Apoptosis, inflammatory response and parasite load in skin of Leishmania (Leishmania) chagasi naturally infected dogs: A histomorphometric analysis

Anatomical Vascular Differences and Leishmania-Induced Vascular Morphological Changes Are Associated with a High Parasite Load in the Skin of Dogs Infected with Leishmania infantum

Canine visceral leishmaniasis (CVL), caused by the protozoan Leishmania infantum, affects several organs, including the skin. Dogs are considered the major domestic reservoir animals for leishmaniasis, and through their highly parasitized skin, they can serve as a source of infection for sandfly vectors. Therefore, studies of the skin parasite-host relationship can contribute to the understanding of the infectious dissemination processes of parasites in the dermis and help to identify targets for diagnosis and treatment. Thus, the aim of this study was to evaluate the association of anatomical vascular differences and Leishmania-induced vascular morphological changes with clinical signs and parasite load by analyzing the ear and abdominal skin from dogs naturally infected with L. infantum. Paired samples of ear and abdominal skin from L. infantum-positive dogs (n = 26) were submitted for histological and immunohistochemistry analyses. The ear skin samples showed a more intense and more diffusely distributed granulomatous inflammatory reaction, a higher number and larger diameter of blood vessels, increased parasite load, higher expression of VEGF+ (vascular endothelial growth factor) and MAC 387+ (calprotectin) recently infiltrating cells, and more intense collagen disruption compared to the abdominal skin samples. Intracellular amastigotes were observed in blood vessels and inside endothelial cells and were diffusely distributed throughout the dermis in the ear skin samples. The NOS2/MAC387+ cell ratio was lower in the ear skin samples than in those of the abdomen, suggesting that in the ear dermis, the inflammatory infiltrate was less capable of producing NO and thereby control the parasite load. Together, these findings indicate how parasites and immune cells are distributed in the skin and suggest an important role for dermal vascularization in cellular influx and thereby in parasite dissemination through the skin of naturally infected dogs.

Enhanced apoptotic index in hepatocytes, Kupffer cells, and inflammatory infiltrate showed positive correlation with hepatic lesion intensity, parasite load, and clinical status in naturally Leishmania-infected dogs

It is unknown if Leishmania amastigote infections affect hepatocytes and Kupffer cell apoptosis, and the role played by apoptosis in liver lesions in leishmaniasis is still unclear. Clinically affected and subclinically infected dogs with leishmaniosis and uninfected controls were assessed. Parasite load, biochemical markers for evaluation of liver damage, morphometry (area, perimeter, number of inflammatory focus, major and minor diameters), apoptosis in hepatic tissue (hepatocytes, Kupffer cells, and inflammatory infiltrates) and cellularity in inflammatory foci were quantified. The parasite load in clinically affected dogs proved to be higher than in the other groups. All morphometric parameters (area, perimeter, number of inflammatory focus, major and minor diameters) from clinically affected were higher than the values found in the subclinically infected and uninfected control dogs. Only clinically affected dogs presented high levels of ALT, FA, GGT and cholesterol in serum. Strong positive correlation was observed between biochemical markers for evaluation of liver damage (ALT, FA, GGT and cholesterol) and hepatic apoptosis (hepatocytes, Kupffer cells, and inflammation). Clinically affected dogs showed a more intense hepatic lesion. Hepatocytes showed a higher rate of apoptosis in Leishmania-infected dogs than in uninfected control dogs. The Kupffer cell apoptotic index and apoptosis within the inflammatory infiltrates were higher in clinically affected dogs. The apoptotic index evaluated in hepatocytes, Kupffer cells, and inflammatory infiltrates showed a positive correlation with the intensity of the hepatic lesion, parasite load, and clinical status. Apoptotic cells also showed positive immunostaining for TUNEL, Bcl2, and Bax. Our data showed that hepatic apoptosis was related to the severity of liver damage, the progression of infection, and the parasite load in leishmaniasis. Apoptotic regulated cell recruitment modulated the inflammatory response and favored the survival and dissemination of parasites, depending on the clinical status of the Leishmania-infected dogs.

