Phenotypic and functional differences between wild-type and CCR2-/- dendritic cells: implications for islet transplantation

CCR2 enhances CD25 expression by FoxP3+ regulatory T cells and regulates their abundance independently of chemotaxis and CCR2+ myeloid cells

A wide array of chemokine receptors, including CCR2, are known to control Treg migration. Here, we report that CCR2 regulates Tregs beyond chemotaxis. We found that CCR2 deficiency reduced CD25 expression by FoxP3⁺ Treg cells. Such a change was also consistently present in irradiation chimeras reconstituted with mixed bone marrow from wild-type (WT) and CCR2-/- strains. Thus, CCR2 deficiency resulted in profound loss of CD25^hi FoxP3⁺ Tregs in secondary lymphoid organs as well as in peripheral tissues. CCR2-/- Treg cells were also functionally inferior to WT cells. Interestingly, these changes to Treg cells did not depend on CCR2⁺ monocytes/moDCs (the cells where CCR2 receptors are most abundant). Rather, we demonstrated that CCR2 was required for TLR-stimulated, but not TCR- or IL-2-stimulated, CD25 upregulation on Treg cells. Thus, we propose that CCR2 signaling can increase the fitness of FoxP3⁺ Treg cells and provide negative feedback to counter the proinflammatory effects of CCR2 on myeloid cells.

CCR2 mediates Helicobacter pylori-induced immune tolerance and contributes to mucosal homeostasis

BACKGROUND

We previously demonstrated that H. pylori infection leads to increased induction of regulatory T cells in local and systemic immune compartments. Here, we investigate the role of CCR2 in the tolerogenic programing of dendritic cells in a mouse model of H. pylori infection.

MATERIALS AND METHODS

CCR2 deficient (CCR2KO) mice and wild-type (Wt) mice infected with H. pylori SS1 strain were analyzed by qPCR and FACS analysis. In vitro, bone marrow-derived DC on day 6 from CCR2KO and Wt mice cocultured with or without H. pylori were examined to determine the impact of CCR2 signaling on dendritic cells function by qPCR, ELISA, and FACS analyses.

RESULTS

Acute H. pylori infection was associated with a threefold increase in CCR2 mRNA expression in the gastric mucosa. H. pylori-infected CCR2KO mice exhibited a higher degree of mucosal inflammation, that is, increased gastritis scores and pro-inflammatory cytokine mRNA levels, but lower degree of H. pylori gastric colonization compared to infected Wt mice. Peripheral H. pylori-specific immune response measured in the CCR2KO spleen was characterized by a higher Th17 response and a lower Treg response. In vitro, CCR2KO bone marrow-derived DC was less mature and shown a lower Treg/Th17 ratio. Moreover, blockade of CCR2 signaling by MCP-1 neutralizing antibody inhibited H. pylori-stimulated bone marrow-derived DC maturation.

CONCLUSIONS

Our results indicate that CCR2 plays an essential role in H. pylori-induced immune tolerance and shed light on a novel mechanism of CCR2-dependent DC Treg induction, which appears to be important in maintaining mucosal homeostasis during H. pylori infection.

Role of CCL7 in Type I Hypersensitivity Reactions in Murine Experimental Allergic Conjunctivitis

Molecules that are necessary for ocular hypersensitivity reactions include the receptors CCR1 and CCR3; CCL7 is a ligand for these receptors. Therefore, we explored the role of CCL7 in mast cell activity and motility in vitro and investigated the requirement for CCL7 in a murine model of IgE-mediated allergic conjunctivitis. For mast cells treated with IgE and Ag, the presence of CCL7 synergistically enhanced degranulation and calcium influx. CCL7 also induced chemotaxis in mast cells. CCL7-deficient bone marrow-derived mast cells showed decreased degranulation following IgE and Ag treatment compared with wild-type bone marrow-derived mast cells, but there was no difference in degranulation when cells were activated via an IgE-independent pathway. In vivo, CCL7 was upregulated in conjunctival tissue during an OVA-induced allergic response. Notably, the early-phase clinical symptoms in the conjunctiva after OVA challenge were significantly higher in OVA-sensitized wild-type mice than in control challenged wild-type mice; the increase was suppressed in CCL7-deficient mice. In the OVA-induced allergic response, the numbers of conjunctival mast cells were lower in CCL7-deficient mice than in wild-type mice. Our results demonstrate that CCL7 is required for maximal OVA-induced ocular anaphylaxis, mast cell recruitment in vivo, and maximal FcεRI-mediated mast cell activation in vitro. A better understanding of the role of CCL7 in mediating ocular hypersensitivity reactions will provide insights into mast cell function and novel treatments for allergic ocular diseases.

