Dendritic cell-mediated vaccination relies on interleukin-4 receptor signaling to avoid tissue damage after Leishmania major infection of BALB/c mice

Immunization With Lipopolysaccharide-Activated Dendritic Cells Generates a Specific CD8+ T Cell Response That Confers Partial Protection Against Infection With Trypanosoma cruzi

Lipopolysaccharide (LPS) induces the activation of dendritic cells (DCs) throughout the engagement of toll-like receptor 4. LPS-activated DCs show increased capacity to process and present pathogen-derived antigens to activate naïve T cells. DCs-based vaccines have been successfully used to treat some cancer types, and lately transferred to the field of infectious diseases, in particular against HIV. However, there is no vaccine or DC therapy for any parasitic disease that is currently available. The immune response against Trypanosoma cruzi substantially relies on T cells, and both CD4⁺ and CD8⁺ T lymphocytes are required to control parasite growth. Here, we develop a vaccination strategy based on DCs derived from bone marrow, activated with LPS and loaded with TsKb20, an immunodominant epitope of the trans-sialidase family of proteins. We extensively characterized the CD8⁺ T cell response generated after immunization and compared three different readouts: a tetramer staining, ELISpot and Activation-Induced Marker (AIM) assays. To our knowledge, this work shows for the first time a proper set of T cell markers to evaluate specific CD8⁺ T cell responses in mice. We also show that our immunization scheme confers protection against T. cruzi, augmenting survival and reducing parasite burden in female but not male mice. We conclude that the immunization with LPS-activated DCs has the potential to prime significant CD8⁺ T cell responses in C57BL/6 mice independently of the sex, but this response will only be effective in female, possibly due to mice sexual dimorphisms in the response generated against T. cruzi.

Unravelling the unsolved paradoxes of cytokine families in host resistance and susceptibility to Leishmania infection

Leishmaniasis is a neglected disease caused by protozoan parasites of the genus Leishmania. Successful clearance of Leishmania relies on a robust human immune response and various cytokines have been implicated in resistance and susceptibility to Leishmania infection. Accordingly, various immunotherapeutic approaches involving cytokines and cytokine receptors are being considered as novel avenues of treatment given the limited efficacy of current anti-leishmanial drugs. These approaches target canonical T helper (Th)1/Type 1 cytokines as intended mediators of host-protection to infection whilst concomitantly suppressing Th2/Type 2 cytokines and their anticipated disease-promoting roles. However, the use of cytokine and cytokine receptor gene-deficient mice over the years has challenged this simplistic view of Th1/Type 1-mediated resistance and Th2/Type 2-mediated susceptibility. Indeed, contribution to susceptibility vs resistance is only a partial consequence to cytokine action as the overall response is multi-faceted due to the pleiotropic, redundant, antagonistic and synergistic action of cytokines and interactions with immune cells in the diseased state. Notably, while the responses of certain cytokines are selectively host-protective or characteristic disease-enhancers, some ligands exert a response depending on the parasite-species initiating infection. Paradoxically, others play dual or contradictory roles in different Leishmania immunopathologies. Hence, cytokines in disease is an unsolved paradox and a comprehensive knowledge of cytokine interplay is important to guide the development of novel immunotherapeutics against leishmaniasis. In this review, we characterize various cytokine families in persistence and clearance of the Leishmania parasite and particularly elucidate unsolved cytokine puzzles in leishmaniasis based on information acquired from "gain of knowledge by loss of function" studies in cytokine and cytokine receptor gene-deficient mice.

Can We Harness Immune Responses to Improve Drug Treatment in Leishmaniasis?

Leishmaniasis is a vector-borne parasitic disease that has been neglected in priority for control and eradication of malaria, tuberculosis, and HIV/AIDS. Collectively, over one seventh of the world’s population is at risk of being infected with 0.7–1.2 million new infections reported annually. Clinical manifestations range from self-healing cutaneous lesions to fatal visceral disease. The first anti-leishmanial drugs were introduced in the 1950′s and, despite several shortcomings, remain the mainstay for treatment. Regardless of this and the steady increase in infections over the years, particularly among populations of low economic status, research on leishmaniasis remains under funded. This review looks at the drugs currently in clinical use and how they interact with the host immune response. Employing chemoimmunotherapeutic approaches may be one viable alternative to improve the efficacy of novel/existing drugs and extend their lifespan in clinical use.

Leishmaniasis immunopathology-impact on design and use of vaccines, diagnostics and drugs

Leishmaniasis is a disease complex caused by 20 species of protozoan parasites belonging to the genus Leishmania. In humans, it has two main clinical forms, visceral leishmaniasis (VL) and cutaneous or tegumentary leishmaniasis (CL), as well as several other cutaneous manifestations in a minority of cases. In the mammalian host Leishmania parasites infect different populations of macrophages where they multiply and survive in the phagolysosomal compartment. The progression of both VL and CL depends on the maintenance of a parasite-specific immunosuppressive state based around this host macrophage infection. The complexity and variation of immune responses and immunopathology in humans and the different host interactions of the different Leishmania species has an impact upon the effectiveness of vaccines, diagnostics and drugs.

