Interleukin-10-mediated regulatory T-cell responses to epitopes on a human red blood cell autoantigen

Regulatory T-cell dysfunctions are associated with increase in tumor necrosis factor α in autoimmune hemolytic anemia and participate in Th17 polarization

Warm autoimmune hemolytic anemia (wAIHA) is a rare acquired autoimmune disease mediated by antibodies targeting red blood cells. The involvement of CD4 T-helper cells has been scarcely explored, with most findings extrapolated from animal models. Here, we performed quantification of both effector T lymphocytes (Teff) and regulatory T cells (Treg), associated with functional and transcriptomic analyses of Treg in human wAIHA. We observed a shift of Teff toward a Th17 polarization concordant with an increase in serum interleukin-17 concentration that correlates with red blood cell destruction parameters, namely lactate dehydrogenase and bilirubin levels. A decrease in circulating Treg, notably effector Treg, associated with a functional deficiency, as represented by their decrease capability to inhibit Teff proliferation, were also observed. Treg deficiency was associated with a reduced expression of Foxp3, the master transcription factor known to maintain the Treg phenotype stability and suppressive functions. Transcriptomic profiling of Treg revealed activation of the tumor necrosis facto (TNF)-α pathway, which was linked to increased serum TNF-α concentrations that were twice as high as in controls. Treg transcriptomic profiling also suggested that post-translational mechanisms possibly accounted for Foxp3 downregulation and Treg dysfunctions. Since TNF-α participates in the rupture of immune tolerance during wAIHA, its inhibition could be of interest. To this end, the effects of fostamatinib, a SYK inhibitor, were investigated in vitro, and we showed that besides the inhibition of erythrocyte phagocytosis by monocytes, fostamatinib is also able to dampen TNF-α production, thus appearing as a promising multitargeting therapy in wAIHA (clinicaltrials gov. Identifier: NCT02158195).

PepAnalyzer: predicting peptide properties using its sequence

Peptides are short linear molecules consisting of amino acids that play an essential role in most biological processes. They can treat diseases by working as a vaccine or antimicrobial agent and serves as a cancer molecule to deliver the drug to the target site for the treatment of cancer. They have the potential to solve the drawbacks of current medications and can be industrially produced in large quantities at low cost. However, poor chemical and physical stability, short circulating plasma half-life, and solubility are some issues that need solutions before they can be used as therapeutics. PepAnalyzer tool is a user-friendly tool that predicts 15 different properties such as binding potential, half-life, transmembrane patterns, test tube stability, charge, isoelectric point, molecular weights, and molar extinction coefficients only using the sequence. The tool is designed using BioPython utility and has even results with standard tools, such as Expasy, EBI, Genecorner, and Geneinfinity. The tool assists students, researchers, and the pharmaceutical sector. The PepAnalyzer tool's online platform is accessible at the link: http://www.iksmbrlabdu.in/peptool .

Interleukin-27 Regulates the Function of the Gastrointestinal Epithelial Barrier in a Human Tissue-Derived Organoid Model

A treatment with direct healing effects on the gastrointestinal epithelial barrier is desirable for inflammatory bowel disease (IBD). Interleukin-27 (IL-27) is an immunoregulatory cytokine, and oral delivery is an effective treatment in murine models of IBD. We aimed to define IL-27 effects on the human gastrointestinal epithelial barrier. We characterised gene and protein expression of permeability mediators in a human colon-derived organoid model. Functional permeability was determined in an organoid-derived 2D monolayer by transepithelial electrical resistance. IL-27 effects on epithelial innate immune responses were assessed through expression of cytokines, anti-microbial peptides and MUC genes. IL-27 effects on wound healing and proliferation were determined in human colon epithelial cell lines. IL-27 led to restoration of permeability regulation following inflammatory cytokine insult (p = 0.001), associated with differential expression of tight junction mediators with decrease in claudin 2 (p = 0.024) and increase in claudin 4 (p < 0.001), E-cadherin (p < 0.001) and zona occludens (p = 0.0014). IL-27 evoked differential gene expression of epithelial-derived innate immune responses (reduced IL1B and IL18, and increased IL33, HBD1, MUC1 and MUC2; p < 0.012). IL-27 induced epithelial barrier wound healing through restitution (p < 0.001), and increased proliferation (p < 0.001) following injury. Overall, IL-27 provokes mucosal healing of the human gastrointestinal epithelial barrier.

TGFβ2 Induces the Soluble Isoform of CTLA-4 - Implications for CTLA-4 Based Checkpoint Inhibitor Antibodies in Malignant Melanoma

Malignant melanoma is an aggressive form of cancer, which can be treated with anti-CTLA-4 and anti-PD-1 checkpoint inhibitor antibodies but while anti-CTLA-4 antibodies have clear benefits for some patients with melanoma, productive responses are difficult to predict and often associated with serious immune related adverse events. Antibodies specific to CTLA-4 bind two major isoforms of CTLA-4 in humans, the receptor isoform and a second naturally secretable, soluble isoform - sCTLA-4. The primary aim here was to examine the effect of selectively blocking the function of sCTLA-4 on in vitro immune responses from volunteer healthy or melanoma patient PBMC samples. Addition of recombinant sCTLA-4 to healthy PBMC samples demonstrated sCTLA-4 to have immunosuppressive capacity comparable to recombinant CTLA4-Ig, partially reversible upon antibody blockade. Further, we identified a mechanistic relationship where melanoma patient TGFβ2 serum levels correlated with sCTLA-4 levels and provided the basis for a novel protocol to enhance sCTLA-4 production and secretion by T cells with TGFβ2. Finally, a comparison of selective antibody blockade of sCTLA-4 demonstrated that both healthy and melanoma patient effector cytokine responses can be significantly increased. Overall, the data support the notion that sCTLA-4 is a contributory factor in cancer immune evasion.

Identification of Serum Cytokine Biomarkers Associated with Multidrug Resistant Tuberculosis (MDR-TB)

Existing tools (including GeneXpert) for diagnosis of multidrug resistant TB (MDR-TB) have limited utility when sputum samples for microbiological analyses cannot be obtained. There is the need for immunological biomarkers which could serve as putative diagnostic markers of MDR-TB. We measured and compared the serum cytokine levels of inflammatory cytokines (IFN-γ, TNF-α, IL12p70, IL-17A, granzyme B) and anti-inflammatory cytokines (IL-10, IL-6, IL-4) among MDR-TB, drug-susceptible (DS)-TB and healthy controls (no-TB) using the Human Magnetic Luminex Multiplex Immunoassay. Levels of IFN-γ and IL-4 were respectively 1.5 log lower and 1.9 log higher in MDR-TB compared to DS-TB cases. Moreover, IFN-γ, TNF-α, IL-10, IL-6, and IL-4 levels were significantly higher in individuals with MDR-TB and DS-TB cases compared to healthy controls. Pairs of cytokines, IL-4 and IFN-γ (p = 0.019), IL-4 and TNF (p = 0.019), and Granzyme B and TNF-α (p = 0.019), showed significant positive correlation in MDR-TB. Serum cytokine profiles can be exploited for immunodiagnostics, as made evident by the Interferon Gamma Release Assays (IGRAs) for TB infection. Using area under the curve values, no single or multiple cytokine combinations could discriminate between DS- and MDR-TB in this study. Studies with a larger sample size and more cytokines could better address the issue.

