The contribution of L3T4+ T cells to lymphoproliferation and autoantibody production in MRL-lpr/lpr mice

Effect of mizoribine on pulmonary lesions in MRL/lpr/lpr mice

The present study was made to investigate the effect of mizoribine (MZR), an imidazole nucleoside immunosuppressant, on pulmonary lesions and immunological mode of action of MRL/lpr/lpr mice. Four-week-old female MRL/lpr/lpr mice were injected subcutaneously with 20 mg/kg body weight of MZR every other day. For control, mice were given phosphate-buffered saline (PBS) every other day. MZR caused the delay in the histological development of peribronchial and perivascular lymphocytic infiltrations in the lungs of MRL/lpr/lpr (MRL/lpr) mice. And then, MZR suppressed the number of immunoglobulin (Ig) (IgG and IgM) secreting B cells and anti-DNA-secreting B cells in the spleen of MRL/lpr/lpr mice. The above data indicate that MZR could be useful for the treatment of pulmonary lesions associated with autoimmune disorders such as systemic lupus erythematosus (SLE).

Short-term administration of selected anti-T-cell receptor V beta chain specific MoAb reduces sialadenitis in MRL/lpr mice

Sialadenitis develops spontaneously in MRL/Mp mice bearing a lymphoproliferative gene, lpr (MRL/Mp-lpr/lpr). Based on recent observations of an oligoclonal expansion of T-cell receptor (TCR) expressing V beta chain families (V beta 4, V beta 8.1,2, V beta 10b) in salivary glands of these mice we have initiated selective antibody therapy. Treatment with monoclonal antibodies (MoAb) specific for T cells expressing a mixture of TCR V beta 4, V beta 8.1,2 and V beta 10b was applied to MRL/lpr mice before and after the spontaneous development of sialadenitis. The in vivo treatment with V beta 4, V beta 8.1,2 and V beta 10b MoAb did not prevent the development of sialadenitis. However, in animals with established sialadenitis, treatment with the MoAb significantly decreased the inflammation compared with the control groups. Immunohistochemical staining of cell phenotypes demonstrated a change in the ratio of CD4/CD8 in the animals with established sialadenitis. Altogether, these findings illustrate that it is possible to modulate sialadenitis and infiltrate cell phenotypes in vivo in MRL/lpr mice with specific anti-TCR V beta MoAb treatment.

Glycobiology: 'the function of sugar in the IgG molecule'

Immunoglobulin G (IgG) is glycosylated in both the Fc and the Fab regions of the protein with a heterogeneous ensemble of structures (glycoforms) that is both highly reproducible (i.e. nonrandom) and site specific. In normal IgG, the 2 highly conserved oligosaccharides of the Fc region are found buried between the CH2 domains, forming specific protein-saccharide interactions with the Fc protein surface. One of the functions attributed to the Fc oligosaccharides of normal IgG is to maintain the conformational arrangements of the Fc domains as well as the hinge regions. These structural features are necessary for Fc effector functions such as Clq and monocyte binding. A hallmark of rheumatoid arthritis (RA) patients is a dramatic increase in the presence of serum IgG containing Fc oligosaccharides lacking an outer arm galactose residue (termed 'G0' glycoforms). The increased level of G0 has been shown to be directly related to the pathogenesis of RA. Nuclear magnetic resonance relaxation studies of the Fc region from normal and RA IgG, as well as examination of x-ray structures, show that the G0 oligosaccharides have an increased mobility resulting from the loss of binding between the G0 oligosaccharide and the Fc protein surface. From these observations it follows that regions of the protein surface that are normally covered by the oligosaccharide are revealed. The newly accessible protein surface could have lectin-like activity and also be inherently antigenic. In addition, the more mobile G0 oligosaccharide can be recognised by mannose binding protein. As the mannose binding protein can activate complement, and the Fc oligosaccharide would not normally be accessible to protein recognition, this finding might suggest a specific role for the G0 glycoform in inflammation when the appropriate IgG glycoforms are clustered.

Dysregulation of T helper cell cytokines in autoimmune prone NZB x NZW F1 mice

Multifactorial involvement in the pathogenesis of autoimmune NZB/W F1 mice has been well documented. To further elucidate the role of cytokines in the disease development of murine lupus, single spleen cells isolated from NZB/W F1 and non-autoimmune C57BL/6 mice were stimulated with T cell mitogens or anti-CD3 antibody at pre-determined optimal concentration. Supernatants were collected and assayed for production of cytokines including IL-2, gamma-IFN, IL-3, IL-4, IL-5 and IL-10. In both young and old mice, cytokine profiles by mitogen-stimulated T cells showed higher TH2 (type 2 T helper) cell-related cytokine production in NZB/W F1 mice compared to those in non-autoimmune C57BL/6 mice. In contrast, cytokines produced by TH1 (type 1 T helper) cells, such as gamma-IFN and IL-2, were lower in NZB/W F1 mice by stimulation with either mitogen or anti-CD3 antibody. In addition, cytokine production at different time points also demonstrated decreased gamma-IFN and increased IL-4 levels by anti-CD3 stimulated splenic cells in autoimmune NZB/W F1 mice. Furthermore, the IL-10 levels produced by lipopolysaccharide (LPS)-stimulated splenic and peritoneal exudate cells were higher in young NZB/W F1 mice compared to those in C57BL/6 mice. Our data suggest that dysregulation between TH1 and TH2 cells may play an important role in the pathogenesis of autoimmunity in NZB/W F1 mice.