Effects of anti-stress agents on the growth performance and immune function in broiler chickens with vaccination-induced stress

The aim of this study was to evaluate the effects of anti-stress agents on the growth performance and immune function of broilers under immune stress conditions induced by vaccination. A total of 128, 1-day-old Arbor Acres broilers were randomly divided into four groups. Group normal control (NC) was the control group. Group vaccination control (VC), T 0.5%, and T 1% were the treatment groups, which were nasally vaccinated with two doses of the Newcastle disease virus (NDV) vaccine. The chicks in groups T 0.5% and T 1% were fed conventional diets containing 0.5% and 1% anti-stress agents. Thereafter, these broilers were slaughtered on 1, 7, 14, and 21 days post-vaccination. The results indicated that anti-stress agents could significantly reduce serum adrenocorticotropic hormone (ACTH) (P < 0.01) and cortisol (CORT) (P < 0.05) levels, and improve the growth performance (P < 0.05) and immune function of broilers (P < 0.05); However, the levels of malondialdehyde (MDA) (P < 0.05) were decreased, and the decreased total antioxidant capacity (T-AOC) (P < 0.01) levels mediated by vaccination were markedly improved. In addition, anti-stress agents could attenuate apoptosis in spleen lymphocytes (P < 0.01) by upregulating the ratio of Bcl-2 to BAX (P < 0.01) and downregulating the expression of caspase-3 and -9 (P < 0.01), which might be attributed to the inhibition of the enzymatic activities of caspase-3 and -9 (P < 0.05). In conclusion, anti-stress agents may improve growth performance and immune function in broilers under immune-stress conditions.RESEARCH HIGHLIGHTS Investigation of effects and mechanism of immune stress induced by vaccination.Beneficial effect of anti-stress agents on growth performance, immune function, oxidative stress, and regulation of lymphocyte apoptosis.Demonstration of the effects of apoptosis on immune function in the organism.

Enhanced apoptotic index, chemokines and inflammatory recruitment in renal tissues shows relationship with the clinical signs in Leishmania-infected dogs

Apoptosis is associated with resolution of inflammation. However, apoptosis may also occur in active inflammation, balancing inflammatory recruitment instead of a resolution event. To test that hypothesis, we measured apoptosis and chemokines expression, involved in recruitment of inflammatory cells. Clinical affected and subclinically infected dogs with canine leishmaniosis (CanL) and uninfected controls were assessed. Apoptosis in renal tissue (glomeruli, tubules, and inflammatory infiltrate) and cellularity in inflammatory foci were quantified. Messenger RNA of CCL5, CCL4, MCP-1, MCP-2, Caspase (Casp) 3, Casp 8, Casp 9, Bax, Bcl₂ and Fas were quantified by qRT PCR. Clinical affected dogs showed more intense inflammation and higher cellularity in the inflammatory infiltrates than subclinically infected ones, which were higher than controls. Glomerular and tubular cells showed higher apoptotic index in clinical affected dogs when compared to controls. Apoptosis within the inflammatory infiltrates was higher in clinical affected dogs. Bax/Bcl₂ ratio and CCL4 showed higher expression in kidney from clinical affected when compared to subclinically infected dogs. Casp 3/CCL4 ratio expression were higher in subclinically infected dogs than in the clinical affected group. Additionally, results suggest that Casp 3/CCL4 ratio is balancing towards an inflammatory recruitment and CCL4 and Bax/Bcl₂ ratio expression is associated with active inflammation in clinical affected CanL. Data demonstrate that apoptosis was not always correlated with resolution of inflammation, when a morphometric and a molecular evaluation were performed concomitantly. In kidneys of Leishmania infected dogs, apoptosis and chemokines may be balancing inflammatory recruitment. In conclusion, Bax/Bcl₂ ratio, chemokines, Casp 8, Casp 3 and Fas were associated with renal apoptosis, active inflammation and increased inflammatory recruitment observed in clinical affected animals, influencing the clinical presentation of leishmaniosis.

Leishmania Parasites Drive PD-L1 Expression in Mice and Human Neutrophils With Suppressor Capacity

Neutrophils play an important role in the outcome of leishmaniasis, contributing either to exacerbating or controlling the progression of infection, a dual effect whose underlying mechanisms are not clear. We recently reported that CD4⁺ and CD8⁺ T cells, and dendritic cells of Leishmania amazonensis-infected mice present high expression of PD-1 and PD-L1, respectively. Given that the PD-1/PD-L1 interaction may promote cellular dysfunction, and that neutrophils could interact with T cells during infection, we investigated here the levels of PD-L1 in neutrophils exposed to Leishmania parasites. We found that both, promastigotes and amastigotes of L. amazonensis induced the expression of PD-L1 in the human and murine neutrophils that internalized these parasites in vitro. PD-L1-expressing neutrophils were also observed in the ear lesions and the draining lymph nodes of L. amazonensis-infected mice, assessed through cell cytometry and intravital microscopy. Moreover, expression of PD-L1 progressively increased in neutrophils from ear lesions as the disease evolved to the chronic phase. Co-culture of infected neutrophils with in vitro activated CD8⁺ T cells inhibits IFN-γ production by a mechanism dependent on PD-1 and PD-L1. Importantly, we demonstrated that in vitro infection of human neutrophils by L braziliensis induced PD-L1⁺ expression and also PD-L1⁺ neutrophils were detected in the lesions of patients with cutaneous leishmaniasis. Taken together, these findings suggest that the Leishmania parasite increases the expression of PD-L1 in neutrophils with suppressor capacity, which could favor the parasite survival through impairing the immune response.

