T cell determinants from autoantibodies to DNA can upregulate autoimmunity in murine systemic lupus erythematosus

Mechanism of ovarian autoimmunity: induction of T cell and antibody responses by T cell epitope mimicry and epitope spreading

Autoimmune diseases are often manifested as organ inflammation with loss of function, and detectable autoreactive T cell and autoantibody responses. In the proper genetic context, we have shown that these parameters of autoimmunity can result from a single pivotal event: the induction of a strong and persistent T cell response for a foreign or unrelated self peptide that mimics the target self peptide. This may apply to organ-specific and systemic autoimmunity, independent of whether the tissue inflammation results from T cell immune mechanism or antibodies. T cell peptide mimicry, through sharing of critical residues or by a less defined mechanism, can result in autoimmune disease. Once triggered, the helper T cell response leads rapidly to a concomitant autoantibody response spreading to distant B cell determinants of the self protein antigen. Evidently, with T cell help, endogenous antigens can stimulate B cells to provoke a functional autoantibody response against conformational antigenic determinants. These findings are based on recent studies on a novel autoimmune ovarian disease model induced by a self peptide with well-defined T and B cell epitopes. However, studies reported on systemic lupus erythematosus models have shown that similar events may result in autoantibody response in systemic autoimmunity.

Analysis of Vbeta4 T cell receptor CDR3 repertoire in BALB/c and (NZB x NZW)F1 mice

To examine the unique TCR repertoire in auto-immune-prone (NZB x NZW)F1 (B/WF1) mice, we analysed the Vbeta4 CDR3 region of TCRbeta chain in spleens of young (1 month old) and aged (6 month old) BALB/c and B/WF1 mice. Total RNA from spleens was used for cDNA synthesis and TCRVbeta4 PCR products were cloned and sequenced. Young B/WF1 mice showed high frequency (38.5%) of anionic amino acid residues at position beta100 in TCRVbeta4 chain compared to that (19.0%) in young BALB/c mice. Aged BALB/c mice and B/WF1 mice showed increase of frequency (38.1 and 51.9%, respectively) of anionic residues at beta100. These results indicate that Vbeta4-T cells that have anionic residues at beta100 in CDR3 region of TCRbeta chain increase with age in normal mice. Auto-immune prone mice show high frequency of anionic residues at beta100 in TCRVbeta4 chain even at the age of 1 month. These T cells may interact with cationic self-antigen(s) and might contribute to the onset and/or the progression of systemic autoimmunity in concert with other genetic elements in B/WF1 mice.

T cell tolerance to kappa light chain (L kappa): identification of a naturally processed self-C kappa-peptidic region by specific CD4+ T cell hybridomas obtained in L kappa-deficient mice

In contrast to H-2d kappa light chain-deficient mice (kappa-/-), BALB/c (kappa+/+) mice fail to respond to kappa light chains (L kappa). This suggests that C kappa-specific T cells are tolerant to this self-antigen in kappa+/+ mice. To get insights into the cellular and molecular basis of this tolerance, we first characterized the presented L kappa-derived C kappa-peptidic region(s). Among a library of overlapping peptides spanning the whole C kappa sequence, only three consecutive peptides are recognized by CD4+ T cell hybridomas obtained in L kappa-immunized kappa-/- mice. This C kappa-peptidic region, which is also the only one containing the I-Ed-binding consensus motif, is immunogenic since it is able to prime lymph node cells of kappa-/- mice to subsequent in vitro proliferative response to either L kappa or kappa+/+ APC. Conversely, no kappa+/+ T cell proliferation is observed under the same conditions. Activation of our hybridomas by cells from central and peripheral lymphoid tissues reveals that this C kappa region is naturally expressed on BALB/c kappa+/+ APC. In addition to B cells, macrophages and dendritic cells are able to present this region. Taken together our data suggest that the described self-C kappa region is implicated in the C kappa-specific CD4+ T cell tolerization in BALB/c mice.

