Inhibitory signal override increases susceptibility to mercury-induced autoimmunity

After exposure to subtoxic doses of heavy metals such as mercury, H-2(s) mice develop an autoimmune syndrome consisting of the rapid production of IgG autoantibodies that are highly specific for nucleolar autoantigens and a polyclonal increase in serum IgG1 and IgE. In this study, we explore the role of two inhibitory immunoreceptors, CTLA-4 and FcgammaRIIB, in the regulation of mercury-induced autoimmunity. In susceptible mice treated with mercuric chloride (HgCl(2)), administration of a blocking anti-CTLA-4 Ab resulted in a further increase in anti-nucleolar autoantibodies and in total serum IgG1 levels. Furthermore, in some DBA/2 mice, which are normally resistant to heavy metal-induced autoimmunity, anti-CTLA-4 treatment leads to the production of anti-nucleolar Abs, thereby overcoming the genetic restriction of the disease. In mice deficient for the FcgammaRIIB, HgCl(2) administration did not trigger autoantibody production, but resulted in an increase in IgE serum levels. Taken together, these results indicate that different inhibitory mechanisms regulate various manifestations of this autoimmune syndrome.     

IL-4 is required for the IgE and IgG1 increase and IgG1 autoantibody formation in mice treated with mercuric chloride

Previous studies have established that in susceptible mouse strains, such as A.SW (H-2s), repeated injections of subtoxic doses of HgCl2 induce increased serum levels of total IgE and IgG1, high serum titers of antinuclear autoantibodies (ANo1A), and immune-complex glomerulonephritis. Moreover, it has been shown that susceptibility is determined by H-2As and that Th cells are required for the induction of these immunopathologic alterations by HgCl2. In the present study we showed that treatment in vivo with anti-IL-4 mAb completely abrogated the HgCl2-induced increase in total IgE and partially inhibited the increase in IgG1, but failed to suppress the increase in IgG2A. Furthermore, we showed that IL-4 influences the pattern of IgG subclass distribution among ANo1A of HgCl2-treated mice. Whereas treatment with anti-IL-4 mAb significantly reduced the titers of IgG1 ANolA, it increased those of IgG2A, IgG2B, and IgG3 ANolA. Thus, these results show that IL-4 contributes to the optimal formation in vivo of murine IgG1 and that it is involved in the autoantibody formation of a systemic autoimmune disease. The available evidence suggests that HgCl2 induces an increased production of IL-4 by Th2 cells. If this is correct, it implies that MHC class II alleles determine whether the preferential response to HgCl2 is made by Th1 or Th2 cells and, hence, the type of immunopathologic alterations ensuing.     

A role for B cell-activating factor of the TNF family in chemically induced autoimmunity

After exposure to subtoxic doses of heavy metals such as mercury, H-2s mice develop an autoimmune syndrome consisting of the rapid production of IgG autoantibodies that are highly specific for nucleolar autoantigens and a polyclonal increase in serum IgG1 and IgE. In this study, we observe that HgCl2 administration in susceptible mice results in the elevated production of B cell-activating factor of the TNF family ((BAFF) also known as BLyS, TALL-1, zTNF-4, THANK, and TNSF13B), a B cell growth factor belonging to the TNF family. A transmembrane activator and calcium-modulating and cyclophilin ligand interactor (TACI)-Ig fusion protein (which neutralizes both BAFF and a proliferation-inducing ligand (APRIL), another TNF family member) inhibited Hg-induced autoantibody or serum IgE production. These results are discussed in the context of the inhibitory effect of TACI-Ig on B cell maturation at the transitional stage.     

Amelioration of mercury-induced autoimmunity by 4-1BB

In certain strains of mice, subtoxic doses of HgCl2 (mercuric chloride; mercury) induce a complex autoimmune condition characterized by the production of antinucleolar IgG Abs, lymphoproliferation, increased serum levels of IgG1/IgE Abs, and deposition of renal immune complexes. 4-1BB is an important T cell costimulatory molecule that has been implicated in T cell proliferation and cytokine production, especially production of IFN-gamma. To elucidate T cell control mediated by the 4-1BB signaling pathway in this syndrome, we assessed the effect of administering agonistic anti-4-1BB mAb on mercury-induced autoimmunity. Groups of A.SW mice (H-2s) received mercury/control Ig or mercury/anti-4-1BB or PBS alone. Anti-4-1BB mAb treatment resulted in a dramatic reduction of mercury-induced antinucleolar Ab titers, serum IgG1/IgE induction, and renal Ig deposition. These effects may be related to the present finding that anti-4-1BB mAb decreases B cell numbers and function. The anti-4-1BB mAb-treated mercury group also showed a marked reduction in Th2-type cytokines but an increase in Th1-type cytokines and chemokines. Increased IFN-gamma production due to anti-4-1BB mAb treatment appears to be responsible for the observed B cell defects because neutralization of IFN-gamma in vivo substantially restored B cell numbers and partly restored IgG1/IgE. Collectively, our results indicate that 4-1BB mAb can down-regulate mercury-induced autoimmunity by affecting B cell function in an IFN-gamma-dependent manner and thus, preventing the development of autoantibody production and tissue Ig deposition.     

