syndrome in MRL-lpr/lpr mice. In contrast, mice treated with anti-CD4 mAb failed to develop a lupus-like syndrome, while they still developed the lpr DN T cell subset, the predominant population in their lymph nodes, although absolute numbers were markedly diminished. Our results support the idea that CD8+ T cells are a major source of the lpr DN T cells, and that the lpr DN T cells play a minor, if any, role in the pathogenesis of lupus-like autoimmune syndrome in MRL-lpr/lpr mice.

Selective enhancing effect of the Yaa gene on immune responses against self and foreign antigens

The BXSB Y chromosome-linked mutant gene, Yaa, accelerates the progression of a lupus-like autoimmune syndrome only in mice that are predisposed to autoimmune diseases. Unlike the lpr gene, which causes the defects in the Fas antigen-mediating apoptosis, the autoimmune enhancing activity of the Yaa gene is selective, depending on autoantigens, and varies among lupus-prone mice. To obtain a better definition of the role of the Yaa gene in the acceleration of autoimmune disease, we have investigated immune responses to several foreign antigens to determine whether the Yaa gene is able to potentiate immune responses to foreign antigens in a selective manner. We report here that the Yaa gene potentiated immune responses against foreign antigens only in mice which are genetically (H-2-linked) low responding, but not high or non-responding. Moreover, studies on Yaa(+)-Yaa- double bone marrow chimeric mice revealed that B cells from Yaa+ mice were selectively stimulated to produce antibodies to low-responding antigen, human IgG, while both B cell populations similarly responded to high-responding antigen, ovalbumin. Our results suggest that first, the selective immune enhancing activity of the Yaa gene may be related to differences in the capacity of T helper cells specific for given self or foreign antigens; and second, a specific cognate interaction of T helper cells with Yaa+ B cells is apparently responsible for the selective enhancement of immune responses to antigens, to which mice are genetically low responding.

Bcl-2 and Bcl-x: regulatory switches for lymphoid death and survival

The survival and death of lymphoid cells is under the control of a genetic program. Cell death is activated at different stages of development and serves to remove unnecessary and autoreactive lymphocytes, as well as to limit the immune response. The survival of cells is regulated by a set of genes that act as repressors of the cell death mechanism. Of these, bcl-2 and bcl-x exhibit a striking pattern of regulation during lymphoid maturation and can inhibit several forms of apoptotic cell death. Here, Gabriel Núñez and colleagues review recent developments in the field, particularly focusing on the role of the Bcl-2 and Bcl-x proteins in regulating lymphoid death and survival.

Bcl-2 expression during T-cell development: early loss and late return occur at specific stages of commitment to differentiation and survival

During T-cell development CD3-CD4-CD8- (double-negative) thymocytes proliferative and produce an enormous number of CD3loCD4+CD8+ (double-positive) thymocytes which are destined to die intrathymically unless rescued by positive selection. Those which survive become mature CD3hiCD4/8+ (single-positive) cells and are the precursor of peripheral blood lymphocytes. The product of the bcl-2 protooncogene has been implicated in preventing programmed cell death and is required for prolonged lymphocyte survival following maturation. Previously we and others have reported that Bcl-2 protein expression is biphasic, being high in proliferating double-negative stem cells, low in all double-positive thymocytes except for 1-5% of these cells, and restored in mature, single-positive thymocytes. However, it remained unclear which signaling and selection events regulate Bcl-2 during T-cell maturation. Now we have utilized four-color flow cytometry in normal and genetically altered mice for a detailed analysis of Bcl-2 expression as it relates to T-cell receptor (TCR) expression and positive selection. These studies show that (i) expression of a transgenic TCR in double-negative thymocytes does not lead to premature loss of Bcl-2; thus, Bcl-2 downregulation is not solely due to TCR expression; (ii) Bcl-2 expression is lost at the early transitional CD3-/loCD4-CD8+ stage, prior to expression of CD4; (iii) the Bcl-2+ double-positive thymocytes are those which have undergone positive selection; and (iv) upregulation of Bcl-2 during positive selection requires participation of the CD4 or CD8 co-receptor. These results demonstrate that Bcl-2 and TCR expression are regulated independently during T-cell development, and suggest a role for the CD4 or CD8 co-receptor in Bcl-2 induction during positive selection.

