Human Interleukin-32γ Plays a Protective Role in an Experimental Model of Visceral Leishmaniasis in Mice

Single nucleotide polymorphisms in genes involved in immune responses and outcome of tegumentary leishmaniasis

Leishmaniases are neglected tropical diseases with a broad clinical spectrum. Tegumentary leishmaniasis (TL) is a disease caused by different Leishmania species, transmitted by phlebotomine sand flies and distributed worldwide. TL can present a cutaneous (CL) or mucocutaneous (MCL) clinical form depending on factors inherent to the parasite, the host and the vector. Polymorphisms in the immune response genes are host genetic factors that influence the pathogenesis or control of leishmaniasis. Single nucleotide polymorphisms (SNPs) in immune genes have been evaluated in several countries where leishmaniasis is endemic. In this review, we report studies on SNPs in several immune genes that might be associated with susceptibility or resistance to TL. We summarize studies from around the world and in Brazil, highlight the difficulties of these studies and future analyses needed to enhance our knowledge regarding host genetic factors in TL. Understanding the genetic characteristics of the host that facilitate resistance or susceptibility to leishmaniasis can contribute to the development of immunotherapy schedules for this disease. The current treatment methods are toxic, and no human vaccine is available.

Cytokines and Signaling Networks Regulating Disease Outcomes in Leishmaniasis

Cytokines play crucial roles in commencing and coordinating the organized recruitment and activation of immune cells during infection. These molecular regulators play an important part in deciding the fate of disease outcomes in leishmaniasis, a parasitic disease of tropical and subtropical countries. T helper 1 (Th1) cell-mediated inflammatory cytokines usually play a host-protective role, while T helper 2 (Th2) cell activation produces an anti-inflammatory milieu necessary for parasite survival. It is noteworthy that in such a multifaceted disease, the role played by any particular cytokine cannot be generalized as either beneficial or detrimental. For example, a "host-favorable" cytokine in one form of the disease has been found to be "pathogen friendly" in another form of leishmaniasis. On the other hand, the complex signaling network regulating the production of cytokines is further complicated by the nature of the host as well as the presence of other cytokines in the milieu. The present review focuses on the differential roles played by cytokines and the intricate signaling network responsible for the regulation of such cytokines during infection by different species of Leishmania. While many more studies are required in the future to better understand the role of these molecules in both animal models and patient samples, current studies indicate that these molecules are potential candidates to be targeted for therapy against this deadly disease.

A Critical Overview of Interleukin 32 in Leishmaniases

Interleukin-32 (IL-32) has several immune regulatory properties, which have driven its investigation in the context of various diseases. IL-32 expression is reported to be induced in the lesions of patients with American tegumentary leishmaniasis (ATL) by the New World Leishmania spp. that are responsible for causing ATL and visceral leishmaniasis (VL). IL-32 expression may elevate the inflammatory process through the induction of pro-inflammatory cytokines and also via mechanisms directed to kill the parasites. The genetic variants of IL-32 might be associated with the resistance or susceptibility to ATL, while different isoforms of IL-32 could be associated with distinct T helper lymphocyte profiles. IL-32 also determines the transcriptional profile in the bone marrow progenitor cells to mediate the trained immunity induced by β-glucan and BCG, thereby contributing to the resistance against Leishmania. IL-32γ is essential for the vitamin D-dependent microbicidal pathway for parasite control. In this context, the present review report briefly discusses the data retrieved from the studies conducted on IL-32 in leishmaniasis in humans and mice to highlight the current challenges to understanding the role of IL-32 in leishmaniasis.