B7RP-1 is not required for the generation of Th2 responses in a model of allergic airway inflammation but is essential for the induction of inhalation tolerance

The recently described ICOS-B7RP-1 costimulatory pathway has been implicated in the generation of effector Th2 responses and, hence, has become an attractive therapeutic target for allergic diseases. In the present study, we used B7RP-1-deficient mice to investigate the role of B7RP-1 in the generation and maintenance of Th2 responses in a model of mucosal allergic airway inflammation. We found that exposure of B7RP-1 knockout mice to aerosolized OVA in the context of GM-CSF leads to airway eosinophilic inflammation. This response was long lasting because rechallenge of mice with the same Ag recapitulated airway eosinophilia. Moreover, significant expression of T1/ST2 on T cells and production of Th2-affiliated cytokines (IL-5, IL-4, and IL-13) and Igs (IgE and IgG1) conclusively demonstrate the generation of a Th2 response in the absence of B7RP-1. In addition, expression of two major Th2-associated costimulatory molecules-CD28 and ICOS-indicates T cell activation in the absence of B7RP-1 signaling. Finally, B7RP-1 knockout mice are resistant to the induction of inhalation tolerance as indicated by the sustained eosinophilia in the lung and IL-5 production. In summary, our results demonstrate that in a model of mucosal allergic sensitization, the ICOS-B7RP-1 pathway is redundant for the generation of Th2 responses but essential for the induction of inhalation tolerance.     

Involvement of inducible costimulator-B7 homologous protein costimulatory pathway in murine lupus nephritis

Inducible costimulator (ICOS)-B7 homologous protein (B7h) is a new member of the CD28-B7 family of costimulatory molecules that regulates T cell-dependent humoral immune responses. In this study, we examined the involvement of this costimulatory pathway in the development and progression of lupus in NZB/W F(1) mice. Expression of ICOS on T cells was enhanced with disease progression, whereas B7h expression on B cells was down-regulated. Administration of anti-B7h mAb before the onset of renal disease significantly delayed the onset of proteinuria and prolonged survival. Blockade of B7h effectively inhibited all subclasses of IgG autoantibody production and accumulation of both Th1 and Th2 cells. Hypercellularity and deposition of IgG and C3 in glomeruli were significantly reduced. B7h blockade after the onset of proteinuria prevented the disease progression and improved the renal pathology. Our results demonstrated the involvement of the ICOS-B7h costimulatory pathway in the pathogenesis of lupus nephritis, and the blockade of this pathway may be beneficial for the treatment of human systemic lupus erythematosus.     

LPS promotes CB3-induced myocarditis in resistant B10.A mice.

Coxsackie virus B3 (CB3) infection of A/J or A.SW mice results in autoimmune myocarditis characterized by a diffuse mononuclear cell infiltrate and heart-specific autoantibodies. C57BL/10 congenic mice that are identically treated are resistant to this disease. CB3-infected resistant B10.A mice were treated with LPS to determine if this immunomodulator alters disease susceptibility. In contrast to mice infected only with CB3 or treated only with LPS. CB3-infected/LPS-treated (CB3/LPS) B10.A mice developed autoimmune myocarditis similar to that observed in susceptible A/J or A.SW mice. By Day 14, CB3/LPS-induced disease was characterized by significant mortality, myocardial immunoglobulin deposition, and mononuclear cell infiltration of the heart. Immunohistochemical examination revealed deposits of IgG in the heart tissue and serum IgG autoantibodies reactive with sarcolemmal and fibrillary antigens in normal heart tissue. This serum IgG reacted with normal mouse cardiac antigens of a wide range of molecular weights by Western immunoblotting. Because LPS treatment is capable of increasing cytokine levels as well as MHC Class I and Class II expression in heart tissue, it suggests that these factors may contribute to susceptibility to autoimmune myocarditis in CB3-infected mice.     