The Yaa gene abrogates the major histocompatibility complex association of murine lupus in (NZB x BXSB)F1 hybrid mice

To investigate the specific contribution of select MHC class II genes on the development of murine lupus, H-2 congenic (NZB x BXSB)F1 hybrid mice bearing either H-2b/b, H-2d/b, or H-2d/d haplotypes were generated. We compared the clinical development (autoantibody production and glomerulonephritis) of systemic lupus erythematosus (SLE) in these three F1 hybrids in the presence or absence of the mutant gene, Yaa (Y chromosome-linked autoimmune acceleration), which normally accelerates the progression of murine SLE. (NZB x BXSB)F1 hybrid female mice bearing either the H-2b/b or H-2d/b haplotype developed a rapid course of severe SLE, while the appearance of disease was markedly delayed in H-2d/d hybrid females. However, in the presence of the Yaa gene, H-2d/d F1 males developed SLE as severe as H-2b/b and H-2d/b F1 males. These data indicate that (a) the conventional H-2b is a haplotype leading to susceptibility for murine SLE, while H-2d is a relatively resistant haplotype; (b) the H-2b haplotype exhibits a dominant effect on autoimmune responses, similar to the classical MHC-linked Ir gene effect; and (c) most strikingly, the Yaa gene totally abrogates the MHC effect on murine lupus in (NZB x BXSB)F1 hybrid mice.

Lack of association of V beta 8+ T cells with lupus-like syndrome in MRL-lpr/lpr mice

To evaluate the role of V beta 8+ T cells in the development of lupus-like autoimmune syndrome in MRL-lpr/lpr mice, we treated them with the F23.1 anti-V beta 8 monoclonal antibody (mAb) from birth to 4 months of age. Here we report that almost complete depletion of V beta 8+ T cells by the F23.1 mAb treatment neither inhibited nor delayed the development of hypergammaglobulinemia, autoantibody production and autoimmune glomerulonephritis in MRL-lpr/lpr mice. In addition, the F23.1 mAb treatment did not prevent the development of lymphadenopathy and the generation of a CD4-CD8- double-negative T cell subset, characteristically accumulating in lpr lymph nodes. Our results strongly argue against the idea that the V beta 8+ T cells play a critical role in the development of lupus-like autoimmune syndrome in MRL-lpr/lpr mice.

c-myc and bcl-2 modulate p53 function by altering p53 subcellular trafficking during the cell cycle

We have studied the ability of c-myc and bcl-2 oncogenes to modulate p53 function. Our studies show that coincident expression of human Bcl-2 protein with p53 prolongs survival of murine erythroleukemia cells. This effect was associated with a loss of the G1 specificity of p53-mediated cell cycle arrest. Furthermore, we found that the c-myc and bcl-2 genes cooperate to inhibit p53 functions. Coexpression of bcl-2 and c-myc can totally overcome p53-induced apoptosis and cell cycle arrest by altering the subcellular trafficking of p53 during the cell cycle: the p53 remains in the cytoplasm of the cotransfected cells during a critical period in G1. This finding suggests a mechanism by which normal hematopoietic progenitors can survive and proliferate despite p53 expression and by which the inappropriate expression of bcl-2 and c-myc can cooperate in transformation.

Differences in non-MHC alloantigens promote tissue rejection but fail to mediate allogeneic co-operation and autoimmunity in mice neonatally injected with semi-allogeneic F1 B cells