Murine lupus in MRL/lpr mice lacking CD4 or CD8 T cells

MRL/lpr mice develop a systemic autoimmune disease similar to systemic lupus erythematosus in humans. The mice show progressive lymphadenopathy due to the accumulation of an unusual population of CD4-8-(DN) B220+ alpha beta+ T cells. We bred MRL/lpr mice with mice lacking CD4+ or CD8+ T cells by gene targeting via homologous recombination in embryonal stem cells to determine the roles of these cells in the autoimmune disease. No difference in survival or autoantibody levels was noted between CD8-/-lpr and littermate controls. Interestingly, these CD8-/- lpr mice have a reduced level of B220+ DN T cells despite the fact that the degree of lymphadenopathy was unaltered. CD4-/- lpr mice had a diminished autoimmune disease with a reduction in autoantibody production and skin vasculitits, and increased survival compared to littermate controls. However, CD4-/- lpr mice had an enhanced splenomegaly that developed massively by 16-20 weeks of age (5 to 8 greater than lpr control mice) due to the accumulation of DN B220+ T cells. In addition, there were no differences in peripheral lymph node enlargement, although the proportion of DN B220+ T cells was about twofold higher in the CD4-/- lpr mice. These cells were phenotypically identical to the DN population in control lpr mice, indicating that the accumulating DN T cells can be dissociated from the autoimmune disease in these mice. Collectively, our results reveal that the autoimmune disease is dependent on CD4+, but not CD8+ T cells, and that many of the B220+ DN T cells traverse a CD8 developmental pathway.

Combined effects of FK506 (tacrolimus) and cyclophosphamide on atypical B220+ T cells, cytokine gene expression and disease activity in MRL/MpJ-lpr/lpr mice

Groups of female MRL/MpJ-lpr/lpr mice received either saline or FK506 (tacrolimus; 2 mg/kg intraperitoneally) three times weekly, cyclophosphamide (CY; 20 mg/kg) once monthly, or both drugs from 8 weeks of age. Median survival for untreated and CY-treated mice was 26 weeks, and for FK506- and FK506 + CY-treated groups was > or = 44 weeks. Severity of skin lesions and lymph node hyperplasia was markedly reduced by the drug combination, whereas either drug alone was less effective. FK506 or CY alone delayed the onset of proteinuria, but by 24 weeks all of these animals were positive. In contrast, drug combination reduced the prevalence of proteinuria to < or = 60% throughout the 44 weeks of study. Sequential monitoring of peripheral blood lymphocytes revealed that combination therapy but not monotherapy markedly reduced the proportion of atypical CD3+ B220+ and CD3+CD4-CD8- T cells. Neither FK506 nor CY affected the reduction in IL-2 and IL-4 mRNA levels observed in lymph nodes of diseased animals compared with normals. Although the drug combination also did not affect IL-2 mRNA levels, IL-4 mRNA transcripts were increased six-fold compared with saline-treated controls. IL-10 and interferon-gamma (IFN-gamma) mRNAs were induced by FK506, CY and by the drug combination. Serum levels of anti-dsDNA antibodies were reduced in all treatment groups. These data demonstrate improved efficacy of combined T and B cell-directed immunosuppression in murine lupus, associated with marked inhibition of atypical T cells and selective augmentation of IL-4 within the affected lymphoid tissue.

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.

Influence of the lpr environment on the lymph node cell phenotypes in C57BL/6 nubg and nulpr chimeras

Mice homozygous for the lpr gene show a marked lymphoproliferative syndrome. Most T cells which accumulate in their lymphoid organs belong to a fairly unusual subpopulation. Although being CD44+ T cells expressing neither CD4 nor CD8, they are CD3 T-cell receptor (TCR) alpha beta positive and express both Thy-1 and B220, the B-cell form of the CD45 marker. To support engraftment and development of transferred lpr lymphomyeloid cells, athymic recipients must be genetically lpr. While nude/beige (nubg) recipients do not allow the development of any lymphoproliferative syndrome, this is variable in nude/lpr (nulpr) recipients, and the genotypic origin of the proliferating lymphocytes in nulpr recipients is unclear. In this study, the surface phenotype of lymph node cells from nulpr recipients of lpr grafts ([lpr-->nulpr] chimeras) was analysed by flow cytometry, and compared with various chimeras and parental (donor and recipient) strains as controls. Abnormal cells of the lpr type were not detectable either in [lpr-->nubg] chimeras or in [wild-->nubg] controls. Absence of lpr cells was also seen in neonatal lpr thymus-grafted nubg mice engrafted previously with lpr haematopoietic cells. In contrast, a substantial emergence of double-positive B220+ Thy-1+ cells occurred in [lpr-->nulpr] chimeras, together with high levels of CD4+ cells, a substantial fraction of which might express B220. Finally, in thymus-grafted nulpr mice, the levels of B220+ Thy-1+ cells were as high as in lpr mice and there was again an expansion of CD4+ (potentially B220+) cells. Abnormality of the nulpr haemopoietic environment was also shown by the low percentages of T cells, particularly CD8+ cells, in short-lived [wild-->nulpr] chimeras. Taken together, our results underline the differences between the nubg and nulpr environments.

The effects of thymopentin on the development of SLE-like syndrome in the MRL/lpr-lpr mouse

Thymopentin (TP-5) is a synthetic pentapeptide that corresponds to the active 32-36 amino acid sequence of the thymic hormone thymopoietin, of which it retains all the immunomodulatory properties. In this study, we have evaluated the effects of long term prophylactic treatment with TP-5 on the clinical, immunological and histological parameters of the SLE-like syndrome that spontaneously occurs in MRL/lpr-lpr (MRL-lpr) mice. TP-5, administered (s.c.) to these mice at the doses of 1, 10 and 100 mg/kg, was given daily, five times a week, from the 9th to the 26th weeks of life. The prophylactic treatment with TP-5 prolonged in a clear dose-dependent fashion the lifespan of MRL-lpr mice as compared with PBS-treated control mice, and the effect reached statistical significance at the doses of 10 and 100 mg/kg. In parallel ex vivo studies, this clinical effect was associated with multiple profound modifications of the immune system including: (i) the reduction of the spontaneous and Con A-induced release of interleukin-4 (IL-4); (ii) the increased secretion of interferon-gamma (IFN-gamma) and IL-6 upon polyclonal mitogenic stimulation, and (iii) the amelioration of the defective Con A-induced lymphoproliferative response. In contrast, although the drug diminished the severity of proteinuria in MRL-lpr mice, it neither reduced histological signs of lupus nephritis nor diminished the serum titres of anti-native DNA and anti-histone autoantibodies. These results indicate that TP-5 displayed powerful immunodulatory activities in a well known model of human SLE.

