Mucosal Administration of Collagen V Ameliorates the Atherosclerotic Plaque Burden by Inducing Interleukin 35-dependent Tolerance

Immunotherapeutic potential of collagen V oral administration in mBSA/CFA-induced arthritis

We hypothesized that after synovial injury, collagen V (Col V) expose occult antigens, and Col V autoantibodies develop, indicating the loss of immune tolerance against this molecule, thus leading to damage to mesenchymal-derived cells as well as the extracellular matrix in experimental arthritis. Thus, the present study investigated the effects of oral administration of Col V on the synovium after the development of inflammation in mBSA/CFA-induced arthritis. After fourteen days of intraarticular administration of mBSA, 10 male Lewis rats were orally administered Col V (500 μg/300 μL) diluted in 0.01 N acetic acid (IA-Col V group). The arthritic group (IA group, n = 10) received only intraarticular mBSA. An intra-articular saline injection (20 μL) was given to the control group (CT-Col V, n = 5). IA group presented damaged synovia, the expansion of the extracellular matrix by cellular infiltrate, which was characterized by T and B lymphocytes, and fibroblastic infiltration. In contrast, after Col V oral immunotherapy IA-Col V group showed a significant reduction in synovial inflammation and intense expression of IL-10+ and FoxP3+ cells, in addition to a reduction in Col V and an increase in Col I in the synovia compared to those in the IA group. Furthermore, an increase in IL-10 production was detected after IA-Col V group spleen cell stimulation with Col V in vitro. PET imaging did not differ between the groups. The evaluation of oral treatment with Col V, after mBSA/CFA-induced arthritis in rats, protects against inflammation and reduces synovial tissue damage, through modulation of the synovial matrix, showing an immunotherapeutic potential in inhibiting synovitis.

TAX1BP1/A20 inhibited TLR2-NF-κB activation to induce tolerant expression of IL-6 in endothelial cells

The inflammatory cascadedriven by interleukin-6 (IL-6) plays a crucial role in the initiation and progression of chronic inflammatory conditions such as atherosclerosis. Research has demonstrated that prolonged exposure to inflammatory stimuli leads to the development of "immune tolerance" in specialized immune cells such as monocytes and macrophages, serving as a mechanism to prevent tissue damage and curb the inflammatory cascade. However, our recent investigation revealed that immune tolerance did not effectively regulate the production of IL-6 in human umbilical vein endothelial cells (HUVECs) when stimulated by a Toll-like receptor 2 (TLR2) ligand Pam3CSK4, which is a potent activator of the pro-inflammatory transcription factor NF-κB. Furthermore, the negative regulator of NF-κB signaling, A20, was ineffective in suppressing TLR2-induced IL-6 synthesis in this context. Notably, all A20 auxiliary molecules, with the exception of TAX1BP1, were found to be significantly expressed in HUVECs. DNA methylation in TAX1BP1 was confirmed in GEO database. According to the information provided, it is hypothesized that altered DNA methylation in HUVECs could potentially lead to decreased expression of TAX1BP1, thereby impeding A20's capacity to modulate continuous activation of the TLR2-NF-κB pathway. This may consequently lead to unregulated production of IL-6, evading immune tolerance mechanisms. Subsequent investigations suggested that demethylating TAX1BP1 could enhance its expression, potentially reducing the endogenous IL-6 levels induced by repeated TLR2 stimulation and restoring A20's inhibitory role in NF-κB signaling. Additionally, over-expression of TAX1BP1 coulddecrease the production of atherosclerosis-associated cytokines like IL-6, MCP-1, ICAM-1, and VCAM-1, while increasing NO release following repeated Pam3cks4 stimulation, along with enhanced co-localization of TAX1BP1 and A20. These findings indicate that inducing immune tolerance in endothelial cells may effectively suppress endogenous IL-6 production and halt the IL-6-mediated inflammatory cascade, with TAX1BP1/A20 identified as crucial components in this process.These insights provide novel perspectives and potential targets for therapeutic strategies in inflammatoryimmunological disorders involving the overproduction of IL-6.

