Juan Pablo Mackern-Oberti

Role of dendritic cells in the initiation, progress and modulation of systemic autoimmune diseases

Dendritic cells (DCs) play a key role in the activation of the immune response against pathogens, as well as in the modulation of peripheral tolerance to self-antigens (Ags). Furthermore, an imbalance in the activating/inhibitory receptors expressed on the surface of DCs has been linked to increased susceptibility to develop autoimmune diseases underscoring their immunogenicity potential. It has been described that modulation of activating or inhibitory molecules expressed by DCs, such as CD86, TLRs, PDL-1 and FcγRs, can define the immunogenic phenotype. On the other hand, T cell tolerance can be achieved by tolerogenic DCs, which have the capacity of blocking undesired autoimmune responses in several experimental models, mainly by inducing T cell anergy, expansion of regulatory T cells and limiting B cell responses. Due to the lack of specific therapies to treat autoimmune disorders and the tolerogenic capacity of DCs shown in experimental autoimmune disease models, autologous tolDCs are a potential therapeutic strategy for fine-tuning the immune system and reestablishing tolerance in human autoimmune diseases. New advances in the role of DCs in systemic lupus erythematosus (SLE) pathogenesis and the identification of pathogenic self-Ags may favor the development of novel tolDC based therapies with a major clinical impact. In this review, we discuss recent data relative to the role of DCs in systemic autoimmune pathogenesis and their use as a therapy to restore tolerance.

Susceptibility of Prostate Epithelial Cells to Chlamydia muridarum Infection and Their Role in Innate Immunity by Recruitment of Intracellular Toll-Like Receptors 4 and 2 and MyD88 to the Inclusion

ABSTRACT Although Chlamydia infections are widespread throughout the world, data about immunopathogenesis of genitourinary tract infections in males are very limited. In the present work we present an in vitro model of male genital tract-derived epithelial cells, more precisely prostate epithelial cells (PEC), to analyze if they are susceptible and able to respond to Chlamydia muridarum infection. Our results demonstrate that rat PEC are susceptible to C. muridarum infection and respond to this pathogen by up-regulating different proinflammatory cytokine and chemokine genes that could participate in the recruitment and local activation of immune cells, therefore influencing innate and adaptive immune responses during Chlamydia infection. Moreover, we analyzed the expression of Toll-like receptor 4 (TLR4), TLR2, and related molecules on PEC and the effect of C. muridarum infection on their expression. Our results demonstrate that PEC express significant levels of TLR4, CD14, TLR2, and the adaptor molecule MyD88 and up-regulate these proteins in response to C. muridarum infection. Indeed, TLR4, CD14, TLR2, and the adaptor MyD88 are specifically recruited to the vicinity of the bacterial inclusion, suggesting that these TLRs are actively engaged in signaling from this intracellular location in these cells. This is, to our knowledge, the first time that an in vitro model of infection with Chlamydia of male tract-derived epithelial cells has been achieved, and it provides the opportunity to determine how these cells respond and participate in modulating innate and adaptive immune response during Chlamydia infections.

Tolerogenic dendritic cells as a therapy for treating lupus.

Systemic lupus erythematosus (SLE) is a chronic autoimmune disorder that is characterized by the over production of auto-antibodies against nuclear components. Thus, SLE patients have increased morbidity and, mortality compared to healthy individuals. Available therapies are not curative and are associated with unwanted adverse effects. During the last few years, important advances in immunology research have provided rheumatologists with new tools for designing novel therapies for treating autoimmunity. However, the complex nature of SLE has played a conflicting role, hindering breakthroughs in therapeutic development. Nonetheless, new advances about SLE pathogenesis could open a fruitful line of research. Dendritic cells (DCs) have been established as essential players in the mechanisms underlying SLE, making them attractive therapeutic targets for fine-tuning the immune system. In this review, we discuss the recent advances made in revealing the mechanisms of SLE pathogenesis, with a focus on the use of DCs as a target for therapy development.

Surface expression of the hRSV nucleoprotein impairs immunological synapse formation with T cells

