In vitro T-cell functions specific to an anti-DNA idiotype and serological markers in patients with systemic lupus erythematosus (SLE)

Triggers of Autoimmunity: The Role of Bacterial Infections in the Extracellular Exposure of Lupus Nuclear Autoantigens

Infections are considered important environmental triggers of autoimmunity and can contribute to autoimmune disease onset and severity. Nucleic acids and the complexes that they form with proteins—including chromatin and ribonucleoproteins—are the main autoantigens in the autoimmune disease systemic lupus erythematosus (SLE). How these nuclear molecules become available to the immune system for recognition, presentation, and targeting is an area of research where complexities remain to be disentangled. In this review, we discuss how bacterial infections participate in the exposure of nuclear autoantigens to the immune system in SLE. Infections can instigate pro-inflammatory cell death programs including pyroptosis and NETosis, induce extracellular release of host nuclear autoantigens, and promote their recognition in an immunogenic context by activating the innate and adaptive immune systems. Moreover, bacterial infections can release bacterial DNA associated with other bacterial molecules, complexes that can elicit autoimmunity by acting as innate stimuli of pattern recognition receptors and activating autoreactive B cells through molecular mimicry. Recent studies have highlighted SLE disease activity-associated alterations of the gut commensals and the expansion of pathobionts that can contribute to chronic exposure to extracellular nuclear autoantigens. A novel field in the study of autoimmunity is the contribution of bacterial biofilms to the pathogenesis of autoimmunity. Biofilms are multicellular communities of bacteria that promote colonization during chronic infections. We review the very recent literature highlighting a role for bacterial biofilms, and their major components, amyloid/DNA complexes, in the generation of anti-nuclear autoantibodies and their ability to stimulate the autoreactive immune response. The best studied bacterial amyloid is curli, produced by enteric bacteria that commonly cause infections in SLE patients, including Escherichia coli and Salmonella spps. Evidence suggests that curli/DNA complexes can trigger autoimmunity by acting as danger signals, molecular mimickers, and microbial chaperones of nucleic acids.

Anticitrullinated Protein Antibodies Induce Inflammatory Gene Expression Profile in Peripheral Blood Cells from CCP-positive Patients with RA

OBJECTIVE

Anticitrullinated protein antibodies (ACPA) have major diagnostic significance in rheumatoid arthritis (RA). ACPA are directed against different citrullinated antigens, including filaggrin, fibrinogen, vimentin, and collagen. The presence of ACPA is associated with joint damage and extraarticular manifestations, suggesting that ACPA may have a significant role in the pathogenesis of RA.

METHODS

To verify the effect of ACPA on RA-immune cells, peripheral blood mononuclear cells (PBMC) from cyclic citrullinated peptide (CCP)-positive patients with RA and healthy controls were cocultured in vitro with ACPA. ACPA-positive stained cells were analyzed by flow cytometry and the effect of ACPA on mRNA expression levels was evaluated by real-time PCR. We tested whether the stimulatory effects induced by ACPA could be inhibited by the addition of a new multiepitope citrullinated peptide (Cit-ME).

RESULTS

We found that ACPA bind specifically to PBMC from CCP-positive patients with RA through the Fab portion. ACPA induce upregulation of pathogenic cytokine expression (4- to 13-fold increase) in PBMC derived from CCP-positive patients with RA. Moreover, ACPA upregulated IL-1β and IL-6 mRNA expression levels by 10- and 6-fold, respectively, compared to control IgG. Cit-ME, a genuine ligand of ACPA, inhibited the ACPA-induced upregulation of IL-1β and IL-6 by 30%.

CONCLUSION

ACPA bind to a limited percentage of PBMC and upregulate inflammatory cytokine expression, suggesting that ACPA is involved in RA pathogenesis. Targeting ACPA to decrease their pathogenic effects might provide a novel direction in developing therapeutic strategies for RA.