Combination peptide immunotherapy suppresses antibody and helper T-cell responses to the major human platelet autoantigen glycoprotein IIb/IIIa in HLA-transgenic mice

Platelet destruction in immune thrombocytopenia is caused by autoreactive antibody and T-cell responses, most commonly directed against platelet glycoprotein IIb/IIIa. Loss of self-tolerance in the disease is also associated with deficient activity of regulatory T cells. Having previously mapped seven major epitopes on platelet glycoprotein IIIa that are recognized by helper T cells from patients with immune thrombocytopenia, the aim was to test whether peptide therapy with any of these sequences, alone or in combination, could inhibit responses to the antigen in humanized mice expressing HLA-DR15. None of the individual peptides, delivered by a putative tolerogenic regimen, consistently suppressed the antibody response to subsequent immunization with human platelet glycoprotein IIb/IIIa. However, the combination of glycoprotein IIIa peptides aa6-20 and aa711-725, which contain the predominant helper epitopes in patients and elicited the strongest trends to suppress when used individually, did abrogate this response. The peptide combination also blunted, but did not reverse, the ongoing antibody response when given after immunization. Suppression of antibody was associated with reduced splenocyte T-cell responsiveness to the antigen, and with the induction of a regulatory T-cell population that is more responsive to the peptides than to purified platelet glycoprotein IIb/IIIa. Overall, these data demonstrate that combinations of peptides containing helper epitopes, such as platelet glycoprotein IIIa aa6-20 and aa711-725, can promote in vivo suppression of responses to the major antigen implicated in immune thrombocytopenia. The approach offers a promising therapeutic option to boost T-cell regulation, which should be taken forward to clinical trials.

Induction of IL-10 cytokine and the suppression of T cell proliferation by specific peptides from red cell band 3 and in vivo effects of these peptides on autoimmune hemolytic anemia in NZB mice

PURPOSE

The anion channel protein band 3 is the main target of the pathogenic red blood cells (RBC) autoantibodies in New Zealand black (NZB) mice. CD4 T cells from NZB mice with autoimmune hemolytic anemia respond to band 3. Previously, we have shown that IL-10 and peptides containing a dominant T cell epitope from red cell band 3 modulate autoimmune hemolytic anemia in NZB mice. Because of the immunoregulatory role of IL-10 in autoimmune diseases, we aim to identify individual band 3 peptides that induce high IL-10 production and simultaneously suppress CD4 T cell proliferation and to investigate the effect intranasal administration of IL-10 producing band 3 peptides on autoantibody responses of NZB mice.

METHODS

Splenic CD4 T cells of NZB mice were isolated and stimulated by co-culture of T cells with individual band 3 peptides. IL-10 production was measured by enzyme-linked immunosorbent assay and proliferative response of CD4 T cells was estimated by incorporation of [³H] thymidine assay. NZB mice were given either PBS, or peptides 25 (241-251) and 29 (282-296) or both peptides intranasally on three occasions at 2-day intervals. The mice were bled at 6, 10 and 18 weeks after peptide inhalation, and the number of RBC auto-antibodies was measured by DELAT and hematocrit values were assessed.

RESULTS

Peptides 25 (241-251) and 29 (282-296) induced the highest IL-10 production by CD4 T cells. These peptides also inhibited the peak T cell proliferative response. 6 and 10 weeks after peptide inhalation, the total IgG, IgG1 and IgG2a in mice treated with both peptides 241-251 and 282-296 were significantly higher than control (P < 0.05). However, no significant difference in the mean hematocrit between of the peptide-treated mice and the control group was found.

CONCLUSIONS

Although band 3 peptides 241-251 and 282-296 induced to the highest IL-10 production by CD4 T cells in vitro but fail to reverse the RBC autoantibody response in vivo. Modifications to improve solubility these peptides might help to modulate the immune response toward a T helper-2 profile and decrease the severity of anemia.

Characterisation of the Immunophenotype of Dogs with Primary Immune-Mediated Haemolytic Anaemia

Background

Immune-mediated haemolytic anaemia (IMHA) is reported to be the most common autoimmune disease of dogs, resulting in significant morbidity and mortality in affected animals. Haemolysis is caused by the action of autoantibodies, but the immunological changes that result in their production have not been elucidated.

Aims

To investigate the frequency of regulatory T cells (Tregs) and other lymphocyte subsets and to measure serum concentrations of cytokines and peripheral blood mononuclear cell expression of cytokine genes in dogs with IMHA, healthy dogs and dogs with inflammatory diseases.

Animals

19 dogs with primary IMHA, 22 dogs with inflammatory diseases and 32 healthy control dogs.

Methods

Residual EDTA-anti-coagulated blood samples were stained with fluorophore-conjugated monoclonal antibodies and analysed by flow cytometry to identify Tregs and other lymphocyte subsets. Total RNA was also extracted from peripheral blood mononuclear cells to investigate cytokine gene expression, and concentrations of serum cytokines (interleukins 2, 6 10, CXCL-8 and tumour necrosis factor α) were measured using enhanced chemiluminescent assays. Principal component analysis was used to investigate latent variables that might explain variability in the entire dataset.

Results

There was no difference in the frequency or absolute numbers of Tregs among groups, nor in the proportions of other lymphocyte subsets. The concentrations of pro-inflammatory cytokines were greater in dogs with IMHA compared to healthy controls, but the concentration of IL-10 and the expression of cytokine genes did not differ between groups. Principal component analysis identified four components that explained the majority of the variability in the dataset, which seemed to correspond to different aspects of the immune response.

Conclusions

The immunophenotype of dogs with IMHA differed from that of dogs with inflammatory diseases and from healthy control dogs; some of these changes could suggest abnormalities in peripheral tolerance that permit development of autoimmune disease. The frequency of Tregs did not differ between groups, suggesting that deficiency in the number of these cells is not responsible for development of IMHA.