IL-13-mediated worm expulsion is B7 independent and IFN-gamma sensitive

B7 costimulation is a required component of many type 2 immune responses, including allergy and protective immunity to many nematode parasites. This response includes elevations in Th2 cytokines and associated effector functions including elevations in serum IgG1 and IgE and parasite expulsion. In studies of mice infected with Trichuris muris, blocking B7 ligand interactions inhibited protective immunity, suppressed IL-4 production, and enhanced IFN-gamma production, but unexpectedly did not inhibit production of the Th2 cytokine, IL-13. Blocking both IFN-gamma and B7 restored protective immunity, which was IL-13 dependent, but did not restore IL-4 or associated IgE responses. Although IL-13 was required for worm expulsion in mice in which both IFN-gamma and B7 were blocked, IL-4 could mediate expulsion in the absence of both IL-13 and IFN-gamma. These studies demonstrate that 1) B7 costimulation is required to induce IL-4, but not IL-13 responses; 2) IL-13 is elevated in association with the IFN-gamma response that occurs following inhibition of B7 interactions, but can only mediate IL-4-independent protection when IFN-gamma is also inhibited; and 3) increased IL-13 production, in the absence of increased IL-4 production, is not associated with an IgE response, even in the absence of IFN-gamma.     

Mechanism of reduced T-cell effector functions and class-switched antibody responses to herpes simplex virus type 2 in the absence of B7 costimulation

T-cell costimulation molecules B7-1 and B7-2 play an important role in activation of T cells to cytolytic effector function and production of cytokines. Interaction with B7 also causes T cells to upregulate surface molecules, such as CD40L, that effectively stimulate antibody responses in conjunction with cytokines. We have shown that mice lacking both B7-1 and B7-2 (B7KO mice), when infected intravaginally with virulent herpes simplex virus type 2 (HSV-2), developed more severe disease and higher mortality than their wild-type counterparts. We have now investigated the effects of B7 costimulation deficiency on induction of immune responses to HSV-2 infection of the genital tract. Fewer gamma interferon (IFN-gamma)-producing T cells were present in the genital lymph nodes of B7KO mice compared to wild-type mice, either acutely after primary infection or in recall responses. Less IFN-gamma and especially interleukin-10 were produced by B7KO mice, and cytolytic T-lymphocyte activity was also attenuated. Reduced expression of CD25 on CD4(+) T cells after infection of B7KO mice was consistent with deficits in T-cell activation to effector functions. Although HSV-specific immunoglobulin M (IgM) titers were comparable for both B7KO mice and wild-type mice, B7KO mice had significant deficits in HSV-specific serum IgG responses, with markedly reduced levels of IgG2a and IgG1. In addition, significantly less IgG was detected in the vaginal secretions of B7KO mice than in those from wild-type mice. CD4(+) T-cell expression of CD40L was depressed in B7KO mice in vivo and in vitro. Together with reduced cytokine production, these results suggest a mechanism for decreased IgG class switching or production. Thus, in the absence of B7 costimulation, na?ve T cells fail to undergo proper activation in response to HSV-2, which limits T-cell cytokine production, cytotoxic T lymphocyte activity, and provision of help for class-switched antibody responses.     

The Th2 lymphoproliferation developing in LatY136F mutant mice triggers polyclonal B cell activation and systemic autoimmunity

Lat(Y136F) knock-in mice harbor a point mutation in Tyr(136) of the linker for activation of T cells and show accumulation of Th2 effector cells and IgG1 and IgE hypergammaglobulinemia. B cell activation is not a direct effect of the mutation on B cells since in the absence of T cells, mutant B cells do not show an activated phenotype. After adoptive transfer of linker for activation of T cell mutant T cells into wild-type, T cell-deficient recipients, recipient B cells become activated. We show in vivo and in vitro that the Lat(Y136F) mutation promotes T cell-dependent B cell activation leading to germinal center, memory, and plasma cell formation even in an MHC class II-independent manner. All the plasma and memory B cell populations found in physiological T cell-dependent B cell responses are found. Characterization of the abundant plasmablasts found in secondary lymphoid organs of Lat(Y136F) mice revealed the presence of a previously uncharacterized CD93-expressing subpopulation, whose presence was confirmed in wild-type mice after immunization. In Lat(Y136F) mice, B cell activation was polyclonal and not Ag-driven because the increase in serum IgG1 and IgE concentrations involved Abs and autoantibodies with different specificities equally. Although the noncomplement-fixing IgG1 and IgE are the only isotypes significantly increased in Lat(Y136F) serum, we observed early-onset systemic autoimmunity with nephritis showing IgE autoantibody deposits and severe proteinuria. These results show that Th2 cells developing in Lat(Y136F) mice can trigger polyclonal B cell activation and thereby lead to systemic autoimmune disease.     

