Leishmania-specific lymphoproliferative responses and IgG1/IgG2 immunodetection patterns by Western blot in asymptomatic, symptomatic and treated dogs

Humoral and Cellular Immune Response in Asymptomatic Dogs with Visceral Leishmaniasis: A Review

Visceral leishmaniasis is one of the deadliest parasitic diseases in the world and affects both humans and dogs. The host immune response to Leishmania infection plays a critical role in the evolution of canine visceral leishmaniasis (CVL) and consequently in the manifestation of clinical signs. The asymptomatic form of the disease is a major concern in the diagnosis of CVL and in the transmission control of Leishmania infection. Asymptomatic dogs are found in large proportions in endemic areas and are an unquantifiable source of infection. The present review analyzes the possible relationship between the activation of the antigen-specific immune response of the host and resistance or susceptibility to CVL. The review focuses on works that address the characterization of the humoral and cellular immune response profile, at both the functional and phenotypic levels, in infected dogs. Most studies relate the absence of clinical symptomatology to an increased proliferative response and a Th1 cytokine profile. Despite the numerous findings pointing to a differential immune response in asymptomatic dogs, the contradictory results reported in this review highlight the importance of establishing a precise clinical classification of the disease, performing more longitudinal studies, and including a higher number of animals in trials.

Prognostic Value of Immunoglobulin G (IgG) Patterns by Western Blotting Immunodetection in Treated Dogs Previously Infected with Leishmania infantum

Leishmaniasis is a heterogeneous group of neglected tropical diseases with various clinical syndromes, which is caused by obligate intracellular protozoa of the genus Leishmania and transmitted by the bite of a female phlebotomine sandfly. Humans and several animal species are considered as reservoirs of the disease. Among other animal species, dogs are the most important reservoirs in a domestic environment, maintaining the endemic focus of the parasite. The behavior of the disease progression and the clinical symptoms of the disease in the infected dog is mainly associated with depressed cellular immunity and strong humoral response. This study aimed to assess the role of Western blotting in the analysis of the idiotype expression of the two main immunoglobulins (IgG1 and IgG2) in dogs that are naturally infected with Leishmania infantum (L. infantum) and treated with N-methyl meglumine antimoniate. Interestingly, for the first time, our study identified several L. infantum antigen polypeptides (14, 31, 33, 49, 64, 66, 99, and 169 kDa) that more frequently stimulate an immune reaction in recovered dogs after treatment, whereas in the non-recovered group of dogs, four antigen polypeptides of L. infantum with molecular weights of 31, 49, 66, and 115 kDa with unfavorable prognosis were identified. Clearly, these interesting findings confirm the strong association between the detected immunodominant bands and the successful recovery in treated dogs that can be used for differentiating the treated dogs from the untreated dogs, as well as the markers of a favorable or unfavorable prognosis and, as a consequence, the prediction of the clinical outcome of the disease. Likewise, these data could be helpful in the implementation of novel vaccines from the detected antigens.

Feline Leishmaniosis in Northwestern Italy: Current Status and Zoonotic Implications

Leishmaniasis remains one of the major neglected tropical diseases. The epidemiological profile of the disease comprises a wide range of hosts, including dogs and cats. Despite several studies about feline Leishmaniosis, the role of cats in disease epidemiology and its clinical impact is still debated. The present study raises awareness about the impact of leishmaniasis in cats from an endemic region in of Northwestern Italy (Liguria). A total number of 250 serum and 282 blood samples were collected from cats, then assessed for Leishmania infantum (L. infantum) serologically using western blot (WB) and molecularly using polymerase chain reaction (PCR). We also tested the association of Leishmania infection with some infectious agents like haemotropic Mycoplasma, Feline immunodeficiency virus (FIV) and Feline leukemia virus (FeLV) together with the hematobiochemical status of the examined animals. Interestingly, all tested animals were asymptomatic and out of 250 examined serum samples, 33 (13.20%) samples (confidence interval (CI) 95% 9.56-17.96%) were positive at WB for L. infantum, whereas of the 282 blood samples, 80 (28.36%) returned a positive PCR (CI 95% 23.43-33.89%). Furthermore, there was a statistical association between PCR positivity for L. infantum and some hematological parameters besides FIV infection as well as a direct significant correlation between Mycoplasma infection and WB positivity. Taken together, the present findings report high prevalence of L. infantum among cats, which reinforces the significance of such positive asymptomatic animals and confirms the very low humoral response in this species. In addition, the laboratory values provide evidence that infection by the parasite is linked to alteration of some hematological parameters and is correlated to some infectious agents. These data are of interest and suggest future research for accurate diagnosis of such zoonosis.