Identification of tonsillar CD4+CD25-LAG3+ T cells as naturally occurring IL-10-producing regulatory T cells in human lymphoid tissue

IL-10-producing regulatory T cells (IL-10-producing Tregs) are one of the regulatory T cell subsets characterized by the production of high amounts of IL-10, the lack of FOXP3 expression and the strong immunosuppressive capabilities. IL-10-producing Tregs have been primarily reported as induced populations thus far, in part because identifying naturally occurring IL-10-producing Tregs was difficult due to the lack of definitive surface markers. Lymphocyte-activation gene 3 (LAG3) is a CD4 homologue that we have identified as being expressed on IL-10 producing Tregs. In human PBMC, LAG3 combined with CD49b efficiently identifies IL-10-producing Tregs. However, naturally occurring IL-10-producing Tregs in human secondary lymphoid tissue have not been described. In this report, we identified CD4⁺CD25^-LAG3⁺ T cells in human tonsil. This T cell subset produced high amounts of IL-10 and expressed low levels of FOXP3. Surface markers and microarray analysis revealed that this is a distinct tonsillar CD4⁺ T cell subset. CD4⁺CD25^-LAG3⁺ T cells expressed interleukin 10 (IL10), PR/SET domain 1 (PRDM1), and CD274 at high levels and chemokine receptor 5 (CXCR5) at low levels. CD4⁺CD25^-LAG3⁺ T cells suppressed antibody production more efficiently than CD4⁺CD25⁺ T cells, and CD4⁺CD25^-LAG3⁺ T cells induced B cell apoptosis. Moreover, analysis of humanized mice revealed that this cell subset suppressed a graft-versus-host disease (GVHD) reaction in vivo. Our study reveals the existence of naturally occurring IL-10-producing Tregs in human secondary lymphoid tissue and their function in immune regulation.

Immunoregulatory soluble CTLA-4 modifies effector T-cell responses in systemic lupus erythematosus

Background

The inhibitory CTLA-4 molecule is a crucial regulator of immune responses and a target for therapeutic intervention in both autoimmunity and cancer. In particular, CTLA-4 is important in controlling antigen-specific immunity, including responses to autoantigens associated with autoimmune disease. Here, we investigate cytokine responses to a range of lupus-associated autoantigens and assess whether the alternatively spliced isoform of CTLA-4, soluble CTLA-4 (sCTLA-4), contributes to immune regulation of autoantigen-specific immunity in systemic lupus erythematosus (SLE).

Methods

The cell culture supernatant production of sCTLA-4 as well as the cytokines IL-10, IFN-γ, and IL-17 from peripheral blood mononuclear cells (PBMC) from lupus patients and age- and sex-matched healthy volunteer donors were measured in response to previously identified histone and small nuclear ribonucleoprotein (snRNP) autoantigen-derived peptides (H3_91-105, H4_71-93, and U170K_131-151) by ELISA. We also examined the functional contribution of sCTLA-4 to immune regulation in the context of these autoantigenic peptides following blockade of sCTLA-4 with a selective anti-sCTLA-4 monoclonal antibody, JMW-3B3.

Results

We identified responses to autoantigenic peptides, which revealed qualitative differences in cytokine (IL-10, IL-17, and IFN-γ) profiles between SLE patients and healthy donors. PBMC from healthy donors responded to each of the lupus peptides by secreting IFN-γ and IL-17, but PBMC from SLE patients produced IL-10. Although we did not observe differences in the levels of serum or PBMC culture supernatant sCTLA-4 in either cohort, blockade of sCTLA-4 in PBMC cultures responding to antigen enhanced the cytokine profiles associated with each group.

Conclusion

The results show that lupus autoantigen-derived peptides display varied immunogenicity in lupus versus healthy volunteer donors, while sCTLA-4 acts to regulate the T-cell activity independently of response profile.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-1075-1) contains supplementary material, which is available to authorized users.

T cell participation in autoreactivity to NC16a epitopes in bullous pemphigoid

Bullous pemphigoid is a blistering skin disease characterized by autoantibodies against the NC16a domain of bullous pemphigoid 180. This study was performed to characterize and map the fine specificity of T cell responses to NC16a. Peripheral blood mononuclear cells (PBMC) from a total of 28 bullous pemphigoid patients and 14 matched controls were tested for proliferative and cytokine responses to recombinant NC16a and a complete panel of 21 overlapping peptides spanning this region of BP180. Proliferative responses to NC16A and the peptide panel in the patients with active disease were similar in frequency and magnitude to those in healthy donors, and included late responses typical of naive cells in approximately 60% of each group. Interleukin (IL)-4 responses were slightly stronger for six peptides, and significantly stronger for Nc16a, in patients than in controls. Factor analysis identified factors that separate responses to the peptide panel discretely into IL-4, T helper type 2 (Th2) pattern, interferon (IFN)-γ, Th1 pattern and IL-10 or transforming growth factor [TGF-β, regulatory T cell (Treg )] pattern. Factors segregating IL-10 versus IFN-γ were predicted by active blistering or remission, and TGF-β or IL-10 versus IFN-γ by age. Finally, we confirmed a significant up-regulation of IgE responses to BP180 in the patients with pemphigoid. This shows the complexity of T cell phenotype and fine autoreactive specificity in responses to NC16A, in patients and in normal controls. Important disease-associated factors determine the balance of cytokine responses. Of these, specific IL-4 and IgE responses show the strongest associations with pemphigoid, pointing to an important contribution by Th2 cytokines to pathogenesis.

Emergence of long-lived autoreactive plasma cells in the spleen of primary warm auto-immune hemolytic anemia patients treated with rituximab

Primary warm autoimmune hemolytic anemia (wAIHA) is a rare autoimmune disease in which red blood cells are eliminated by IgG autoantibodies. We analyzed the antibody-secreting cells in the spleen and the peripheral blood of wAIHA patients in various contexts of treatment. Plasmablasts were observed in peripheral blood of newly diagnosed wAIHA patients and, accordingly, active germinal center reactions were present in the spleen of patients receiving short-term corticosteroid therapy. Long-term corticosteroid regimens markedly reduced this response while splenic plasma cells were able to persist, a fraction of them secreting anti-red blood cell IgG in vitro. In wAIHA patients treated by rituximab and who underwent splenectomy because of treatment failure, plasma cells were still present in the spleen, some of them being autoreactive. By using a set of diagnostic genes that allowed us to assess the plasma cell maturation stage, we observed that these cells displayed a long-lived program, differing from the one of plasma cells from healthy donors or from wAIHA patients with various immunosuppressant treatments, and more similar to the one of normal long-lived bone-marrow plasma cells. Interestingly, an increased level of B-cell activating factor (BAFF) was observed in the supernatant of spleen cell cultures from such rituximab-treated wAIHA patients. These results suggest, in line with our previous report on primary immune thrombocytopenia, that the B-cell depletion induced by rituximab promoted a suitable environment for the maturation and survival of auto-immune long-lived plasma cells in the spleen.