Mice injected at birth with semi-allogeneic lymphoid cells develop a lupus-like autoimmune syndrome in which donor B cells are polyclonally activated by host alloreactive CD4+ T cells, producing autoantibodies and immune complex-mediated glomerulonephritis. It has been demonstrated that the recognition of major histocompatibility complex (MHC) class II alloantigens triggers the development of a complete disease. But differences in either MHC class I molecules or Mls-1 antigens are not sufficient to induce production of autoantibodies. Here we have investigated whether differences in other non-MHC alloantigens could induce a similar autoimmune disease and whether the maternal environment could modulate the T-B allogeneic co-operation in this model. For this purpose (BALB/c x BC20)F1 hybrid females were backcrossed with BC20 males. R2 mice obtained in this backcross were neonatally injected with 10(8) (C57BL/6 x BALB.Igb)F1 spleen cells and the tolerance against maternal derived BALB/c alloantigens as well as the development of autoimmune manifestations were subsequently evaluated. In contrast to R2 mice injected at birth with (C57BL/6 x BALB.Igb)F1 cells, control R2 mice rejected skin grafts from BALB/c mice and B cells from (C57BL/6 x BALB.Igb)F1 mice, independently of their H-2 haplotype (H-2b/d or H-2b/b). Nevertheless, after neonatal injection of (C57BL/6 x BALB.Igb)F1 cells, none of 19 H-2b/d R2 injected mice presented autoimmune manifestations, in contrast with the typical autoimmune disease observed in all neonatally injected H-2b/b R2 mice (26 mice). These results support that the development of autoimmunity in this model depends exclusively upon differences in MHC class II alloantigens and that the relationship between mother and fetus, through the pregnancy or the breast suckling, is not sufficient to inhibit cytolytic and allo-helper responses against non-inherited maternal-derived alloantigens.

Molecular and cellular basis for pathogenicity of autoantibodies

Using two different kinds of monoclonal autoantibodies, anti-mouse RBC (MRBC) autoantibodies and IgG3 rheumatoid factor (RF) cryoglobulins, we have attempted to better define the molecular and cellular basis of the pathogenicity of autoantibodies. Among eight anti-MRBC monoclonal antibodies (mAbs) obtained from NZB mice, only five of them are able to cause anemia. The distinct differences in specificity between pathogenic and non-pathogenic anti-MRBC mAbs emphasize the importance of autoantibody specificity for the pathogenesis of autoimmune hemolytic anemia. Histological examination has revealed that Fc gamma receptor-mediated erythrophagocytosis and sequestration of agglutinated RBC in spleens and livers are the major pathogenic mechanisms of hemolytic anemia. This indicates that the affinity of autoantibodies for the Fc gamma receptors of phagocytes and/or the ability to cause hemagglutination, both of which vary among immunoglobulin isotypes, are additional factors determining the pathogenic activity of anti-MRBC autoantibodies. Studies on a panel of anti-IgG2a RF mAbs derived from MRL-lpr/lpr mice have demonstrated that only the IgG3 isotypes of RF mAb are able to generate cryoglobulins and to induce skin leukocytoclastic vasculitis and glomerulonephritis in normal mice. Although the cryoglobulin activity of RF mAb associated with the IgG3 isotype has been shown to be solely responsible for the generation of glomerular lesions (both RF and cryoglobulin activities are necessary for cutaneous vascular lesions), the absence of nephritogenic activity by some IgG3 monoclonal cryoglobulins supports the idea that qualitative features of cryoglobulins are critical to determine their pathogenic activities. Of interest, IgG3 autoantibodies lacking the cryoglobulin activity may not be harmful, but even protective against the development of IgG3 cryoglobulin-mediated tissue lesions, because they inhibit the cryoglobulin formation of pathogenic IgG3 autoantibodies as a result of their nonspecific IgG3 Fc-Fc interaction. Our results on monoclonal autoantibodies clearly indicate the importance of certain subpopulations of autoantibodies in the pathogenesis of autoantibody-mediated cellular and tissue injuries.

Developmental regulation of the Bcl-2 protein and susceptibility to cell death in B lymphocytes

Cell death is a prominent feature of B cell development. For example, a large population of B cells dies at the pre-B cell stage presumably due to the failure to express a functional immunoglobulin receptor. In addition, developing B cells expressing antigen receptors for self are selectively eliminated at the immature B cell stage. The molecular signals that control B cell survival are largely unknown. The product of the bcl-2 proto-oncogene may be involved as its overexpression inhibits apoptotic cell death in a variety of biological systems. However, the physiological role of the endogenous Bcl-2 protein during B cell development is undetermined. Here we show a striking developmental regulation of the Bcl-2 protein in B lymphocytes. Bcl-2 is highly expressed in CD43+ B cell precursors (pro-B cells) and mature B cells but downregulated at the pre-B and immature B cell stages of development. We found that Bcl-2 expressed by B cells is a long-lived protein with a half-life of approximately 10 h. Importantly, susceptibility to apoptosis mediated by the glucocorticoid hormone dexamethasone is stage-dependent in developing B cells and correlates with the levels of Bcl-2 protein. Furthermore, expression of a bcl-2 transgene rescued pre-B and immature B cells from dexamethasone-induced cell death, indicating that Bcl-2 can inhibit the apoptotic cell death of progenitors and early B cells. Taken together, these findings argue that Bcl-2 is a physiological signal controlling cell death during B cell development.