GK1 Improves the Immune Response Induced by Dendritic Cells of BALB/c Mice Infected with Leishmania mexicana Promastigotes

PURPOSE

Dendritic cells (DCs) are the most potent antigen-presenting cells (APCs), and their capacity to activate the immune response has been widely used in immunotherapies against different diseases, predominantly cancer. However, they have not been so widely used in immunotherapies against infectious diseases. Leishmania mexicana is the causative agent of cutaneous leishmaniasis in Mexico, which can result in localized cutaneous leishmaniasis (LCL) and diffuse cutaneous leishmaniasis (DCL). DCL is characterized by the incapability of the immune response to control the parasite, which thus disseminates to all teguments. Treatments against DCL have shown low efficacy, which is a reason why alternative therapies such as immunotherapies are promising. One adjuvant that has proven its effectiveness in immunotherapies against some cancers and infections is GK1, a component of the SPVac vaccine against porcine cysticercosis. GK1 has the capacity to elicit proinflammatory cytokines and chemokines from DCs and macrophages.

METHODS

We pulsed bone marrow-derived dendritic cells (BMDCs) with GK1 and a lysate obtained from L. mexicana promastigotes and tested the efficacy of this combination against the infection of susceptible mice with L. mexicana.

RESULTS

We found that BMDCs stimulated with GK1 and a lysate of L. mexicana promastigotes secreted IFN-γ and IL-12, and when they were adoptively transferred to BALB/c mice which were then infected with L. mexicana promastigotes, there was a reduction in the size of the lesion and in the parasite load.

CONCLUSIONS

The adjuvant properties of GK1 along with parasite antigens may have a protective effect against the infection of BALB/c mice with L. mexicana.

Deletion of Interleukin-4 Receptor Alpha-Responsive Keratinocytes in BALB/c Mice Does Not Alter Susceptibility to Cutaneous Leishmaniasis

The skin microenvironment at the site of infection plays a role in the early events that determine protective T helper 1/type 1 immune responses during cutaneous leishmaniasis (CL) infection. During CL in nonhealing BALB/c mice, early interleukin-4 (IL-4) can instruct dendritic cells for protective Th1 immunity.

The skin microenvironment at the site of infection plays a role in the early events that determine protective T helper 1/type 1 immune responses during cutaneous leishmaniasis (CL) infection. During CL in nonhealing BALB/c mice, early interleukin-4 (IL-4) can instruct dendritic cells for protective Th1 immunity. Additionally, keratinocytes, which are the principal cell type in the skin epidermis, have been shown to secrete IL-4 early after Leishmania major infection. Here, we investigated whether IL-4/IL-13 signaling via the common IL-4 receptor alpha chain (IL-4Rα) on keratinocytes contributes to susceptibility during experimental CL. To address this, keratinocyte-specific IL-4Rα-deficient (KRT14^cre IL-4Rα^−/lox) mice on a BALB/c genetic background were generated by gene targeting and site-specific recombination (Cre/loxP) under the control of the keratinocyte-specific krt14 locus. Following high-dose infection with L. major IL-81 and LV39 promastigotes subcutaneously in the footpad, footpad swelling, parasite burden, IFN-γ/IL-4/IL-13 cytokine production, and type 1 and type 2 antibody responses were similar between KRT14^cre IL-4Rα^−/lox and littermate control IL-4Rα^−/lox BALB/c mice. An intradermal infection with low-dose L. major IL-81 and LV39 promastigotes in the ear showed results in infected KRT14^cre IL-4Rα^−/lox BALB/c mice similar to those of littermate control IL-4Rα^−/lox BALB/c mice, with the exception of a significant decrease observed in parasite burden only at the site of LV39 infection in the ear. Collectively, our results show that autocrine and paracrine signaling of IL-4/IL-13 through the IL-4Rα chain on keratinocytes does not influence the establishment of a nonhealing Th2 immune response in BALB/c mice during L. major infection.