The mouse idd2 locus is linked to the proportion of immunoregulatory double-negative T cells, a trait associated with autoimmune diabetes resistance

Autoimmune diseases result from a break in immune tolerance. Various mechanisms of peripheral tolerance can protect against autoimmunity, including immunoregulatory CD4(-)CD8(-) double-negative (DN) T cells. Indeed, we have previously shown that diabetes-prone mouse strains exhibit a low proportion of DN T cells relative to that of diabetes-resistant mice, and that a single autologous transfer of DN T cells can impede autoimmune diabetes development, at least in the 3A9 TCR transgenic setting. In this study, we aim to understand the genetic basis for the difference in DN T cell proportion between diabetes-resistant and diabetes-prone mice. We thus perform an unbiased linkage analysis in 3A9 TCR F2 (NOD.H2(k) × B10.BR) mice and reveal that a locus on chromosome 9, which coincides with Idd2, is linked to the proportion of DN T cells in the lymph nodes. We generate two NOD.H2(k).B10-Chr9 congenic mouse strains and validate the role of this genetic interval in defining the proportion of DN T cells. Moreover, we find that the increased proportion of DN T cells in lymphoid organs is associated with a decrease in both diabetes incidence and serum IgG Ab levels. Together, the data suggest that Idd2 is linked to DN T cell proportion and that a physiological increase in DN T cell number may be sufficient to confer resistance to autoimmune diabetes. Altogether, these findings could help identify new candidate genes for the development of therapeutic avenues aimed at modulating DN T cell number for the prevention of autoimmune diseases.

Combination peptide immunotherapy suppresses antibody and helper T-cell responses to the RhD protein in HLA-transgenic mice

The offspring from pregnancies of women who have developed anti-D blood group antibodies are at risk of hemolytic disease of the newborn. We have previously mapped four peptides containing immunodominant T-helper cell epitopes from the RhD protein and the purpose of the work was to develop these into a product for suppression of established anti-D responses. A panel of each of the four immunodominant RhD peptides was synthesized with modifications to improve manufacturability and solubility, and screened for retention of recognition by human T-helper cells. A selected version of each sequence was combined in a mixture (RhDPmix), which was tested for suppressive ability in a humanized murine model of established immune responses to RhD protein. After HLA-DR15 transgenic mice had been immunized with RhD protein, a single dose of RhDPmix, given either intranasally (P=0.008, Mann-Whitney rank sum test) or subcutaneously (P=0.043), rapidly and significantly suppressed the ongoing antibody response. This was accompanied by reduced T-helper cell responsiveness, although this change was less marked for subcutaneous RhDPmix delivery, and by the recruitment of cells with a regulatory T-cell phenotype. The results support human trials of RhDPmix peptide immunotherapy in women with established antibody responses to the RhD blood group.

Indoleamine 2,3 dioxygenase contributes to transferable tolerance in rat red blood cell inducible model of experimental autoimmune haemolytic anaemia

Autoimmune haemolytic anaemia (AIHA) is caused by autoantibodies against red blood cell (RBC) surface antigens that render RBC susceptible to Fc-mediated phagocytosis and complement-mediated lysis. Experimental AIHA can be induced by injection of rat RBC to naive mice, but a lymphocyte-mediated regulatory mechanism eventually suppresses the production of autoantibodies specific for mouse RBC. Critically, this tolerogenic response can be transferred to naive mice by splenocytes from the rat RBC-immunized mouse. Here we investigate whether indoleamine 2,3 dioxygenase (IDO) or the initiators of IDO cascade, including the cytotoxic T lymphocyte antigen (CTLA)-4 receptor and its soluble isoform, contribute to this tolerogenic mechanism. Splenocytes from experimental AIHA mice were transferred adoptively to naive mice under the cover of anti-CTLA-4, anti-soluble CTLA-4 antibodies or IDO inhibitor 1-methyl tryptophan (1-MT). Recipient mice were immunized with rat RBC and levels of antibody against self-RBC and rat-RBC were monitored. Our results indicate that transfer of tolerance to naive recipients is dependent upon IDO-mediated immunosuppression, as mice receiving previously tolerized splenocytes under the cover of 1-MT were refractory to tolerance and developed haemolytic disease upon further challenge with rat RBC. Initiators of IDO activity, CTLA-4 or soluble CTLA-4 did not mediate this tolerogenic process but, on their blockade, boosted antigen-specific effector immune responses.

Predominance of activated, clonally expanded T helper type 17 cells within the CD4+ T cell population in psoriatic lesions

Recent evidence points to the T helper type 17 (Th17) subset as key in the pathogenesis of psoriasis, but cells of this type in lesions remain to be fully characterized. Here we isolated, enumerated, functionally tested and clonotyped the CD4(+) Th cell population ex vivo from lesional biopsies and paired peripheral blood samples from psoriasis patients. Th17 cells were over-represented dramatically in lesions from all patients, representing 49-93% of CD4(+) Th cells compared with 3-18% in blood. Most lesional Th17 cells produced interleukin (IL)-17A ex vivo without further stimulation and expressed the CD45RO(+) phenotype characteristic of activated or memory cells. There was no increase in 'natural' [CD25(hi) forkhead box protein 3 (FoxP3(+))] regulatory T cells in lesions versus peripheral blood, but there was enrichment of 'induced' IL-10(+) regulatory T cell numbers in biopsies from some patients. The lesional Th17 cells exhibited a bias in T cell receptor Vβ chain usage, suggestive of specific expansion by antigen. The therapeutic challenge is to overcome the dominance of overwhelming numbers of such antigen-specific Th17 cells in psoriatic lesions.

A comprehensive review of the phenotype and function of antigen-specific immunoregulatory double negative T cells

Double negative T cells that lack the expression of both CD4 and CD8 T cell co-receptors exhibit a most unique antigen-specific immunoregulatory potential first described over a decade ago. Due to their immunoregulatory function, this rare T cell population has been studied in both mice and humans for their contribution to peripheral tolerance and disease prevention. Consequently, double negative cells are gaining interest as a potential cellular therapeutic. Herein, we review the phenotype and function of double negative T cells with emphasis on their capacity to induce antigen-specific immune tolerance. While the phenotypic and functional similarities between double negative T cells identified in mouse and humans are highlighted, we also call attention to the need for a specific marker of double negative T cells, which will facilitate future studies in humans. Altogether, due to their unique properties, double negative T cells present a promising therapeutic potential in the context of various disease settings.

Red blood cell alloimmunization in sickle cell disease: pathophysiology, risk factors, and transfusion management

Red blood cell transfusions have reduced morbidity and mortality for patients with sickle cell disease. Transfusions can lead to erythrocyte alloimmunization, however, with serious complications for the patient including life-threatening delayed hemolytic transfusion reactions and difficulty in finding compatible units, which can cause transfusion delays. In this review, we discuss the risk factors associated with alloimmunization with emphasis on possible mechanisms that can trigger delayed hemolytic transfusion reactions in sickle cell disease, and we describe the challenges in transfusion management of these patients, including opportunities and emerging approaches for minimizing this life-threatening complication.