Physiological cell death in B lymphocytes: I. Differential susceptibility of WEHI-231 sublines to anti-Ig induced physiological cell death and lack of correlation with bcl-2 expression

WEHI-231 is a murine lymphoma generally considered to represent an immature B cell. Cross-linking of slg on WEHI-231 leads to growth arrest and eventually physiological cell death (PCD). We characterized three sublines of WEHI-231 by flow cytometry and compared their responses with slg cross-linking. All sublines had identical expression of a series of common B cell surface markers (IgM, IgD, Fc gamma R, ICAM-1, and CD45), but one was I-A-. Despite the phenotypic similarities between these sublines, anti-IgM caused aptotosis in only two sublines, although it inhibited growth in all three. The growth arrest induced by anti-IgM was reversible by lipopolysaccharide and Th2 clones and independent of Fc gamma R engagement. Anti-IgD, unlike anti-IgM, induced neither growth arrest nor apoptosis. To further compare the sublines' susceptibility to PCD, we investigated their responses to anti-IgM by ultrastructural morphology, [3H]thymidine release, propidium iodide exclusion, and incorporation into DNA. By all these experimental criteria, two of the WEHI-231 sublines were susceptible to PCD while the third demonstrated remarkable resistance to anti-IgM, but not irradiation or Th1-induced PCD. This differential susceptibility to PCD did not correlate with either bcl-2 levels in the resting cells or to the decrease in bcl-2 expression following slg engagement. We discuss the implications of these findings for our understanding of PCD in B cells.

The role of the Yaa gene in lupus syndrome

The BXSB/MpJ (BXSB) murine strain (H-2b) spontaneously develops an autoimmune syndrome with features of systemic lupus erythematosus (SLE) that affects males much earlier than females. A mutant gene located on the BXSB Y chromosome, designated Yaa (Y chromosome-linked autoimmune acceleration), is responsible for the acceleration of the disease observed in male BXSB mice. Studies on H-2 congenic and I-E transgenic mice have clearly demonstrated that the MHC class II genes play a crucial role in the development or protection of SLE. However, the MHC effect can be completely masked by the presence of the Yaa gene in mice with certain genetic backgrounds. It is intriguing that the Yaa gene effect is selective on autoimmune responses, varying in different lupus-prone mice. Studies on immune responses against foreign antigens have shown that the Yaa gene potentiates immune responses only against antigens to which mice are genetically (H-2-linked) low-responding, but not high-responding. Thus, the selective immune enhancing activity of the Yaa gene may be related to differences in the capacity of T helper cells specific for given antigens. Moreover, studies on Yaa(+)-Yaa- bone marrow cell chimeric mice have suggested that a specific cognate interaction of T helper cells with Yaa+ B cells is responsible for a selective enhancing effect of immune responses to foreign antigens as well as autoantigens. It is significant that unlike the lpr mutation, whose abnormality is associated with the capacity of the Fas antigen to mediate apoptosis, the Yaa gene by itself is unable to induce significant autoimmune responses in mice without apparent SLE background. This suggests that the molecular defect of the Yaa gene is likely to differ from that of the lpr gene, and that the Yaa gene effect requires the abnormal autosomal genome present in lupus-prone mice. Based on these findings, a possible molecular nature of the Yaa gene abnormality will be discussed.

