Distinct Macrophage Fates after in vitro Infection with Different Species of Leishmania: Induction of Apoptosis by Leishmania (Leishmania) amazonensis, but Not by Leishmania (Viannia) guyanensis

Haks M, Persson J, Mashayekhi Goyonlo V, Hadifar S, Erfanian Salim R, Mhaidi I, Riyad M, Akarid K, M. Harandi A, HM Ottenhoff T, Lemrani M, Rafati S. Comparative gene expression pattern of immune-related genes using dual-color RT-MLPA in the lesions of cutaneous leishmaniasis caused by L. major and L. tropica

Cutaneous leishmaniasis (CL) is the most prevalent type of leishmaniasis disease and causes skin lesions, mainly ulcers, on exposed parts of the body. The Americas, Mediterranean basin, Middle East, and Central Asia account for approximately 95% of all CL cases. Leishmania (L.) major and L. tropica are the most significant species causing CL. A better understanding of the molecular mechanisms of CL caused by Leishmania parasite species in patients' skin lesions may help inform intervention approaches. Using dual-color reverse transcriptase multiplex ligation-dependent probe amplification (dcRT-MLPA), we evaluated the expression of 144 host immune-related genes in lesions from CL patients infected with two Leishmania species, L. major and L. tropica, in Morocco and Iran, respectively. Distinct gene expression patterns were identified in the lesions of patients infected with L. major and L. tropica. The results revealed that L. tropica-infected patients had rather more significant gene expression than L. major-infected patients relative to healthy volunteers. However, CD14 and IFI6 (interferon alpha inducible protein 6), were two common genes expressed in the lesions of patients infected with L. major and L. tropica. Our analysis revealed that gene expression changes related to the IFN signaling pathway were significant in both lesion groups. This research advances our understanding of the host immune response to zoonotic and anthroponotic leishmaniasis and shows immune transcript signatures in the skin lesions of CL patients infected with L. major and L. tropica. These findings can inform further investigation into the processes underpinning immunity and immunopathology of CL caused by L. major and L. tropica.

Dog complement system is less effective against Leishmania infantum than human complement

Dogs are important reservoir hosts for Leishmania infantum, the causative agent of visceral leishmaniasis. The complement system, as part of the innate immune defense, is responsible for initiating the fight against pathogens that may invade an organism. A failure of the complement to combat L. infantum may explain, at least in part, why a mammal species is more or less susceptible to visceral leishmaniasis. The objective of this study was to compare the effectiveness of human and dog complement systems against L. infantum parasites. The results showed that dog serum was less effective than human serum at killing promastigote and amastigote-like forms. We also compared the efficiency of human and canine sera in classic and alternative hemolytic assays, as well as the serum efficiency of non-infected and Leishmania-infected dogs. Serum from dogs was less hemolytic than human serum in both pathways tested, but the efficiency of serum from infected dogs was higher than that of non-infected dogs. When testing C3b deposition assays on parasite surfaces, serum from infected dogs was more effective against amastigote-like forms than serum from non-infected dogs. However, both types of serum proved equally effective on promastigotes, while serum from infected dogs was more effective on amastigote-like forms. Considering the efficiency of the complement system, our results indicate that dogs are more susceptible to visceral leishmaniasis than humans are.

Mechanisms regulating host cell death during Leishmania infection

Parasites from the Leishmania genus are the causative agents of leishmaniasis and primarily reside within macrophages during mammalian infection. Their ability to establish intracellular infection provides a secure niche for proliferation while evading detection. However, successful multiplication within mammalian cells requires the orchestration of multiple mechanisms that control host cell viability. In contrast, innate immune cells, such as macrophages, can undergo different forms of cell death in response to pathogenic intracellular microbes. Thus, modulation of these different forms of host cell death is crucial for Leishmaniasis development. The regulation of host cell apoptosis, a form of programmed cell death, is crucial for sustaining parasites within viable host cells. Accordingly, several studies have demonstrated evasion of apoptosis induced by dermotropic and viscerotropic Leishmania species. Conversely, the prevention of pyroptosis, an inflammatory form of cell death, ensures the establishment of infection by silencing the release of mediators that could trigger massive proinflammatory responses. This manuscript explores how Leishmania regulates various host cell death pathways and overviews seminal studies on regulating host cell apoptosis by different Leishmania species.