Identification, immunomodulatory activity, and immunogenicity of the major helper T-cell epitope on the K blood group antigen

The K blood group remains an important target in hemolytic disease of the newborn (HDN), with no immune prophylaxis available. The aim was to characterize the Th response to K as a key step in designing specific immunotherapy and understanding the immunogenicity of the Ag. PBMCs from K-negative women who had anti-K Abs after incompatible pregnancy, and PBMCs from unimmunized controls, were screened for proliferative responses to peptide panels spanning the K or k single amino acid polymorphism. A dominant K peptide with the polymorphism at the C terminus elicited proliferation in 90% of alloimmunized women, and it was confirmed that responding cells expressed helper CD3(+)CD4(+) and "memory" CD45RO(+) phenotypes, and were MHC class II restricted. A relatively high prevalence of background peptide responses independent of alloimmunization may contribute to K immunogenicity. First, cross-reactive environmental Ag(s) pre-prime Kell-reactive Th cells, and, second, the K substitution disrupts an N-glycosylation motif, allowing the exposed amino acid chain to stimulate a Th repertoire that is unconstrained by self-tolerance in K-negative individuals. The dominant K peptide was effective in inducing linked suppression in HLA-transgenic mice and can now be taken forward for immunotherapy to prevent HDN because of anti-K responses.

Production of the effector cytokine interleukin-17, rather than interferon-γ, is more strongly associated with autoimmune hemolytic anemia

BACKGROUND

Interleukin-17A is the signature cytokine of the Th17 subset and drives inflammatory pathology, but its relevance to autoantibody-mediated diseases is unclear. Th1 cells secreting interferon-γ have been implicated in autoimmune hemolytic anemia, so the aim was to determine which cytokine is more closely associated with disease severity.

DESIGN AND METHODS

Interferon-γ and interleukin-17A were measured in the sera of patients with autoimmune hemolytic anemia and healthy donors, and in peripheral blood mononuclear cell cultures stimulated with autologous red blood cells, or a panel of peptides spanning red blood cell autoantigen.

RESULTS

Serum interleukin-17A, but not interferon-γ, was significantly raised in patients with autoimmune hemolytic anemia (P<0.001), and correlated with the degree of anemia. Interleukin-17A was also more prominent in the responses of peripheral blood mononuclear cells from patients with autoimmune hemolytic anemia to red blood cells, and, again unlike interferon-γ, significantly associated with more severe anemia (P<0.005). There were no interleukin-17A responses to red blood cells by peripheral blood mononuclear cells from healthy donors. Specific autoantigenic peptides were identified that elicit patients' interleukin-17A responses.

CONCLUSIONS

Interleukin-17A makes a previously unrecognized contribution to the autoimmune response in autoimmune hemolytic anemia, challenging the model that the disease is driven primarily by Th1 cells. This raises the possibility that Th17, rather than Th1, cells should be the target for therapy.

Mechanisms of anti-D action in the prevention of hemolytic disease of the fetus and newborn: what can we learn from rodent models?

PURPOSE OF REVIEW

Hemolytic disease of the fetus and newborn can be effectively prevented by administration of anti-D to the mother. In this setting, the IgG purified from the plasma of D-alloimmunized donors prevents the maternal immune response to D-positive red blood cells (RBC). Several monoclonal anti-D antibodies have recently been developed for potential use in the setting of hemolytic disease of the fetus and newborn; the functional assays used to assess the potential success of these antibodies have often assumed antigen clearance as the predominant mechanism of anti-D. Unfortunately, the in-vivo success of these monoclonal antibodies has thus far been limited. A similar inhibitory effect of IgG has been observed in animal models with a vast array of different antigens, referred to as antibody-mediated immune suppression (AMIS). Here, studies of AMIS are reviewed and the relevance of these findings for anti-D-mediated immunoprophylaxis is discussed.

RECENT FINDINGS

In animal models of AMIS, IgG-mediated antigen clearance was not sufficient for prevention of the antibody response to RBC. Furthermore, anti-RBC IgG inhibited B-cell priming to foreign RBC, but failed to prevent a T-cell response and immunological memory.

SUMMARY

The applicability of AMIS models for determining the true mechanism of anti-D, though uncertain, may nevertheless provide knowledge as to potential mechanisms of action of anti-RBC antibodies.

The Family of IL-10-secreting CD4+ T cells

Regulatory T cells (Treg cells) play critical roles in the induction of peripheral tolerance to self- and foreign antigens. Naturally occurring CD4(+)CD25(+) Treg cells, which characteristically express the transcription factor forkhead box protein P3 (Foxp3), have been studied intensively because their deficiency abrogates self-tolerance and causes autoimmune disease. However, several lines of evidence suggest that additional important mechanisms other than the Foxp3 system are required to enforce immunological self-tolerance in the periphery. Interleukin-10 (IL-10) is a regulatory cytokine that plays a central role in controlling inflammatory processes, and IL-10-secreting T cells may constitute an additional mechanism that are responsible for peripheral tolerance. Type-1 T regulatory (Tr1) cells, CD46-stimulated IL-10-secreting T cells, and IL-10-secreting T cells induced by vitamin D3 (VitD3) and dexamethasone (Dex) are induced populations with significant regulatory activities. However, assessing the detailed physiological function of these cells is difficult, because of the lack of specific markers that can reliably differentiate the population of IL-10-secreting Treg cells from other T cells. Recently, CD4(+)CD25(-)LAP(+) T cells, CD4(+)NKG2D(+) T cells, CD4(+)IL-7R(-) T cells, and CD4(+)CD25(-)LAG3(+) T cells have been reported as naturally present IL-10-secreting Treg cells. Although the relationship between these induced and naturally present IL-10-secreting Treg cells is unclear, elucidation of their respective roles in modulating immune responses is crucial to understand T cell-mediated tolerance. Furthermore, the identification of specific markers and molecular signatures will enable the purification or induction of IL-10-secreting Treg cells for the treatment of patients having inflammatory diseases.

Type 1 regulatory T cells are associated with persistent split erythroid/lymphoid chimerism after allogeneic hematopoietic stem cell transplantation for thalassemia

BACKGROUND

Thalassemia major can be cured with allogeneic hematopoietic stem cell transplantation. Persistent mixed chimerism develops in around 10% of transplanted thalassemic patients, but the biological mechanisms underlying this phenomenon are poorly understood.

DESIGN AND METHODS

The presence of interleukin-10-producing T cells in the peripheral blood of eight patients with persistent mixed chimerism and five with full donor chimerism was investigated. A detailed characterization was then performed, by T-cell cloning, of the effector and regulatory T-cell repertoire of one patient with persistent mixed chimerism, who developed stable split erythroid/lymphoid chimerism after a hematopoietic stem cell transplant from an HLA-matched unrelated donor.