Polyclonal B cell activation arises from different mechanisms in lupus-prone (NZB x NZW)F1 and MRL/MpJ-lpr/lpr mice

The polyclonal B cell activation is the earliest and most common immunologic abnormality in lupus-prone mice. However, its cellular mechanism(s) has not been well defined. To determine the contribution of CD4+ T cells in this immunologic abnormality, we have depleted CD4+ T cells in lupus-prone (NZB x NZW)F1 and MRL/MpJ-lpr/lpr mice by treating them with anti-CD4 mAb from birth and determined the development of IgM and IgG polyclonal antibody formation. Our results indicate that first, different mechanisms control the development of IgM polyclonal B cell activation in these two autoimmune mice; in (NZB x NZW)F1 mice, IgM polyclonal B cell activation is likely to be a result of an intrinsic B cell defect, whereas CD4+ T cells seem to be responsible for this immunologic abnormality in MRL/MpJ-lpr/lpr mice. Second, the increased production of IgG antibodies, including the IgG3 subclass, was totally regulated by CD4+ T cells in both autoimmune mice. Because IgG3 antibodies can be highly nephritogenic, independent of their immunologic specificities, which is the result of the antibodies' cryoglobulin activity, the active role of CD4+ T cells in the production of IgG3 antibodies in lupus-prone autoimmune mice further strengthens the implication of CD4+ T cells in murine systemic lupus erythematosus.

Polyclonal B cell activation arises from different mechanisms in lupus-prone (NZB x NZW)F1 and MRL/MpJ-lpr/lpr mice

The polyclonal B cell activation is the earliest and most common immunologic abnormality in lupus-prone mice. However, its cellular mechanism(s) has not been well defined. To determine the contribution of CD4+ T cells in this immunologic abnormality, we have depleted CD4+ T cells in lupus-prone (NZB x NZW)F1 and MRL/MpJ-lpr/lpr mice by treating them with anti-CD4 mAb from birth and determined the development of IgM and IgG polyclonal antibody formation. Our results indicate that first, different mechanisms control the development of IgM polyclonal B cell activation in these two autoimmune mice; in (NZB x NZW)F1 mice, IgM polyclonal B cell activation is likely to be a result of an intrinsic B cell defect, whereas CD4+ T cells seem to be responsible for this immunologic abnormality in MRL/MpJ-lpr/lpr mice. Second, the increased production of IgG antibodies, including the IgG3 subclass, was totally regulated by CD4+ T cells in both autoimmune mice. Because IgG3 antibodies can be highly nephritogenic, independent of their immunologic specificities, which is the result of the antibodies' cryoglobulin activity, the active role of CD4+ T cells in the production of IgG3 antibodies in lupus-prone autoimmune mice further strengthens the implication of CD4+ T cells in murine systemic lupus erythematosus.

Prevention of systemic lupus erythematosus in autoimmune BXSB mice by a transgene encoding I-E alpha chain

Males from the BXSB murine strain (H-2b) spontaneously develop an autoimmune syndrome with features of systemic lupus erythematosus (SLE), which results in part from the action of a mutant gene (Yaa) located on the Y chromosome. Like other H-2b mice, the BXSB strain does not express the class II major histocompatibility complex antigen, I-E. Here we report that the expression of I-E (E alpha dE beta b) in BXSB males bearing an E alpha d transgene prevents hypergammaglobulinemia, autoantibody production, and subsequent autoimmune glomerulonephritis. These transgenic mice bear on the majority of their B cells not only I-E molecules, but also an I-E alpha chain-derived peptide presented by a higher number of I-Ab molecules, as recognized by the Y-Ae monoclonal antibody. The I-E+ B cells appear less activated in vivo than the I-E- B cells, a minor population. This limited activation of the I-E+ B cells does not reflect a functional deficiency of this cell population, since it can be stimulated to IgM production in vitro by lipopolysaccharides at an even higher level than the I-E- B cell population. The development of the autoimmune syndrome in the transgenic and nontransgenic bone marrow chimeric mice argues against the possibility that the induction of regulatory T cells or clonal deletion of potential autoreactive T cells as a result of I-E expression is a mechanism of the protection conferred by the E alpha d transgene. We propose a novel mechanism by which the E alpha d transgene protects BXSB mice against SLE: overexpression of I-E alpha chains results in the generation of excessive amounts of a peptide displaying a high affinity to the I-Ab molecule, thereby competing with pathogenic autoantigen-derived peptides for presentation by B lymphocytes and preventing their excessive stimulation.

