Pathways leading to interleukin-12 production and protective immunity in cutaneous leishmaniasis

Immunohistochemical Characterization of M1, M2, and M4 Macrophages in Leprosy Skin Lesions

Mycobacterium leprae is the etiological agent of leprosy. Macrophages (Mφs) are key players involved in the pathogenesis of leprosy. In this study, immunohistochemical analysis was performed to examine the phenotype of Mφ subpopulations, namely M1, M2, and M4, in the skin lesions of patients diagnosed with leprosy. Based on the database of treatment-naïve patients treated between 2015 and 2019 at the Department of Dermatology of the University of the State of Pará, Belém, routine clinical screening samples were identified. The monolabeling protocol was used for M1 macrophages (iNOS, IL-6, TNF-α) and M2 macrophages (IL-10, IL-13, CD163, Arginase 1, TGF-β, FGFb), and the double-labeling protocol was used for M4 macrophages (IL-6, MMP7, MRP8, TNF-α e CD68). To confirm the M4 macrophage lineage, double labeling of the monoclonal antibodies CD68 and MRP8 was also performed. Our results demonstrated a statistically significant difference for the M1 phenotype among the Virchowian (VV) (4.5 ± 1.3, p < 0.0001), Borderline (1.6 ± 0.4, p < 0.0001), and tuberculoid (TT) (12.5 ± 1.8, p < 0.0001) clinical forms of leprosy. Additionally, the M2 phenotype showed a statistically significant difference among the VV (12.5 ± 2.3, p < 0.0001), Borderline (1.3 ± 0.2, p < 0.0001), and TT (3.2 ± 0.7, p < 0.0001) forms. For the M4 phenotype, a statistically significant difference was observed in the VV (9.8 ± 1.7, p < 0.0001), Borderline (1.2 ± 0.2, p < 0.0001), and TT (2.6 ± 0.7, p < 0.0001) forms. A significant correlation was observed between the VV M1 and M4 (r = 0.8712; p = 0.0000) and between the VV M2 × TT M1 (r = 0.834; p = 0.0002) phenotypes. The M1 Mφs constituted the predominant Mφ subpopulation in the TT and Borderline forms of leprosy, whereas the M2 Mφs showed increased immunoexpression and M4 was the predominant Mφ phenotype in VV leprosy. These results confirm the relationship of the Mφ profile with chronic pathological processes of the inflammatory response in leprosy.

Effects of Low-Level Persistent Infection on Maintenance of Immunity by CD4 T Cell Subsets and Th1 Cytokines

CD4 T cells are required, along with antibodies, for complete protection from blood-stage infection with Plasmodium spp., which cause malaria. Without continuous exposure, as on emigration of people from endemic areas, protection from malaria decays. As in other persistent infections, low-level Plasmodium chabaudi infection protects the host from reinfection at 2 months postinfection, a phenomenon termed premunition. Premunition is correlated with T cell responses, rather than antibody levels. We previously showed that while both effector T cells (Teff) and memory T cells (Tmem) are present after infection, Teff protect better than Tmem. Here, we studied T cell kinetics post-infection by labeling dividing Ifng⁺ T cells with 5-bromo-2'-deoxyuridine (BrdU) in infected Ifng reporter mice. Large drops in specific T cell numbers and Ifng⁺ cells upon clearance of parasites suggest a mechanism for decay of protection. Although protection decays, CD4 Tmem persist, including a highly differentiated CD27^- effector memory (Tem) subset that maintains some Ifng expression. In addition, pretreatment of chronically infected animals with neutralizing antibody to interferon gamma (IFN-γ) or with clodronate liposomes before reinfection decreases premunition, supporting a role for Th1-type immunity to reinfection. A pulse-chase experiment comparing chronically infected to treated animals showed that recently divided Ifng⁺ T cells, particularly IFN-γ⁺ TNF⁺ IL-2^- T cells, are promoted by persistent infection. These data suggest that low-level persistent infection reduces CD4⁺ Tmem and multifunctional Teff survival, but promotes IFN-γ⁺ TNF⁺ IL-2^- T cells and Ifng⁺ terminally differentiated effector T cells, and prolongs immunity.