Resveratrol Possesses Protective Effects in a Pristane-Induced Lupus Mouse Model

Background

Systemic lupus erythematosus (SLE) is a multisystemic autoimmune disease characterized by the production of autoantibodies. To date, no therapy has been found to satisfactorily treat SLE. SIRT1 deficiency results in the development of an autoimmune syndrome in mice, including a high titer of anti-nuclear antibody in serum, immunoglobulin deposition in the kidney, and immune complex glomerulonephritis. Resveratrol is an activator of SIRT1 and possesses anti-inflammation and immune-regulatory properties.

Objective

To evaluate the preventative effects of resveratrol on a pristane-induced lupus animal model and assess its putative immune modulation effects.

Methods

BALB/c mice received a single intraperitoneal injection of 0.5 ml of pristane on day 1 and then various doses of resveratrol were given to the mice daily starting on day 2 and continuing for seven months. The autoantibodies in serum and supernatants were measured. Single cells isolated from spleen, isolated CD4+ T cells, and CD19+ B cells were cultured with or without resveratrol in vitro and assessed by flow cytometry.

Results

Resveratrol attenuated proteinuria, immunoglobuin depositon in kidney, and glomerulonephritis as well as IgG1 and IgG2a in serum in pristane-induced lupus mice. Resveratrol also suppressed CD69 and CD71 expression on CD4+ T cells as well as CD4+ T cell proliferation, induced CD4+ T cell apoptosis, and decreased CD4 IFNγ⁺ Th1 cells and the ratio of Th1/Th2 cells in vitro. In vitro antibody production and proliferation of B cells were also inhibited.

Conclusion

Resveratrol possesses protective effects in pristane-induced lupus mice and may represent a novel approach for the management of SLE.     

Autoimmunity induced by HgCl2 in Brown-Norway rats. I. Production of monoclonal antibodies

Mercuric chloride (HgCl2) induces in Brown-Norway rats (BN) a B cell polyclonal activation resulting in autoimmune disease. Spleen cells from BN rats injected with HgCl2 were fused with IR983F, a nonsecreting rat myeloma cell line, in order to obtain monoclonal antibodies reacting with autoantigens or IgE-producing hybridomas. After screening for immunoglobulin-producing clones, we found 5% clones with anti-tissue activity, 8% with anti-TNP activity, and 41% secreting IgE. Among the anti-tissue monoclonal antibodies, one recognizes both TNP and mesangial structures of rat normal glomeruli, which could be an as yet unrecognized mechanism of nephrotoxicity. These experiments 1) confirm that HgCl2 induces polyclonal activation, 2) show that the mercury model is of interest to obtain monoclonal IgE and various autoantibodies, and 3) suggest a new possible mechanism of antibody-mediated renal injury.     

Cardiac myosin-induced myocarditis. Heart autoantibodies are not involved in the induction of the disease

We recently demonstrated that cardiac myosin is capable of inducing autoimmune myocarditis in genetically predisposed mice. This disease parallels coxsackievirus B3-induced autoimmune myocarditis in many respects and is associated with high-titer autoantibodies specific for cardiac myosin. The following lines of evidence suggest that these autoantibodies are not involved in the induction of autoimmune myocarditis: 1) immunoperoxidase staining of heart sections from cardiac myosin-immunized A/J and A.SW mice revealed IgG depositions only along damaged muscle fibres in infiltrated areas, but not in intact tissue; 2) myosin autoantibodies did not bind to the surface of viable cardiac myocytes isolated from mice, but only reacted with myocytes permeabilized with detergent; 3) mice treated with a single high dose of cyclophosphamide, which reduces the humoral immune response, still developed severe myocarditis, despite the fact that their autoantibody titers were reduced to the level of adjuvant-injected controls; and 4) passive transfer of high-titer myosin autoantibodies failed to induce myocarditis, although the titers in the recipients were comparable to those found in mice with cardiac myosin-induced disease. Together, the results suggest that high-titer myosin autoantibodies are secondary rather than primary to the disease.     