An MRL/MpJ-lpr/lpr substrain with a limited expansion of lpr double-negative T cells and a reduced autoimmune syndrome

The autosomal recessive mutant gene, lpr, has been shown to accelerate the progression of lupus-like autoimmune disease, which is associated with a massive expansion of a unique CD4-CD8- double-negative T cell subset, in MRL/MpJ mice. Here we report a substrain of MRL/MpJ-lpr/lpr (MRL-lpr) mice which live almost twice as long with delayed development of glomerulonephritis, compared with conventional MRL-lpr mice. This substrain, termed MRL-lpr.II (II for long-lived), develops generalized lymphadenopathy characteristically seen in MRL-lpr mice. However, the expansion of a double negative lpr T cell subset is markedly limited with a mean value of 15% in their lymph nodes compared to about 70% in conventional MRL-lpr mice. Overall production of autoantibodies, such as anti-DNA and rheumatoid factors, does not significantly differ between the two MRL-lpr mice. However, serum levels of cryoglobulins, whose major component is IgG3, are markedly diminished in MRL-lpr.II mice with a parallel decrease in IgG3. Since MRL-lpr.II mice still carry the lpr mutation, as documented by the presence of defects in the Fas antigen, a possible new mutation in this substrain may play a significant role in the pathogenesis of lupus-like autoimmune syndrome.

Effect of cyclosporin A and zidovudine on immune abnormalities observed in the murine acquired immunodeficiency syndrome

Two therapeutic modalities, zidovudine (targeting retroviral replication) and cyclosporin A (targeting immunopathologic consequences of retroviral expression) were evaluated in a murine model of AIDS. In previous studies, cyclosporin A treatment (40 or 60 mg/kg/day) before and after infection with LP-BM5 murine leukemia viruses protected against the development of immunodeficiency disease. The present study extends these findings. First, a low dose of cyclosporin A (20 mg/kg/day) was ineffective, and treatment initiated 5 days after infection did not protect against virus-induced lymphoproliferation and hypergammaglobulinemia. Second, zidovudine added to drinking water (0.1 mg initiated 5 days after infection and continued for 8 weeks) was more effective than 0.2 mg/mL given day 5-12 after infection. This treatment reduced lymph node size, disease severity as determined histologically, retrovirus-induced gp70 expression, and IgE (but not IgM and IgG) levels. Third, combined treatment had an additive, protective effect on lymphocyte proliferative capacity. This successful dual therapeutic strategy in a mouse model has potential applicability for similar approaches in treating human immunodeficiency virus infection.

Systemic lupus erythematosus: a case report with unusual manifestations and favourable outcome after plasmapheresis

We report a case of systemic lupus erythematosus (SLE) in a 15-year-old girl with severe neurological disease, platelet function disorder and pulmonary haemorrhage, which remitted after plasmapheresis. The patient developed protein-losing enteropathy shrinking lung, and acute pancreatitis with pseudocyst formation. These infrequent complication of SLE are discussed.

Murine autoimmune hemolytic anemia resulting from Fc gamma receptor-mediated erythrophagocytosis: protection by erythropoietin but not by interleukin-3, and aggravation by granulocyte-macrophage colony-stimulating factor

We have evaluated the therapeutic activity of recombinant erythropoietin (rEpo), in comparison with recombinant interleukin-3 (rIL-3) and granulocyte-macrophage colony-stimulating factor (rGM-CSF), on a lethal form of acute anemia resulting from Fc gamma receptor-mediated erythrophagocytosis after a single injection (500 micrograms) of a monoclonal anti-mouse red blood cell (MRBC) autoantibody. Continuous perfusion of rEpo before the administration of anti-MRBC monoclonal antibody completely protected animals from death due to anemia with a rapid recovery, while no protection was obtained by rIL-3 perfusion. In contrast, rGM-CSF perfusion markedly accelerated the progression of anemia and the mortality rate. This was found to result from an enhancement of erythrophagocytosis by Kupffer cells and by polymorphonuclear leukocytes that massively infiltrated the livers. Even after the injection of a sublethal dose (100 micrograms) of anti-MRBC monoclonal antibody, rGM-CSF-perfused mice died of a severe form of acute anemia. Furthermore, we have shown that rEpo was able to treat efficiently a spontaneous form of autoimmune hemolytic anemia in a majority of anemic NZB mice, whereas rGM-CSF markedly aggravated anemia. This may be of clinical importance, because GM-CSF administration could exhibit an adverse effect in some autoimmune diseases that involve autoimmune anemia.