RESULTS

Higher levels of interleukin-10 were produced by peripheral blood mononuclear cells from patients with persistent mixed chimerism than by the same cells from patients with complete donor chimerism or normal donors. T-cell clones of both host and donor origin could be isolated from the peripheral blood of one, selected patient with persistent mixed chimerism. Together with effector T-cell clones reactive against host or donor alloantigens, regulatory T-cell clones with a cytokine secretion profile typical of type 1 regulatory cells were identified at high frequencies. Type 1 regulatory cell clones, of both donor and host origin, were able to inhibit the function of effector T cells of either donor or host origin in vitro.

CONCLUSIONS

Overall these results suggest that interleukin-10 and type 1 regulatory cells are associated with persistent mixed chimerism and may play an important role in sustaining long-term tolerance in vivo. These data provide new insights into the mechanisms of peripheral tolerance in chimeric patients and support the use of cellular therapy with regulatory T cells following hematopoietic stem cell transplantation.

Mechanisms of anti-D action in the prevention of hemolytic disease of the fetus and newborn

Anti-D is routinely and effectively used to prevent hemolytic disease of the fetus and newborn (HDFN) caused by the antibody response to the D antigen on fetal RBCs. Anti-D is a polyclonal IgG product purified from the plasma of D-alloimmunized individuals. The mechanism of anti-D has not been fully elucidated. Antigenic epitopes are not fully masked by anti-D and are available for immune system recognition. However, a correlation has frequently been observed between anti-D-mediated RBC clearance and prevention of the antibody response, suggesting that anti-D may be able to destroy RBCs without triggering the adaptive immune response. Anti-D-opsonized RBCs may also elicit inhibitory FcgammaRIIB signaling in B cells and prevent B cell activation. The ability of antigen-specific IgG to inhibit antibody responses has also been observed in a variety of animal models immunized with a vast array of different antigens, such as sheep RBCs (SRBC). This effect has been referred to as antibody-mediated immune suppression (AMIS). In animal models, IgG inhibits the antibody response, but the T-cell response and memory may still be intact. IgG does not mask all epitopes, and IgG-mediated RBC clearance or FcgammaRIIB-mediated B-cell inhibition do not appear to mediate the AMIS effect. Instead, IgG appears to selectively disrupt B cell priming, although the exact mechanism remains obscure. While the applicability of animal models of AMIS to understanding the true mechanism of anti-D remains uncertain, the models have nevertheless provided us with insights into the possible IgG effects on the immune response.

Cholera toxin B subunit promotes the induction of regulatory T cells by preventing human dendritic cell maturation

Cholera toxin B subunit (CTB) is an efficient mucosal carrier molecule for the generation of immune responses to linked antigens. There is also good evidence that CTB acts as an immunosuppressant, as it is able to down-modulate human monocyte/macrophage cell line activation and to suppress Th1-type responses. In the present study, we examined the possibility that recombinant CTB (rCTB) may affect human dendritic cell (DC) functions in response to LPS stimulation and may induce the generation of DC with the capacity to generate CD4(+) regulatory T cells (Tregs). Our findings show that rCTB partially prevents the LPS-induced maturation process of monocyte-derived DC (MDDC) and decreases their IL-12 production with no relevant effect on IL-10 production. LPS-stimulated MDDC pretreated with rCTB are able to promote the induction of low proliferating T cells, which show an enhanced IL-10 production associated with a reduced IFN-gamma production and the same high levels of TGF-beta as the control. These T cells suppress proliferation of activated autologous T cells. Transwell experiments and blockade of IL-10R and TGF-beta showed that the immunomodulatory effect is mediated by soluble factors. Thus, T cells induced by rCTB-conditioned MDDC acquire a regulatory phenotype and activity similar to those described for type 1 Tregs.

Healthy individuals have Goodpasture autoantigen-reactive T cells

Autoreactive T cells in patients with Goodpasture's disease are specific for epitopes in the Goodpasture antigen (the NC1 domain of the alpha3 chain of type IV collagen) that are rapidly destroyed during antigen processing to a degree that diminishes their presentation to T cells. We hypothesized that patients' autoreactive T cells exist because antigen processing prevents presentation of the self-epitopes they recognize, circumventing specific tolerance mechanisms. We predicted that autoreactive T cells specific for these peptides should also exist in healthy individuals, albeit at low frequency and in an unprimed state. We obtained blood from healthy unrelated donors and, using a panel of 45 alpha3(IV)NC1 peptides, identified alpha3(IV)NC1-specific T cells in all donors. Thirty-six of 45 peptides elicited a proliferative T cell response from at least one subject, and 6 of the peptides evoked a response in >50% of the individuals. This consistency was not caused by selectivity of HLA class II molecules because the donors expressed a diversity of HLA antigens, but was largely a result of the substrate-specificity of the endosomal proteases Cathepsin D and E. There was a significant correlation between high susceptibility to Cathepsin D digestion and the capacity to stimulate primary T cell responses (P = 0.00006). In summary, healthy individuals have low frequencies of unstimulated alpha3(IV)NC1-reactive T cells with similar specificities to the autoreactive T cells found in patients with Goodpasture disease. In both cases, existence of the alpha3(IV)NC1-reactive T cells can be accounted for by destructive processing.

Clonal regulatory T cells specific for a red blood cell autoantigen in human autoimmune hemolytic anemia

Regulatory T (Tr) cells have the potential to treat immune-mediated disease, but cloning such cells for study from patients with autoimmune disease has proven difficult. Here, we describe autoantigen-specific, interleukin-10 (IL-10)-secreting Tr cell clones recovered ex vivo from a patient with autoimmune hemolytic anemia (AIHA) and characterize their phenotype, origin, and regulatory function. These IL-10+ Tr cells recognized a peptide, 72H-86L, derived from the Rh red blood cell autoantigen and shared phenotypic characteristics with both natural and inducible Tr cells. The clones also expressed different Tr markers depending on activation state: high levels of CD25 and LAG-3 when expanding nonspecifically, but FoxP3 after activation by the autoantigen they recognize. Despite a discrete Tr phenotype, these cells stably expressed the T helper 1 (Th1) signature transcription factor T-bet, suggesting they derive from Th1 T cells. Finally, the contribution of CTLA-4 in activating these IL-10+ Tr cells was confirmed by analyzing responses to transgenic B7.1-like molecules that preferentially bind either CD28 or CTLA-4. Overall, these Tr cells have a functional phenotype different from those described in previous studies of human Tr populations, which have not taken account of antigen specificity, and understanding their properties will enable them to be exploited therapeutically in AIHA.