Interleukin-32γ in the Control of Acute Experimental Chagas Disease

Chagas disease (CD) is an important parasitic disease caused by Trypanosoma cruzi. Interleukin-32 (IL-32) plays an important role in inflammation and in the development of Th1/Th17 acquired immune responses. We evaluated the influence of IL-32γ on the immune response profile, pathogenesis of myocarditis in acute experimental CD, and control of the disease. For this, C57BL/6 wild-type (WT) and IL-32γTg mice were infected subcutaneously with 1,000 forms of Colombian strain of T. cruzi. In the histopathological analyzes, T. cruzi nests, myocarditis, and collagen were quantified in cardiac tissue. Cytokine productions (IL-32, IFN-γ, TNF-α, IL-10, and IL-17) were measured in cardiac homogenate by ELISA. The IL-32γTg mice showed a better control of parasitemia and T. cruzi nests in the heart than WT mice. Infected-WT and -IL-32γTg mice showed similar levels of IFN-γ, TNF-α, and IL-17, but IL-10 was significantly higher expressed in IL-32γTg than in WT mice. The cytokine profile found in IL-32γTg animals contributed to body weight maintenance, parasitemia control, and survival. Our results indicate that the presence of human IL-32γ in mice infected with the Colombian strain of T. cruzi is important for infection control during the acute phase of Chagas disease.

Protective immune response mediated by neutrophils in experimental visceral leishmaniasis is enhanced by IL-32γ

Neutrophils are important cells in protection against microbial infections including visceral leishmaniasis (VL). It is well known that IL-32γ increases the protective T helper 17 cell mediated immune response against Leishmania infantum. Thus, in this study we evaluated whether IL-32 γ can increase the protective role of neutrophils against VL. In comparison with wild type (WT) mice, transgenic mice for human IL-32 γ (IL-32 γ Tg) presented a higher frequency and absolute number of neutrophils in both spleen and liver after the establishment of L. infantum infection. The IL-32 concentrations correlated with neutrophil numbers in the infected tissues. The IL-32 γ -induced recruitment of neutrophils was dependent on IL-17, since inhibition of Th17 T cells generation and IL-17 production with digoxin treatment reversed the effects of IL-32 γ. In murine neutrophils, the presence of IL-32 γ enhanced the phagocytosis of L. infantum via CR3. In addition, murine IL-32 γ Tg neutrophils were able to kill L. infantum due to the increased production of ROS when compared with WT neutrophils. In fact, IL-32 γ Tg mice lost their ability to control infection by L. infantum when neutrophils were depleted. In parallel, treatment of human neutrophils with recombinant IL-32 γ increased phagocytosis and ROS-dependent killing of L. infantum, similarly to murine IL-32 γ Tg neutrophils. The data show that IL-32 γ induces neutrophil recruitment to organs affected by VL and increases phagocytosis and killing of L. infantum by neutrophils. Together, data indicate the pivotal axis IL-32 γ -Th17-neutrophils to control VL.

The role of IL-32 in Bacillus Calmette-Guérin (BCG)-induced trained immunity in infections caused by different Leishmania spp

BACKGROUND

Cells of the innate immune system undergo long-term functional reprogramming in response to Bacillus Calmette-Guérin (BCG) exposure via a process called trained immunity, conferring nonspecific protection to unrelated infections. Here, we investigate whether BCG-induced trained immunity is able to protect against infections caused by different Leishmania spp., protozoa that cause cutaneous and mucosal or visceral lesions.

METHODS

We used training models of human monocytes with BCG and subsequent infection by L. braziliensis, L. amazonensis and L. infantum, and the vaccination of wild-type and transgenic mice for IL-32γ before in vivo challenge with parasites.

RESULTS

We demonstrated that monocytes trained with BCG presented enhanced ability to kill L. braziliensis, L. amazonensis and L. infantum through increased production of reactive oxygen species. Interleukin (IL)-32 appears to play an essential role in the development of trained immunity. Indeed, BCG exposure induced IL-32 production in human primary monocytes, both mRNA and protein. We have used a human IL-32γ transgenic mouse model (IL-32γTg) to study the effect of BCG vaccination in different Leishmania infection models. BCG vaccination decreased lesion size and parasite load in infections caused by L. braziliensis and reduced the spread of L. amazonensis to other organs in both infected wild-type (WT) and IL-32γTg mice. In addition, BCG reduced the parasite load in the spleen, liver and bone marrow of both WT and IL-32γTg mice infected with L. infantum. BCG vaccination increased inflammatory infiltrate in infected tissues caused by different Leishmania spp. In all infections, the presence of IL-32γ was not mandatory, but it increased the protective and inflammatory effects of BCG-induced training.