Type V collagen-induced nasal tolerance prevents lung damage in an experimental model: new evidence of autoimmunity to collagen V in COPD

Background

Chronic obstructive pulmonary disease (COPD) has been linked to immune responses to lung-associated self-antigens. Exposure to cigarette smoke (CS), the main cause of COPD, causes chronic lung inflammation, resulting in pulmonary matrix (ECM) damage. This tissue breakdown exposes collagen V (Col V), an antigen typically hidden from the immune system, which could trigger an autoimmune response. Col V autoimmunity has been linked to several lung diseases, and the induction of immune tolerance can mitigate some of these diseases. Evidence suggests that autoimmunity to Col V might also occur in COPD; thus, immunotolerance to Col V could be a novel therapeutic approach.

Objective

The role of autoimmunity against collagen V in COPD development was investigated by analyzing the effects of Col V-induced tolerance on the inflammatory response and lung remodeling in a murine model of CS-induced COPD.

Methods

Male C57BL/6 mice were divided into three groups: one exposed to CS for four weeks, one previously tolerated for Col V and exposed to CS for four weeks, and one kept in clean air for the same period. Then, we proceeded with lung functional and structural evaluation, assessing inflammatory cells in bronchoalveolar lavage fluid (BALF) and inflammatory markers in the lung parenchyma, inflammatory cytokines in lung and spleen homogenates, and T-cell phenotyping in the spleen.

Results

CS exposure altered the structure of elastic and collagen fibers and increased the pro-inflammatory immune response, indicating the presence of COPD. Col V tolerance inhibited the onset of emphysema and prevented structural changes in lung ECM fibers by promoting an immunosuppressive microenvironment in the lung and inducing Treg cell differentiation.

Conclusion

Induction of nasal tolerance to Col V can prevent inflammatory responses and lung remodeling in experimental COPD, suggesting that autoimmunity to Col V plays a role in COPD development.

Immunomodulatory effects of iTr35 cell subpopulation and its research progress

The spotlight in recent years has increasingly focused on inducible regulatory T cells 35 (iTr35), a novel subpopulation of regulatory T cells characterized by phenotypic stability, heightened reactivity, and potent immunosuppressive function through the production of IL-35. Despite being in the exploratory phase, research on iTr35 has garnered significant interest. In this review, we aim to consolidate our understanding of the biological characteristics and immunomodulatory mechanisms of iTr35, offering fresh perspectives that may pave the way for its potential applications in disease diagnosis and treatment.

Interleukin-35: Structure, Function and Its Impact on Immune-Related Diseases

The balance between inflammatory and anti-inflammatory immune responses is maintained through immunoregulatory cell populations and immunosuppressive cytokines. Interleukin-35 (IL-35), an inhibitory cytokine that belongs to the IL-12 family, is capable of potently suppressing T cell proliferation and inducing IL-35-producing induced regulatory T cells (iTr35) to limit inflammatory responses. Over the past decade, a growing number of studies have indicated that IL-35 plays an important role in controlling immune-related disorders, including autoimmune diseases, infectious diseases, and cancer. In this review, we summarize the current knowledge about the biology of IL-35 and its contribution in different diseases, and we discuss the potential of and barriers to harnessing IL-35 as a clinical biomarker or immunotherapy.

Pathological pulmonary vascular remodeling is induced by type V collagen in a model of scleroderma

OBJECTIVE

The pulmonary vascular remodeling in systemic sclerosis (SSc) is poorly understood and animal models are lacking. Type V collagen (COLV) is elevated in SSc and is implicated in the pathogenesis, and immunization with human COLV induces SSc-like skin and lung changes in rabbits and mice. Here we tested the hypothesis that COLV immunization will induce pathological and functional changes that phenocopy SSc-associated pulmonary vascular disease.

METHODS

Pulmonary vascular changes in rabbits immunized with human COLV were extensively characterized by a combination of histology, electron microscopy and immunohistochemistry. Physiologic changes induced by COLV in explanted pulmonary artery rings were evaluated. The pattern of histopathologic alterations and gene expression induced in immunized rabbits were compared to those in SSc patients.