Leishmania Hijacks Myeloid Cells for Immune Escape

Protozoan parasites of the Leishmania genus are the causative agents of leishmaniasis, a group of neglected tropical diseases whose clinical manifestations vary depending on the infectious Leishmania species but also on host factors. Recognition of the parasite by host myeloid immune cells is a key to trigger an effective Leishmania-specific immunity. However, the parasite is able to persist in host myeloid cells by evading, delaying and manipulating host immunity in order to escape host resistance and ensure its transmission. Neutrophils are first in infiltrating infection sites and could act either favoring or protecting against infection, depending on factors such as the genetic background of the host or the parasite species. Macrophages are the main host cells where the parasites grow and divide. However, macrophages are also the main effector population involved in parasite clearance. Parasite elimination by macrophages requires the priming and development of an effector Th1 adaptive immunity driven by specific subtypes of dendritic cells. Herein, we will provide a comprehensive outline of how myeloid cells regulate innate and adaptive immunity against Leishmania, and the mechanisms used by the parasites to promote their evasion and sabotage. Understanding the interactions between Leishmania and the host myeloid cells may lead to the development of new therapeutic approaches and improved vaccination to leishmaniases, an important worldwide health problem in which current therapeutic or preventive approaches are limited.

House dust mite induced allergic airway disease is attenuated in CD11ccreIL-4Rα-/l°x mice

The precise mechanisms leading to development of T helper type (Th)2-driven allergic responses are unknown. We aimed to determine how IL-4 receptor alpha (IL-4Rα) signaling on CD11c⁺ cells influences allergen-induced Th2 responses in mice. CD11c^creIL-4Rα^−/l°^x mice, deficient in IL-4Rα on dendritic cells and alveolar macrophages, were compared to IL-4Rα^−/l°^x littermate controls in models of allergic airway disease induced by OVA/alum, OVA alone or house dust mite. Cytokine responses, eosinophil and neutrophil infiltration into the lungs, airway hyperreactivity and mucus hypersecretion were evaluated after allergen challenge. In the OVA/alum model, CD11c^creIL-4Rα^−/lox mice had similar airway hyperreactivity, eosinophil infiltration, Th2-type cytokine production and mucus hypersecretion to littermate controls. When alum was omitted during sensitization, CD11c^creIL-4Rα^−/lox mice had similar airway hyperreactivity and mucus secretion but reduced Th2-type cytokine production and eosinophils, suggesting alum overrides the requirement for IL-4Rα signaling on CD11c⁺ cells in enhancing Th2-type responses. In the house dust mite model, CD11c^creIL-4Rα^−/lox mice showed similar mucus secretion, but reduced Th2 responses, eosinophils, neutrophils and airway hyperreactivity, unlike previously tested LysM^creIL-4Rα^−/lox mice, which lack IL-4Rα on alveolar macrophages but not on dendritic cells. Therefore, our results indicate that IL-4Rα signaling on dendritic cells promotes allergen-induced Th2 responses and eosinophil infiltration into the lung.

Interleukin-4 Receptor Alpha: From Innate to Adaptive Immunity in Murine Models of Cutaneous Leishmaniasis

The interleukin (IL)-4 receptor alpha (IL-4Rα), ubiquitously expressed on both innate and adaptive immune cells, controls the signaling of archetypal type 2 immune regulators; IL-4 and IL-13, which elicit their signaling action by the type 1 IL-4Rα/gamma common and/or the type 2 IL-4Rα/IL-13Rα complexes. Global gene-deficient mouse models targeting IL-4, IL-13, or the IL-4Rα chain, followed by the development of conditional mice and generation of important cell-type-specific IL-4Rα-deficient mouse models, were indeed critical to gaining in-depth understanding of detrimental T helper (Th) 2 mechanisms in type 1-controlled diseases. A primary example being cutaneous leishmaniasis, which is caused by the protozoan parasite Leishmania major, among others. The disease is characterized by localized self-healing cutaneous lesions and necrosis for which, currently, not a single vaccine has made it to a stage that can be considered effective. The spectrum of human leishmaniasis belongs to the top 10 infectious diseases according to the World Health Organization. As such, 350 million humans are at risk of infection and disease, with an incidence of 1.5–2 million new cases being reported annually. A major aim of our research is to identify correlates of host protection and evasion, which may aid in vaccine design and therapeutic interventions. In this review, we focus on the immune-regulatory role of the IL-4Rα chain from innate immune responses to the development of beneficial type 1 and detrimental type 2 adaptive immune responses during cutaneous Leishmania infection. We discuss the cell-specific requirements of the IL-4Rα chain on crucial innate immune cells during L. major infection, including, IL-4Rα-responsive skin keratinocytes, macrophages, and neutrophils, as well as dendritic cells (DCs). The latter, contributing to one of the paradigm shifts with respect to the role of IL-4 instructing DCs in vivo, to promote Th1 responses against L. major. Finally, we extend these innate responses and mechanisms to control of adaptive immunity and the effect of IL-4Rα-responsiveness on T and B lymphocytes orchestrating the development of CD4⁺ Th1/Th2 and B effector 1/B effector 2 B cells in response to L. major infection in the murine host.