The role of host genetic factors in respiratory tract infectious diseases: systematic review, meta-analyses and field synopsis

Host genetic factors have frequently been implicated in respiratory infectious diseases, often with inconsistent results in replication studies. We identified 386 studies from the total of 24,823 studies identified in a systematic search of four bibliographic databases. We performed meta-analyses of studies on tuberculosis, influenza, respiratory syncytial virus, SARS-Coronavirus and pneumonia. One single-nucleotide polymorphism from IL4 gene was significant for pooled respiratory infections (rs2070874; 1.66 [1.29–2.14]). We also detected an association of TLR2 gene with tuberculosis (rs5743708; 3.19 [2.03–5.02]). Subset analyses identified CCL2 as an additional risk factor for tuberculosis (rs1024611; OR = 0.79 [0.72–0.88]). The IL4-TLR2-CCL2 axis could be a highly interesting target for translation towards clinical use. However, this conclusion is based on low credibility of evidence - almost 95% of all identified studies had strong risk of bias or confounding. Future studies must build upon larger-scale collaborations, but also strictly adhere to the highest evidence-based principles in study design, in order to reduce research waste and provide clinically translatable evidence.

Disruption of the TSLP-TSLPR-LAP signaling between epithelial and dendritic cells through hyperlipidemia contributes to regulatory T-Cell defects in atherosclerotic mice

Regulatory T-Cells (Tregs) play a protective role against the development of atherosclerosis. Moreover, thymic stromal lymphopoietin (TSLP)/thymic stromal lymphopoietin receptor (TSLPR) signaling in myeloid dendritic cells (DCs) promote Treg differentiation. Here, we examined the potential role of TSLP/TSLPR on Treg homeostasis in atherosclerosis. The frequencies of both latency-associated peptide (LAP)(+) and Foxp3(+) Tregs were reduced in the thymus and spleen of ApoE(-/-) mice compared with C57BL/6 mice, and this effect was associated with decreased thymic output. The tolerogenic function of DCs obtained from ApoE(-/-) mice was compromised compared with those from C57BL/6 mice. The expression of TSLP and TSLPR was also inhibited in ApoE(-/-) mice. In addition, we found that ox-LDL attenuated TSLP expression in cultured thymic epithelial cells (TECs) through the activation of retinoid X receptor alpha (RXRA) and IL-1β and decreased LAP and PD-L1 expression in oxLDL-activated DCs while both were up-regulated in TSLP-activated DCs. We also observed that the TSLP-DCs mediated differentiation of Tregs was abrogated through LAP neutralization. Furthermore, TSLP injection rescued Treg defects in ApoE(-/-) mice. These findings suggest that Treg defects in ApoE(-/-) mice might partially be attributed to the disruption of TSLP-TSLPR-LAP signaling in epithelial cells (ECs) and DCs.

The mechanisms of up-regulation of dendritic cell activity by oxidative stress

Whereas DC have increasingly been recognized for their role in activating the inflammatory cascades during IRIs, the mechanisms by which oxidative stress enhances DC activation remain to be explored. We examined the role of oxidative stress on two important features of DC: T cell activation and trafficking. Bone marrow-derived OS-DC were compared with untreated DC. DC exposed to oxidative stress augmented allogeneic T cell proliferation and showed increased migration in a chemotaxis chamber. These results were confirmed by using hypoxanthine and xanthine oxidase as another inducer of oxidative stress. We used OT-II and OT-I mice to assess the effect of oxidative stress on DC activation of OVA-specific CD4(+) and CD8(+) T cells, respectively. Oxidative stress increased DC capacity to promote OVA-specific CD4(+) T cell activity, demonstrated by an increase in their proliferation and production of IFN-γ, IL-6, and IL-2 proinflammatory cytokines. Whereas oxidative stress increased the DC ability to stimulate IFN-γ production by OVA-specific CD8(+) T cells, cellular proliferation and cytotoxicity were not affected. Compared with untreated DC, oxidative stress significantly reduced the capacity of DC to generate T(regs), which were restored by using anti-IL-6. With regard to DC trafficking, whereas oxidative stress increased DC expression of p-Akt and p-NF-κB, targeting PI3Kγ and NF-κB pathways abrogated the observed increase in DC migration. Our data propose novel insights on the activation of DC by oxidative stress and provide rationales for targeted therapies, which can potentially attenuate IRI.