The Yaa gene-dependent B-cell deficiency worsens the generalized lymphadenopathy and autoimmunity of C57BL/6-gld male mice

The BXSB mice are unique among murine models for systemic lupus erythematosus in that males are much more severely affected than females. The BXSB male disease is associated with a Y-chromosome-linked gene, which is an autoimmunity accelerator gene (Yaa). The Yaa mutation affects the B-cell subset, which becomes hyper-responsive to T-cell signals. The Yaa mutation was combined to the generalized lymphadenopathy disease (gld) gene in order to know whether an additional intrinsic B-cell defect might enhance gld disease in the male mice. The B6-gld-Yaa male mice were shown to display earlier and exacerbated lymphoproliferative and autoimmune features. It appeared that the milder gld syndrome observed in B6-gld male mice with a normal Y-chromosome was dependent on the mechanisms of B-cell activation and that the B cells could also accelerate the lymphoproliferation and the differentiation of T cells into Thy-1+ B220+ cells.

The role of B cells in lpr/lpr-induced autoimmunity

The primary roles of T cells and B cells in the initiation of systemic autoimmunity are unclear. To investigate the role of B cells, we crossed the "Jh knockout" mutation onto the autoimmune lpr/lpr background. Animals homozygous for both traits were obtained. As expected, these animals lack B cells. These animals also show no signs of autoimmune kidney destruction nor vasculitis, in spite of carrying the lpr/lpr mutation. In contrast, lpr/lpr littermates that had B cells had severe nephritis and vasculitis, as well as autoantibodies. These results demonstrate a primary role for B cells and/or (auto)antibodies in initiating several types of autoimmune-mediated tissue destruction. The implications of this finding for models and therapy of autoimmunity are discussed.

T cell specialization at environmental interfaces: T cells from the lung and the female genital tract of lpr and gld mice differ from their splenic and lymph node counterparts

Mice homozygous for lpr and gld accumulate CD4- CD8- (double-negative, DN) B220+ CD5loThy-1lo alpha beta T cells in the spleen and lymph nodes (LN), while mucosal gut T cells are normal. To study other mucosa-associated T cell populations, we examined T cell subsets separated according to expression of alpha beta T cell receptor, CD4, CD5, CD8, Thy-1 and B220 in the lung and the female genital tract (FGT) of adult MRL lpr, C3H lpr and C3H gld mice. alpha beta T cell accumulation was detected in both the FGT and the lungs of lpr and gld mice but, in contrast to the spleen and LN, equal proportions of DN B220+ and CD4+ of CD8+ (single-positive, SP) B220- T cells were observed in these sites, and the T cells had an increased expression of Thy-1 and CD5. Staining for CD44, L-selectin, and CD45RB revealed a higher percentage of effector/memory T cells in lpr and gld lungs and FGT compared to spleens and LN. CD69 expression suggested chronic activation of DN and SP T cells in lpr and gld lungs and FGT. Thus, we show that FGT and lung resident T cells are affected by lpr and gld mutations, but that their phenotypes are distinct from those of systemic T cells. These data suggest that T cells associated with FGT and lung mucosal tissues represent a separate lineage from systemic T cells, and/or that the abnormal T cells in lpr and gld mice are selected against in mucosal surfaces exposed to environmental antigen.

Suppression of experimental antiphospholipid syndrome and systemic lupus erythematosus in mice by anti-CD4 monoclonal antibodies

OBJECTIVE

To investigate whether anti-CD4 antibodies can suppress experimental antiphospholipid syndrome (APS) and systemic lupus erythematosus (SLE) induced by an anti-DNA monoclonal antibody (MAb).

METHODS

BALB/c mice were treated with anti-CD4 MAb either before or 2 months after induction of experimental APS and SLE. Control mice were treated with rat IgG or phosphate buffered saline. Serologic and clinical manifestations of the disease were determined.

RESULTS

Treatment of mice with anti-CD4 before or 2 months after disease induction prevented the development of experimental APS and SLE. The treated mice did not develop leukopenia or proteinuria, and had fewer episodes of fetal resorption. Similarly, the treated mice did not develop elevated erythrocyte sedimentation rate, prolonged activated partial thromboplastin time, or thrombocytopenia, and had significantly lower levels of antibodies to double-stranded DNA, histones, MIV-7, cardiolipin, and phosphatidylserine. Levels of CD4+ cells in the lymph nodes declined temporarily after the treatment and then returned to normal.

CONCLUSION

Anti-CD4 antibodies can prevent experimental APS and SLE. These results may suggest a role for anti-CD4 treatment in human autoimmune diseases.

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.

CD4/CD8-negative T cells with alpha beta antigen receptors

A minor population of alpha beta T cells expresses neither CD4 nor CD8. These cells are probably heterogeneous. They are widespread in anatomical distribution, express an abnormal T-cell repertoire largely unaffected by selective processes that act on CD4+ and CD8+ T cells, and exhibit both cytotoxic and Th-2-like functions. Their role in normal immune function is completely obscure, but they are active in murine and human autoimmune disease.

The treatment of autoimmune disease in (NZB/NZW)F1 mice with syngeneic photomodulated splenocytes

(NZB x NZW)F1 (B/W) mice spontaneously develop a disease which is remarkably similar to systemic lupus erythematosus (SLE) in humans. This disease is characterized by the appearance of autoantibodies to double-stranded (ds)DNA and the subsequent development of fatal glomerulonephritis. The prophylactic treatment of B/W mice with syngeneic photomodulated autoimmune spleen cells was found to significantly improve survival, and to inhibit the outgrowth of autoreactive B cells and the production of high-titre IgG anti-dsDNA antibodies. The function of the autoreactive T cells in vivo, however, did not change significantly. Our findings suggested a novel treatment for spontaneously occurring autoantibody-related autoimmune diseases.