Systemic Lupus Erythematosus: Molecular Mimicry between Anti-dsDNA CDR3 Idiotype, Microbial and Self Peptides-As Antigens for Th Cells

Systemic lupus erythematosus (SLE) is marked by a T helper (Th) cell-dependent B cell hyperresponsiveness, with frequent germinal center reactions, and gammaglobulinemia. A feature of SLE is the finding of IgG autoantibodies specific for dsDNA. The specificity of the Th cells that drive the expansion of anti-dsDNA B cells is unresolved. However, anti-microbial, anti-histone, and anti-idiotype Th cell responses have been hypothesized to play a role. It has been entirely unclear if these seemingly disparate Th cell responses and hypotheses could be related or unified. Here, we describe that H chain CDR3 idiotypes from IgG⁺ B cells of lupus mice have sequence similarities with both microbial and self peptides. Matched sequences were more frequent within the mutated CDR3 repertoire and when sequences were derived from lupus mice with expanded anti-dsDNA B cells. Analyses of histone sequences showed that particular histone peptides were similar to VDJ junctions. Moreover, lupus mice had Th cell responses toward histone peptides similar to anti-dsDNA CDR3 sequences. The results suggest that Th cells in lupus may have multiple cross-reactive specificities linked to the IgVH CDR3 Id-peptide sequences as well as similar DNA-associated protein motifs.

Idiotype-specific Th cells support oligoclonal expansion of anti-dsDNA B cells in mice with lupus

Systemic lupus erythematosus (SLE) is marked by a Th cell-dependent B cell hyperresponsiveness, with frequent germinal center reactions and hypergammaglobulinemia. The specificity of Th cells in lupus remains unclear, but B cell Ids have been suggested. A hallmark is the presence of anti-dsDNA, mutated IgG autoantibodies with a preponderance of arginines in CDR3 of the Ig variable H chain (IgVH). B cells can present V region-derived Id peptides on their MHC class II molecules to Id-specific Th cells. We show that Id-specific Th cells support the proliferation of anti-dsDNA Id(+) B cells in mice suffering from systemic autoimmune disease with SLE-like features. Mice developed marked clonal expansions of B cells; half of the IgVH sequences were clonally related. Anti-dsDNA B cells made up 40% of B cells in end-stage disease. The B cells expressed mutated IgVH with multiple arginines in CDR3. Hence, Id-driven T cell-B cell collaboration supported the production of classical anti-dsDNA Abs, recapitulating the characteristics of such Abs in SLE. The results support the concept that Id-specific Th cells may trigger the development of SLE and suggest that manipulation of the Id-specific T cell repertoire could play a role in treatment.

Potential for anti-DNA immunoglobulin peptide therapy in systemic lupus erythematosus

BACKGROUND

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease with elevated morbidity and multi-organ involvement. While many strategies have shown efficacy and improved management of SLE, they have often been associated with adverse effects. Some patients may not respond well to some treatments because of inter-individual variability of the disease. More specific and safer therapies are needed.

OBJECTIVE/METHODS

To review literature on peptide-based therapy of SLE.

RESULTS/CONCLUSIONS

Recently, emphasis has been placed on targeting molecules and pathways involved in the inflammatory response in SLE, including the use of immunogenic peptides derived from anti-DNA antibodies. Encouraging data from murine models of SLE have led to tests in initial clinical trials in humans--which have unfortunately not met the primary endpoints. The current challenge is to design improved strategies for immunotherapeutic use of anti-DNA peptides in SLE.

Cerebrospinal fluid T cell clones from patients with multiple sclerosis: recognition of idiotopes on monoclonal IgG secreted by autologous cerebrospinal fluid B cells

Due to somatic recombination and hypermutation, Ig variable heavy (V(H)) and light (V(L)) regions contain unique immunogenic determinants, idiotopes (Id), which can stimulate T cells. To address the relevance of this in a human disease, monoclonal IgG (mAb)-secreting B cell clones were established from the cerebrospinal fluid (CSF) of two patients with multiple sclerosis (MS). HLA-DR-restricted CD4(+) T cell lines and clones from CSF of both patients specifically recognized autologous CSF mAb. The CSF T cell clones produced IFN-gamma; some also produced TNF-alpha, IL-10 and IL-5. V(H) and V(L) on the monoclonal IgG derived from CSF B cells expressed amino acid replacements due to somatic mutations. A T cell epitope was mapped to a V(H) framework region, where an amino acid replacement was critical for the T cell recognition. The finding of Id-specific T cells and Id-bearing B cells in the CSF indicates that they coexist within the diseased organ, and provide a basis for the study of Id-driven T-B cell collaboration in a human autoimmune disease.