Stimulatory interactions between human coronary smooth muscle cells and dendritic cells

Despite inflammatory and immune mechanisms participating to atherogenesis and dendritic cells (DCs) driving immune and non-immune tissue injury response, the interactions between DCs and vascular smooth muscle cells (VSMCs) possibly relevant to vascular pathology including atherogenesis are still unclear. To address this issue, immature DCs (iDCs) generated from CD14+ cells isolated from healthy donors were matured either with cytokines (mDCs), or co-cultured (ccDCs) with human coronary artery VSMCs (CASMCs) using transwell chambers. Co-culture induced DC immunophenotypical and functional maturation similar to cytokines, as demonstrated by flow cytometry and mixed lymphocyte reaction. In turn, factors from mDCs and ccDCs induced CASMC migration. MCP-1 and TNFα, secreted from DCs, and IL-6 and MCP-1, secreted from CASMCs, were primarily involved. mDCs adhesion to CASMCs was enhanced by CASMC pre-treatment with IFNγ and TNFα ICAM-1 and VCAM-1 were involved, since the expression of specific mRNAs for these molecules increased and adhesion was inhibited by neutralizing antibodies to the counter-receptors CD11c and CD18. Adhesion was also inhibited by CASMC pre-treatment with the HMG-CoA-reductase inhibitor atorvastatin and the PPARγ agonist rosiglitazone, which suggests a further mechanism for the anti-inflammatory action of these drugs. Adhesion of DCs to VSMCs was shown also in vivo in rat carotid 7 to 21 days after crush and incision injury. The findings indicate that DCs and VSMCs can interact with reciprocal stimulation, possibly leading to perpetuate inflammation and vascular wall remodelling, and that the interaction is enhanced by a cytokine-rich inflammatory environment and down-regulated by HMGCoA-reductase inhibitors and PPARγ agonists.

TIM4 Regulates the Anti-Islet Th2 Alloimmune Response

The role of the novel costimulatory molecule TIM4 in anti-islet response is unknown. We explored TIM4 expression and targeting in Th1 (BALB/c islets into C57BL/6 mice) and Th2 (BALB/c islets into Tbet(-/-) C57BL/6 mice) models of anti-islet alloimmune response and in a model of anti-islet autoimmune response (diabetes onset in NOD mice). The targeting of TIM4, using the monoclonal antibody RMT4-53, promotes islet graft survival in a Th1 model, with 30% of the graft surviving in the long term; islet graft protection appears to be mediated by a Th1 to Th2 skewing of the immune response. Differently, in the Th2 model, TIM4 targeting precipitates graft rejection by further enhancing the Th2 response. The effect of anti-TIM4 treatment in preventing autoimmune diabetes was marginal with only minor Th1 to Th2 skewing. B-Cell depletion abolished the effect of TIM4 targeting. TIM4 is expressed on human B-cells and is upregulated in diabetic and islet-transplanted patients. Our data suggest a model in which TIM4 targeting promotes Th2 response over Th1 via B-cells. The targeting of TIM4 could become a component of an immunoregulatory protocol in clinical islet transplantation, aiming at redirecting the immune system toward a Th2 response.

Immunosuppressive Activity of Size-Controlled PEG-PLGA Nanoparticles Containing Encapsulated Cyclosporine A

We encapsulated cyclosporine A (CsA) in poly(ethylene glycol)-b-poly(d,l-lactide-co-glycolide) (PEG-PLGA) nanoparticles (NPs) by nanoprecipitation of CsA and PEG-PLGA. The resulting CsA/PEG-PLGA-NPs were <100 nm in diameter with a narrow particle size distribution. The NP size could be controlled by tuning the polymer concentration, solvent, or water/solvent ratio during formulation. The PEGylated NPs maintained non-aggregated in salt solution. Solid NPs lyoprotected with bovine serum albumin were prepared for the convenience of storage and transportation. The release kinetics of CsA (55.6% released on Day 1) showed potential for maintaining therapeutic CsA concentrations in vivo. In T-cell assays, both free CsA and CsA/PEG-PLGA-NPs suppressed T-cell proliferation and production of inflammatory cytokines dose dependently. In a mixed lymphocyte reaction assay, the IC(50) values for free CsA and CsA/PEG-PLGA-NPs were found to be 30 and 35 ng/mL, respectively. This nanoparticulate CsA delivery technology constitutes a strong basis for future targeted delivery of immunosuppressive drugs with improved efficiency and potentially reduced toxicity.