Significance Human respiratory syncytial virus (hRSV) is the leading cause of bronchiolitis and pneumonia in children worldwide. The induction of poor T-cell immunological memory causes a high susceptibility to reinfections, which contributes to hRSV spread. Previously, we showed that hRSV inhibits T-cell activation by impairing the assembly of the dendritic cell (DC)−T-cell immunological synapse (IS). Here, we show that the nucleoprotein (N) of hRSV—a canonical cytosolic protein—is expressed on the surface of infected DCs. Further, using the supported-lipid-bilayer system (that mimics the DC/ antigen-presenting cells-membrane composition), we observed that the hRSV N interfered with pMHC−T-cell receptor interactions and inhibited IS assembly. We conclude that hRSV N may therefore be instrumental in impairing the host immune response during infection with this virus. Human respiratory syncytial virus (hRSV) is the leading cause of bronchiolitis and pneumonia in young children worldwide. The recurrent hRSV outbreaks and reinfections are the cause of a significant public health burden and associate with an inefficient antiviral immunity, even after disease resolution. Although several mouse- and human cell-based studies have shown that hRSV infection prevents naïve T-cell activation by antigen-presenting cells, the mechanism underlying such inhibition remains unknown. Here, we show that the hRSV nucleoprotein (N) could be at least partially responsible for inhibiting T-cell activation during infection by this virus. Early after infection, the N protein was expressed on the surface of epithelial and dendritic cells, after interacting with trans-Golgi and lysosomal compartments. Further, experiments on supported lipid bilayers loaded with peptide-MHC (pMHC) complexes showed that surface-anchored N protein prevented immunological synapse assembly by naive CD4+ T cells and, to a lesser extent, by antigen-experienced T-cell blasts. Synapse assembly inhibition was in part due to reduced T-cell receptor (TCR) signaling and pMHC clustering at the T-cell−bilayer interface, suggesting that N protein interferes with pMHC−TCR interactions. Moreover, N protein colocalized with the TCR independently of pMHC, consistent with a possible interaction with TCR complex components. Based on these data, we conclude that hRSV N protein expression at the surface of infected cells inhibits T-cell activation. Our study defines this protein as a major virulence factor that contributes to impairing acquired immunity and enhances susceptibility to reinfection by hRSV.

Haem oxygenase 1 expression is altered in monocytes from patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by multiple functional alterations affecting immune cells, such as B cells, T cells, dendritic cells (DCs) and monocytes. During SLE, the immunogenicity of monocytes and DCs is significantly up‐regulated, promoting the activation of self‐reactive T cells. Accordingly, it is important to understand the contribution of these cells to the pathogenesis of SLE and the mechanisms responsible for their altered functionality during disease. One of the key enzymes that control monocyte and DC function is haem oxygenase‐1 (HO‐1), which catalyses the degradation of the haem group into biliverdin, carbon monoxide and free iron. These products possess immunosuppressive and anti‐inflammatory capacities. The main goal of this work was to determine HO‐1 expression in monocytes and DCs from patients with SLE and healthy controls. Hence, peripheral blood mononuclear cells were obtained from 43 patients with SLE and 30 healthy controls. CD14+ monocytes and CD4+ T cells were sorted by FACS and HO‐1 expression was measured by RT‐PCR. In addition, HO‐1 protein expression was determined by FACS. HO‐1 levels in monocytes were significantly reduced in patients with SLE compared with healthy controls. These results were confirmed by flow cytometry. No differences were observed in other cell types, such as DCs or CD4+ T cells, although decreased MHC‐II levels were observed in DCs from patients with SLE. In conclusion, we found a significant decrease in HO‐1 expression, specifically in monocytes from patients with SLE, suggesting that an imbalance of monocyte function could be partly the result of a decrease in HO‐1 expression.

Carbon monoxide exposure improves immune function in lupus‐prone mice

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by multiple alterations affecting the normal function of immune cells, such as lymphocytes, dendritic cells (DCs) and monocytes. Although the understanding of autoimmunity has significantly increased, the breakthrough in effective therapies has been modest, making necessary the development of new therapeutic strategies. Here we propose that a new potential target for therapy is haem oxygenase‐1 (HO‐1), an enzyme that catalyses the degradation of the haem group into biliverdin, carbon monoxide (CO) and Fe2+. These products exhibit immunosuppressive and anti‐inflammatory effects, which can contribute to improving tolerance during organ transplantation. Because HO‐1 is highly expressed by immune cells involved in SLE pathogenesis, such as monocytes and DCs, we evaluated whether induction of HO‐1 expression or the administration of CO could ameliorate disease in the FcγRIIb knockout (KO) mouse model for SLE. We found that CO administration decreased the expansion of CD11b+ cells, prevented the decline of regulatory T cells and reduced anti‐histone antibodies observed in untreated FcγRIIb KO mice. Furthermore, CO‐treated animals and HO‐1 induction showed less kidney damage compared with untreated mice. These data suggest that HO‐1 modulation and CO administration can ameliorate autoimmunity and prevent the lupus symptoms shown by FcγRIIb KO mice, highlighting HO‐1 as a potential new target for autoimmune therapy.

Modulation of antigen processing by haem-oxygenase 1. Implications on inflammation and tolerance.