D-penicillamine-induced autoimmunity in Brown-Norway rats. Similarities with HgCl2-induced autoimmunity

D-penicillamine (DP) has been previously shown to induce an autoimmune disease in Brown-Norway (BN) rats, characterized by a dermatitis, by the production of antinuclear antibodies, by the formation fo circulating immune complexes, and by linear IgG deposits along the glomerular basement membrane. These manifestations are quite similar to those observed in mercuric chloride (HgCl2)-induced autoimmunity. The mechanism of the latter disease has been recently partly elucidated. The aim of this study was to compare DP and HgCl2-induced autoimmunity in BN rats and to compare the mechanisms involved in both situations. A transient increase in the number of spleen cells, affecting B cells and CD4+ T cells, and an increase in serum IgE concentration, previously reported in HgCl2-induced autoimmunity, were observed during DP treatment. Autoreactive anti-class II T cells able to proliferate not only in the presence of autologous B cells but also in the presence of syngeneic normal B cells were found in DP-treated BN rats. Spontaneous regulation occurred, associated with the disappearance of autoreactive T cells. Suppressor CD8+ T cells were not involved in this phenomenon. Mechanisms involved in both the induction and the regulation of DP-induced autoimmunity seem to be quite similar to those reported in HgCl2-induced autoimmunity.     

Amelioration of collagen-induced arthritis by blockade of inducible costimulator-B7 homologous protein costimulation

B7 homologous protein (B7h)/B7-related protein 1 (B7RP-1) is a new member of the B7 family of costimulatory molecules that specifically interacts with inducible costimulator (ICOS) expressed on activated T cells. Collagen type II (CII)-induced arthritis (CIA) is an experimental model of arthritis that has been used to dissect the pathogenesis of human rheumatoid arthritis. In this study, we have investigated the effect of neutralizing anti-B7h mAb on the development and disease progression of CIA. Administration of anti-B7h mAb significantly ameliorated the disease as assessed by clinical arthritis score and histology in the joints, and a beneficial effect was also obtained by a delayed treatment after the onset of disease. Expression of ICOS and B7h was observed in the inflamed synovial tissue as well as in the draining lymph nodes (LNs) and expansion of ICOS(+) T cells in the LN was reduced by the anti-B7h mAb treatment. Expression of mRNA for proinflammatory cytokines such as TNF-alpha, IL-1beta, and IL-6 in the joints was inhibited by the treatment. Proliferative responses and production of IFN-gamma and IL-10 upon restimulation with CII in vitro were significantly inhibited in LN cells from the anti-B7h mAb-treated mice. Serum anti-CII IgG1, IgG2a, and IgG2b levels were also reduced. Our present results showed a beneficial effect of the B7h blockade on CIA through anti-inflammatory actions and inhibition of both Th1- and Th2-mediated immune responses, suggesting that the ICOS-B7h interaction plays an important role in the pathogenesis of CIA and thus the blockade of this pathway may be beneficial for the treatment of human rheumatoid arthritis.     

A critical role for Fc gamma RIIB in the induction of rheumatoid factors

Rheumatoid factors (RF) are autoantibodies with specificity for the Fc portion of IgG, and IgG-containing immune complexes are likely to be the major source of RF autoantigens. Therefore, the activation of RF-producing B cells could be controlled specifically through recognition of IgG immune complexes by the low-affinity IgG FcR, FcgammaRIIB, a potent negative regulator of the BCR. To test this possibility, we determined the development of RF in C57BL/6 (B6) mice lacking FcgammaRIIB, in relation to the H2 haplotype, complement C3, and the Y-linked autoimmune acceleration (Yaa) mutation. FcgammaRIIB-null B6 mice displayed substantial anti-IgG2a RF activities in their sera, in addition to anti-DNA autoantibodies. Their RF and anti-DNA responses were linked to the H2(b) haplotype, but were suppressed almost completely by the H2(d) haplotype. Strikingly, the absence of C3 failed to modulate RF production, but strongly inhibited anti-DNA production. Furthermore, we observed that partial FcgammaRIIB deficiency (i.e., heterozygous level of FcgammaRIIB expression) was sufficient to induce the production of RF and anti-DNA autoantibodies in the presence of the Yaa mutation. In contrast to FcgammaRIIB, the deficiency in another BCR negative regulator, CD22, was unable to promote RF and anti-DNA autoimmune responses in B6 mice. Our results indicate that RF autoimmune responses are critically controlled by FcgammaRIIB, together with the H2(b) and Yaa gene, while C3 regulates positively and specifically anti-DNA, but not RF autoimmune responses.     