Photodynamic therapy; a comparison with other immunomodulatory treatments of adjuvant-enhanced arthritis in MRL-lpr mice

Although numerous experimental immunomodulatory regimens have been reported to be effective in the treatment of rheumatoid arthritis, they also produce undesirable side effects. An alternative specific modality of localized treatment is photodynamic therapy (PDT). In this study we treated 13-week-old MRL-lpr mice whose spontaneous arthritis was enhanced by intradermal injection of Freund's complete adjuvant (FCA). One group received transcutaneous photodynamic therapy at days 0, 10, and 20, following the FCA injection. The other groups were injected with 1 mg/kg per day indomethacin, 40 mg/kg per day cyclosporin A (CsA), or treated with 3 Gy sublethal whole body irradiation (WBI). The development of swelling was monitored for 1 month, at which time proteinuria, lymphadenopathy and the histopathology of the joints and kidneys were assessed. The results demonstrated that PDT and the conventional treatments significantly ameliorated swelling of the hindlimbs from 70% in the untreated FCA-injected animals to below the 19% level characteristic of the unmanipulated control. Histological examination showed a reduction in pannus formation, and cartilage and bone destruction, the characteristics of adjuvant-enhanced arthritis. PDT did not affect the survival rate, lymphoproliferation, or proteinuria of the treated animals. However, indomethacin increased proteinuria, and was less effective in preventing cartilage and bone destruction. Furthermore, lower doses of CsA and WBI exacerbated arthritis activity. These results indicate that photodynamic therapy can inhibit the development of adjuvant-enhanced arthritis in MRL-lpr mice with similar effectiveness to the conventional treatments, but without their negative side effects.

Reversal of hyporesponsiveness in lpr CD4-CD8- T cells is achieved by induction of cell cycling and normalization of CD2 and p59fyn expression

T cells freshly isolated from the peripheral lymph nodes of autoimmune MRL lpr/lpr (lpr) mice contain a large proportion of functionally non-mature T cell receptor (TcR)-alpha beta+CD3+CD2-CD4-CD8- T cells displaying the B cell isoform of CD45, B220. These cells are hyporesponsive as defined by minimal interleukin-2 (IL-2) production and proliferation in response to stimulation. However, increased levels of inositol phosphates and a rapid mobilization of Ca2+ do occur upon stimulation of the TcR/CD3 complex. Furthermore, lpr CD4-CD8-T cells contain high levels of transcripts for the src-family tyrosine kinase p59fyn, and express a constitutively tyrosine-phosphorylated CD3-zeta chain. These features bear a certain resemblance to anergized T cells. These similarities are extended to show that culturing of lpr CD4-CD8- T cells in the presence of IL-2 in combination with phorbol 12-myristate 13-acetate and ionomycin initiates cell cycling and results in the gain of function; re-stimulation now yields IL-2-dependent proliferation in the absence of exogenous IL-2. In parallel with this gain in function, the population of cells obtained after 1 week in culture retains the TcR-alpha beta + CD4-CD8- phenotype, yet displays increased levels of CD2, decreased surface B220, and normal amounts of p59fyn-specific transcripts. These findings show that cell cycling is associated with the recovery of functional capabilities by lprCD4-CD8-T cells and is closely allied with surface CD2 expression. Thus, the hyporesponsiveness of lpr T cells is not a fixed state.

Gld and lpr mice: single gene mutant models for failed self tolerance

Mice homozygous for the gld or lpr mutations develop autoimmunity, and a lymphoproliferative disorder involving accumulation of huge numbers of unusual CD4-CD8-TCR alpha beta lo T cells. Here we review our past work with gld mice, and attempt to explain lymphoproliferation in terms of current models of T cell maturation and self-tolerance induction. The availability of molecular probes to the gene products of lpr and gld should shortly lead to a better understanding of the acquisition of self tolerance during T cell maturation and of autoimmunity.

Non-MHC-linked genes in autoimmune diseases

Single-locus mutations in mice associated with autoimmune manifestations or influencing them, including lpr, motheaten and xid have been characterized at the molecular level. Mutations have been described in the genes encoding Fc gamma RI, interleukin-2 and natural resistance associated macrophage protein, which are all candidate genes for susceptibility loci associated with autoimmune diabetes in non-obese diabetic mice. Twelve regions of DNA that are associated with disease susceptibility have now been identified in this polygenic model of autoimmunity. In human autoimmune diseases, the region of DNA surrounding the insulin gene that is associated with susceptibility to insulin dependent diabetes mellitus has been narrowed down to 4.1 kilobases.

Nucleosome: a major immunogen for pathogenic autoantibody-inducing T cells of lupus

Only a fraction (12%) of 268 "autoreactive" T cell clones derived from lupus-prone mice can selectively induce the production of pathogenic anti-DNA autoantibodies in vitro and accelerate the development of lupus nephritis when transferred in vivo. The CDR3 loops of T cell receptor beta chains expressed by these pathogenic T helper (Th) clones contain a recurrent motif of anionic residues suggesting that they are selected by autoantigens with cationic residues. Herein, we found that approximately 50% of these pathogenic Th clones were specific for nucleosomal antigens, but none of them responded to cationic idiopeptides shared by variable regions of pathogenic anti-DNA autoantibodies. Nucleosomes did not stimulate the T cells as a nonspecific mitogen or superantigen. Only the pathogenic Th cells of lupus responded to nucleosomal antigens that were processed and presented via the major histocompatibility class II pathway. Although the presentation of purified mononucleosomes to the Th clones could be blocked by inhibitors of endosomal proteases, neither of the two components of the nucleosomes--free DNA or histones by themselves--could stimulate the Th clones. Thus critical peptide epitopes for the Th cells were probably protected during uptake and processing of the nucleosome particle as a whole. The nucleosome-specific Th clones preferentially augmented the production of IgG autoantibodies to histone-DNA complex in vitro. In vivo, nucleosome-specific, CD4+ T cells were not detectable in normal mice, but they were found in the spleens of lupus-prone mice as early as 1 mo of age, long before other autoimmune manifestations. Immunization of young, preautoimmune lupus mice with nucleosomes augmented the production of autoantibodies and markedly accelerated the development of severe glomerulonephritis. Previously, crude preparations containing nucleosomes were shown by others to have polyclonal mitogenic activity for B cells from normal as well as lupus mice. Identification here of pure mononucleosome as a lupus-specific immunogen for the Th cells that selectively help the pathogenic anti-DNA autoantibody producing B cells of lupus could lead to the design of specific therapy against this pathogenic autoimmune response.