The balance between IL-12/IL4 in renal tissue switches the inflammatory response arm and shows relationship with the clinical signs in Leishmania-infected dogs

The pathogenesis of Canine leishmaniosis (CanL) is associated with altered cytokine expression and parasitic tissue shows a lot of inflammation. The aim of this study was to assess the renal inflammation and cytokine expression in eight symptomatic and eight asymptomatic Leishmania- infected dogs, and seven uninfected control dogs. Kidney fragments were stained with hematoxylin and eosin for morphometric evaluation. mRNA expression levels of interferon gamma (IFN-γ), tumor necrosis factor alpha (TNF-α), interleukin (IL)-2, IL-4, IL-10, and IL-12 were assessed in the kidney fragments using quantitative real time-polymerase chain reaction. Inflammation, quantified by the average area of the infiltrated immune cells, was greater in symptomatic dogs than in those asymptomatic, whereas asymptomatic dogs exhibited higher inflammation than the control dogs (p > 0.05, Tukey's test). Expression levels of IFN-γ, TNF-α, IL-4, IL-10, and IL-12 were upregulated in symptomatic dogs and downregulated in asymptomatic dogs compared with those of the uninfected group. Furthermore, IL-4 showed higher expression in symptomatic dogs than in asymptomatic ones (p < 0.05, Mann-Whitney test), which was directly associated with clinical manifestations (p < 0.05, Chi-square test). However, IL-12 was predominantly expressed in symptomatic dogs, shifting the balance from IL-12/IL-4 to IL-12, which elicits a change in the inflammatory response. Leishmania was not found in the renal tissues in any one of the studied groups. Our data suggests that the balance between IL-12 and IL-4 plays an important role in the regulation of inflammation in renal tissue and clinical presentations in CanL.

Neutrophils and Visceral Leishmaniasis: Impact on innate immune response and cross-talks with macrophages and dendritic cells

Neutrophils with their array of microbicidal activities are the first innate immune cells to guard against infection. They are also most crucial for the host's initial defense against Leishmania parasites which cause clinically diverse diseases ranging from self-healing cutaneous leishmaniasis (CL) to a more severe visceral form, visceral leishmaniasis (VL). Neutrophils are recruited in large numbers at the infection site after bite of sandfly, which is the vector for the disease. The initial interaction of neutrophils with the parasites may modulate the subsequent innate and adaptive immune responses and hence affect the disease outcome. The purpose of this review is to comprehensively appraise the role of neutrophils during the early stages of Leishmania infection with a focus on the visceral form of the disease. In the past decade, new insights regarding the role of neutrophils in VL have surfaced which have been extensively elaborated in the present review. In addition, since much of the information regarding neutrophil-Leishmania early interaction has accumulated through studies on mouse models of CL, these studies are also revisited. We begin by reviewing the factors which drive the recruitment of neutrophils at the site of injection by the sandfly. We then discuss the studies delineating the molecular mechanisms involved in the uptake of the Leishmania parasite by neutrophils and how the parasite subverts their microbicidal functions. In the end, the interaction of infected neutrophils with macrophages and dendritic cells is summarized.

Effects of extracellular vesicles released by peritoneal B-1 cells on experimental Leishmania (Leishmania) amazonensis infection

B-1 cells are a B-lymphocyte subtype whose roles in immunity are not completely defined. These cells can produce cytokines (mainly IL-10) and natural and specific antibodies. Currently, extracellular vesicles (EVs) released by immune cells have emerged as new important entities in cell-cell communication. Immune cells release EVs that can activate and/or modulate other immune cells. Here, we characterized the EVs released by peritoneal B-1 cells infected or not with Leishmania (Leishmania) amazonensis. This Leishmania species causes cutaneous leishmaniasis and can infect macrophages and B-1 cells. Our results showed that peritoneal B-1 cells spontaneously release EVs, but the parasite stimulated an increase in EVs production by peritoneal B-1 cells. The treatment of BALB/c and C57BL/6 bone marrow-derived macrophages (BMDM) with EVs from infected peritoneal B-1 cells led to differential expression of iNOS, IL-6, IL-10, and TNF-α. Additionally, BALB/c mice previous treated with EVs released by peritoneal B-1 cells showed a significant lower lesion size and parasite burden. Thus, this study demonstrated that peritoneal B-1 cells could release EVs that can alter the functions of macrophages in vitro and in vivo these EVs altered the course of L. amazonensis infection. These findings represent the first evidence that EVs from peritoneal B-1 cells can act as a new mechanism of cellular communication between macrophages and B-1 cells, contributing to immunity against experimental leishmaniasis.