RESULTS

COLV immunization was accompanied by striking pulmonary vascular abnormalities, characterized by reduced capillary density, perivascular inflammation, endothelial cell injury and collagen accumulation, that closely phenocopy changes seen in SSc patients. Moreover, pulmonary arteries from immunized rabbits showed impaired ex vivo vascular relaxation. Expression of COL5A2 was significantly increased in the lungs from immunized rabbits (p = 0.02), as well as in patients with SSc (P = 0.02).

CONCLUSION

COLV immunity in rabbits is associated with marked vascular remodeling in the lung that phenocopies early-stage human SSc-associated pulmonary vascular disease. COLV immunization therefore represents a novel approach to model SSc pulmonary vascular pathology. Moreover, our findings suggest that COLV might represent a novel pathogenic autoantigen in SSc and future studies with the present model should be developed for possible association with PAH.

Identification of Autoimmunity to Peptides of Collagen V α1 Chain as Newly Biomarkers of Early Stage of Systemic Sclerosis

Patients with Systemic sclerosis (SSc) presents immune dysregulation, vasculopathy, and fibrosis of the skin and various internal organs. Pulmonary fibrosis leads to SSc-associated interstitial lung disease (ILD), which is the main cause of morbidity and mortality in SSc. Recently autoimmunity to type V collagen (Col V) has been characterized in idiopathic pulmonary fibrosis and show promise to be related to the development in SSc. Our aim was to evaluate autoimmunity to Col V α1(V) and α2(V) chains and to the antigenic peptides of these Col V chains in early-SSc sera employing lung tissue of SSc-ILD, as antigen source. We found that sera samples from patients with early-SSc were reactive to Col V (41.18%) and presented immunoreactivity for Col5A1(1.049) and Col5A1(1.439) peptides. The IgG isolated from early-SSc patients-anti-Col V positive sera (anti-ColV IgG) was adsorbed with α1(V) chain (anti-ColV IgG/ads-α1(V)) and α2(V) chain (anti-ColV IgG/ads-α2(V)) and biotinylated to evaluate the spectrum of reactivity in SSc-ILD patients lung biopsies by immunofluorescence. The SSc-ILD lung tissue samples immunostained with anti-ColV IgG showed increased green fluorescence in the vascular basement membrane, bronchiolar smooth muscle, and adventitial layer, contrasting with the tenue immunostaining in control lungs. Col V protein expression in these pulmonary compartments immunostained with early-SSc anti-ColV IgG was confirmed by immune colocalization assays with commercial anti-human Col V antibodies. In addition, SSc-ILD lung tissues immunostained with anti-ColV IgG/ads-α1(V) (sample in which Col V α1 chain-specific antibodies were removed) showed decreased green fluorescence compared to anti-ColV IgG and anti-ColV IgG/ads-α2(V). Our data show that autoimmunity to Col V in early-SSc was related to peptides of the α1(V) chain, suggesting that these antibodies could be biomarkers of SSc stages and potential target of immunotherapy with Col V immunogenic peptides.

Different histological patterns of type-V collagen levels confer a matrices-privileged tissue microenvironment for invasion in malignant tumors with prognostic value

Previous studies have reported a close relationship between type V collagen (Col V) and tumor invasion and motility in both breast cancer (BC) and lung cancer (LC). The present work aims to determine whether the extracellular-matrix (ECM)-defined microenvironment influences patient clinical outcome and investigate to which extent histological patterns of Col V expression in malignant cells have a prognostic effect in patients. To that end, we examined the expression of Col V in the tissues of 174 primary tumors (MM, N = 82; LC, N = 41; and BC, N = 46) by immunohistochemistry. We found: (1) diffuse strong green birefringence in membrane and cytoplasm individualizing malignant cells in MM; (2) a focal and weak birefringence mainly in cytoplasmic membrane involving groups of malignant cells in LC and BC; (3) higher average H-score of Col V in MM than in LC and BC samples; (4) a direct correlation between Col V histologic pattern and TNM stage IV, status and median overall survival; (5) patients with LC in TNM stage I, and Col V ≤ 41.7 IOD/mm2 had a low risk of death and a median survival time more than 20 months; (6) patients with MM in TNM stage IV and Col V > 41.7 IOD/mm2 presented a high risk of death and a median survival time of just 20 months. These findings suggest that high levels of Col V individualizing malignant cells, as observed in MM, and low levels grouping malignant cells, as observed in LC and BC, confers different immune-privileged tissue microenvironment for tumor invasion with impact on prognosis of the patients.