Leishmania major drives host phagocyte death and cell-to-cell transfer depending on intracellular pathogen proliferation rate

The virulence of intracellular pathogens relies largely on the ability to survive and replicate within phagocytes but also on release and transfer into new host cells. Such cell-to-cell transfer could represent a target for counteracting microbial pathogenesis. However, our understanding of the underlying cellular and molecular processes remains woefully insufficient. Using intravital 2-photon microscopy of caspase-3 activation in the Leishmania major-infected (L. major-infected) live skin, we showed increased apoptosis in cells infected by the parasite. Also, transfer of the parasite to new host cells occurred directly without a detectable extracellular state and was associated with concomitant uptake of cellular material from the original host cell. These in vivo findings were fully recapitulated in infections of isolated human phagocytes. Furthermore, we observed that high pathogen proliferation increased cell death in infected cells, and long-term residency within an infected host cell was only possible for slowly proliferating parasites. Our results therefore suggest that L. major drives its own dissemination to new phagocytes by inducing host cell death in a proliferation-dependent manner.

A Mouse Model of Ulcerative Cutaneous Leishmaniasis by Leishmania (Viannia) panamensis to Investigate Infection, Pathogenesis, Immunity, and Therapeutics

A mouse model of cutaneous leishmaniasis (CL) by Leishmania (Viannia) panamensis (L(V)p) that reproduces the characteristics of the human disease remains elusive. Here we report the development of a CL model that uses a mouse-adapted L(V)p isolate to reproducibly induce a dermal disease with a remarkable similarity to human CL. BALB/c mice infected intradermally in the ear with 105 stationary UA-946 L(V)p promastigotes develop a progressive cutaneous disease that exhibits the typical ulcerated lesions with indurated borders observed in CL patients. Although most of parasites in the inoculum die within the first week of infection, the survivors vigorously multiply at the infection site during the following weeks, paralleling disease appearance and aggravation. Regional lymphadenopathy as well as lymphatic dissemination of parasites to draining lymph nodes (dLN) was evidenced early after infection. Viable parasites were also isolated from spleen at later timepoints indicating systemic parasitic dissemination, but, strikingly, no signs of systemic disease were observed. Increasing numbers of myeloid cells and T lymphocytes producing IFNγ and IL-4 were observed in the dLN as disease progressed. A mixed adaptive L(V)p-specific T cell-mediated response was induced, since ex vivo recall experiments using dLN cells and splenocytes revealed the production of type 1 (IFNγ, IL-2), type 2 (IL-4, IL-13), regulatory (IL-10), and inflammatory (GM-CSF, IL-3) cytokines. Humoral adaptive response was characterized by early production of IgG1- followed by IgG2a-type of L(V)p-specific antibodies. IFNγ/IL-4 and IgG2a/IgG1 ratios indicated that the initial non-protective Th2 response was redirected toward a protective Th1 response. In situ studies revealed a profuse recruitment of myeloid cells and of IFNγ- and IL-4-producing T lymphocytes to the site of infection, and the typical histopathological changes induced by dermotropic Leishmania species. Evidence that this model is suitable to investigate pharmacological and immunomodulatory interventions, as well as for antigen discovery and vaccine development, is also presented. Altogether, these results support the validity and utility of this novel mouse model to study the pathogenesis, immunity, and therapeutics of L(V)p infections.

Delineating infection strategies of Leishmania donovani secretory proteins in Human through host-pathogen protein Interactome prediction

Interactions of Leishmania donovani secretory virulence factors with the host proteins and their interplay during the infection process in humans is poorly studied in Visceral Leishmaniasis. Lack of a holistic study of pathway level de-regulations caused due to these virulence factors leads to a poor understanding of the parasite strategies to subvert the host immune responses, secure its survival inside the host and further the spread of infection to the visceral organs. In this study, we propose a computational workflow to predict host-pathogen protein interactome of L.donovani secretory virulence factors with human proteins combining sequence-based Interolog mapping and structure-based Domain Interaction mapping techniques. We further employ graph theoretical approaches and shortest path methods to analyze the interactome. Our study deciphers the infection paths involving some unique and understudied disease-associated signaling pathways influencing the cellular phenotypic responses in the host. Our statistical analysis based in silico knockout study unveils for the first time UBC, 1433Z and HS90A mediator proteins as potential immunomodulatory candidates through which the virulence factors employ the infection paths. These identified pathways and novel mediator proteins can be effectively used as possible targets to control and modulate the infection process further aiding in the treatment of Visceral Leishmaniasis.

