Cytokines in the generation and function of regulatory T cell subsets in leishmaniasis

Activation of neutrophils excels the therapeutic potential of Mycobacterium indicus pranii and heat-induced promastigotes against antimony-resistant Leishmania donovani infection

Repurposing drugs and adjuvants is an attractive choice of present therapy that reduces the substantial costs, chances of failure, and systemic toxicity. Mycobacterium indicus pranii was originally developed as a leprosy vaccine but later has been found effective against Leishmania donovani infection. To extend our earlier study, here we reported the immunotherapeutic modulation of the splenic and circulatory neutrophils in favour of hosts as neutrophils actually serve as the pro-parasitic portable shelter to extend the Leishmania infection specifically during the early entry into the hosts' circulation. We targeted to disrupt this early pro-parasitic incidence by the therapeutic combination of M. indicus pranii and heat-induced promastigotes against antimony-resistant L. donovani infection. The combination therapy induced the functional expansion of CD11b+Ly6CintLy6Ghi neutrophils both in the post-infected spleen, and also in the circulation of post-treated animals followed by the immediate Leishmania infection. More importantly, the enhanced expression of MHC-II, phagocytic uptake of the parasites by the circulatory neutrophils as well as the oxidative burst were induced that limited the chances of the very early establishment of the infection. The enhanced expression of pro-inflammatory cytokines, like IL-1α and TNF-α indicated resistance to the parasite-mediated takeover of the neutrophils, as these cytokines are critical for the activation of T cell-mediated immunity and host-protective responses. Additionally, the induction of essential transcription factors and cytokines for early granulocytic lineage commitment suggests that the strategy not only contributed to the peripheral activation of the neutrophils but also promoted granulopoiesis in the bone marrow.

Topical application of ozonated sunflower oil accelerates the healing of lesions of cutaneous leishmaniasis in mice under meglumine antimoniate treatment

Besides being scarce, the drugs available for treating cutaneous leishmaniasis have many adverse effects. Ozone is an option to enhance the standard treatment due to the wound-healing activity reported in the literature. In this study, we evaluated the efficiency of ozonated sunflower oil as an adjuvant in treating cutaneous lesions caused by Leishmania amazonensis. BALB/c mice were infected with L. amazonensis, and after the lesions appeared, they were treated in four different schedules using the drug treatment with meglumine antimoniate (Glucantime®), with or without ozonated oil. After thirty days of treatment, the lesions' thickness and their parasitic burden, blood leukocytes, production of NO and cytokines from peritoneal macrophages and lymph node cells were analyzed. The group treated with ozonated oil plus meglumine antimoniate showed the best performance, improving the lesion significantly. The parasitic burden showed that ozonated oil enhanced the leishmanicidal activity of the treatment, eliminating the parasites in the lesion. Besides, a decrease in the TNF levels from peritoneal macrophages and blood leukocytes demonstrated an immunomodulatory action of ozone in the ozonated oil-treated animals compared to the untreated group. Thus, ozonated sunflower oil therapy has been shown as an adjuvant in treating Leishmania lesions since this treatment enhanced the leishmanicidal and wound healing effects of meglumine antimoniate.

Regulatory T cells in parasite infections: susceptibility, specificity and specialisation

Regulatory T cells (Tregs) are essential to control immune system responses to innocuous self-specificities, intestinal and environmental antigens. However, they may also interfere with immunity to parasites, particularly in chronic infection. Susceptibility to many parasite infections is, to a greater or lesser extent, controlled by Tregs, but often they play a more prominent role in moderating the immunopathological consequences of parasitism, and dampening bystander reactions in an antigen-nonspecific manner. More recently, Treg subtypes have been defined which may preferentially act in different contexts; we also discuss the degree to which this specialisation is now being mapped onto how Tregs maintain the delicate balance between tolerance, immunity, and pathology in infection.

Immunisation with Transgenic L. tarentolae Expressing Gamma Glutamyl Cysteine Synthetase from Pathogenic Leishmania Species Protected against L. major and L. donovani Infection in a Murine Model

Leishmaniasis is a protozoan disease responsible for significant morbidity and mortality. There is no recommended vaccine to protect against infection. In this study, transgenic Leishmania tarentolae expressing gamma glutamyl cysteine synthetase (γGCS) from three pathogenic species were produced and their ability to protect against infection determined using models of cutaneous and visceral leishmaniasis. The ability of IL-2-producing PODS® to act as an adjuvant was also determined in L. donovani studies. Two doses of the live vaccine caused a significant reduction in L. major (p < 0.001) and L. donovani (p < 0.05) parasite burdens compared to their respective controls. In contrast, immunisation with wild type L. tarentolae, using the same immunisation protocol, had no effect on parasite burdens compared to infection controls. Joint treatment with IL-2-producing PODS® enhanced the protective effect of the live vaccine in L. donovani studies. Protection was associated with a Th1 response in L. major and a mixed Th1/Th2 response in L. donovani, based on specific IgG1 and IgG2a antibody and cytokine production from in vitro proliferation assays using antigen-stimulated splenocytes. The results of this study provide further proof that γGCS should be considered a candidate vaccine for leishmaniasis.