Use of N-acetylcysteine as treatment adjuvant regulates immune response in visceral leishmaniasis: Pilot clinical trial and in vitro experiments

This investigation aimed to assess the effect of N-acetylcysteine (NAC) as an adjuvant treatment to alleviate visceral leishmaniasis (VL). The present work includes both blinded randomized clinical intervention and experimental in vitro studies. The clinical trial included 60 patients with VL randomly allocated into two groups: a test group (n = 30) treated with meglumine antimoniate plus NAC (SbV + NAC) and a control group (n = 30) treated with meglumine antimoniate only (SbV). The primary outcome was clinical cure (absence of fever, spleen and liver sizes reduction, and hematological improvement) in 180 days. The cure rate did not differ between the groups; both groups had similar results in all readout indices. The immunological parameters of the patients treated with SbV + NAC showed higher sCD40L in sera during treatment, and the levels of sCD40L were negatively correlated with Interleukin-10 (IL-10) serum levels. In addition, data estimation showed a negative correlation between the sCD40L levels and the spleen size in patients with VL. For the in vitro experiments, peripheral blood mononuclear cells (PBMCs) or PBMC-derived macrophages from healthy donors were exposed to soluble Leishmania antigen (SLA) or infected with stationary promastigotes of Leishmania infantum in the presence or absence of NAC. Results revealed that NAC treatment of SLA-stimulated PBMCs reduces the frequency of monocytes producing IL-10 and lowers the frequency of CD4+ and CD8+ T cells expressing (pro-)inflammatory cytokines. Together, these results suggest that NAC treatment may modulate the immune response in patients with VL, thus warranting additional investigations to support its case use as an adjuvant to antimony therapy for VL.

Exploring the paradox of defense between host and Leishmania parasite

Leishmaniasis, a neglected tropical disease, still remains a global concern for the healthcare sector. The primary causative agents of the disease comprise diverse leishmanial species, leading to recurring failures in disease diagnosis and delaying the initiation of appropriate chemotherapy. Various species of the Leishmania parasite cause diverse clinical manifestations ranging from skin ulcers to systemic infections. Therefore, host immunity in response to different forms of infecting species of Leishmania becomes pivotal in disease progression or regression. Thus, understanding the paradox of immune arsenals during host and parasite interface becomes crucial to eliminate this deadly disease. In the present review, we have elaborated on the immunological perspectives of the disease and discussed primary host immune cells that form a defense line to counteract parasite infection. Furthermore, we also have shed light on the immune cells and effector molecules responsible for parasite survival in host lethal milieu/ environment. Next, we have highlighted recent molecules/compounds showing potent leishmanicidal activities pertaining to their pro-oxidant and immuno-modulatory mechanisms. This review addresses an immuno-biological overview of the factors influencing the parasitic disease, as this knowledge can aid in the unraveling/ identification of potential biomarkers, novel therapeutics, and vaccine candidates against leishmaniasis.

Mechanisms of Immunopathogenesis in Cutaneous Leishmaniasis And Post Kala-azar Dermal Leishmaniasis (PKDL)

Leishmaniasis is a neglected tropical disease that affects 12 million people worldwide. The disease has high morbidity and mortality rates and is prevalent in over 80 countries, leaving more than 300 million people at risk of infection. Of all of the manifestations of this disease, cutaneous leishmaniasis (CL) is the most common form and it presents as ulcerating skin lesions that can self-heal or become chronic, leading to disfiguring scars. This review focuses on the different pathologies and disease manifestations of CL, as well as their varying degrees of severity. In particular, this review will discuss self-healing localized cutaneous leishmaniasis (LCL), leishmaniasis recidivans (LR), mucocutaneous leishmaniasis (MCL), anergic diffuse cutaneous leishmaniasis (ADCL), disseminated leishmaniasis (DL), and Post Kala-azar Dermal Leishmaniasis (PKDL), which is a cutaneous manifestation observed in some visceral leishmaniasis (VL) patients after successful treatment. The different clinical manifestations of CL are determined by a variety of factors including the species of the parasites and the host's immune response. Specifically, the balance between the pro and anti-inflammatory mediators plays a vital role in the clinical presentation and outcome of the disease. Depending upon the immune response, Leishmania infection can also transition from one form of the disease to another. In this review, different forms of cutaneous Leishmania infections and their immunology are described.