Malignant fibrous histiocytoma of the aorta complicated by anuria

Tumors of the aorta have been reported infrequently in the literature. We report a case of a 63-year-old woman diagnosed with malignant aortic fibrous histiocytoma (also known as fibroxanthosarcoma). She was referred to us with suspected occlusion of the right renal artery in a single functioning kidney, with a clinical picture of anuria during the previous 48 hours. We also review 31 previously published cases in the literature.

H-2-linked control of the Yaa gene-induced acceleration of lupus-like autoimmune disease in BXSB mice

The accelerated development of lupus-like autoimmune disease in male BXSB mice (H-2b, I-E-) is associated to the presence of a mutant gene, designated Yaa, located on their Y chromosome. To investigate whether the H-2b haplotype and/or the lack of expression of I-E molecules play any role in the Yaa-linked acceleration of autoimmune disease, an I-E+ BXSB.H-2d congenic strain was created by backcross procedures. We compared the development of autoimmune disease in the novel BXSB.H-2d (I-E+) strain to that of BXSB.H-2b (I-E-) and BXSB.H-2b/d (I-E+) heterozygous mice. Male BXSB.H-2d (I-E+) mice exhibited only a limited production of autoantibodies and a lower incidence of glomerulonephritis with a markedly prolonged survival rate, which were essentially identical to those of female BXSB mice of both-H-2b and H-2d haplotypes. However, BXSB.H-2b/d (I-E+) heterozygous males developed an accelerated disease comparable to that of conventional BXSB.H-2b (I-E-) male mice. These results indicate that the expression of I-E molecules and consequent clonal deletion or anergy of I-E reactive T cells does not appear to be responsible for the prevention of accelerated autoimmune disease in BXSB.H-2d (I-E+) male mice. The finding that the Yaa gene-induced acceleration of lupus-like autoimmune disease is modulated by gene(s) within or closely linked to the H-2 complex underlines the crucial role of the major histocompatibility complex and the polygenetic nature of autoimmune disease in BXSB mice.

Selective autoantibody production by Yaa+ B cells in autoimmune Yaa(+)-Yaa- bone marrow chimeric mice

The accelerated autoimmune syndrome observed in BXSB/MpJ male mice is associated with the presence on the Y chromosome of an as yet unidentified mutant gene, designated Y chromosome-linked autoimmune acceleration (Yaa). To study the mechanisms by which the Yaa gene accelerates and/or induces the production of autoantibodies, we have developed double-congenic bone marrow chimeras containing B cells from autoimmune males carrying the Yaa gene, and from nonautoimmune male or female mice lacking it and differing by the Igh allotype. The analysis of the allotype of total immunoglobulins and anti-DNA antibodies in Yaa+ male-normal female (Yaa-) chimeric mice revealed that the selective activation of B cells from autoimmune Yaa+ male mice was responsible for the hypergammaglobulinemia and autoantibody production. This phenomenon was not due to an anti-HY interaction between female T helper cells and male B cells, because first, Yaa+ B cells were selectively stimulated to produce autoantibodies in Yaa+ male-Yaa- male chimeric mice; and second, normal male and female chimeras failed to develop an autoimmune syndrome. In addition, the fact that both B cell populations in Yaa(+)-Yaa- chimeras similarly responded to a foreign antigen, human IgG, argues against the possibility that the selective activation of Yaa+ B cells may be due to their hyper-responsiveness to T helper signals. We propose that a cognate interaction of T helper cells with Yaa+ B cells, because of possible T cell recognition of a Yaa-related molecule expressed on Yaa+ B cells, may be responsible for the acceleration and/or induction of autoantibodies in BXSB/MpJ mice.