Treg-Cell-Derived IL-35-Coated Extracellular Vesicles Promote Infectious Tolerance

Interleukin-35 (IL-35) is an immunosuppressive cytokine composed of Epstein-Barr-virus-induced protein 3 (Ebi3) and IL-12α chain (p35) subunits, yet the forms that IL-35 assume and its role in peripheral tolerance remain elusive. We induce CBA-specific, IL-35-producing T regulatory (Treg) cells in Treg^Ebi3WT C57BL/6 reporter mice and identify IL-35 producers by expression of Ebi3^TdTom gene reporter plus Ebi3 and p35 proteins. Curiously, both subunits of IL-35 are displayed on the surface of tolerogen-specific Foxp3⁺ and Foxp3^neg (iTr35) T cells. Furthermore, IL-35 producers, although rare, secrete Ebi3 and p35 on extracellular vesicles (EVs) targeting a 25- to 100-fold higher number of T and B lymphocytes, causing them to acquire surface IL-35. This surface IL-35 is absent when EV production is inhibited or if Ebi3 is genetically deleted in Treg cells. The unique ability of EVs to coat bystander lymphocytes with IL-35, promoting exhaustion in, and secondary suppression by, non-Treg cells identifies a novel mechanism of infectious tolerance.

Donor HLA-DR Drives the Development of De Novo Autoimmunity Following Lung and Heart Transplantation

Individuals harbor preexisting HLA−DR/DQ−restricted responses to collagen type V (ColV) mediated by Th17 cells under Treg control, both specific to peptides that bind to inherited HLA class II antigens. Yet after transplant, the donor−DR type somehow influences graft outcome. We hypothesized that, long after a lung or heart allograft, the particular HLA−DR type of the mismatched transplant donor transforms the specificity of the “anti−self” response. This could explain why, over long term, certain donor DRs could be more immunogenic than others.

Infectious Tolerance as Seen With 2020 Vision: The Role of IL-35 and Extracellular Vesicles

Originally identified as lymphocyte regulation of fellow lymphocytes, our understanding of infectious tolerance has undergone significant evolutions in understanding since being proposed in the early 1970s by Gershon and Kondo and expanded upon by Herman Waldman two decades later. The evolution of our understanding of infectious tolerance has coincided with significant cellular and humoral discoveries. The early studies leading to the isolation and identification of Regulatory T cells (Tregs) and cytokines including TGFβ and IL-10 in the control of peripheral tolerance was a paradigm shift in our understanding of infectious tolerance. More recently, another potential, paradigm shift in our understanding of the "infectious" aspect of infectious tolerance was proposed, identifying extracellular vesicles (EVs) as a mechanism for propagating infectious tolerance. In this review, we will outline the history of infectious tolerance, focusing on a potential EV mechanism for infectious tolerance and a novel, EV-associated form for the cytokine IL-35, ideally suited to the task of propagating tolerance by "infecting" other lymphocytes.

Proposition of a novel animal model of systemic sclerosis induced by type V collagen in C57BL/6 mice that reproduces fibrosis, vasculopathy and autoimmunity

BACKGROUND

Type V collagen (Col V) has the potential to become an autoantigen and has been associated with the pathogenesis of systemic sclerosis (SSc). We characterized serological, functional, and histopathological features of the skin and lung in a novel SSc murine model induced by Col V immunization.

METHODS

Female C57BL/6 mice (n = 19, IMU-COLV) were subcutaneously immunized with two doses of Col V (125 μg) emulsified in complete Freund adjuvant, followed by two intramuscular boosters. The control group (n = 19) did not receive Col V. After 120 days, we examined the respiratory mechanics, serum autoantibodies, and vascular manifestations of the mice. The skin and lung inflammatory processes and the collagen gene/protein expressions were analyzed.