Effects of fermented Chinese herbal medicines on milk performance and immune function in late-lactation cows under heat stress conditions

Heat stress (HS) causes significant economic losses and has become a continual challenge in the dairy industry worldwide. The objective of this study was to evaluate the effects of a dietary supplement on milk performance and immune function in late-lactation cows under HS conditions. The supplement was a fermented Chinese herbal medicines (CHMs) mixture consisting of 18 herbs. Forty lactating Holstein cows (560 ± 51.0 kg of initial BW, 230 ± 10.0 DIM, 16 ± 3.0 kg of milk per day) were randomly assigned into 4 treatment groups (10 cows per group). Each group was fed a dietary supplemented with 0, 25, 50, or 100 g CHMs per cow per day. Cows were housed at high ambient temperature-humidity index (average 74.5) for an experimental period of 42 d during the summer months. Milk yield, composition, immune responses involving blood lymphocyte apoptosis rate, serum biochemical parameters, and genes expression in lymphocytes were evaluated on days 14, 28, and 42, respectively. Results showed that milk yield, milk fat, and protein content were greater (all P < 0.05) for 50 or 100 g/d CHMs compared with the group without CHMs supplements throughout the experimental period. On the other hand, increasing CHMs dose demonstrated a greater lymphocyte or leukocyte count (P < 0.01). By flow cytometry analysis, early or late apoptosis rate of the lymphocytes was decreased (P < 0.05) by CHMs supplements. The immunity-related biochemistry and genes transcript responses involving cytokines (IL-1, IL-2, IL-6, and IL-12), apoptosis (Bak, Mcl-1, Bax, Bcl-2, Bcl-xl, and P53), and immunoglobulins (IgA, IgG, and IgM) were investigated. Compared with the unsupplemented group, the serum IL-2 and IL-6 levels, as well as IL-2 mRNA expression, increased (P < 0.05) for 100 g/d. However, the serum IL-1 level tended to decrease (P = 0.08) with increasing CHMs dose, and IL-1 mRNA expression was down-regulated (P = 0.02) by up to 24% for 100 g/d. Additionally, the serum Bax level decreased (P < 0.01) and Bcl-2 level increased (P = 0.01) for 100 g/d. Bax and Bak mRNA expressions were down-regulated (P < 0.05), and Bcl-2 and Bcl-xl expression were up-regulated (P < 0.05) for 50 or 100 g/d. The mRNA expressions of P53 and Mcl-1 were not affected by CHMs (P > 0.10). Besides, serum IgG levels were greater (P < 0.01) for 50 or 100 g/d, compared with unsupplemented group. In conclusion, CHMs supplements may improve milk performance and immune function in dairy cows under HS conditions.

PD-1 and PD-L1 regulate cellular immunity in canine visceral leishmaniasis

PD-1 is a negative costimulator of chronic infectious diseases In this study, we investigated the expression of PD-1 and its ligands in the spleen of dogs with visceral leishmaniasis and lymphoproliferative response to soluble antigen, in lymph node cells in the presence or absence of antibodies blocking PD-1 and its ligands. Our results showed expression of PD-1 and its ligands is higher after L. infantum infection and in the spleen of infected dogs, PD-1 blockage was able to restore the antigen-dependent lymphoproliferative response and regulated production of the cytokines IL-4 and IL-10 and NO production. We concluded that L. infantum infection modulates PD-1 and its ligands expression in canine VL and that blockage of PD-1 restores the immune response. Thus, blockage of PD-1 is a target for therapeutic drug development.

Survival Mechanisms Used by Some Leishmania Species to Escape Neutrophil Killing

Neutrophils are the most abundant leukocytes in human blood. Upon microbial infection, they are massively and rapidly recruited from the circulation to sites of infection where they efficiently kill pathogens. To this end, neutrophils possess a variety of weapons that can be mobilized and become effective within hours following infection. However, several microbes including some Leishmania spp. have evolved a variety of mechanisms to escape neutrophil killing using these cells as a basis to better invade the host. In addition, neutrophils are also present in unhealing cutaneous lesions where their role remains to be defined. Here, we will review recent progress in the field and discuss the different strategies applied by some Leishmania parasites to escape from being killed by neutrophils and as recently described for Leishmania mexicana, even replicate within these cells. Subversion of neutrophil killing functions by Leishmania is a strategy that allows parasite spreading in the host with a consequent deleterious impact, transforming the primary protective role of neutrophils into a deleterious one.