CONCLUSIONS

BCG's ability to train innate immune cells, providing protection against leishmaniasis, as well as the participation of IL-32γ in this process, pave the way for new treatment strategies for this neglected infectious disease.

Cytokine saga in visceral leishmaniasis

In humans, infection with Leishmania manifests into a spectrum of diseases. The manifestation of the diseases depend on the resultant evasion of the parasite to immune responses namely by macrophages, which is an exclusive host of Leishmania. The B cells valiantly mount antibody responses, however, to no avail as the Leishmania parasites occupy the intracellular niches of the macrophages and subvert the immune response. Extensive studies have been documented on the role of cell-mediated immunity (CMI) in protection and counter survival strategies of the parasites leading to downregulation of CMI. The present review attempts to discuss the cytokines in progression or resolution of visceral form of leishmaniasis or kala-azar, predominantly affecting the Indian subcontinent. The components/cytokine(s) responsible for the regulation of the critical balance of T helper cells and their subsets have been discussed in the perspective. Therefore, any strategy involving the treatment of visceral leishmania (VL) needs to consider the balance and regulation of T cell function.

β-Glucan-Induced Trained Immunity Protects against Leishmania braziliensis Infection: a Crucial Role for IL-32

American tegumentary leishmaniasis is a vector-borne parasitic disease caused by Leishmania protozoans. Innate immune cells undergo long-term functional reprogramming in response to infection or Bacillus Calmette-Guérin (BCG) vaccination via a process called trained immunity, conferring non-specific protection from secondary infections. Here, we demonstrate that monocytes trained with the fungal cell wall component β-glucan confer enhanced protection against infections caused by Leishmania braziliensis through the enhanced production of proinflammatory cytokines. Mechanistically, this augmented immunological response is dependent on increased expression of interleukin 32 (IL-32). Studies performed using a humanized IL-32 transgenic mouse highlight the clinical implications of these findings in vivo. This study represents a definitive characterization of the role of IL-32γ in the trained phenotype induced by β-glucan or BCG, the results of which improve our understanding of the molecular mechanisms governing trained immunity and Leishmania infection control.

Molecular interactions and functions of IL-32

IL-32 is a multifaceted cytokine associated with several diseases and inflammatory conditions. Its expression is induced in response to cellular stress such as hypoxia, infections, and pro-inflammatory cytokines. IL-32 can be secreted from cells and can induce the production of pro-inflammatory cytokines from several cell types but are also described to have anti-inflammatory functions. The intracellular form of IL-32 is shown to play an important role in various cellular processes, including the defense against intracellular bacteria and viruses and in modulation of cell metabolism. In this review, we discuss current literature on molecular interactions of IL-32 with other proteins. We also review data on the role of intracellular IL-32 as a metabolic regulator and its role in antimicrobial host defense.

Liposomal Formulation of ChimeraT, a Multiple T-Cell Epitope-Containing Recombinant Protein, Is a Candidate Vaccine for Human Visceral Leishmaniasis

Background: Leishmaniases are neglected diseases caused by infection with Leishmania parasites and there are no human vaccines in use routinely. The purpose of this study was to examine the immunogenicity of ChimeraT, a novel synthetic recombinant vaccine against visceral leishmaniasis (VL), incorporated into a human-compatible liposome formulation. Methods: BALB/c mice were immunized subcutaneously with ChimeraT/liposome vaccine, ChimeraT/saponin adjuvant, or ChimeraT/saline and immune responses examined in vitro and in vivo. Results: Immunization with the ChimeraT/liposome formulation induced a polarized Th1-type response and significant protection against L. infantum infection. ChimeraT/liposome vaccine stimulated significantly high levels of interferon (IFN)-γ, interleukin (IL)-12, and granulocyte macrophage-colony stimulating factor (GM-CSF) cytokines by both CD4 and CD8 T-cells, with correspondingly lower levels of IL-4 and IL-10 cytokines. Induced antibodies were predominantly IgG2a isotype, and homologous antigen-stimulated spleen cells produced significant nitrite as a proxy for nitric oxide (NO). Furthermore, we examined a small number of treated VL patients and found higher levels of circulating anti-ChimeraT protein IgG2 antibodies, compared to IgG1 levels. Conclusions: Overall, the liposomal formulation of ChimeraT induced a protective Th1-type immune response and thus could be considered in future studies as a vaccine candidate against human VL.