RESULTS

Vascular manifestations were characterized by endothelial cell activity and apoptosis, as shown by the increased expression of VEGF, endothelin-1, and caspase-3 in endothelial cells. The IMU-COLV mice presented with increased tissue elastance and a nonspecific interstitial pneumonia (NSIP) histologic pattern in the lung, combined with the thickening of the small and medium intrapulmonary arteries, increased Col V fibers, and increased COL1A1, COL1A2, COL3A1, COL5A1, and COL5A2 gene expression. The skin of the IMU-COLV mice showed thickness, epidermal rectification, decreased papillary dermis, atrophied appendages, and increased collagen, COL5A1, and COL5A2 gene expression. Anti-collagen III and IV and ANA antibodies were detected in the sera of the IMU-COLV mice.

CONCLUSION

We demonstrated that cutaneous, vascular, and pulmonary remodeling are mimicked in the Col V-induced SSc mouse model, which thus represents a suitable preclinical model to study the mechanisms and therapeutic approaches for SSc.

Specific Donor HLA-DR Types Correlate With Altered Susceptibility to Development of Chronic Lung Allograft Dysfunction

BACKGROUND

The greatest challenge to long-term graft survival is the development of chronic lung allograft dysfunction. Th17 responses to collagen type V (colV) predispose lung transplant patients to the severe obstructive form of chronic lung allograft dysfunction, known as bronchiolitis obliterans syndrome (BOS). In a previous study cohort (n = 54), pretransplant colV responses were increased in recipients expressing HLA-DR15, consistent with the high binding avidity of colV (α1) peptides for HLA-DR15, whereas BOS incidence, which was known to be strongly associated with posttransplant autoimmunity to colV, was higher in patients who themselves lacked HLA-DR15, but whose lung donor expressed it.

METHODS

To determine if this DR-restricted effect on BOS incidence could be validated in a larger cohort, we performed a retrospective analysis of outcomes for 351 lung transplant recipients transplanted between 1988 and 2008 at the University of Wisconsin. All subjects were followed until graft loss, death, loss to follow-up, or through 2014, with an average follow-up of 7 years. Comparisons were made between recipients who did or did not develop BOS. Grading of BOS followed the recommendations of the international society for heart and lung transplantation.

RESULTS

Donor HLA-DR15 was indeed associated with increased susceptibility to severe BOS in this population. We also discovered that HLA-DR7 expression by the donor or HLA-DR17 expression by the recipient decreased susceptibility.

CONCLUSIONS

We show in this retrospective study that specific donor HLA class II types are important in lung transplantation, because they are associated with either protection from or susceptibility to development of severe BOS.

The immunomodulatory role of interleukin-35 in fibrotic diseases

INTRODUCTION

Fibrosis makes numerous diseases in all organs more complicated and leads to severe consequences in the lung, liver, heart, kidney, and skin. In essence, fibrosis results from excessive, persistent and oftentimes nonreversible aggregation of extracellular matrix (ECM) or simply as collagen during the process of tissue injury and repair. Recent studies suggest the pathology of fibrosis, especially in pulmonary and liver fibrosis, involves various types of immune cells and soluble mediators including interleukin (IL)-35, a recently identified heterodimeric cytokine that belongs to the IL-12 cytokine family. Furthermore, IL-35 may inhibit fibrotic diseases. However, the side effects of inhibiting IL-35 also need attention and we have a long way to go to make better use of it in fibrotic diseases. Areas covered: This review focuses on recent evidence regarding the role of IL-35 in the pathogenesis of pulmonary, hepatic, cardiac, renal and skin fibrosis. It also discusses targeting of IL-35 as a promising novel strategy for treatment of fibrotic diseases. Expert commentary: Understanding as fully as possible the relationship between IL-35 and fibrotic diseases is important for the development of new therapeutic approaches.