New species of Eimeria (Apicomplexa: Eimeriidae) from Thrichomys fosteri and Clyomys laticeps (Rodentia: Echimyidae) of the Brazilian Pantanal

The echimyid rodents Thrichomys fosteri and Clyomys laticeps are among the most commonly recorded small mammals in the Pantanal wetland of Brazil. These species play important ecological roles since they are the basis of the food chain of some predators and are parasitized by some pathogens. Knowledge of the eimerians that parasitize echimyid rodents in Brazil is absent, and only one report is available for South America. We therefore investigated parasitism by coccidians in the echimyids T. fosteri and C. laticeps in the Pantanal. Using morphological and morphometric features and associated statistical analyses, we describe five new eimerian species parasitizing T. fosteri (Eimeria nhecolandensis n. sp., Eimeria jansenae n. sp., and Eimeria fosteri n. sp.) and C. laticeps (E. nhecolandensis n. sp., Eimeria corumbaensis n. sp., and Eimeria laticeps n. sp.) in different types of infection associations. We document the developmental forms in the tissues, and describe lesions in the enteric tract of some infected animals. We also discuss some approaches regarding epidemiological and ecological data. Our results demonstrate that echimyid rodents in the Brazilian Pantanal are important hosts for the maintenance of enteric coccidia. Moreover, in some circumstances, this parasitism may threaten the health of the hosts.

Influence of apoptosis on liver and spleen resistance in dogs with visceral leishmaniosis

Abstract The aim of this study was to evaluate apoptosis and parasite load in the liver and spleen of dogs with visceral leishmaniosis (VL), using immunohistochemistry. Liver and spleen samples from 71 dogs with VL were used. The parasite load in the spleen and liver showed significant difference between organs in infected group (P=0.0219). The density of the parasite load in the spleen (median=2.4) was higher than liver (median=0.8). Immunodetection of apoptotic cells was predominant in lymphocytes and differ between the infected and control group in spleen (P=0.0307) and liver (P=0.0346). There was a significant correlation between apoptosis and parasite load (P = 0.0084; r=0.3104) only in the spleen of the infected group, where it was observed that, when increasing the number of apoptotic cells increases the parasitic load. It was concluded that the liver and spleen of infected dogs presented greater numbers of cells undergoing apoptosis (lymphocytes) than the control group, thus suggesting that this process may be contributing towards the survival of Leishmania in these organs, because lymphocyte in apoptosis did not have the ability to present and recognize the antigen, allowing the survival of the parasite.

Insights on adaptive and innate immunity in canine leishmaniosis

Canine leishmaniosis (CanL) is caused by the parasite Leishmania infantum and is a systemic disease, which can present with variable clinical signs, and clinicopathological abnormalities. Clinical manifestations can range from subclinical infection to very severe systemic disease. Leishmaniosis is categorized as a neglected tropical disease and the complex immune responses associated with Leishmania species makes therapeutic treatments and vaccine development challenging for both dogs and humans. In this review, we summarize innate and adaptive immune responses associated with L. infantum infection in dogs, and we discuss the problems associated with the disease as well as potential solutions and the future direction of required research to help control the parasite.