Deletion of the dominant autoantigen in NZB mice with autoimmune hemolytic anemia: effects on autoantibody and T-helper responses

The mechanisms underlying apparently spontaneous autoimmune diseases, such as autoimmune hemolytic anemia (AIHA) in New Zealand Black (NZB) mice, are unknown. Here, we determine the contribution of the dominant red blood cell (RBC) autoantigen, the anion exchanger protein Band 3, to the development of NZB autoimmune responses. The approach was to prevent Band 3 expression in NZB mice by disrupting the AE1 gene. AE1(-/-) NZB mice produced RBC autoantibodies at the same levels as the wild-type strain, but they differed in recognizing antigens that correspond to glycophorins, rather than Band 3. Splenic T-helper (Th) cells from wild-type NZB mice proliferated strongly against multiple Band 3 peptides, particularly the dominant epitope within aa861-874. This helper response was severely attenuated in AE1(-/-) animals, leaving only weak proliferation to peptide aa861-874. The results demonstrate that the defect in self-tolerance in NZB AIHA is directed to the RBC type, and is not specific for, or dependent on, Band 3. However, the predisposition to RBC autoimmunity may be focused onto Band 3 by weak Th cell cross-reactivity between the helper dominant epitope and an exogenous antigen. The redundancy of the major autoantigen illustrates the requirement for specific therapy to induce dominant forms of tolerance, such as T-cell regulation.

Different Forms of Helper Tolerance to Carcinoembryonic Antigen: Ignorance and Regulation

PURPOSE

Understanding the mechanisms of immune tolerance to tumor-associated antigens (TAA) is an important step in the design of cancer immunotherapy. The aim was to determine how T helper (Th) cell tolerance is mediated for a prototypic TAA, carcinoembryonic antigen (CEA).

EXPERIMENTAL DESIGN

Peripheral blood mononuclear cells from 50 healthy volunteers were stimulated with CEA, and the type and fine specificity of any Th cell responses were identified. The inhibitory effects of T regulatory (Tr) populations were determined by depleting "natural" CD25(+) Tr cells or neutralizing cytokine produced by the "induced" Tr form.

RESULTS

Proliferative Th cell responses were consistently induced by CEA in 22 of 50 individuals. Responding cells were drawn from the CD45RA(+) "naive" or quiescent population. Depleting the CD25(+) fraction did not enhance CEA responsiveness. However, CEA elicited secretion of the Tr cytokine interleukin-10 (IL-10) in 23 of 50 donors, including 20 of 22 where no proliferation was induced. Neutralizing IL-10 revealed previously unseen proliferation to CEA by CD45RO(+) "memory" Th cells. Epitope maps revealed differences in the fine specificities of Th cells capable of proliferating or secreting IL-10.

CONCLUSIONS

There are at least two major forms of CEA tolerance in different individuals. One is "ignorance," a failure of specific Th cells to respond to antigen presented in vivo. The other, seen when ignorance is lost, is mediated by IL-10-secreting Tr cells that recognize CEA. TAA tolerance, for example to colorectal carcinoma cells expressing CEA, may be overcome by peptide vaccines that exploit the differences in epitopes recognized by effector and Tr responses.

Controlling autoimmunity—Lessons from the study of red blood cells as model antigens

The characterization of human and animal red blood cell (RBC) autoantigens in autoimmune hemolytic anemia (AIHA) has provided an opportunity study the control of specific autoimmune responses of unequivocal pathogenic relevance. The results reveal that censorship of the autoimmune helper T (Th) cell repertoire by deletion and anergy is very incomplete in healthy individuals, even for widely distributed, abundant self-antigens on RBC. There is strong evidence that autoaggression by surviving Th cells is normally held in check by other mechanisms, including failure to display the epitopes that they recognize, and active immunoregulation. AIHA is one of the first human autoimmune diseases in which regulatory T (Tr) cells that are specific for the major autoantigens have been identified. These Tr cells recognize the dominant naturally processed epitopes, and recent studies suggest that disease develops when other determinants, to which such tolerance is less secure, and which are normally inefficiently presented, are displayed at higher levels. Together, the results raise the possibility that therapy for diseases such as AIHA could be based on switching the balance of the response back towards regulation, in particular by the administration of the dominant peptides recognized by specific Tr cells.

Interleukin-10-secreting type 1 regulatory T cells in rodents and humans

Interleukin-10 (IL-10)-secreting T regulatory type 1 (Tr1) cells are defined by their specific cytokine production profile, which includes the secretion of high levels of IL-10 and transforming growth factor-beta(TGF-beta), and by their ability to suppress antigen-specific effector T-cell responses via a cytokine-dependent mechanism. In contrast to the naturally occurring CD4+ CD25+ T regulatory cells (Tregs) that emerge directly from the thymus, Tr1 cells are induced by antigen stimulation via an IL-10-dependent process in vitro and in vivo. Specialized IL-10-producing dendritic cells, such as those in an immature state or those modulated by tolerogenic stimuli, play a key role in this process. We propose to use the term Tr1 cells for all IL-10-producing T-cell populations that are induced by IL-10 and have regulatory activity. The full biological characterization of Tr1 cells has been hampered by the difficulty in generating these cells in vitro and by the lack of specific marker molecules. However, it is clear that Tr1 cells play a key role in regulating adaptive immune responses both in mice and in humans. Further work to delineate the specific molecular signature of Tr1 cells, to determine their relationship with CD4+ CD25+ Tregs, and to elucidate their respective role in maintaining peripheral tolerance is crucial to advance our knowledge on this Treg subset. Furthermore, results from clinical protocols using Tr1 cells to modulate immune responses in vivo in autoimmunity, transplantation, and chronic inflammatory diseases will undoubtedly prove the biological relevance of these cells in immunotolerance.

Regulatory T-cells in the control of immunological diseases

The immune system is challenged by randomly generated immune receptors that by chance can recognize self-antigens. Immunological tolerance functions as a fundamental concept in the control of a broad spectrum of immune responses not only to autoantigens but also to foreign antigens. During the past decade, CD4+ CD25+ regulatory T-cells (Tregs) have emerged as key players in the development of immunological tolerance. This review will present an update on the current knowledge about the phenotype, function, and clinical relevance of this regulatory T-cell population. The therapeutical potential of Tregs to specifically suppress immune responses in autoimmunity and transplantation and their inhibitory effects in anti-tumor immune responses will be discussed.

Tr1 cells: from discovery to their clinical application

Peripheral tolerance is mediated by multiple mechanisms such as anergy and/or active suppression of effector T cells by T regulatory (Tr) cells. Among the CD4(+) Tr cells, T regulatory type 1 cells (Tr1) have been shown to down-modulate immune responses through production of the immunosuppressive cytokines IL-10 and TGF-beta. Tr1 cells maintain peripheral tolerance, control autoimmunity, and prevent allograft rejection and graft versus host disease (GvHD). Cellular therapy with ex vivo generated Tr1 cells has been proven to be effective in several preclinical models of T cell-mediated pathologies and therefore, represents a promising approach for clinical application. This review will summarize the new findings on Tr1 cells, the recent development of methods for their ex vivo expansion, and their potential clinical relevance as cellular therapy.