MRL/lpr-->severe combined immunodeficiency mouse allografts produce autoantibodies, acute graft-versus-host disease or a wasting syndrome depending on the source of cells

MRL/lpr (lpr) mice spontaneously develop a lupus-like illness as well as massive lymphadenopathy. Attempts to transfer autoimmunity by adoptive transfer or radiation bone marrow chimeras have been unsuccessful. Since severe combined immunodeficiency (SCID) mice have been engrafted with human and rat xenografts without apparent graft-versus-host disease (GVHD), we subjected SCID mice to low-dose irradiation and reconstituted the mice with spleen cells from young or old lpr mice or with lpr bone marrow. Fourteen out of twenty (70%) of SCID mice engrafted with spleen cells from old lpr mice produced autoantibodies (anti-DNA and anti-Sm) without evidence of the severe lymphoid atrophy previously described for lpr spleen-->+/+ chimeras. SCID mice engrafted with spleen cells from young lpr mice developed acute GVHD and 5/6 (83%) died within 4 weeks post-transfer. Although 8/11 (73%) of lpr-->SCID bone marrow allografts survived for at least 4 months, these mice developed a wasting disease characterized by lymphoid atrophy and fibrosis without the production of autoantibodies. None of the lpr-->SCID grafts resulted in the transfer of double negative T cells or the lymphoproliferative syndrome characteristic of MRL/lpr mice. These findings indicate that SCID mice can be engrafted with splenocytes from old MRL/lpr mice and that B cells continue to secrete autoantibodies for several months in the SCID recipients. This study also demonstrates that, unlike i.p. transplant of xenogeneic cells, acute GVHD is a consistent feature of i.p. transplants of normal allogeneic mononuclear cells into SCID mice.

Cytokines play a central role in the pathogenesis of systemic lupus erythematosus

Excessive production of pathogenic autoantibodies is one of the hallmarks of systemic lupus erythematosus (SLE). The mechanisms that underlie this excessive production are still unclear. Although there is considerable evidence to suggest that both T cells and B cells play an important role in the etiology of SLE, convincing abnormalities at the T cell receptor or immunoglobulin gene loci have not been demonstrated. In this regard, because cytokines play such a pivotal role in the inflammatory response, a defect in the immunoregulation of B cells by cytokines should be considered as possible contender in disease etiology. The hypothesis that is proposed here is that multiple defects mediated by cytokines are present in individuals with lupus and that both cytokine production and the response of B cells to cytokines may be defective. These abnormalities could then be a central factor in the etiology of systemic lupus erythematosus.

Genetic and immunological mechanisms in the pathogenesis of systemic lupus erythematosus

Recent research in systemic lupus erythematosus and animal models of lupus has provided new insight into the pathogenesis of this complex autoimmune disease. Progress has been made towards understanding the genetic contributions to disease susceptibility and induction, as well as towards elucidation of the lymphocyte abnormalities involved in pathogenic autoantibody production.

Functional analyses of lpr gene in MRL/Mp-lpr/lpr mice. Role of lymph node stromal cells in lpr-lymphadenopathy

To clarify the mechanism by which the lpr gene causes lymphadenopathy, we established an experimental system to induce lymph node (LN) swelling in unaffected mice. In MRL-(+)/+ mice that had been 5 Gy-irradiated and grafted with bone marrow cells (BMCs) plus LN from MRL-lpr/lpr mice, a remarkable enlargement of the LN grafts was seen. The enlarged grafts lacked normal LN structure and were indistinguishable from LNs of MRL-lpr/lpr mice. The induction of LN swelling by this method was achieved not only in [MRL-lpr/lpr-->MRL-(+)/+] but also in [MRL-lpr/lpr-->BALB/c], [MRL-lpr/lpr-->C3H], [B6-lpr/lpr-->B10.Thy1.1], and [B6-lpr/lpr-->BALB/c] combinations. Furthermore, the lpr/lpr LN grafts developed lymph node swelling even without the transplantation of BMCs. Most cells in the grafted LNs disappeared within a few days, and large clear fibroblast-like cells then became dominant for 1 to 4 weeks. Thereafter, lymphoid cells increased and had filled the graft by the 8th week. The LN grafts obtained from MRL-lpr/lpr (but not MRL-(+)/+) mice showed the ability to transfer LN node swelling into the secondary MRL-(+)/+ hosts two weeks after the primary transplantation. These results strongly suggest that the fibroblast-like LN stromal cells play a crucial role in lpr-associated lymphadenopathy.

The onset of nephritis in the (NZB × SWR)F1 murine model for systemic lupus erythematosus correlates with an increase in the ratio of CD4 to CD8 T lymphocytes specific for the nephritogenic idiotype (IdLNF1)

An idiotypically related family of nephritogenic antibodies (IdLNF1) has been shown to be important in the pathogenesis of autoimmune glomerulonephritis in the (NZB x SWR)F1 hybrid, SNF1. Idiotype-specific T lymphocytes which modulate expression of antibody bearing that idiotype may be important in the pathogenesis of systemic lupus erythematosus (SLE). Here, IdLNF1-reactive T lymphocytes were not only found to be present in the NZB, SWR, and SNF1, but a significantly (P < or = 0.05) greater number of IdLNF1-reactive Thy 1.2+ splenic lymphocytes were observed as early as 12 weeks of age in the SNF1. Further, a significant shift in the ratio of CD4+ to CD8+ IdLNF1-reactive T lymphocytes in favor of CD4+ IdLNF1-reactive T cells was observed at 20 to 24 weeks of age only in the SNF1. This shift correlated with an increase in IdLNF1+IgG, and deposition of IdLNF1 bearing immunoglobulin in the kidney glomeruli. These observations suggest a role for idiotype-specific T lymphocytes in the induction of glomerulonephritis in this murine model of SLE.

Do cytokines play a role in systemic lupus erythematosus?