An impedimetric genosensor for Leishmania infantum based on electrodeposited cadmium sulfide nanosheets

It is estimated that there are 400000 new cases of visceral leishmaniasis each year, with about 30,000 deaths. Therefore, detection of this pathogen and its species is highly vital for overall health of the community. In the present research, a DNA-based biosensor, namely genosensor, was introduced for detection of genomic DNA of Leishmania infantum. The genosensor was fabricated based on the transduction of cadmium sulfide nanosheets and recognition of a particular single stranded DNA sequence, and worked in label-, marker-, tag- and PCR-free manners. Impedimetric measurements were performed in a wide range of frequency (recording Nyquist diagrams) without applying external force (working at open circuit potential) upon hybridization of DNA targets with the cadmium sulfide nanosheets surface-immobilized probe. The genosensor detected the complementary DNA strand in a concentration range of 1.0 × 10^-14 to 1.0 × 10^-6 mol L^-1 and a detection limit (DL) of 0.81 fmol L^-1 (6.5 fg mL^-1), and genomic DNA of Leishmania infantum in a concentration range of 5-50 ng μL^-1 and a DL of 1.2 ng μL^-1. The genosensor had a very good selectivity, fabrication reproducibility and stability, and was applicable for practical applications.

Genetic variation in Interleukin-32 influence the immune response against New World Leishmania species and susceptibility to American Tegumentary Leishmaniasis

Interleukin-32 is a novel inflammatory mediator that has been described to be important in the immunopathogenesis and control of infections caused by Leishmania parasites. By performing experiments with primary human cells in vitro, we demonstrate that the expression of IL-32 isoforms is dependent on the time exposed to L. amazonensis and L. braziliensis antigens. Moreover, for the first time we show the functional consequences of three different genetic variations in the IL32 (rs4786370, rs4349147, rs1555001) modulating IL-32γ expression, influencing innate and adaptive cytokine production after Leishmania exposure. Using a Brazilian cohort of 107 American Tegumentary Leishmaniasis patients and a control cohort of 245 healthy individuals, the IL32 rs4786370 genetic variant was associated with protection against ATL, whereas the IL32 rs4349147 was associated with susceptibility to the development of localized cutaneous and mucosal leishmaniasis. These novel insights may help improve therapeutic strategies and lead to benefits for patients suffering from Leishmania infections.

In this study, we described how IL-32 isoforms are crucial to host defense against new world Leishmania species infections. Furthermore, by accessing the genotype frequency of genetic variations in IL32 in a cohort of Brazilian patients with American Tegumentary Leishmaniasis (ATL) and controls, we have obtained indications that IL-32 is associated with disease susceptibility and the development of different clinical manifestations. Thus, this study provides us an extra evidence that the isoforms of IL-32 shape the immune response favoring the development of different cytokines produced by peripheral blood mononuclear cells that might contribute to skin/mucosal inflammation and host defense.

Interleukin-32: An endogenous danger signal or master regulator of intracellular pathogen infections-Focus on leishmaniases

Interleukin 32 (IL-32) is an intracellular cytokine produced by immune and non immune cells after different stimuli. It contributes to inflammation and control of intracellular pathogens mainly by inducing proinflammatory cytokines and microbicidal molecules. Evidence is rising showing that IL-32 can be considered an endogenous danger signal after tissue injury, amplifying the inflammatory process and acquired immune responses. It seems to be a master regulator of intracellular infectious diseases. In this review, first the general properties of IL-32 are described followed by its role in the immunopathogenesis of inflammatory and infectious diseases. Roles of IL-32 in the control of infectious diseases caused by intracellular pathogens are reported, and later a focus on IL-32 in leishmaniases, diseases caused by an intracellular protozoan, is presented.