Collagen V oral administration decreases inflammation and remodeling of synovial membrane in experimental arthritis

Because collagen type V (Col V) can be exposed in tissue injury, we hypothesized that oral administration of this collagen species modulates the inflammation and remodeling of experimental synovitis, avoiding joint destruction, and that the modulation may differ according to the temporal administration. Arthritis (IA, n = 20) was induced in Lewis rats by intraarticular (ia) injection of 500 μg of methylated bovine serum albumin (mBSA) emulsified in complete Freund’s adjuvant (CFA) (10 μl) followed by an intraarticular booster of mBSA (50 μg) in saline (50 μl) administered at 7 and 14 days. The control group received saline (50 μl, ia). After the first intraarticular injection, ten IA animals were supplemented via gavage with Col V (500 μg/300 μl) daily for 30 days (IA/Suppl). The control group received saline (50 μL) and Col V supplement in the same way (Suppl). Col V oral administration in IA/Suppl led to 1) inhibited edema and severe inflammatory cell infiltration, 2) decreased collagen fiber content, 3) decreased collagen type I, 4) inhibited lymphocyte subpopulations and macrophages, 5) inhibited IL-1β, IL-10, IL-17 and TNF-α production and 6) increased expression of caspase-9 in the synovial tissue. In conclusion, Col V supplementation decreased synovial inflammation and the fibrotic response, possibly by increased the apoptosis of inflammatory cells.

Leukocyte-Associated Ig-like Receptor 1 Inhibits Th1 Responses but Is Required for Natural and Induced Monocyte-Dependent Th17 Responses

Leukocyte-associated Ig-like receptor 1 (LAIR1) is an ITIM-bearing collagen receptor expressed by leukocytes and is implicated in immune suppression. However, using a divalent soluble LAIR1/Fc recombinant protein to block interaction of cell surface LAIR1 with matrix collagen, we found that whereas T_h1 responses were enhanced as predicted, T_h17 responses were strongly inhibited. Indeed, LAIR1 on both T cells and monocytes was required for optimal T_h17 responses to collagen type (Col)V. For pre-existing "natural" T_h17 response to ColV, the LAIR1 requirement was absolute, whereas adaptive T_h17 and T_h1/17 immune responses in both mice and humans were profoundly reduced in the absence of LAIR1. Furthermore, the addition of C1q, a natural LAIR1 ligand, decreased T_h1 responses in a dose-dependent manner, but it had no effect on T_h17 responses. In IL-17-dependent murine organ transplant models of chronic rejection, LAIR1^+/+ but not LAIR1^-/- littermates mounted strong fibroproliferative responses. Surface LAIR1 expression was higher on human T_h17 cells as compared with T_h1 cells, ruling out a receptor deficiency that could account for the differences. We conclude that LAIR1 ligation by its natural ligands favors T_h17 cell development, allowing for preferential activity of these cells in collagen-rich environments. The emergence of cryptic self-antigens such as the LAIR1 ligand ColV during ischemia/reperfusion injury and early acute rejection, as well as the tendency of macrophages/monocytes to accumulate in the allograft during chronic rejection, favors T_h17 over T_h1 development, posing a risk to long-term graft survival.

Recent advances on CD4+ T cells in atherosclerosis and its implications for therapy

Atherosclerosis is an arterial inflammatory disease and the primary cause of cardiovascular disease. T helper (Th) cells are an important part in atherosclerotic plaque as they can be either disease promoting or protective. A body of evidence points to a pro-atherosclerotic role of Th1 cells, whereas the role of Th2, Th17 and iNKT cells seems more complex and dependent on surrounding factors, including the developmental stage of the disease. Opposed to Th1 cells, there is convincing support for an anti-atherogenic role of Tregs. Recent data identify the plasticity of Th cells as an important challenge in understanding the functional role of different Th cell subsets in atherosclerosis. Much of the knowledge of Th cell function in atherosclerosis is based on findings from experimental models and translating this into human disease is challenging. Targeting Th cells and/or their specific cytokines represents an attractive option for future therapy against atherosclerosis, although the benefits and the risk of modulation of Th cells with these novel drug targets must first be carefully assessed.