Excessive production of pathogenic autoantibodies is one of the hallmarks of systemic lupus erythematosus (SLE). The mechanisms that underlie this excessive production are still unclear. Although there is considerable evidence to suggest that both T-cells and B-cells play an important role in the aetiology of SLE, convincing abnormalities at the T-cell receptor or immunoglobulin gene loci have not been demonstrated. In this regard, because cytokines play a pivotal role in the inflammatory response, a defect in the immunoregulation of B-cells by cytokines should be considered as a potential contender in disease aetiology. The hypothesis proposed here is that multiple cytokine-mediated defects are present in individuals with lupus and that both cytokine production and the response of B-cells to cytokines may be defective.

Autoreactive kidney-infiltrating T-cell clones in murine lupus nephritis

T-cells have been implicated in autoimmune renal injury. To examine the role of T-cells in lupus nephritis we propagated T-cell clones from the cortical interstitium of MRL/lpr mice. All isolated kidney-infiltrating (KI) T-cell clones [6] express surface markers identical to the T-cells regulated by the lpr gene (Thy 1.2+, TCR alpha/beta +, Lyt-2-, L3T4-, B220+). Although KI T-cell clones have the same surface markers as lymph node-infiltrating (LNI) T-cells, they differ functionally. KI T-cells, but not LNI T-cells, are autoreactive and kidney-specific, exclusively proliferating to renal tubular epithelial (TEC) and mesangial cells. In addition, unlike LNI T-cell supernatants (SN), KI T-cell clones SN induce class II and ICAM-1 on cultured TEC. When KI T-cell clones are injected under the renal capsule, class II is increased on TEC. All clones transcribe mRNA for cytokines capable of inducing class II and ICAM-1 (IL-4, TNF-alpha, IFN-gamma). Anti-IFN-gamma mAb prevents the induction of class II and ICAM-1 on cultured TEC. Since class II and ICAM-1 expression on TEC precedes renal injury, the ability to propagate autoreactive, kidney-specific T-cell clones that induce these molecules provides evidence for their role in initiating renal injury in MRL/lpr mice.

Effect of anti-CD4 antibody treatment on inflammatory arthritis in MRL-lpr/lpr mice

MRL-lpr/lpr mice develop an inflammatory arthritis in association with other manifestations of autoimmunity. Although a variety of immune cell disturbances have been described in these mice, the relationship of these abnormalities to the pathogenesis of arthritis has not yet been determined; the role of T cells is especially unclear since synovial hypertrophy and joint erosions have been noted in some studies in the absence of a significant T cell infiltrate. Therefore, to determine if T cells are required for arthritis in MRL-lpr/lpr mice, we evaluated the effects of prolonged treatment with a monoclonal anti-CD4 antibody. Knee joints from treated mice had markedly reduced arthritis compared to saline-treated control animals as measured by the degree of synovial hypertrophy and inflammation. Nephritis in these mice was concomitantly reduced. In contrast, rheumatoid factor levels were not affected by CD4+ cell depletion, despite significant effects on anti-DNA. These results indicate that in MRL-lpr/lpr mice anti-CD4 therapy can inhibit arthritis, suggesting an important role of T cells in the pathogenesis of this lesion.

A novel lymphoproliferative/autoimmune syndrome resembling murine lpr/gld disease

In mice, the two distinct autosomal recessive genes lpr and gld can induce a syndrome characterized by autoantibody formation and the progressive accumulation of an unusual CD4-CD8- T cell population in peripheral lymphoid tissue. This phenotype does not precisely mirror any human disease. In this report we describe two patients with a progressive lymphoproliferative disorder associated with autoimmunity. The peripheral blood and lymph nodes of these patients contained large numbers of an unusual CD4-CD8- T cell population. These CD4-CD8- T cells express surface markers characteristic of mature peripheral blood T cells (CD3, CD2, CD5), express the alpha/beta form of the T cell receptor, and do not express surface markers characteristic of immature thymocytes (CD1) or NK cells (CD16, CD56). Functionally, these cells exhibited deficient proliferation and lymphokine production upon stimulation with mitogenic antibodies to CD3 or CD2. Both proliferation and lymphokine production could be augmented by co-stimulation with an antibody directed at the CD28 determinant. The clinical and immunological features of this syndrome resemble the lymphoproliferative/autoimmune disease seen in lpr and gld mice.

Inhibition of abnormal T cell development and autoimmunity in gld mice by transgenic T cell receptor beta chain

Mice homozygous for the gld (generalized lymphoproliferative disease) mutation developed systemic autoimmune disease and severe lymphadenopathy due to an age-related accumulation in the peripheral lymphoid organs of polyclonal T cells bearing a unique phenotype (CD4-CD8-TCR alpha beta+B220+). These T cells overexpress T cell receptor (TcR) alpha beta chain RNA, proto-oncogenes c-myb and fyn, and proliferate poorly in response to TcR-mediated stimulation. The origin of these T cells is poorly understood. To study the influence of a functionally rearranged TcR beta chain on the T cell developmental abnormality of the gld mutation and autoimmunity, we have backcrossed TcR V beta 8.1-transgenic mice to C3H-gld/gld to homozygosity (transgenic gld mice). In transgenic gld mice, lymphadenopathy was markedly inhibited and the accumulation of CD4-CD8- T cells did not occur, although the remaining T cells overexpressed c-myb and proliferated poorly in response to TcR occupancy. These features indicate that the pattern of proto-oncogene expression and abnormal function persist in phenotypically normal T cells in transgenic gld mice, and that these characteristics can be dissociated from the accumulation of CD4-CD8- T cells. The hypergammaglobulinemia and anti-double-stranded DNA (anti-dsDNA) antibody production was partially improved in transgenic gld mice, supporting the critical role of T cells in abnormal B cell activation described in autoimmunity-prone mice. To investigate further the mechanisms underlying the inhibition of CD4-CD8- T cell accumulation in transgenic gld mice, the fetal ontogeny of T cells in transgenic mice was compared with that of non-transgenic mice. In transgenic thymus, development of TcR alpha beta+ cells was accelerated as detected by earlier expression of CD4, CD8 and TcR in fetal thymus. In contrast, the number of TcR gamma delta+ cells was reduced. We suggest that altered T cell development in transgenic mice directly or indirectly inhibits the accumulation of abnormal T cells in gld mice.