Modulation of autoreactive responses of peripheral blood lymphocytes of patients with systemic lupus erythematosus by peptides based on human and murine anti-DNA autoantibodies

Two peptides, based on the sequences of the complementarity-determining regions (CDR) 1 and 3 of a pathogenic murine monoclonal anti-DNA autoatibody that bears the 16/6 idiotype (Id), were shown to either prevent or treat an already established systemic lupus erythematosus (SLE) in two murine models of lupus. Two additional peptides based on the human monoclonal anti-DNA, 16/6 Id were synthesized. This study was undertaken in order to investigate the ability of the CDR-based peptides to immunomodulate SLE-associated responses of peripheral blood lymphocytes (PBL) of SLE patients. PBL of 24 of the 62 SLE patients tested proliferated in vitro following stimulation with the human 16/6 Id. Peptides based on the CDRs of both the human and murine anti-DNA autoantibodies inhibited efficiently and specifically the 16/6 Id-induced proliferation and IL-2 production. The latter inhibitions correlated with an up-regulated production (by 2.5-3.5-fold) of the immunosuppressive cytokine, TGF-beta. Overall, the results of our study demonstrate that the CDR-based peptides are capable of down-regulating in vitro autoreactive T cell responses of PBL of SLE patients. Thus, these peptides are potential candidates for a novel specific treatment of SLE patients.

Immune response of SLE patients to peptides based on the complementarity determining regions of a pathogenic anti-DNA monoclonal antibody

We have examined the humoral and cellular responses of SLE patients to peptides based on the complementarity-determining regions (CDR) of a monoclonal anti-DNA antibody with a major idiotype- 16/6 Id, in comparison to their responses to the whole 16/6 Id-bearing antibody. Sera of 63% of the SLE patients had antibodies that bound the 16/6 Id, 80% had antibodies to one of the CDR-based peptides, and 40% of the patients reacted with both CDRs. Sera of only a few controls reacted with either the 16/6 Id (6%) or the CDR based peptides (4%) (P < 0.01). Peripheral blood lymphocytes (PBL) of 39% of the patients proliferated in response to the 16/6 Id or to one of the CDR-based peptides (37%), while in the control group the proliferation rates were 66% to the 16/6 Id and 59% to one of the CDR-based peptides (P < 0.05). The correlation between (both) the humoral and cellular immune responses to the CDR-based peptides and to the 16/6 Id suggests the relevance of these peptides to the 16/6 Id and provides additional information on the pathogenic moiety of the latter antibody.

Anti-idiotype and immunosuppressant treatment of murine lupus

The effect of the administration of a xenogeneic anti-idiotype antibody (anti-Id33) to a cross-reactive idiotype (Id33) present on anti-dsDNA antibody was examined in 6-week-old (NZB/NZW) F1 (BWF1) female mice. The administration of anti-Id33 led to a transient reduction in immunoglobulins expressing Id33, followed by a rise at 30 and 34 weeks that was significantly higher than in untreated mice (P less than 0.05). Likewise, anti-dsDNA antibody levels were significantly higher at 10 and 18 weeks than in untreated mice (P less than 0.01). No differences were seen in survival to 40 weeks, proteinuria or the severity of glomerulonephritis. Concurrent administration of cyclosporin A (CyA) with anti-Id33 markedly ameliorated glomerular injury and proteinuria and improved survival. By contrast, glomerular injury, proteinuria and survival were worse in mice treated with cyclophosphamide plus anti-Id33, compared with untreated mice. Neither CyA nor cyclophosphamide treatment, when given with anti-Id33 altered serum levels of anti-dsDNA, anti-ssDNA or Id33+ immunoglobin, compared with untreated mice. The different effects of CyA and cyclophosphamide on T lymphocytes and their discrepant effects on glomerular injury when given with anti-Id33 in this model lead us to postulate a role for T lymphocytes in the glomerular injury of BWF1 lupus.

Anti-DNA idiotype- and anti-idiotype-specific T cell responses in patients with systemic lupus erythematosus and their first-degree relatives

We examined the proliferative responses of T cells of patients with systemic lupus erythematosus (SLE), their first-degree relatives, and healthy donors, to a human monoclonal antibody that bears a common anti-DNA idiotype, 16/6 Id, and to a murine, 16/6 Id-specific, monoclonal antibody. Both 16/6 Id+ and 16/6 Id-specific antibodies were previously shown to be involved in the induction of experimental SLE in mice. Here we show that T cells of fewer SLE patients, as compared with healthy donors, could proliferate to both antibodies. The difference between T cell responses of patients and controls to the 16/6 was found to be significant. The proliferative responses of T cells of first degree relatives of SLE patients to the anti-16/6 Id were found to be significantly lower compared with the responses detected in healthy donors and in SLE patients. The responses of T cells of SLE relatives to the 16/6 Id were found to be lower than those of healthy donors, but this difference was not significant. The present study suggests a possible involvement of T cells, and specifically of idiotype and anti-idiotype specific T cells, in SLE.