Leishmaniasis: Immune Cells Crosstalk in Macrophage Polarization

Leishmaniasis is a complex infectious parasitic disease caused by protozoa of the genus Leishmania, belonging to a group of neglected tropical diseases. It establishes significant global health challenges, particularly in socio-economically disadvantaged regions. Macrophages, as innate immune cells, play a crucial role in initiating the inflammatory response against the pathogens responsible for this disease. Macrophage polarization, the process of differentiating macrophages into pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes, is essential for the immune response in leishmaniasis. The M1 phenotype is associated with resistance to Leishmania infection, while the M2 phenotype is predominant in susceptible environments. Notably, various immune cells, including T cells, play a significant role in modulating macrophage polarization by releasing cytokines that influence macrophage maturation and function. Furthermore, other immune cells can also impact macrophage polarization in a T-cell-independent manner. Therefore, this review comprehensively examines macrophage polarization's role in leishmaniasis and other immune cells' potential involvement in this intricate process.

Role of Treg, Breg and other cytokine sets in host protection and immunopathology during human leishmaniasis: Are they potential valuable markers in clinical settings and vaccine evaluation?

Leishmaniasis is a vector-borne disease caused by obligate intracellular protozoan parasites that can infect humans and other mammals. Pro- and anti-inflammatory cytokines are important regulators of innate and specific responses in Leishmania infection. Resistance to leishmaniasis is related to T helper 1 (Th1) response with the production of pro-inflammatory cytokines: IL-12, IL-1β, IFN-γ, TNF-α, IL-2 leading to activation of macrophages and parasite killing. Instead, a more intense Th2 (IL-4, IL-5, IL-13), Treg (IL-10 and TGF-β) and Breg response (IL-10 and IL-35) are related to parasite persistence through the inhibition of macrophage activation, which promotes the escape from host immune system. Interestingly, a cytokine involved in the parasite killing in one form of leishmaniasis may be "pathogen friendly" in another form of the disease. To date, few studies are focusing on the role of Treg and Breg cytokines in human models of leishmaniasis; therefore, further investigations are needed to clarify their potential role in the diagnosis and prognosis of such protozoan infections, as well as in the development of vaccines against leishmaniasis. This review summarizes the current knowledge about the role of cytokines produced by Th1, Th2, Treg, and Breg cells involved in Leishmania disease progression and host protection. Some cytokines might play a role as diagnostic and prognostic clinical markers, or they could represent a novel approach leading to new anti-leishmaniasis therapies. Overall, advances in knowledge of the complex network of cytokines secreted by immune cells could help to better understand signaling pathways and host immune responses during Leishmania infection. This approach would allow these mediators to be used as therapeutic strategies against leishmaniasis.

Chemokine receptors on human regulatory T cells during cutaneous leishmaniasis

The aim of this work was to define the population of regulatory T cells (Tregs) which are circulating in the blood of Leishmania infected individuals clinically displaying a lesion (active disease-AD) and sub-clinical (SC) ones. We have individually collected blood samples, processed the PBMC and stained with fluorochrome-conjugated antibodies against CD3, CD4, Foxp3, CD25, CTLA-4, Ki-67, CCR4, CCR5, and CCR7. Cells were analyzed by flow cytometry. Our results suggest that CD25 and CTLA-4 are upregulated in Tregs of AD patients when compared to SC and uninfected (UN) controls. Moreover, Tregs proliferate upon infection based on Ki-67 nuclear antigen staining. Finally, we have observed that these Tregs of SC and AD patients upregulate CCR4, but not CCR5 and CCR7. There is an increase in the number of circulating Tregs in the blood of Leishmania infected individuals. These cells are potentially more suppressive based on the increased upregulation of CD25 and CTLA-4 during clinical infection (AD) when compared to SC infection. Tregs of both SC and AD cohorts are proliferating and express CCR4, which potentially guide them to the skin, but do not upregulate CCR5 and CCR7.

T Lymphocyte Exhaustion During Human and Experimental Visceral Leishmaniasis

A key point of immunity against protozoan Leishmania parasites is the development of an optimal T cell response, which includes a low apoptotic rate, high proliferative activity and polyfunctionality. During acute infection, antigen-specific T cells recognize the pathogen resulting in pathogen control but not elimination, promoting the development and the maintenance of a population of circulating effector cells that mount rapid response quickly after re-exposure to the parasite. However, in the case of visceral disease, the functionality of specific T cells is lost during chronic infection, resulting in inferior effector functions, poor response to specific restimulation, and suboptimal homeostatic proliferation, a term referred to as T cell exhaustion. Multiple factors, including parasite load, infection duration and host immunity, affect T lymphocyte exhaustion. These factors contribute to antigen persistence by promoting inhibitory receptor expression and sustained production of soluble mediators, influencing suppressive cell function and the release of endogenous molecules into chronically inflamed tissue. Together, these signals encourage several changes, reprogramming cells into a quiescent state, which reflects disease progression to more severe forms, and development of acquired resistance to conventional drugs to treat the disease. These points are discussed in this review.