Modulation of murine systemic lupus erythematosus with peptides based on complementarity determining regions of a pathogenic anti-DNA monoclonal antibody

Experimental systemic lupus erythematosus (SLE) can be induced in naive mice by immunization with a murine monoclonal anti-DNA antibody (mAb), 5G12, that bears a major idiotype designated 16/6 Id. Strain-dependent differences were observed in the proliferative responses of lymph node cells of mice immunized with two peptides based on the sequences of the complementarity determining region (CDR) 1 and 3 of mAb 5G12. The capacity of the peptides to bind to major histocompatibility complex class II molecules correlated with the proliferative responses. Immunization of high responder strains with the CDR-based peptides led to production of autoantibodies and clinical manifestations characteristic to experimental SLE. The CDR-based peptides could prevent autoantibody production in neonatal mice that were immunized later either with the peptide or with the pathogenic autoantibody. Furthermore, the peptides inhibited specific proliferation of lymph node cells of mice immunized with the same peptide, with mAb 5G12 or with the human mAb anti-DNA, 16/6 Id. Thus, the CDR-based peptides are potential candidates for therapy of SLE.

T cells of lupus and molecular targets for immunotherapy

A major advance in understanding the basic mechanism driving the pathogenic autoimmune response in SLE has been the identification of nucleosome as a primary immunogen. The production of pathogenic antinuclear antibodies in SLE is mediated by a MHC class II restricted, cognate interaction between select populations of autoimmune T helper cells and autoimmune B cells that recognize epitopes in the different molecular components of the nucleosome particle: a form of intermolecular-intrastructural help. In the SNF1 model, we have localized the critical peptide autoepitopes for lupus nephritis-inducing Th cells in the core histones of nucleosomes, at amino acid positions 10-33 of H-2B and 16-39 and 71-94 of H4. Remarkabely, the nephritogenic epitopes are located in the regions of histones that are also targeted by lupus B cells, as well as the sites where the histones contact DNA in the nucleosome, indicating that they are specially protected during antigen processing. Identification of the peptide epitopes is a basic step toward defining how the pathogenic Th cells emerge in lupus. In addition, we found that the pathogenic Th cells and B cells of lupus have a regulatory defect in the expression of CD40 ligand (CD40L or gp39), which results in abnormal costimulatory signals that sustain the production of pathogenic autoantibodies. Specific immunotherapy that blocks the pathogenic T and B cell interaction in lupus can be designed based on the knowledge of these disease mechanisms.

CD4-reactive antibodies in systemic lupus erythematosus

An important place in the immune network is reserved for specific interactions between regulatory antibodies (Ab) and their ligands on T and B lymphocytes. Several lines of evidence indicate that the CD4 glycoprotein may be recognized by such Ab. High levels of CD4-reactive Ab occur in approximately 10-20% of HIV-infected patients. Moreover, between 20 and 30% SLE patients have Ab preferentially reactive with the CD4+ T cells. In relation to this, we have done studies aimed at demonstrating the existence and characteristics of Ab directly targeting CD4 in patients with SLE in comparison with rheumatoid arthritis and normal controls. Assessment of the CD4-reactive Ab by different approaches revealed a several-fold increase in serum concentration of anti-CD4 Ab restricted to a subset of SLE patients (n = 15/87, 17.2%). Enhanced binding was shown to occur specifically both on native CD4 (by immunofluorescence) and on recombinant CD4 (by ELISA and Western blot). Anti-CD4 Ab belonged to IgM and/or IgG isotypes. The overall binding of immunoglobulins to the CD4 molecule was not significantly contributed by DNA/anti-DNA and other circulating immune complexes, and there was no restriction in the usage of kappa and lambda light chains. Clinically, high CD4 reactivity occurred in SLE patients with active disease, as measured by the SLEDAI, and was associated with particular clinical manifestations, including neuropsychiatric disease and lymphopenia.