Kidney-derived mesenchymal stromal cells modulate dendritic cell function to suppress alloimmune responses and delay allograft rejection

BACKGROUND

Mesenchymal stromal cells (MSCs) are multipotent cells with immunoregulatory capacity that are present in most adult organs. We previously demonstrated that co-culture of C57BL/6 kidney-derived MSCs (KSCs) in syngeneic bone marrow-derived dendritic cell (DC) culture induced a DC phenotype (KSC-DC) with reduced major histocompatibility complex (MHC) class II/increased CD80 expression and ability to suppress T-cell responses.

METHODS

To study their effects on allogeneic DCs, C57BL/6 KSCs were added to incipient BALB/c DC culture, with surface expression of MHC class II/CD80 measured by fluorescence-activated cell sorting. The ability to stimulate T-cell responses was then assessed in an allogeneic mixed leukocyte response. Next, we isolated either BALB/c (donor) or C57BL/6 (recipient) KSC-DCs from co-culture and measured the tempo of rejection after cotransplantation with islet grafts in a mouse model of islet transplantation. Finally, we measured the effects of KSC-DC stimulation on B-cell proliferation and IgM/IgG production in allogeneic cultures.

RESULTS

C57BL/6 KSCs induced a BALB/c DC phenotype with significantly decreased MHC class II, increased CD80 expression, and decreased T-cell stimulatory capacity in the mixed leukocyte response (P<0.01 vs. control). Cotransplantation of donor (BALB/c) but not recipient (C57BL/6) KSC-DCs resulted in significant delay of rejection after islet transplantation (P<0.01 vs. control). Finally, stimulation by KSC-DCs resulted in significantly reduced B-cell proliferation and antibody production in allogeneic culture (P<0.01 vs. control).

CONCLUSIONS

Our results highlight an important mechanism of MSC-based immunotherapy and its potential for use in clinical transplantation as prevention of rejection and possibly sensitization.

Polylactide-cyclosporin A nanoparticles for targeted immunosuppression

Polymeric nanoparticles (NPs), prepared via coprecipitation of drugs and polymers, are promising drug delivery vehicles for treating diseases with improved efficacy and reduced toxicity. Here, we report an unprecedented strategy for preparing polylactide-cyclosporine A (PLA-CsA) NPs (termed CsA-NPs) through CsA-initiated ring-opening polymerization of lactide (LA) followed by nanoprecipitation. The resulting CsA-NPs have sub-100 nm sizes and narrow particle size distributions, and release CsA in a sustained manner without a "burst"-release effect. Both free CsA and CsA-NPs displayed comparable suppression of T-cell proliferation and production of inflammatory cytokines in various T-cell assays in a dose-dependent manner. The IC(50) values for CsA and CsA-NPs were 27.5 and 72.0 ng/ml, respectively. As lymph nodes are the main loci for T-cell activation, we coupled dendritic cells (DCs) with CsA-NPs and successfully delivered CsA selectively to the lymph nodes. Our studies indicated that CsA-NPs could be internalized in the DCs with a sustained release of CsA to the culture medium, suppressing alloreactive T-cell proliferation. Allogeneic DCs loaded with CsA-NPs were able to migrate to the draining lymph nodes where the T-cell priming was significantly reduced without any systemic release. This innovative nanoparticulate CsA delivery technology constitutes a strong basis for future targeted delivery of immunosuppressive drugs with improved efficiency and reduced toxicity.

CCR2 plays a critical role in dendritic cell maturation: possible role of CCL2 and NF-kappa B

We postulated that CCR2-driven activation of the transcription factor NF-kappaB plays a critical role in dendritic cell (DC) maturation (e.g., migration, costimulation, and IL-12p70 production), necessary for the generation of protective immune responses against the intracellular pathogen Leishmania major. Supporting this notion, we found that CCR2, its ligand CCL2, and NF-kappaB were required for CCL19 production and adequate Langerhans cell (LC) migration both ex vivo and in vivo. Furthermore, a role for CCR2 in upregulating costimulatory molecules was indicated by the reduced expression of CD80, CD86, and CD40 in Ccr2(-/-) bone marrow-derived dendritic cells (BMDCs) compared with wild-type (WT) BMDCs. Four lines of evidence suggested that CCR2 plays a critical role in the induction of protective immunity against L. major by regulating IL-12p70 production and migration of DC populations such as LCs. First, compared with WT, Ccr2(-/-) lymph node cells, splenocytes, BMDCs, and LCs produced lower levels of IL-12p70 following stimulation with LPS/IFN-gamma or L. major. Second, a reduced number of LCs carried L. major from the skin to the draining lymph nodes in Ccr2(-/-) mice compared with WT mice. Third, early treatment with exogenous IL-12 reversed the susceptibility to L. major infection in Ccr2(-/-) mice. Finally, disruption of IL-12p70 in radioresistant cells, such as LCs, but not in BMDCs resulted in the inability to mount a fully protective immune response in bone marrow chimeric mice. Collectively, our data point to an important role for CCR2-driven activation of NF-kappaB in the regulation of DC/LC maturation processes that regulate protective immunity against intracellular pathogens.