Selective modulation of CD4+ T cells from lupus patients by a promiscuous, protective peptide analog

A peptide encompassing residues 131-151 of the spliceosomal U1-70K protein and its analog phosphorylated at Ser140 were synthesized as potential candidates for the treatment of patients with lupus. Studies in the MRL/lpr and (NZB x NZW)F1 lupus models have demonstrated that these sequences contain a CD4+ T cell epitope but administration of the phosphorylated peptide only ameliorates the clinical manifestations of treated MRL/lpr mice. Binding assays with soluble HLA class II molecules and molecular modeling experiments indicate that both peptides behave as promiscuous epitopes and bind to a large panel of human DR molecules. In contrast to normal T cells and T cells from non-lupus autoimmune patients, we found that PBMCs from 40% of lupus patients selected randomly and CFSE-labeled CD4+ T cells proliferate in response to peptide 131-151. Remarkably, however, we observed that phosphorylation of Ser140 prevents CD4+ T cells proliferation but not secretion of regulatory cytokines, suggesting a striking immunomodulatory effect of phosphorylated analog on lupus CD4+ T cells that was unique to patients. The analog might act as an activator of regulatory T cells or as a partial agonist of TCR.

Phenotypic and functional differences between human CD4+CD25+ and type 1 regulatory T cells

T regulatory (Tr) cells have an essential role in the induction and maintenance of tolerance to both and foreign self-antigens. Many types of T cells with regulatory activity have been described in mice and humans, and those within the CD4+ subset have been extensively characterized. CD4+ Type-1 regulatory T (Tr1) cells produce high levels of IL-10 and mediate IL-10-dependent suppression, whereas the effects of naturally occurring CD4+CD25+ Tr cells appear to be cell-contact-dependent. Tr1 cells arise in the periphery upon encountering antigen in a tolerogenic environment. In contrast, it appears that CD4+CD25+ Tr cells can either arise directly in the thymus or be induced by antigen in the periphery. We have been interested in defining the phenotype and function of different subsets of CD4+ Tr cells present in human peripheral blood, with the ultimate aim of designing therapeutic strategies to harness their immunoregulatory effects. This review will discuss the similarities and differences between human Tr1 and naturally occurring CD4+CD25+ Tr cells, as well as evidence that indicates that they have nonoverlapping, but synergistic roles in immune homeostasis.

Autoimmune Pathogenesis and Autoimmune Hemolytic Anemia

Autoimmune hemolytic anemia (AIHA) is an autoimmune disorder in which autoantibodies are directed against an individual's own red blood cells (RBCs), leading to enhanced clearance through Fc receptor (FcR)-mediated phagocytosis. Although there is a large literature relating to clinical aspects of AIHA, relatively little work addresses how IgG autoantibodies are actually produced against RBC autoantigens. This review will first discuss the current understanding of autoimmunity in general and then focus on the knowledge of the immunopathogenic mechanisms responsible for autoantibody production in AIHA. Both human and animal studies will be discussed. Understanding theses mechanism is vital for developing antigen-specific immunotherapies to treat the disease.

IL-10 and the Cytokine Network in the Pathogenesis of Human Autoimmune Hemolytic Anemia

In animal and human autoimmune hemolytic anemia (AIHA) immunologic tolerance loss against RBC self-antigens could be originated by several mechanisms: ignored self-antigens' epitopes, polyclonal lymphocyte activation, molecular mimicry between self- and foreign antigens, central or peripheral tolerance errors, or immunoregulatory disturbances including the alteration of a cytokine network. To identify the immunologic factors contributing to autoimmune onset and maintenance, several murine strains (such as NZB and NZB/NZW) that spontaneously develop a complex autoimmune syndrome, including AIHA, have been extensively studied. In human AIHA, the respective roles of IL-2, IL-4, IFN-gamma, IL-10, and IL-12 were investigated by examining the spontaneous and mitogen-induced (OKT3 or LPS) production of these cytokines. ELISA methods were used in PBMCs to evaluate whether the manipulation of IL-10/IL-12 balance can have an effect on the incidence of autoimmune diseases and whether this might be useful for the control of AIHA. Results affirmed that AIHA is a disease that exhibits an increased basal synthesis of IL-4 and decreased levels of IFN-gamma by AIHA PBMCs compared with controls and that there is a basal increase of Th2 cytokines. Th1-type cytokine decrease in the basal state occurred in parallel with an increase of constitutive IL-10 production and an IL-12 decrease. In conclusion, decreased production of Th1-type cytokines and the production of autoantibodies in AIHA may be secondary to the imbalance between IL-10 and IL-12, and the neutralization of IL-10 may be efficacious in diminishing the clinical pathology associated with Th2 subset prevalence. In the same way, the treatment with IL-12 could offer a second and independent level of blockade against the consequences of the overstimulation of B cells associated with AIHA.

Controlling the complement system for prevention of red cell destruction

PURPOSE OF REVIEW

Complement sensitization of red blood cells (RBCs) can lead to both intravascular and extravascular red cell destruction. Altered levels of naturally occurring complement regulatory proteins on red cells can result in hemolysis, while defective expression of these proteins on immune cells can cause breakdown of tolerance to self antigens and is associated with autoimmune disease.

RECENT FINDINGS

To date several complement inhibitors, including recombinant forms of complement regulatory proteins, humanized antibodies, and synthetic molecules have been described that limit complement activation by interfering with different steps in the complement cascade. However, few have been evaluated for prevention of complement-mediated RBC destruction. In this review, possible applications of these complement inhibitors for treatment of complement-mediated hemolysis in specific disease states are described. Furthermore, the implication of the regulatory role of complement in the development of autoimmune hemolytic anemia is discussed.

SUMMARY

Complement therapeutics has potential for effective and safe prophylactic use and treatment of hemolytic transfusion reactions and complement-mediated hemolytic diseases. Furthermore, the regulatory function of complement may be exploited to prevent and treat autoimmune hemolytic anemia.

Rh autoantigen presentation to helper T cells in chronic lymphocytic leukemia by malignant B cells

Chronic lymphocytic leukemia (CLL) is frequently associated with autoimmune diseases directed against constituents of the blood, including hemolytic anemia (AIHA). We hypothesized that CLL cells predispose to hematologic autoimmunity by acting as aberrant antigen-presenting cells (APCs). Initially, it was confirmed that all studied patients with AIHA secondary to CLL harbored activated helper T (TH) cells specific for epitopes on the dominant red blood cell (RBC) autoantigens in primary AIHA, the Rh proteins. Rh-specific TH cells were also detected in a number of patients with CLL who, although they did not have AIHA, had low levels of anti-RBC antibody in their sera. Fractionation of putative APC populations from the peripheral blood of patients by negative selection showed that CD5+ CLL cells are the most effective cell type in processing and presenting purified Rh protein to autoreactive TH cells. This ability was confirmed using positively selected CD5+ CLL cells. Thus, our study provides the first evidence for malignant cells driving an autoimmune response by acting as aberrant APCs.