Melittin as a promising anti-protozoan peptide: current knowledge and future prospects

Protozoan diseases such as malaria, leishmaniasis, Chagas disease, and sleeping sickness still levy a heavy toll on human lives. Deplorably, only few classes of anti-protozoan drugs have thus far been developed. The problem is further compounded by their intrinsic toxicity, emergence of drug resistance, and the lack of licensed vaccines. Thus, there is a genuine exigency to develop novel anti-protozoan medications. Over the past years, melittin, the major constituent in the venom of European honeybee Apis mellifera, has gathered the attention of researchers due to its potential therapeutic applications. Insofar as we are aware, there has been no review pertinent to anti-protozoan properties of melittin. The present review outlines the current knowledge about anti-protozoan effects of melittin and its underlying mechanisms. The peptide has proven to be efficacious in killing different protozoan parasites such as Leishmania, Plasmodium, Toxoplasma, and Trypanosoma in vitro. Apart from direct membrane-disruptive activity, melittin is capable of destabilizing calcium homeostasis, reducing mitochondrial membrane potential, disorganizing kinetoplast DNA, instigating apoptotic cell death, and induction of autophagy in protozoan pathogens. Emerging evidence suggests that melittin is a promising candidate for future vaccine adjuvants. Transmission-blocking activity of melittin against vector-borne pathogens underscores its potential utility for both transgenic and paratransgenic manipulations. Nevertheless, future research should focus upon investigating anti-microbial activities of melittin, alone or in combination with the current anti-protozoan medications, against a far broader spectrum of protozoan parasites as well as pre-clinical testing of the peptide in animal models.

Potential biomarkers of immune protection in human leishmaniasis

Leishmaniasis is a vector-borne neglected tropical disease endemic in over 100 countries around the world. Available control measures are not always successful, therapeutic options are limited, and there is no vaccine available against human leishmaniasis, although several candidate antigens have been evaluated over the last decades. Plenty of studies have aimed to evaluate the immune response development and a diverse range of host immune factors have been described to be associated with protection or disease progression in leishmaniasis; however, to date, no comprehensive biomarker(s) have been identified as surrogate marker of protection or exacerbation, and lack of enough information remains a barrier for vaccine development. Most of the current understanding of the role of different markers of immune response in leishmaniasis has been collected from experimental animal models. Although the data generated from the animal models are crucial, it might not always be extrapolated to humans. Here, we briefly review the events during Leishmania invasion of host cells and the immune responses induced against Leishmania in animal models and humans and their potential role as a biomarker of protection against human leishmaniasis.

Unraveling the Role of Immune Checkpoints in Leishmaniasis

Leishmaniasis are Neglected Tropical Diseases affecting millions of people every year in at least 98 countries and is one of the major unsolved world health issues. Leishmania is a parasitic protozoa which are transmitted by infected sandflies and in the host they mainly infect macrophages. Immunity elicited against those parasites is complex and immune checkpoints play a key role regulating its function. T cell receptors and their respective ligands, such as PD-1, CTLA-4, CD200, CD40, OX40, HVEM, LIGHT, 2B4 and TIM-3 have been characterized for their role in regulating adaptive immunity against different pathogens. However, the exact role those receptors perform during Leishmania infections remains to be better determined. This article addresses the key role immune checkpoints play during Leishmania infections, the limiting factors and translational implications.

The importance of T cell-derived cytokines in post-kala-azar dermal leishmaniasis

Infection with the same species of Leishmania (L)donovani causes different manifestations including visceral leishmaniasis (VL) and post kala-azar dermal leishmaniasis (PKDL), indicating that the host-related immunological parameters perform a decisive role in the pathogenesis of diseases. As PKDL is a reservoir of the parasite, a better understanding of the host immune responses is necessary to restrict the L. donovani transmission. The proper local production of Th1 cell-related cytokines (including IFN-γ, TNF-α and IL-12), Th17 cell-derived cytokines (such as IL-17A, IL-17F and IL-22), and CD8⁺ cytotoxic T lymphocyte (CTL)-derived IFN-γ are protective against PKDL. However, dominant production of regulatory CD4⁺ T cell-derived cytokines (such as IL-10 and TGF-β), Th2 cell-derived cytokines (such as IL-4/IL-13), M2 macrophage-derived cytokines (such as IL-4 and IL-10), keratinocyte-derived IL-10, regulatory CD8⁺ T cell-derived IL-10, and dendritic cell-derived IL-10, IL-27 and IL-21 can contribute to the parasite persistence and PKDL development. Understanding of the T cell-related cytokine network within PKDL lesions gives rise to novel insights concerning the role of each cytokine in the protection or susceptibility to disease. Manipulation of the cytokine network can be considered as an interesting immunotherapeutic strategy for the treatment of L. donovani-mediated PKDL.