Anti-CD4 monoclonal antibody therapy suppresses autoimmune disease in MRL/Mp-lpr/lpr mice

MRL/Mp-lpr/lpr (MRL/lpr) mice spontaneously develop systemic autoimmune disease, characterized by vasculitis, lymphadenopathy, glomerulonephritis, and autoantibody formation. The target organ inflammatory lesions are composed largely of CD4+ "helper" T cells, while the massively enlarged lymph nodes are composed primarily of CD3+ CD4- CD8- TCR alpha/beta + "double-negative" T cells. In this study we investigated the effect of treatment of MRL/lpr mice with anti-CD4 monoclonal antibody (mAb); control groups consisted of animals treated with normal saline or rat immunoglobulin (Ig). Anti-CD4 mAb treatment, which was started at 4 weeks and continued through 20 weeks of age, resulted in a dramatic reduction of both the frequency and severity of the autoimmune disease, as demonstrated histologically and serologically. Anti-CD4 mAb therapy markedly reduced the frequency of glomerulonephritis and eliminated vasculitis of the major renal arterial branches. Glomerulonephritis was detected in 9 of 9 saline-treated, 9 of 9 rat Ig-treated, but in only 1 of 9 anti-CD4 mAb-treated mice; vasculitis was detected in 6 of 9 saline-treated, 7 of 9 rat Ig-treated, but in none of 9 anti-CD4 mAb-treated mice. The frequency of antinuclear antibodies, titer of anti-dsDNA antibodies, and total Ig levels were all significantly reduced by anti-CD4 mAb therapy. These data support the hypothesis that CD4+ T cells play a central role in the disease process in this autoimmune strain.

Transgenic T cell receptor interactions in the lymphoproliferative and autoimmune syndromes of lpr and gld mutant mice

To investigate the role of T cell receptor (TcR) expression and interactions in development of lymphoproliferation and autoimmunity in lpr and gld mutant mice, and to determine whether these autoimmune mutations affect T cell selection and repertoire formation, we generated mice homozygous for either the gld or the lpr mutation and containing TcR alpha/beta transgenes (Von Boehmer, H., Annu. Rev. Immunol. 1990. 8: 531) specific for the male (H-Y) antigen in the context of H-2Db. Four main results emerged from analysis of these mice. First, expression of transgenic TcR had no effect on disease incidence and progression. Second, the accumulating T cells reflected normal processes of positive and negative selection. Third, cells expressing the transgenic TcR participated equally in lymphoproliferation regardless of whether their antigenic peptide and/or presenting major histocompatibility complex molecules were present or not. Fourth, expression of the TcR transgenes markedly altered the phenotype of the major accumulating lymphocyte subset. Thus, in these models of lymphoproliferation and autoimmunity. T cell repertoire formation proceeds normally, specific T cell recognition of antigen has no effect on the participation of individual clones, and the phenotype of the cells accumulating is sensitive to either the timing or the amount of TcR expression. These results are discussed in the context of the primary cause vs. secondary manifestations of autoimmunity in these models.

Quantitative and functional analyses of spleen and in situ islet immune cells before and after diabetes onset in the NOD mouse

Cytofluorometric analysis using specific monoclonal antibodies directed against the T cell antigens Thy-1.2, CD4, CD8, CD4V beta(8.1 + 8.2 + 8.3), and the antigen Mac-1 expressed by mature macrophages and NK cells were used to characterize and quantify the phenotypes of (1) unfractionated and Percoll gradient fractionated in situ islet immune cells isolated from prediabetic and diabetic female NOD mouse spleens. We found in prediabetic female mice that the majority (approximately 70%) of the in situ islet immune cells were Thy-1.2 positive T cells. CD4 positive T cells (approximately 40%) were the most abundant phenotype together with double negative T cells (approximately 20%). The percentage of CD8 positive T cells were approximately 10%, and only approximately 4% of the immune cells were Mac-1 positive. The percentages of CD4V beta (8.1 + 8.2 + 8.3) positive and double negative T cells in diabetic spleens were significantly higher in comparison to prediabetic spleens. In C57B1/6J control nondiabetic mice the percentage of double negative T cells in the spleens was significantly 4-fold lower when compared to diabetic NOD spleens. The specific cytolytic activity mediated by in situ islet immune cells against 51Cr-labeled dispersed syngeneic single-cell islet cells at an effector to target ratio of 20 was twenty- to thirty-fold higher than that mediated by prediabetic splenic lymphoid cells. It is concluded that prediabetic NOD mouse in situ islet immune cells are mostly CD4 positive and double negative T cells, and that CD4 and CD8 positive T cells in the intra-islet infiltrate warrants further evaluation as potential effector T cells in target beta-cell destruction.

Autoregulation of the immune response in autoimmune disease and cardiac transplantation by photoinactivated autologous lymphocytes

These studies demonstrate that photochemotherapy can be successfully evaluated in animal models. The therapy mediates specific suppression of immune responses and appears to operate at the level of the effector T cells. Future studies will focus on isolation and characterization of the host response to photochemotherapy. The extention of this form of therapy to conditions mediated by dysfunctional regulation of effector T cells is already in progress in clinical trials of cardiac allograft transplantation and autoimmune disease. The results of these trials will provide more evidence on the role of this form of therapy in autoregulation of the immune response.

Long-term anti-CD4 treatment of MRL/lpr mice ameliorates immunopathology and lymphoproliferation but fails to suppress rheumatoid factor production

MRL/lpr mice were treated with anti-CD4 mAb to define the role of CD4+ T cells in the pathogenesis of autoimmune disease and the lymphoproliferation characteristic of the strain. Anti-CD4 treatment was not associated with adverse effects, and survival of treated mice was increased over that of rat IgG-treated controls. Renal function was preserved, and the histologic severity of glomerulonephritis was minimal in treated mice. Lymphoid tissues of mice receiving anti-CD4 were effectively depleted of CD4+ T cells, and lymphoproliferation was markedly reduced. Serum IgG, anti-Sm, and anti-dsDNA levels were reduced significantly, while serum IgM and IgM rheumatoid factor levels were unaffected by anti-CD4 treatment. These data show that in MRL/lpr mice lymphoproliferation, renal disease, anti-Sm and anti-dsDNA antibody production, and elevated IgG levels are all linked to CD4+ T cell function. In contrast, both total IgM and IgM rheumatoid factor production appear to be the result of B-cell activity that is not regulated by CD4+ T cells.