Galectin-3 plays a protective role in Leishmania (Leishmania) amazonensis infection

Leishmania (L.) amazonensis is one of the species responsible for the development of cutaneous leishmaniasis in South America. After entering the vertebrate host, L. (L.) amazonensis invades mainly neutrophils, macrophages, and dendritic cells. Studies have shown that gal-3 acts as a pattern recognition receptor. However, the role of this protein in the context of L. (L.) amazonensis infection remains unclear. Here, we investigated the impact of gal-3 expression on experimental infection by L. (L.) amazonensis. Our data showed that gal-3 plays a role in controlling parasite invasion, replication and the formation of endocytic vesicles. Moreover, mice with gal-3 deficiency showed an exacerbated inflammatory response. Taken together, our data shed light to a critical role of gal-3 in the host response to infection by L. (L.) amazonensis.

Molecular signatures of anthroponotic cutaneous leishmaniasis in the lesions of patients infected with Leishmania tropica

Anthroponotic cutaneous leishmaniasis (CL) caused by Leishmania tropica (L. tropica) represents a public health challenge in several resource poor settings. We herein employed a systems analysis approach to study molecular signatures of CL caused by L. tropica in the skin lesions of ulcerative CL (UCL) and non-ulcerative CL (NUCL) patients. Results from RNA-seq analysis determined shared and unique functional transcriptional pathways in the lesions of the UCL and NUCL patients. Several transcriptional pathways involved in inflammatory response were positively enriched in the CL lesions. A multiplexed inflammatory protein analysis showed differential profiles of inflammatory cytokines and chemokines in the UCL and NUCL lesions. Transcriptional pathways for Fcγ receptor dependent phagocytosis were among shared enriched pathways. Using L. tropica specific antibody (Ab)-mediated phagocytosis assays, we could substantiate Ab-dependent cellular phagocytosis (ADCP) and Ab-dependent neutrophil phagocytosis (ADNP) activities in the lesions of the UCL and NUCL patients, which correlated with L. tropica specific IgG Abs. Interestingly, a negative correlation was observed between parasite load and L. tropica specific IgG/ADCP/ADNP in the skin lesions of CL patients. These results enhance our understanding of human skin response to CL caused by L. tropica.

Leishmania aethiopica cell-to-cell spreading involves caspase-3, AkT, and NF-κB but not PKC-δ activation and involves uptake of LAMP-1-positive bodies containing parasites

Development of human leishmaniasis is dependent on the ability of intracellular Leishmania parasites to spread and enter macrophages. The mechanism through which free promastigotes and amastigotes bind and enter host macrophages has been previously investigated; however, little is known about intracellular trafficking and cell-to-cell spreading. In this study, the mechanism involved in the spreading of Leishmania aethiopica and Leishmania mexicana was investigated. A significant increase in phosphatidylserine (PS) exhibition, cytochrome C release, and active caspase-3 expression was detected (P < 0.05) during L. aethiopica, but not L. mexicana spreading. A decrease (P < 0.05) of protein kinase B (Akt) protein and BCL2-associated agonist of cell death (BAD) phosphorylation was also observed. The nuclear factor kappa-light-chain enhancer of activated B cells (NF-kB) signaling pathway and pro-apoptotic protein protein kinase C delta (PKC-δ) were downregulated while inhibition of caspase-3 activation prevented L. aethiopica spreading. Overall suggesting that L. aethiopica induces host cell's apoptosis during spreading in a caspase-3-dependent manner. The trafficking of amastigotes within macrophages following cell-to-cell spreading differed from that of axenic parasites and involved co-localization with lysosomal-associated membrane protein 1 (LAMP-1) within 10 min postinfection. Interestingly, following infection with axenic amastigotes and promastigotes, co-localization of parasites with LAMP-1-positive structures took place at 1 and 4 h, respectively, suggesting that the membrane coat and LAMP-1 protein were derived from the donor cell. Collectively, these findings indicate that host cell apoptosis, demonstrated by PS exhibition, caspase-3 activation, cytochrome C release, downregulation of Akt, BAD phosphorylation, NF-kB activation, and independent of PKC-δ expression, is involved in L. aethiopica spreading. Moreover, L. aethiopica parasites associate with LAMP-rich structures when taken up by neighboring macrophages.