The polyclonal and antigen-specific IgE and IgG subclass response of mice injected with ovalbumin in alum or complete Freund's adjuvant

BALB/c mice were injected ip with 1 microgram ovalbumin (OVA) in alum or complete Freund's adjuvant (cFA) and the changes of the IgE and IgG subclass serum levels and isotypes of the anti-OVA specific antibodies determined by radioimmunoassays. By Day 10, OVA in alum had induced a 5- to 10-fold increase of the IgE serum level and an initial decrease of the IgG subclass levels which subsequently increased to two to threefold over the preinjection level. OVA in cFA induced a gradual twofold increase of the IgE serum level, a rapid fourfold increase of the IgG2a level occurring by Day 7, and a gradual two to threefold increase of the other IgG subclasses. Over 90% of the anti-OVA antibodies were of the IgGl isotype with both adjuvants; OVA in alum induced slightly more IgGl anti-OVA antibodies than cFA. In contrast, the OVA in alum injected mice formed significantly more (5- to 10-fold) IgE anti-OVA antibodies than the cFA-injected mice. OVA in alum also induced a large nonspecific increase of the IgE serum level because only approximately 40% of the increase observed on Day 14 was absorbable with OVA, whereas approximately 90% the IgE increase in cFA injected mice was absorbable with OVA. The data demonstrate that mice form mainly IgGl and IgE antibodies to OVA irrespective of the adjuvant. The low specific and lack of nonspecific IgE formation by mice injected with OVA in cFA may be the result of cFA-induced interferon-gamma (IFN-gamma) production because IFN-gamma has been shown to stimulate IgG2a and inhibit IgE secretion in vitro.     

Anti-M(3) peptide IgG from Sjögren's syndrome triggers apoptosis in A253 cells

Primary Sj?gren's syndrome (pSS) is an autoimmune disease that targets salivary and lachrymal glands, characterized by anti-cholinergic autoantibodies directed against the M(3) muscarinic acetylcholine receptor (mAChR). The aim of this work was to evaluate if cholinergic autoantibodies contained in IgG purified from Sj?gren sera could trigger apoptosis of A253 cell line. We also determined if caspase-3 and matrix metalloproteinase-3 (MMP-3) are involved in the induction of A253 cell death. Our results demonstrated that anti-cholinergic autoantibodies stimulate apoptosis and inositol phosphate (InsP) accumulation accompanied by caspase-3 activation and MMP-3 production. All of these effects were blunted by atropine and J104794, indicating that M(3) mAChRs are impacted by the anti-cholinergic autoantibodies. The intracellular pathway leading to autoantibody-induced biological effects involves phospholipase C (PLC), calcium/calmodulin (CaM) and extracellular calcium as demonstrated by treatment with U-73122, W-7, verapamil, BAPTA and BAPTA-AM, all of which blocked the effects of the anti-cholinergic autoantibodies. In conclusion, anti-cholinergic autoantibodies in IgG purified from pSS patient's sera mediates apoptosis of the A253 cell line in an InsP, caspase-3 and MMP-3 dependent manner.     

Allotype-specific immunoregulation of autoantibody production by host B cells in chronic graft-versus host disease

A chronic graft-vs-host (GVH) reaction induced in nonautoimmune mice by the transfer of Ia-incompatible spleen cells results in a syndrome that closely resembles SLE in the spectrum of autoantibodies and immunopathology. We have utilized Ia- and Igh-congenic strains to study the immunoregulation of autoantibody-producing B cells in this model. We have found that the autoantibodies are produced almost entirely by the host B cells. The transferred donor B cells contributed neither to the autoimmune response nor to the total serum Ig, with rare exceptions. The donor cell population did, however, exert an Igh allotype-specific immunoregulatory effect on the host B cells. For example, in allotype-heterozygous recipients, the autoantibodies were preferentially made by those host cells that expressed the donor allotype, whereas those host B cells that expressed nondonor allotype were relatively suppressed. In allotype-homozygous recipients, the donor cells frequently suppressed the host IgG2a allotype completely. This suppression sometimes prevented the IgG antichromatin response, although in other cases the response occurred with the use of a different isotype. In a final set of experiments, a chronic GVH reaction was induced in which both the donors and the recipients were Igh allotype heterozygous and yet differed at Ia. In this case, no donor influence on allotype should be expected; yet the IgG2a autoantibodies were clearly skewed toward the b allotype. These results show that host B cells play a unique role in the GVH autoimmune syndrome. In addition, they are immunoregulated in allotype-specific manners, some of which presumably involve interaction with donor T cells.