Antigen-presenting dendritic cells rescue CD4-depleted CCR2-/- mice from lethal Histoplasma capsulatum infection

Excessive production of interleukin-4 impairs clearance of the fungal pathogen Histoplasma capsulatum in mice lacking the chemokine receptor CCR2. An increase in the interleukin-4 level is associated with decreased recruitment of dendritic cells to lungs; therefore, we investigated the possibility that these cells influence interleukin-4 production. Adoptive transfer of wild-type or CCR2(-/-) bone marrow-derived dendritic cells loaded with heat-killed yeast cells to infected CCR2(-/-) mice suppressed interleukin-4 transcription. Surprisingly, transfer of cells did not reduce the fungal burden despite the fact that it limited interleukin-4 transcription. Yeast cell-loaded bone marrow-derived dendritic cell-mediated regulation of interleukin-4 transcription was dependent on major histocompatibility complex II antigen presentation to CD4(+) T cells. We previously showed that CD4(+) T cells were a source of interleukin-4 in infected CCR2(-/-) mice, but their contribution to the TH2 phenotype was unclear. Here we demonstrated that these cells were functionally important since elimination of them prior to infection, but not elimination of them at the time of infection, reduced the interleukin-4 level in infected CCR2(-/-) mice. However, the fungal burden was reduced only in CD4-depleted CCR2(-/-) mice that received yeast cell-loaded bone marrow-derived dendritic cells. Taken together, the data indicate that generation of excess interleukin-4 in lungs of H. capsulatum-infected CCR2(-/-) mice is at least partially a consequence of decreased recruitment of dendritic cells capable of antigen presentation. Furthermore, CD4(+) T cells had a deleterious impact on immunity in infected CCR2(-/-) mice.

The CCL7-CCL2-CCR2 axis regulates IL-4 production in lungs and fungal immunity

Expression of the chemokine receptor CCR2 can be detrimental or beneficial for infection resolution. Herein, we examined whether CCR2 was requisite for control of infection by the dimorphic fungus Histoplasma capsulatum. H. capsulatum-infected CCR2(-/-) mice manifested defects in inflammatory cell recruitment, increased IL-4, and progressive infection. Increased IL-4 in CCR2(-/-) mice primarily contributed to decreased host resistance as demonstrated by the ability of IL-4-neutralized CCR2(-/-) mice to resolve infection without altering inflammatory cell recruitment. Surprisingly, numerous alveolar macrophages and dendritic cells contributed to IL-4 production in CCR2(-/-) mice. IL-4-mediated impairment of immunity in CCR2(-/-) mice was associated with increased arginase-1 and YM1 transcription and increased transferrin receptor expression by phagocytic cells. Immunity in mice lacking the CCR2 ligand CCL2 was not impaired despite decreased inflammatory cell recruitment. Neutralization of the CCR2 ligand CCL7 in CCL2(-/-) mice, but not wild type, resulted in increased IL-4 and fungal burden. Thus, CCL7 in combination with CCL2 limits IL-4 generation and exerts control of host resistance. Furthermore, increased phagocyte-derived IL-4 in CCR2(-/-) mice is associated with the presence of alternatively activated phagocytic cells.

Dendritic cells and chemokine-directed migration in transplantation: where are we headed?

The role of dendritic cells (DC) in transplantation is often overshadowed by the more prominent roles of T and B cells, which interact directly with and, in the absence of immunosuppressive therapy, destroy the allograft. It has become increasingly recognized, however, that these potent antigen-presenting cells exert control over the immune response and regulate the balance between tolerance and immunity to transplanted organs and tissues. The role that chemokines play in influencing DC function with impact on regulation of immune responses against the graft is only beginning to be understood. This article considers how the manipulation of DC trafficking during an alloimmune response can affect graft outcome.

Innate immunity and heat shock response in islet transplantation

Islet transplantation is an extremely effective therapy for patients with type I diabetes, providing tight control of blood glucose and persistent insulin release. Islet grafts struggle with various stress responses and immunity attacks, which contribute to loss of islet grafts in the long term. In this review we focus upon the innate immunity and heat shock responses, which are closely relevant to the outcome of islet grafts. Potential strategies provided by more comprehensive interventions to control innate immunity and by selective induction of heat shock proteins may ameliorate the outcome of islet transplantation.