Case Report: Hyper IgM Syndrome Identified by Whole Genome Sequencing in a Young Syrian Man Presenting With Atypical, Severe and Recurrent Mucosal Leishmaniasis

A previously healthy 19-year-old Syrian man presented with atypical and severe mucosal leishmaniasis caused by Leishmania tropica. During a 2-year period, he had three severe relapses despite various treatment strategies, including liposomal amphotericin B and Miltefosine. Because of the unusual clinical presentation, potential underlying immunodeficiency was investigated. Normal T and NK cell counts were found. The B cell count was slightly elevated at 0.7 × 109 cells/L (0.09 × 109 to 0.57 × 109 cells/L), but the proportions of memory and isotype switched memory B cells were severely diminished IgG levels were low, at 309 mg/dL (610-1490 mg/dL). The initial IgM and IgA levels were within normal range, but the IgA levels decreased to 57 mg/dL (70-430 mg/dL) during follow up. Common variable immunodeficiency (CVID) was initially suspected, because the immunological results of low IgG and IgA, low switched memory B cells, no profound T cell deficiency found and absence of secondary cause of hypogammaglobulinemia were compatible with this diagnosis (ESID 2019). However, the highly unusual and severe clinical presentation of L. tropica is not suggestive of B-cell deficiency or CVID. Eventually a pathogenic nonsense variant in the CD40 ligand gene [p.(Arg11∗)] was identified by whole genome sequencing, thus enabling the diagnosis of X-linked hyper IgM syndrome. This case illustrates and supports the potential for the use of whole genome sequencing in accurate diagnosis of primary immunodeficiencies.

β2 Integrins-Multi-Functional Leukocyte Receptors in Health and Disease

β2 integrins are heterodimeric surface receptors composed of a variable α (CD11a-CD11d) and a constant β (CD18) subunit and are specifically expressed by leukocytes. The α subunit defines the individual functional properties of the corresponding β2 integrin, but all β2 integrins show functional overlap. They mediate adhesion to other cells and to components of the extracellular matrix (ECM), orchestrate uptake of extracellular material like complement-opsonized pathogens, control cytoskeletal organization, and modulate cell signaling. This review aims to delineate the tremendous role of β2 integrins for immune functions as exemplified by the phenotype of LAD-I (leukocyte adhesion deficiency 1) patients that suffer from strong recurrent infections. These immune defects have been largely attributed to impaired migratory and phagocytic properties of polymorphonuclear granulocytes. The molecular base for this inherited disease is a functional impairment of β2 integrins due to mutations within the CD18 gene. LAD-I patients are also predisposed for autoimmune diseases. In agreement, polymorphisms within the CD11b gene have been associated with autoimmunity. Consequently, β2 integrins have received growing interest as targets in the treatment of autoimmune diseases. Moreover, β2 integrin activity on leukocytes has been implicated in tumor development.

miR-21 Expression Determines the Early Vaccine Immunity Induced by LdCen -/- Immunization

No vaccine exists against visceral leishmaniasis. Toward developing vaccines against VL, we have reported previously on the immunogenicity of live attenuated LdCen ^-/- parasites in animal models. Immunization with LdCen ^-/- parasites has been shown to induce durable protective immunity in pre-clinical animal models. Although the innate immune responses favoring a Th1 type immunity are produced following LdCen ^-/- immunization, the molecular determinants of such responses remain unknown. To identify early biomarkers of immunogenicity associated with live attenuated parasitic vaccines, we infected macrophages derived from healthy human blood donors with LdCen ^-/- or LdWT parasites ex vivo and compared the early gene expression profiles. In addition to altered expression of immune related genes, we identified several microRNAs that regulate important cytokine genes, significantly altered in LdCen ^-/- infection compared to LdWT infection. Importantly, we found that LdCen ^-/- infection suppresses the expression of microRNA-21 (miR-21) in human macrophages, which negatively regulates IL12, compared to LdWT infection. In murine DC experiments, LdCen ^-/- infection showed a reduced miR-21 expression with a concomitant induction of IL12. Silencing of miR-21 using specific inhibitors resulted in an augmented induction of IL12 in LdWT infected BMDCs, illustrating the role of miR-21 in LdWT mediated suppression of IL12. Further, exosomes isolated from LdCen ^-/- infected DCs contained significantly reduced levels of miR-21 compared to LdWT infection, that promoted proliferation of CD4⁺ T cells in vitro. Similar miR-21 mediated IL12 regulation was also observed in ex vivo human macrophage infection experiments indicating that miR-21 plays a role in early IL12 mediated immunity. Our studies demonstrate that LdCen ^-/- infection suppresses miR-21 expression, enables IL12 mediated induction of adaptive immunity including proliferation of antigen experienced CD4⁺ T cells and development of a Th1 immunity, and suggest that miR-21 could be an important biomarker for LdCen ^-/- vaccine immunity in human clinical trials.

One Sentence Summary

Role of miR-21 in vaccine induced immunity.