Reduction of lupus nephritis in MRL/lpr mice by a bacterial superantigen treatment

The effects of biweekly intravenous injections of Staphylococcus Enterotoxin B (SEB) into autoimmune MRL-lpr/lpr (MRL/lpr) mice were investigated. Rather than causing the expansion of V beta 8+ T cells, SEB administration resulted in the reduction V beta 8+, CD4-CD8- "double-negative" (DN) T cells. This was shown by FACS analysis as this putative pathogenic population was diminished in both spleen and lymph node. The symptoms of systemic lupus erythematosus (SLE) in MRL/lpr, which include high titers of anti-DNA antibodies and circulating immune complexes and proteinuria, were reduced in SEB-treated mice in a dose-dependent manner. The clinical parameters of SLE in MRL/lpr, which include lymph node hyperplasia and necrotic vasculitis, were suppressed in 50-micrograms SEB-treated mice. T cells bearing V beta 6 T cell receptor, which does not interact with SEB, were not reduced with SEB administration. Thus, disease suppression was associated with a specific reduction in the number of V beta 8+, DN T cells. These results implicate a possible therapeutic role of superantigen-based immunotherapy in V beta-restricted, T cell-dominated clinical syndromes.

Renal immunopathology in murine host-versus-graft disease

BALB/c mice neonatally injected with 1 x 10(8) (A/J x BALB/c)F1 hybrid spleen cells develop polyclonal B cell activation and autoimmune features as a consequence of a host-versus-graft (HVG) reaction. In this study, we first analyzed the time-course development of the renal lesions in HVG mice. From week 2 to week 6, linear deposits of IgG were observed by immunofluorescence along the glomerular capillary walls. From week 8 to week 12, the immunofluorescence pattern of IgG changed from linear to granular, and by immunoelectron microscopy, the IgG deposits were located on the epithelial side of the glomerular basement membrane (GBM). In addition, focal glomerulosclerosis complicated this membranous glomerulopathy in about 50% of the 12-week-old HVG mice and albuminuria was increased in most of them. Circulating antibodies to antigens of the GBM (laminin, type IV collagen) and of the renal tubular epithelial (RTE) cells (dipeptidyl peptidase IV, gp330) were already detected at week 2 and were still present at week 12. Immunoglobulins eluted from isolated glomeruli contained antibodies directed against type IV collagen, laminin, and to a lesser degree against gp330. F1 donor B cells were involved in the production of nephritogenic antibodies as indicated by (a) the presence of A/J allotypic determinants on serum anti-laminin antibodies and (b) the abrogation of the in vitro production of anti-GBM, anti-laminin and anti-RTE antibodies when spleen cells from HVG mice were depleted of F1 donor B cells. Finally, mixed lymphocyte culture experiments established that T cells from HVG mice stimulate normal B cells from F1 donor hybrids to produce anti-GBM, anti-laminin, anti-type IV collagen, anti-RTE, anti-gp330 and anti-dipeptidyl peptidase IV antibodies. We conclude that mice neonatally injected with semi-allogeneic spleen cells develop a glomerulonephritis characterized by the transition from a linear to a granular IF pattern, and that the production of nephritogenic antibodies results from the activation of donor B cells by host helper T cells.

Immunological effects of high dose administration of anti-CD4 antibody in rheumatoid arthritis patients

A phase I/II trial of the anti-CD4 monoclonal antibody (mAb) was undertaken in seven rheumatoid arthritis patients in order, (1) to investigate changes in clinical symptoms and possible side effects, and (2) to study the pharmacokinetics and to determine the dose required to achieve saturation of antibody binding sites on blood leucocytes. BL4mAb is a murine IgG2a which binds to the group 2B epitope of the V1 N terminal domain of the CD4 molecule. It inhibits syncitium formation by human immunodeficiency virus-infected cells. BL4 was administered by one hour-long intravenous infusion each day, for 10 days. Doses were steadily increased from 20 mg/d to 40 mg/d in the first three patients (group I) in an attempt to reach a serum antibody residual level sufficient to saturate CD4+ circulating cells. The three other patients (group II) received a dose of 40 mg/d during 10 consecutive days. One patient who presented chills and mild fever during the first BL4 infusion was not included in the analysis. No clinical side effects were observed in the six other BL4-treated patients. Clinical parameters of disease activity were improved within the first 14 days. Clinical improvement was still significant at day 30 in five patients, but at day 60, only the Ritchie index was still below pretreatment levels. Delayed type hypersensitivity reactions decreased in the three patients who exhibited positive reactions before BL4 administration. A transient drop in peripheral blood CD4+ lymphocyte counts occurred during each infusion in the first days of treatment. Pre-infusion CD4+ lymphocyte counts were moderately decreased within the first 8 days, but rose to pretreatment levels 3 days after the last infusion. BL4 residual levels in serum steadily increased to reach 8.0 micrograms/ml in group I and 9.8 micrograms/ml in group II. Saturation of BL4 binding sites was achieved after 2 days of treatment in all patients of group II but in only one of group I. Four out of six patients produced antibodies against the anti-CD4 mAb. Immunization appeared between days 12 and 50. This study shows that saturation of anti-CD4 mAb binding sites can be achieved by infusions of high doses (40 mg/d) of BL4 without clinical side effects. The results would encourage further placebo-controlled trials, since no definite conclusion can be drawn from the present study as regards clinical efficacy.

Clonal deletion of autospecific B lymphocytes

Using mice transgenic for functional, rearranged immunoglobulin heavy and light chain genes, it can be demonstrated that B lymphocytes reactive with cell surface-bound class I MHC antigen can be controlled by clonal elimination. Even low-affinity cell-bound ligands can induce deletion. Deletion can occur in the pre-B to B cell transitional stage or after the B cells exist the bone marrow, depending on where the cells first encounter autoantigen. IgD appears to play no role in protecting cells from deletion. It is argued that defects in B-cell tolerance alone may be sufficient to lead to systemic autoimmunity.