Leishmania (Viannia) guyanensis in tegumentary leishmaniasis

Leishmania (Viannia) guyanensis is a causal agent of American tegumentary leishmaniasis (ATL). This protozoan has been poorly investigated; however, it can cause different clinical forms of ATL, ranging from a single cutaneous lesion to severe lesions that can lead to destruction of the nasopharyngeal mucosa. L. (V.) guyanensis and the disease caused by this species can present unique aspects revealing the need to better characterize this parasite species to improve our knowledge of the immunopathological mechanisms and treatment options for ATL. The mechanisms by which some patients develop a more severe form of ATL remain unclear. It is known that the host immune profile and parasite factors may influence the clinical manifestations of the disease. Besides intrinsic parasite factors, Leishmaniavirus RNA 1 (LRV1) infecting L. guyanensis can contribute to ATL immunopathogenesis. In this review, general aspects of L. guyanensis infection in humans and mouse models are presented.

Resistance to apoptosis in Leishmania infantum-infected human macrophages: a critical role for anti-apoptotic Bcl-2 protein and cellular IAP1/2

Apoptosis is essential for maintaining tissue homoeostasis in multi-cellular organisms, also occurring as a defence mechanism against a number of infectious agents, such as parasites. Among intracellular protozoan parasites reported to interfere with the apoptotic machinery of the host cell, Leishmania (L.) sp. have been described, although the various species might activate different pathways in their host cells. Since until now it is not yet well clarified the signalling pathway involved in the apoptosis modulation by L. infantum, the aim of this work was to investigate the role of the anti-apoptotic protein, Bcl-2, and the inhibitors of apoptosis IAP1/2 (cIAP1/2) in cell death resistance showed in L. infantum-infected human macrophages. We observed that actinomycin D-induced apoptosis in U-937 cells, evaluated by Annexin V-CY3, DNA fragmentation and caspase-3, caspase-8, caspase-9 activation assays, was inhibited in the presence of L. infantum promastigotes and that, in these conditions, Bcl-2 protein expression resulted significantly upregulated. Interestingly, L. infantum infection in combination with the Bcl-2 inhibitor, ABT-737, significantly increased the apoptotic process in actinomycin D-treated cells, suggesting a role for Bcl-2 in the anti-apoptotic regulation of human macrophages induced by L. infantum infection. Moreover, Western blotting analysis demonstrated not only a significantly upregulation of cIAP1/2 in infected U-937 cells, but also that the inhibition of cIAPs, employing specific siRNAs, restored the apoptotic effect of actinomycin in infected macrophages. These results clearly support the hypothesis that Bcl-2 and cIAPs are strongly involved in the anti-apoptotic action played by L. infantum in human macrophages.

NOX2-Derived Reactive Oxygen Species Control Inflammation during Leishmania amazonensis Infection by Mediating Infection-Induced Neutrophil Apoptosis

Reactive oxygen species (ROS) produced by NADPH phagocyte oxidase isoform (NOX2) are critical for the elimination of intracellular pathogens in many infections. Despite their importance, the role of ROS following infection with the eukaryotic pathogen Leishmania has not been fully elucidated. We addressed the role of ROS in C57BL/6 mice following intradermal infection with Leishmania amazonensis. Despite equivalent parasite loads compared with wild-type (WT) mice, mice deficient in ROS production by NOX2 due to the absence of the gp91 subunit (gp91^phox-/-) had significantly more severe pathology in the later stages of infection. Pathology in gp91^phox-/- mice was not associated with alterations in CD4⁺ T cell-mediated immunity but was preceded by enhanced neutrophil accumulation at the dermal infection site. Ex vivo analysis of infected versus uninfected neutrophils revealed a deficiency in infection-driven apoptosis in gp91^phox-/- mice versus WT mice. gp91^phox-/- mice presented with higher percentages of healthy or necrotic neutrophils but lower percentages of apoptotic neutrophils at early and chronic time points. In vitro infection of gp91^phox-/- versus WT neutrophils also revealed reduced apoptosis and CD95 expression but increased necrosis in infected cells at 10 h postinfection. Provision of exogenous ROS in the form of H₂O₂ reversed the necrotic phenotype and restored CD95 expression on infected gp91^phox-/- neutrophils. Although ROS production is typically viewed as a proinflammatory event, our observations identify the importance of ROS in mediating appropriate neutrophil apoptosis and the importance of apoptosis in inflammation and pathology during chronic infection.