Nucleosomal peptide epitopes for nephritis-inducing T helper cells of murine lupus

Nucleosome-specific T helper (Th) cells provide major histocompatibility complex class II-restricted, cognate help to nephritogenic antinuclear autoantibody-producing B cells in lupus. However, the lupus Th cells do not respond when components of the nucleosome, such as free DNA or histones, are individually presented by antigen-presenting cells. Thus critical peptide epitopes for the pathogenic Th cells are probably protected during uptake and processing of the native nucleosome particle as a whole. Therefore, herein we tested 145 overlapping peptides spanning all four core histones in the nucleosome. We localized three regions in core histones, one in H2B at amino acid position 10-33 (H2B(10-33)), and two in H4, at position 16-39 (H4(16-39)) and position 71-94 (H4(71-94)), that contained the peptide epitopes recognized by the pathogenic autoantibody-inducing Th cells of lupus. The peptide autoepitopes also triggered the pathogenic Th cells of (SWR x NZB)F1 lupus mice in vivo to induce the development of severe lupus nephritis. The nucleosomal autoepitopes stimulated the production of Th1-type cytokines, consistent with immunoglobulin IgG2a, IgG2b, and IgG3 being the isotypes of nephritogenic autoantibodies induced in the lupus mice. Interestingly, the Th cell epitopes overlapped with regions in histones that contain B cell epitopes targeted by autoantibodies, as well as the sites where histones contact with DNA in the nucleosome. Identification of the disease-relevant autoepitopes in nucleosomes will help in understanding how the pathogenic Th cells of spontaneous systemic lupus erythematosus emerge, and potentially lead to the development of peptide-based tolerogenic therapy for this major autoimmune disease.

Hyperexpression of CD40 ligand by B and T cells in human lupus and its role in pathogenic autoantibody production

We investigated the role of the costimulatory molecules, CD40 and its ligand CD40L, in the pathogenesis of human SLE. In comparison to normal subjects or patients in remission, PBMC from active lupus patients had a 21-fold increase in the frequency of CD40L-expressing, CD4+T cells. However, the expression of CD40L induced in either lupus or normal T cells by mitogenic stimulation could be down-regulated equally well by CD40 molecules on autologous B cells. Active lupus patients also had a 22-fold increase in percentage of CD8+ T cells expressing CD40L, consistent with their unusual helper activity in SLE. Surprisingly, patients with active lupus had a 20.5-fold increase in B cells that spontaneously expressed high levels of CD40L, as strongly as their T cells. Although lupus patients in remission had low levels of CD40L+ cells in the range of normal subjects, mitogen-induced upregulation of CD40L expression in the T and B cells was markedly greater than normal, suggesting an intrinsic defect. A mAb to CD40L blocked significantly the ability of lymphocytes from lupus patients with active and established disease to produce the pathogenic variety of antinuclear autoantibodies in vitro, bolstering the possibility of anti-CD40L immunotherapy for lupus. Future studies on the hyperexpression of CD40L could elucidate a regulatory defect in the pathogenic T and B cells of lupus.

Neonatal peptide exposure can prime T cells and, upon subsequent immunization, induce their immune deviation: implications for antibody vs. T cell-mediated autoimmunity

Neonatal exposure to antigen is believed to result in T cell clonal inactivation or deletion. Here we report that, contrary to this notion, neonatal injection of BALB/c mice with a hen egg lysozyme peptide 106-116 in putative "tolergenic" doses induced a T cell proliferative and an immunoglobulin G (IgG) antibody (Ab) response of both T helper cell 1 (Th1)- (IgG2a, IgG2b, and IgG 3) and Th2-dependent (IgG1) isotopes. Upon subsequent challenge with the peptide in complete Freund's adjuvant in adult life, although this neonatal regimen suppressed proliferation and the production of Th1 cytokines (interleukin[IL]-2 and interferon gamma), Th2 cytokine (IL-5, IL-4, and IL-10) secretion was increased, and the serum levels of Th1- and Th2-dependent isotypes of peptide-specific Ab remained elevated. The in vitro proliferative unresponsiveness in Th1 cells could be reversed by Abs to Th2 cytokines (IL-4 and IL-10). Thus, neonatal treatment with a peptide antigen induces T cell priming including production of IgG Abs of both Th1- and Th2-dependent isotypes. Upon subsequent peptide exposure, the peptide-specific T cell responses undergo an effective class switch in the direction of Th2, resulting in T cell proliferative unresponsiveness. Accordingly, this shift towards increased Ab production to autoantigen could be deleterious in individuals prone to antibody-mediated diseases. Indeed, neonatal treatment with a self-autoantigenic peptide from an anti-DNA monoclonal Ab (A6H 58-69) significantly increased the IgG anti-double-stranded DNA Ab levels in lupus-prone NZB/NZW F1 mice, despite suppressing peptide-specific T cell proliferation. This adverse clinical response is in sharp contrast to the beneficial outcome of neonatal treatment with autoantigens in Th1-mediated autoimmune diseases, such as autoimmune encephalomyelitis, as reported by others. A Th1 to Th2 immune deviation can explain the discordant biological responses after the presumed induction of neonatal tolerance in autoantibody- vs. Th-1 mediated autoimmune diseases.