Haem‐oxygenase‐1 (HO‐1) is an enzyme responsible for the degradation of haem that can suppress inflammation, through the production of carbon monoxide (CO). It has been shown in several experimental models that genetic and pharmacological induction of HO‐1, as well as non‐toxic administration of CO, can reduce inflammatory diseases, such as endotoxic shock, type 1 diabetes and graft rejection. Recently, it was shown that the HO‐1/CO system can alter the function of antigen‐presenting cells (APCs) and reduce T‐cell priming, which can be beneficial during immune‐driven inflammatory diseases. The molecular mechanisms by which the HO‐1 and CO reduce both APC‐ and T‐cell‐driven immunity are just beginning to be elucidated. In this article we discuss recent findings related to the immune regulatory capacity of HO‐1 and CO at the level of recognition of pathogen‐associated molecular patterns and T‐cell priming by APCs. Finally, we propose a possible regulatory role for HO‐1 and CO over the recently described mitochondria‐dependent immunity. These concepts could contribute to the design of new therapeutic tools for inflammation‐based diseases.

Targeting dendritic cell function during systemic autoimmunity to restore tolerance.

Systemic autoimmune diseases can damage nearly every tissue or cell type of the body. Although a great deal of progress has been made in understanding the pathogenesis of autoimmune diseases, current therapies have not been improved, remain unspecific and are associated with significant side effects. Because dendritic cells (DCs) play a major role in promoting immune tolerance against self-antigens (self-Ags), current efforts are focusing at generating new therapies based on the transfer of tolerogenic DCs (tolDCs) during autoimmunity. However, the feasibility of this approach during systemic autoimmunity has yet to be evaluated. TolDCs may ameliorate autoimmunity mainly by restoring T cell tolerance and, thus, indirectly modulating autoantibody development. In vitro induction of tolDCs loaded with immunodominant self-Ags and subsequent cell transfer to patients would be a specific new therapy that will avoid systemic immunosuppression. Herein, we review recent approaches evaluating the potential of tolDCs for the treatment of systemic autoimmune disorders.

Hormonal Modulation of Dendritic Cells Differentiation, Maturation and Function: Implications for the Initiation and Progress of Systemic Autoimmunity

Hormonal homeostasis is crucial for keeping a competent and healthy immune function. Several hormones can modulate the function of various immune cells such as dendritic cells (DCs) by influencing the initiation of the immune response and the maintenance of peripheral tolerance to self-antigens. Hormones, such as estrogens, prolactin, progesterone and glucocorticoids may profoundly affect DCs differentiation, maturation and function leading to either a pro-inflammatory or an anti-inflammatory (or tolerogenic) phenotype. If not properly regulated, these processes can contribute to the pathogenesis of autoimmune disease. An unbalanced hormonal status may affect the production of pro-inflammatory cytokines, the expression of activating/inhibitory receptors and co-stimulatory molecules on conventional and plasmacytoid DCs (pDCs), conferring susceptibility to develop autoimmunity. Estrogen receptor (ER)-α signaling in conventional DCs can promote IFN-α and IL-6 production and induce the expression of CD40, CD86 and MHCII molecules. Furthermore, estrogen modulates the pDCs response to Toll-like receptor ligands enhancing T cell priming. During lupus pathogenesis, ER-α deficiency decreased the expression of MHC II on pDCs from the spleen. In contrast, estradiol administration to lupus-prone female mice increased the expression of co-stimulatory molecules, enhanced the immunogenicity and produced large amounts of IL-6, IL-12 and TNF-α by bone marrow-derived DCs. These data suggest that estradiol/ER signaling may play an active role during lupus pathology. Similarly, understanding hormonal modulation of DCs may favor the design of new therapeutic strategies based on autologous tolerogenic DCs transfer, especially in sex-biased systemic autoimmune diseases. In this review, we discuss recent data relative to the role of different hormones (estrogen, prolactin, progesterone and glucocorticoids) in DC function during systemic autoimmune pathogenesis.

Carbon monoxide inhibits T cell activation in target organs during systemic lupus erythematosus.

Systemic lupus erythematosus is characterized by the presence of circulating anti‐nuclear antibodies (ANA) and systemic damage that includes nephritis, haematological manifestations and pulmonary compromise, among others. Although major progress has been made in elucidating the molecular mechanisms responsible for autoimmunity, current therapies for lupus have not improved considerably. Because the exposure of carbon monoxide (CO) has been shown to display beneficial immunoregulatory properties in different immune‐mediated diseases, we investigated whether CO therapy improves lupus‐related kidney injury in lupus mice. MRL‐Faslpr lupus mice were exposed to CO and disease progression was evaluated. ANA, leucocyte‐infiltrating populations in spleen, kidney and lung and kidney lesions, were measured. CO therapy significantly decreased the frequency of activated B220+ CD4− CD8− T cells in kidneys and lungs, as well as serum levels of ANA. Furthermore, we observed that CO therapy reduced kidney injury by decreasing proliferative glomerular damage and immune complexes deposition, decreased proinflammatory cytokine production and finally delayed the impairment of kidney function. CO exposure ameliorates kidney and lung leucocyte infiltration and delays kidney disease in MRL‐Faslpr lupus mice. Our data support the notion that CO could be explored as a potential new therapy for lupus nephritis.