Apoptotic induction induces Leishmania aethiopica and L. mexicana spreading in terminally differentiated THP-1 cells

Leishmaniasis develops after parasites establish themselves as amastigotes inside mammalian cells and start replicating. As relatively few parasites survive the innate immune defence, intracellular amastigotes spreading towards uninfected cells is instrumental to disease progression. Nevertheless the mechanism of Leishmania dissemination remains unclear, mostly due to the lack of a reliable model of infection spreading. Here, an in vitro model representing the dissemination of Leishmania amastigotes between human macrophages has been developed. Differentiated THP-1 macrophages were infected with GFP expressing Leishmania aethiopica and Leishmania mexicana. The percentage of infected cells was enriched via camptothecin treatment to achieve 64·1 ± 3% (L. aethiopica) and 92 ± 1·2% (L. mexicana) at 72 h, compared to 35 ± 4·2% (L. aethiopica) and 36·2 ± 2·4% (L. mexicana) in untreated population. Infected cells were co-cultured with a newly differentiated population of THP-1 macrophages. Spreading was detected after 12 h of co-culture. Live cell imaging showed inter-cellular extrusion of L. aethiopica and L. mexicana to recipient cells took place independently of host cell lysis. Establishment of secondary infection from Leishmania infected cells provided an insight into the cellular phenomena of parasite movement between human macrophages. Moreover, it supports further investigation into the molecular mechanisms of parasites spreading, which forms the basis of disease development.

Macrophage cell death in microbial infections

Macrophages can respond to microbial infections with programmed cell death. The major cell death pathways of apoptosis, pyroptosis and necroptosis are tightly regulated to ensure adequate immune reactions to virulent and persistent invaders. Macrophage death eliminates the replicative niche of intracellular pathogens and induces immune attack. Not surprisingly, successful pathogens have evolved strategies to modulate macrophage cell death pathways to enable microbial survival and replication. Uncontrolled macrophage death can also lead to tissue damage, which may augment bacterial dissemination and pathology. In this review, we highlight how pathogens hijack macrophage cell death signals to promote microbial survival and immune evasion.

Copper Nanoparticles and Copper Sulphate Induced Cytotoxicity in Hepatocyte Primary Cultures of Epinephelus coioides

Copper nanoparticles (Cu-NPs) were widely used in various industrial and commercial applications. The aim of this study was to analyze the cytotoxicity of Cu-NPs on primary hepatocytes of E.coioides compared with copper sulphate (CuSO₄). Cultured cells were exposed to 0 or 2.4 mg Cu L^-1 as CuSO₄or Cu-NPs for 24-h. Results showed either form of Cu caused a dramatic loss in cell viability, more so in the CuSO₄ than Cu-NPs treatment. Compared to control, either CuSO₄ or Cu-NPs significantly increased reactive oxygen species(ROS) and malondialdehyde(MDA) concentration in hepatocytes by overwhelming total superoxide dismutase (T-SOD) activity, catalase(CAT) activity and glutathione(GSH) concentration. In addition, the antioxidative-related genes [SOD (Cu/Zn), SOD (Mn), CAT, GPx4] were also down-regulated. The apoptosis and necrosis percentage was significantly higher after the CuSO₄ or Cu-NPs treatment than the control. The apoptosis was induced by the increased cytochrome c concentration in the cytosol and elevated caspase-3, caspase-8 and caspase-9 activities. Additionally, the apoptosis-related genes (p53, p38β and TNF-α) and protein (p53 protein) were up-regulated after the CuSO₄ or Cu-NPs treatment, with CuSO₄ exposure having a greater effect than Cu-NPs. In conclusion, Cu-NPs had similar types of toxic effects as CuSO₄ on primary hepatocytes of E.coioides, but toxicity of CuSO₄ was more severe than that of Cu-NPs.