Immunogenic properties of empty pcDNA3 plasmid against zoonotic cutaneous leishmaniasis in mice

Background

Leishmania (L) parasite, the causative agent of zoonotic cutaneous leishmaniasis (ZCL), effectively stimulates the mammalian cells to mount strong humoral responses by enhancing T-helper-2 (Th2)-associated cytokines for its survival. The best strategy to decrease the intensity of infection in the host is induction of cellular immunity.

Methods

We evaluated the effects of the empty bacterial pcDNA3 plasmid on mice infected with L. major and quantified the immune mediators including IFN-γ, IL-4, IL-10, IgG2a, IgG1, arginase activity and nitric oxide (NO) in the mice. Moreover, the footpad lesion size and parasite load were assessed.

Results

We observed that pcDNA3 could modulate the immune responses in favor of host cells and decrease the disease severity. Th2- associated mediators, including arginase, IL-4, and IL-10 are downregulated, while cellular responses are upregulated in line with an increase in the levels of nitric oxide (NO) and interfero-gamma (IFN-γ). Interestingly, pcDNA3 induced specific Th1-associated antibodies, IgG2a isotype; however, it suppressed the production of humoral IgG1. The stimulation of the immune response by the empty pcDNA3 is able to shift the immune function to predominant cellular responses caused by Th1, and it had a positive effect on the treatment of zoonotic cutaneous leishmaniasis (ZCL).

Conclusions

Altogether, we introduced the pcDNA3 as a potential interfering factor in the modulation of the immune system against ZCL. Since this vector has been widely used as a control group in different studies, we suggest that the potential function of the empty vector should be deeply assessed, as it exerts anti-parasitic effects on mice infected with L. major.

Nitric Oxide Induction in Peritoneal Macrophages by a 1,2,3-Triazole Derivative Improves Its Efficacy upon Leishmania amazonensis In Vitro Infection

1,2,3-Triazole is one of the most flexible chemical scaffolds broadly used in various fields. Here, we report the antileishmanial activity of 1,2,3-triazole derivatives, the ultrastructural alterations induced by their treatment, and the nitric oxide (NO) modulation effect on their efficacy against Leishmania amazonensis in vitro infection. After the screening of eleven compounds, compound 4 exhibited better results against L. amazonensis promastigotes (IC₅₀ = 15.52 ± 3.782 μM) and intracellular amastigotes (IC₅₀ = 4.10 ± 1.136 μM), 50% cytotoxicity concentration at 84.01 ± 3.064 μM against BALB/c peritoneal macrophages, and 20.49-fold selectivity for the parasite over the cells. Compound 4 induced ultrastructural mitochondrial alterations and lipid inclusions in L. amazonensis promastigotes, upregulated tumor necrosis factor α, interleukin (IL)-1β, IL-6, IL-12, and IL-10 messenger RNA expressions, and enhanced the NO production, verified by nitrite (p = 0.0095) and inducible nitric oxide synthase expression (p = 0.0049) quantification, which played an important role in its activity against intramacrophagic L. amazonensis. In silico prediction in association with antileishmanial activity results showed compound 4 as a hit compound with promising potential for further studies of new leishmaniasis treatment options.

A mushroom derived 'carbohydrate-fraction' reinstates host-immunity and protects from Leishmania donovani infection

The anti-leishmanial effect of the 'carbohydrate-fraction', isolated from an edible mushroom Astraeus hygrometricus, was evaluated against Leishmania donovani infection both in vitro and in vivo. Ah_f-Car induced the expression of inducible nitric oxide synthase 2 (iNOS2) and pro-inflammatory cytokines like TNF-α and IL-12, with subsequent downregulation of the anti-inflammatory cytokines as TGF-β and IL-10, in vitro and in vivo along with a remarkable increase in the expressions of IL-6, IL-1β, IFN-γ and IRFs, IRF-7 and IRF-8 in vivo. Ah_f-Car also reduced the parasite burden in the spleen and liver dose-dependently with a simultaneous proliferation of Ly6C⁺ cells in the bone marrow of Leishmania-infected experimental animals. It also increased the monocyte population dose-dependently and the expression of the myeloid transcription factor PU.1, in vivo, which presumably signifies the expansion of protective macrophages. Thus, Ah_f-Car might be a potent anti-leishmanial lead with unique and effective adjuvant capacity.