Th17 Responses to Collagen Type V, kα1-Tubulin, and Vimentin Are Present Early in Human Development and Persist Throughout Life

T helper 17 (Th17)-dependent autoimmune responses can develop after heart or lung transplantation and are associated with fibro-obliterative forms of chronic rejection; however, the specific self-antigens involved are typically different from those associated with autoimmune disease. To investigate the basis of these responses, we investigated whether removal of regulatory T cells or blockade of function reveals a similar autoantigen bias. We found that Th17 cells specific for collagen type V (Col V), kα1-tubulin, and vimentin were present in healthy adult peripheral blood mononuclear cells, cord blood, and fetal thymus. Using synthetic peptides and recombinant fragments of the Col V triple helical region (α1[V]), we compared Th17 cells from healthy donors with Th17 cells from Col V-reactive heart and lung patients. Although the latter responded well to α1(V) fragments and peptides in an HLA-DR-restricted fashion, Th17 cells from healthy persons responded in an HLA-DR-restricted fashion to fragments but not to peptides. Col V, kα1-tubulin, and vimentin are preferred targets of a highly conserved, hitherto unknown, preexisting Th17 response that is MHC class II restricted. These data suggest that autoimmunity after heart and lung transplantation may result from dysregulation of an intrinsic mechanism controlling airway and vascular homeostasis.

Cardiac Autoimmunity: Myocarditis

Myocarditis is the inflammation of the muscle tissues of the heart (myocardium). After a pathologic cardiac-specific inflammatory process, it may progress to chronic damage and dilated cardiomyopathy. The latter is characterized by systolic dysfunction, whose clinical correlate is heart failure. Nevertheless, other acute complications may arise as consequence of tissue damage and electrophysiologic disturbances. Different etiologies are involved in triggering myocarditis. In some cases, such as giant cell myocarditis or eosinophilic necrotizing myocarditis, it is an autoimmune process. Several factors predispose the development of autoimmune myocarditis such as systemic/local primary autoimmunity, viral infection, HLA and gender bias, exposure of cryptic antigens, mimicry, and deficient thymic training/Treg induction. Once the anti-myocardium autoimmune process is triggered, several components of the immune response orchestrate a sustained attack toward myocardial tissues with particular timing and immunopathogenic features. Innate response mediated by monocytes/macrophages, neutrophils, and eosinophils parallels the adaptive response, playing a final effector role and not only a priming function. Stromal cells like fibroblast are also involved in the process through specific cytokines. Furthermore, adaptive T cell responses have anti-paradigmatic features, as Th17 response is dispensable for acute myocarditis but is the main driver of the process leading to dilated cardiomyopathy. Humoral response, thought to be a bystander, is important in the appearance of late-stage hemodynamic complications. The complexity of that process, as well as the unspecific and variable clinical presentation, had generated difficulties for diagnosis and treatment, which remain suboptimal. In this chapter, we will discuss the most relevant immunopathogenic findings from a basic science and clinical perspective.

Kinetics of Alloantigen-Specific Regulatory CD4 T Cell Development and Tissue Distribution After Donor-Specific Transfusion and Costimulatory Blockade

BACKGROUND

The influence of donor-side regulation toward recipient antigens on graft outcome is poorly understood.

METHODS

Because this influence might be due in part to the accumulation of tissue-resident memory T cells in the donor organ, we used a standard murine tolerization model (donor-specific transfusion plus CD40L blockade) to determine the kinetics of development and peripheralization of allospecific regulatory T cell in lymphoid tissues and liver, a secondary lymphoid organ used in transplantation.

RESULTS

We found that donor-specific transfusion and CD40L blockade leads to a progressive and sustained T regulatory allospecific response. The cytokines IL10, TGFβ, and IL35 all contributed to the regulatory phenomenon as determined by trans vivo delayed hypersensitivity assay. Unexpectedly, an early and transient self-specific regulatory response was found as well. Using double reporter mice (forkhead box p 3 [Foxp3]-yellow fluorescent protein, Epstein-Barr virus-induced gene 3 [Ebi3]-TdTomRed), we found an increase in Foxp3+CD25+ regulatory T (Treg) cells paralleling the regulatory response. The Ebi3+ CD4 T cells (IL35-producing) were mainly classic Treg cells (Foxp3+CD25+), whereas TGFβ+ CD4 T cells are mostly Foxp3-negative, suggesting 2 different CD4 Treg cell subsets. Liver-resident TGFβ+ CD4 T cells appeared more rapidly than Ebi3-producing T cells, whereas at later timepoints, the Ebi3 response predominated both in lymphoid tissues and liver.

CONCLUSIONS

The timing of appearance of donor organ resident Treg cell subsets should be considered in experiments testing the role of bidirectional regulation in transplant tolerance.