PD-1 function in apoptosis of T lymphocytes in canine visceral leishmaniasis

Dogs infected with Leishmania infantum have a reduced number of T lymphocytes. PD-1 (Programmed cell death 1) a new member of the B7-CD28 family that is expressed by immune cells, and its binding to PD-L1 (CD274) or PD-L2 (CD273) induces the deactivation or apoptosis of T cells. This study aimed to evaluate the expression of PD-1 and its ligands, as well as blocking in the induction of apoptosis in T lymphocytes, TNF-α, IL-4 and nitric oxide production by leucokocytes from PBMC and spleen and the parasite load in dogs with visceral leishmaniasis (VL). Our results showed that the expression of PD1 and its ligands was increased in CD3(+) T cells and CD21(+) B lymphocytes within the peripheral blood and splenic mononuclear cells of dogs with VL. In peripheral blood monocytes, only PD-1 ligands exhibited increased expression; however, in spleen macrophages, increased expression of both PD-1 and its ligands was observed. Levels of apoptosis in peripheral blood and splenic T lymphocytes were higher in dogs with VL compared to healthy dogs. Blocking monoclonal antibodies to PD-1 and its ligands in the culture of mononuclear cells from the peripheral blood and spleen decreased the amount of CD3(+) T lymphocyte apoptosis. The concentration of nitric oxide, TNF-α and IL-4 increased in the culture supernatants of peripheral blood mononuclear cells treated with a blocking monoclonal antibody against PD-1. The TNF-α concentration increased in the culture supernatants of splenic cells following all treatments with antibodies blocking PD-1 and its ligands; however, the amount of IL-4 increased only in the presence of a PD-1 blocking agent. Treatment with a PD-1 blocking monoclonal antibody in the mononuclear peripheral blood of dogs with VL reduced the parasite burden while increased TNF-α. We conclude that in canine visceral leishmaniasis, PD-1 and its ligands are involved in the induction of T lymphocyte apoptosis and in regulating the production of nitric oxide, TNF-α, and IL-4, as well as the parasitic load.

Occurrence of Leishmania infantum and associated histological alterations in the genital tract and mammary glands of naturally infected dogs

The objectives of this study were to evaluate the occurrence of Leishmania infantum in the male and female genital tract and female mammary glands of dogs and the parasite burden and to identify histological alterations associated with this protozoan. Twenty male and 20 female Leishmania-seropositive dogs with isolation of L. infantum were examined. Tissue samples of the prepuce, glans, epididymis, testes, prostate, vulva, vagina, uterus, uterine tubes, and mammary glands were analyzed by immunohistochemistry and histopathology. For parasitological culture and in situ hybridization, samples were collected from the testis, epididymis, and uterus. Additionally, seminal fluid was aspirated from the epididymis for parasitological culture. In the genital tract, 34 (85 %) dogs, including 18 males and 16 females, were positive for Leishmania. Of these, 27 (79 %) animals were symptomatic. Leishmania was detected in the mammary glands of 13 (65 %) females. L. infantum was isolated for the first time from the seminal fluid and uterus of naturally infected dogs. The parasite burden and intensity of the inflammatory reaction were greater in the prepuce and glans of males and in the vulva and mammary glands of females. In addition to inflammation, testicular degeneration, atrophy, absence of spermatogenesis, and necrosis were observed. Detection of amastigote forms in the mammary gland lumen indicates possible elimination of this parasite in milk. The frequent parasitism observed in the genital tract of infected males and females and the viability of L. infantum in seminal fluid and uterus suggest the possibility of bidirectional venereal and vertical transmission.

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

Leishmania is an intracellular parasite in vertebrate hosts, including man. During infection, amastigotes replicate inside macrophages and are transmitted to healthy cells, leading to amplification of the infection. Although transfer of amastigotes from infected to healthy cells is a crucial step that may shape the outcome of the infection, it is not fully understood. Here we compare L. amazonensis and L. guyanensis infection in C57BL/6 and BALB/c mice and investigate the fate of macrophages when infected with these species of Leishmania in vitro. As previously shown, infection of mice results in distinct outcomes: L. amazonensis causes a chronic infection in both strains of mice (although milder in C57BL/6), whereas L. guyanensis does not cause them disease. In vitro, infection is persistent in L. amazonensis-infected macrophages whereas L. guyanensis growth is controlled by host cells from both strains of mice. We demonstrate that, in vitro, L. amazonensis induces apoptosis of both C57BL/6 and BALB/c macrophages, characterized by PS exposure, DNA cleavage into nucleosomal size fragments, and consequent hypodiploidy. None of these signs were seen in macrophages infected with L. guyanensis, which seem to die through necrosis, as indicated by increased PI-, but not Annexin V-, positive cells. L. amazonensis-induced macrophage apoptosis was associated to activation of caspases-3, -8 and -9 in both strains of mice. Considering these two species of Leishmania and strains of mice, macrophage apoptosis, induced at the initial moments of infection, correlates with chronic infection, regardless of its severity. We present evidence suggestive that macrophages phagocytize L. amazonensis-infected cells, which has not been verified so far. The ingestion of apoptotic infected macrophages by healthy macrophages could be a way of amastigote spreading, leading to the establishment of infection.