Cinnamic Acid Bornyl Ester Derivatives from Valeriana wallichii Exhibit Antileishmanial In Vivo Activity in Leishmania major-Infected BALB/c Mice

Human leishmaniasis covers a broad spectrum of clinical manifestations ranging from self-healing cutaneous leishmaniasis to severe and lethal visceral leishmaniasis caused among other species by Leishmania major or Leishmania donovani, respectively. Some drug candidates are in clinical trials to substitute current therapies, which are facing emerging drug-resistance accompanied with serious side effects. Here, two cinnamic acid bornyl ester derivatives (1 and 2) were assessed for their antileishmanial activity. Good selectivity and antileishmanial activity of bornyl 3-phenylpropanoate (2) in vitro prompted the antileishmanial assessment in vivo. For this purpose, BALB/c mice were infected with Leishmania major promastigotes and treated with three doses of 50 mg/kg/day of compound 2. The treatment prevented the characteristic swelling at the site of infection and correlated with reduced parasite burden. Transmitted light microscopy and transmission electron microscopy of Leishmania major promastigotes revealed that compounds 1 and 2 induce mitochondrial swelling. Subsequent studies on Leishmania major promastigotes showed the loss of mitochondrial transmembrane potential (ΔΨm) as a putative mode of action. As the cinnamic acid bornyl ester derivatives 1 and 2 had exhibited antileishmanial activity in vitro, and compound 2 in Leishmania major-infected BALB/c mice in vivo, they can be regarded as possible lead structures for the development of new antileishmanial therapeutic approaches.

Innate immunity to Leishmania infection: within phagocytes

Infection by Leishmania takes place in the context of inflammation and tissue repair. Besides tissue resident macrophages, inflammatory macrophages and neutrophils are recruited to the infection site and serve both as host cells and as effectors against infection. Recent studies suggest additional important roles for monocytes and dendritic cells. This paper addresses recent experimental findings regarding the regulation of Leishmania major infection by these major phagocyte populations. In addition, the role of IL-4 on dendritic cells and monocytes is discussed.

Genetic dissection of dendritic cell homeostasis and function: lessons from cell type-specific gene ablation

Dendritic cells (DCs) are a heterogeneous cell population of great importance in the immune system. The emergence of new genetic technology utilizing the CD11c promoter and Cre recombinase has facilitated the dissection of functional significance and molecular regulation of DCs in immune responses and homeostasis in vivo. For the first time, this strategy allows observation of the effects of DC-specific gene deletion on immune system function in an intact organism. In this review, we present the latest findings from studies using the Cre recombinase system for cell type-specific deletion of key molecules that mediate DC homeostasis and function. Our focus is on the molecular pathways that orchestrate DC life span, migration, antigen presentation, pattern recognition, and cytokine production and signaling.

Deletion of IL-4 receptor alpha on dendritic cells renders BALB/c mice hypersusceptible to Leishmania major infection

In BALB/c mice, susceptibility to infection with the intracellular parasite Leishmania major is driven largely by the development of T helper 2 (Th2) responses and the production of interleukin (IL)-4 and IL-13, which share a common receptor subunit, the IL-4 receptor alpha chain (IL-4Rα). While IL-4 is the main inducer of Th2 responses, paradoxically, it has been shown that exogenously administered IL-4 can promote dendritic cell (DC) IL-12 production and enhance Th1 development if given early during infection. To further investigate the relevance of biological quantities of IL-4 acting on DCs during in vivo infection, DC specific IL-4Rα deficient (CD11c(cre)IL-4Rα(-/lox)) BALB/c mice were generated by gene targeting and site-specific recombination using the cre/loxP system under control of the cd11c locus. DNA, protein, and functional characterization showed abrogated IL-4Rα expression on dendritic cells and alveolar macrophages in CD11c(cre)IL-4Rα(-/lox) mice. Following infection with L. major, CD11c(cre)IL-4Rα(-/lox) mice became hypersusceptible to disease, presenting earlier and increased footpad swelling, necrosis and parasite burdens, upregulated Th2 cytokine responses and increased type 2 antibody production as well as impaired classical activation of macrophages. Hypersusceptibility in CD11c(cre)IL-4Rα(-/lox) mice was accompanied by a striking increase in parasite burdens in peripheral organs such as the spleen, liver, and even the brain. DCs showed increased parasite loads in CD11c(cre)IL-4Rα(-/lox) mice and reduced iNOS production. IL-4Rα-deficient DCs produced reduced IL-12 but increased IL-10 due to impaired DC instruction, with increased mRNA expression of IL-23p19 and activin A, cytokines previously implicated in promoting Th2 responses. Together, these data demonstrate that abrogation of IL-4Rα signaling on DCs is severely detrimental to the host, leading to rapid disease progression, and increased survival of parasites in infected DCs due to reduced killing effector functions.

WITHDRAWN: Co-administration of CCL5 and IL4 enhances DNA vaccine-induced protective immunity to Ascaris suum infection in mice

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