T cells in murine lupus: propagation and regulation of disease

MRL/Mp-lpr/lpr mice develop a spontaneous lupus syndrome, including hypergammaglobulinemia, autoantibodies, glomerulonephritis, and lymphadenopathy. To investigate the role of lymphocytes subsets in the pathogenesis of disease, lupus-prone MRL mice deficient in alpha beta T cells, gamma delta T cells, or both were generated. Mice deficient in alpha beta T cells developed a partially penetrant lupus syndrome, characterized by lymphadenopathy, elevated levels of class-switched immunoglobulins, an increased incidence of antinuclear antibodies, and immune deposits in kidneys which progressed to renal insufficiency over time. In comparison to wild type animals, gamma delta T cell-deficient animals developed an accelerated and exacerbated disease phenotype, characterized by accelerated hypergammaglobulinemia and enhanced autoantibody production and mortality. Repertoire analysis of these latter animals identified polyclonal expansion (V beta) of alpha beta CD4+ B220-cells. Mice lacking both alpha beta and gamma delta T cells failed to generate class-switched autoantibodies and immune complex renal disease. First, these findings demonstrate that murine lupus in the setting of Fas-deficiency does not absolutely require the presence of alpha beta T cells, and they also suggest that a significant basis for MRL/lpr disease, including renal disease, involves alpha beta T cell-independent, gamma delta T cell dependent, polyreactive B cell autoimmunity, upon which alpha beta T cell-dependent mechanisms aggravate specific autoimmune responses. Second, these data indicate that gamma delta T cells partake in the regulation of systemic autoimmunity, presumably via their effects on alpha beta CD4+ B220-T cells that provide B cell help. Finally, these results demonstrate that MRL/lpr B cells, despite their intrinsic abnormalities, cannot per se cause tissue injury without T cell help.

Immune tolerance to autoantibody-derived peptides delays development of autoimmunity in murine lupus

Mechanisms that initiate and maintain autoantibody (autoAb) production in individuals with autoimmune diseases like SLE are poorly understood. Inadequate suppression of autoreactive T cells and/or unusual activation of T and B cells may underlie the persistence of pathogenic autoAbs in lupus. Here, we examine the possibility that in mice with lupus, autoAb molecules may be upregulating their own production by activating self-reactive T cells via their own processed peptides; downregulation of this circuit may decrease autoAb production and delay the development of lupus. We found that before the onset of clinical disease, lupus-prone (NZB/NZW) F1 [BWF1] (but not MHC-matched nonautoimmune mice) developed spontaneous T cell autoimmunity to peptides from variable regions of heavy chains (VH) of syngeneic anti-DNA mAbs but not to peptides from the VH region of an mAb to an exogenous antigen. Tolerizing young BWF1 mice with intravenous injections of autoAb-derived determinants substantially delayed development of anti-DNA antibodies and nephritis and prolonged survival. Thus, in such an autoAb-mediated disease, the presence of autoreactive T cells against VH region determinants of autoAbs may represent an important mechanism involved in the regulation of autoimmunity. Our findings show that tolerizing such autoreactive T cells can postpone the development of an autoimmune disease like SLE.

Mechanisms of the pathogenic autoimmune response in lupus: prospects for specific immunotherapy

A major step towards understanding the basic mechanism of systemic lupus erythematosus (SLE), the prototypic autoimmune disease that develops spontaneously, has been the identification of nucleosomes as a primary immunogen in this disease. The production of pathogenic autoantibodies in SLE results from an MHC class-II-restricted, cognate interaction between select populations of T helper cells and B cells that are specific for nucleosomal components. These observations pave the way for specific immunotherapy that blocks this pathogenic T and B cell interaction.