Permissive and protective roles for neutrophils in leishmaniasis

Leishmania parasites are the causative agents of leishmaniasis, a neglected tropical disease that causes substantial morbidity and considerable mortality in many developing areas of the world. Recent estimates suggest that roughly 10 million people suffer from cutaneous leishmaniasis (CL), and approximately 76,000 are afflicted with visceral leishmaniasis (VL), which is universally fatal without treatment. Efforts to develop therapeutics and vaccines have been greatly hampered by an incomplete understanding of the parasite's biology and a lack of clear protective correlates that must be met in order to achieve immunity. Although parasites grow and divide preferentially in macrophages, a number of other cell types interact with and internalize Leishmania parasites, including monocytes, dendritic cells and neutrophils. Neutrophils appear to be especially important shortly after parasites are introduced into the skin, and may serve a dual protective and permissive role during the establishment of infection. Curiously, neutrophil recruitment to the site of infection appears to continue into the chronic phase of disease, which may persist for many years. The immunological impact of these cells during chronic leishmaniasis is unclear at this time. In this review we discuss the ways in which neutrophils have been observed to prevent and promote the establishment of infection, examine the role of anti-neutrophil antibodies in mouse models of leishmaniasis and consider recent findings that neutrophils may play a previously unrecognized role in influencing chronic parasite persistence.

Cutaneous immune mechanisms in canine leishmaniosis due to Leishmania infantum

Canine leishmaniosis (CanL) caused by the parasite Leishmania infantum is a systemic disease with variable clinical signs. The disease is endemic in the Mediterranean countries and dogs are the main domestic reservoir of the parasite. The quite complicated immune response against the parasite is crucial for the evolution of CanL infection with the skin playing a major role in its immunopathogenesis. After the inoculation of Leishmania promastigotes into the dermis by sand fly bites, complement factors, Langerhan's cells, neutrophils, fibroblasts and keratinocytes are involved in the activation of the innate arm of the skin immune system, with the macrophages and dendritic cells to play a major key role. The effective activation of cellular immunity is the cornerstone of dog's resistance against the parasite. Promastigotes reaching the dermis are engulfed, processed and transferred by APCs to draining lymph nodes to stimulate naïve T-cells for proliferation and differentiation into armed effector T-cells. Th1 cells activate the infected macrophages to kill Leishmania, whereas Th2 cells divert the immune response to humoral immunity and down regulation of cellular immunity with Th1 cell anergy. Inhibition of co-stimulatory molecules expression by infected macrophages contributes to T-cell anergy. In canine subclinical infections cutaneous lymphocytic infiltrate and parasites are absent, as opposed to dogs with clinical leishmaniosis. CD8+ cells constitute a significant population of cellular immunity in CanL since they outnumber CD4+ cells in the dermis, producing IFN-γ in sub clinically infected dogs and high levels of IL-4 in dogs with clinical leishmaniosis. Numerous B-lymphocytes have been shown to heavily infiltrate the dermis at least in exfoliative dermatitis in CanL. A mixed Th1/Th2 cytokine profile has been found in the dermis of naturally infected with L. infantum dogs. In the skin of dogs with clinical leishmaniosis, where plasma cells outnumber T lymphocytes in the dermal infiltrate, there is an overproduction of IL-4, IL-13 and TNF-α leading to Th2-biased humoral immune response. The issue of humoral immunity polarization in CanL remains controversial. Much still needs to be learned about other mechanisms underlying the complex interaction between the skin immune system and the parasite.

Alteration of sFAS and sFAS ligand expression during canine visceral leishmaniosis

Visceral leishmaniosis (VL) is caused by intracellular parasites of the genus Leishmania that affect humans and several animal species. Dogs are one of the main urban reservoirs of Leishmania infantum and play a central role in the transmission cycle to humans via sandflies. CD3+ cells apoptosis is involved in the immune response in VL. Dysregulation of apoptosis has been implicated in various disease states. An important regulator of apoptosis is the FAS-FAS-associated death domain protein (cluster of differentiation 95 - CD95) and FASL-FAS ligand protein (cluster of differentiation 178 - CD178) system involved in the down-regulation of immune reactions and in T cell-mediated cytotoxicity. FAS is a member of the tumor necrosis factor (TNF) receptor super family, which can be expressed in transmembrane or soluble forms. The soluble levels of FAS (sFAS), FASL (sFASL) and active Caspase-3, this last related to apoptotic cascade, were investigated in the spleen of 19 symptomatic dogs presenting moderate VL and 6 healthy dogs, determined by ELISA assay. The splenic parasite load was determined by real-time PCR monitoring of amplification of the intergenic internal transcribed spacer (ITS1) gene of parasite rRNA. sFAS levels were lower (p<0.05). sFASL and active Caspase-3 levels were higher (p<0.05) in dogs with VL compared with controls. Negative correlation was observed between parasite burden and sFASL levels. The increase in sFASL could be related to the mechanism involved in the elimination of the parasite.

Pathologic mechanisms underlying the clinical findings in canine leishmaniasis due to Leishmania infantum/chagasi

In dogs with symptomatic or asymptomatic leishmaniasis, Leishmania infantum appears to induce a mixed Th1/Th2 immune response that in the sick dog may eventually result in tissue damage via different pathomechanisms, notably granulomatous inflammation (eg, nodular dermatitis, osteomyelitis), immune complex deposition (eg, glomerulonephritis), and/or autoantibody production (eg, polymyositis). This is a compensatory but detrimental mechanism generated mainly because of the insufficient killing capacity of macrophages against the parasite in the susceptible dog. Clinical disease is typically exemplified as exfoliative and/or ulcerative dermatitis, with or without nasodigital hyperkeratosis and onychogryphosis, glomerulonephritis, atrophic myositis of masticatory muscles, anterior uveitis, keratoconjunctivitis sicca, epistaxis, and/or polyarthritis, appearing alone or in various combinations. The pathogenesis of these clinical conditions has recently been highlighted, to a greater or lesser extent. The usually subclinical conditions expressed as chronic colitis, chronic hepatitis, vasculitis, myocarditis, osteomyelitis, orchiepididymitis, and meningoencephalomyelitis, though uncommon, are of pathologic importance from a differential point of view. The leading cause of death among canine leishmaniasis patients is chronic proteinuric nephritis that may progress to end-stage kidney disease, nephrotic syndrome, and/or systemic hypertension. However, even the asymptomatic proteinuria, when profuse, may be a serious problem because it predisposes to arterial thromboembolism and eventually contributes to the deterioration of the body condition.

Leishmania amazonensis amastigotes trigger neutrophil activation but resist neutrophil microbicidal mechanisms

Neutrophils are the first cells to infiltrate to the site of Leishmania promastigote infection, and these cells help to reduce parasite burden shortly after infection is initiated. Several clinical reports indicate that neutrophil recruitment is sustained over the course of leishmaniasis, and amastigote-laden neutrophils have been isolated from chronically infected patients and experimentally infected animals. The goal of this study was to compare how thioglycolate-elicited murine neutrophils respond to L. amazonensis metacyclic promastigotes and amastigotes derived from axenic cultures or from the lesions of infected mice. Neutrophils efficiently internalized both amastigote and promastigote forms of the parasite, and phagocytosis was enhanced in lipopolysaccharide (LPS)-activated neutrophils or when parasites were opsonized in serum from infected mice. Parasite uptake resulted in neutrophil activation, oxidative burst, and accelerated neutrophil death. While promastigotes triggered the release of tumor necrosis factor alpha (TNF-α), uptake of amastigotes preferentially resulted in the secretion of interleukin-10 (IL-10) from neutrophils. Finally, the majority of promastigotes were killed by neutrophils, while axenic culture- and lesion-derived amastigotes were highly resistant to neutrophil microbicidal mechanisms. This study indicates that neutrophils exhibit distinct responses to promastigote and amastigote infection. Our findings have important implications for determining the impact of sustained neutrophil recruitment and amastigote-neutrophil interactions during the late phase of cutaneous leishmaniasis.

CD95 (FAS) and CD178 (FASL) induce the apoptosis of CD4+ and CD8+ cells isolated from the peripheral blood and spleen of dogs naturally infected with Leishmania spp

Infected dogs are urban reservoirs of Leishmania chagasi, which is a causative agent of visceral leishmaniasis (VL). Dogs exhibit immune suppression during the course of this disease, and lymphocyte apoptosis is involved in this process. To investigate apoptosis and the expression levels of FAS-FAS-associated death domain protein (CD95 or APO-1), FASL-FAS ligand protein (CD178), and TRAIL-TNF-related apoptosis-inducing ligand (CD253) receptors in peripheral blood mononuclear cells and spleen leukocytes from 38 symptomatic dogs with moderate VL and 25 healthy dogs were evaluated by flow cytometry. The apoptosis rate of blood and splenic CD4+ and CD8+ cells was higher in infected dogs than in healthy dogs. The expression levels of FAS and FASL in blood and splenic CD4+ cells were lower in infected dogs than in healthy dogs. FAS expression in CD8+ cells was higher in infected dogs than in healthy dogs; in contrast, FASL expression was lower in infected dogs. The expression of the TRAIL receptor increased only in splenic CD8+ cells from infected dogs. The FAS and FAS-L blocking antibodies confirmed the importance of these receptors in apoptosis. Our results enhance the current understanding of the immune response in dogs infected with L. chagasi, facilitating the future development of therapeutic interventions to reduce lymphocyte depletion.