Relationships between specific antibody responses and clinical signs of dogs living in Tunisian endemic areas of canine leishmaniasis caused by Leishmania infantum

The first step of the diagnostic process of canine leishmaniasis (CanL) is initiated by veterinarians and relies on their assessment of a high number of clinical signs common to other infectious diseases. We investigated herein the relationship between the clinical profile of 64 domestic dogs living in Tunisian endemic areas and their serological immune status with the aim to identify leishmanial serological markers of diagnosis and disease staging. Seven clinical signs were examined and a total clinical score that describes the number (TCS1) and the number plus the intensity of the clinical signs (TCS2) were determined. Laboratory tests consisted of parasitological examination (PE) of Giemsa-stained popliteal lymph node smears, indirect fluorescent antibody test (IFAT), IgG-, IgG1-, IgG2-Enzyme-Linked-Immunosorbent-Assay (ELISA), and IgG1-, IgG2- Western blotting (WB). Dogs' categorization according to the results of routine diagnostic tests, the TCS1 and TCS2, and the relative IgG1 and IgG2 specific reactivity allowed us to show that active CanL is characterized by an increased reactivity of the IgG2 specific antibodies. Interestingly, the IgG1 levels increased in parallel with the TCS1 and especially with the TCS2, indicating that this isotype is a better marker of dogs' health deterioration. PE & IFAT positive dogs which presented the highest TCS2 and IgG1 reactivity demonstrated significantly more severe weight loss and paleness of the mucosal membranes, suggesting that these signs characterize the latest stages of the disease. WB analysis showed that threeleishmanial polypeptides merit attention and further investigations. The antigens with MWs 32kDa reacting with IgG1 and 37kDa reacting withIgG2 antibodies were found associated with the results of diagnostic tests and late CanL stages, whereas the 24kDa antigen reacting with the IgG2 isotype and associated with low TCS2 seems to be a marker of the early stages.

Antileishmanial efficacy and tolerability of combined treatment with non-ionic surfactant vesicle formulations of sodium stibogluconate and paromomycin in dogs

Infection with Leishmania infantum causes the disease visceral leishmaniasis (VL), which is a serious clinical and veterinary problem. The drugs used to treat canine leishmaniasis (CanL) do not cause complete parasite clearance; they can be toxic, and emerging drug resistance in parasite populations limits their clinical utility. Therefore, in this study we have evaluated the toxicity and efficacy of joint treatment with a 1:1 mixture of sodium stibogluconate-NIV (SSG-NIV, 10 mg Sb^v/day) and paromomycin-NIV (PMM-NIV, 10 mg PMM/kg/day), given intravenously daily for seven days from day 270 post-infection, to nine-month-old female beagle dogs (n = 6) experimentally infected with Leishmania infantum. Treatment significantly improved the clinical symptoms of VL infection in all the treated dogs, reduced parasite burdens in lymph nodes and bone marrow, and all symptomatic treated dogs, were asymptomatic at 90 days post-treatment. Treatment was associated with a progressive and significant decrease in specific IgG anti-Leishmania antibodies using parasite soluble antigen (p < 0.01) or rK39 (p < 0.01) as the target antigen. In addition, all dogs were classified as parasite negative based on Leishmania nested PCR and quantitative real time PCR tests and as well as an inability to culture of promastigote parasites from lymph nodes and bone marrow tissue samples taken at day 90 post-treatment. However, treatment did not cure the dogs as parasites were detected at 10 months post-treatment, indicating that a different dosing regimen is required to cause long term cure or prevent relapse.

Infection of dogs by Leishmania infantum elicits a general response of IgG subclasses

Leishmania infantum is the etiological agent of zoonotic visceral leishmaniasis. In endemic areas, canine infections are considered the main source of infection for human populations. Therefore, any control of human leishmaniasis must include the control of canine infections. Chemotherapy of leishmaniasis is inadequate and canine immunoprophylaxis has important limitations. Reports on the response of infected dogs are abundant but no clear picture of immune events has emerged. To shed some light on these shortcomings the specific IgG subclass response was followed in 20 Beagle dogs experimentally infected with L. infantum using monoclonal antibodies (MAb) specific for canine IgG₁, IgG₂, IgG₃ and IgG₄, along with ELISA and flow cytometry. Results showed that parasitic infection elicits a general response of all IgG subclasses, with a predominant IgG₁ response and without any evidence of IgG₁/IgG₂ dichotomy. These findings suggest that the inconsistent results reported previously could be related to the lack of specific reagents and not to the actual differences in the immune response of infected animals. Differential IgG subclass reactivity in ELISA and cytometry and the analysis of the reacting antigens could facilitate the diagnosis and prognosis of the disease and provide a useful tool for adequate therapeutics and vaccine development against leishmaniasis.

Early antibody response and clinical outcome in experimental canine leishmaniasis

Infected dogs are the main reservoir of zoonotic visceral leishmaniasis, a widespread parasitic disease caused by Leishmania infantum. Therefore, the control of canine infections is required to reduce the incidence of human cases. Disease outcome in dogs depends on the fine balance between parasite virulence and efficacy of the immune system. Thus, knowledge of early response could yield relevant information for diagnosis and follow-up. In our study, 20 Beagle dogs were intravenously infected with 10⁸ amastigotes of a fresh isolate of L. infantum and monitored along 16 weeks post inoculation. Specific antibody response and clinical evolution of infected animals were highly variable. Immunofluorescence antibody test (IFAT) and enzyme linked immunosorbent assay (ELISA) were useful to assess infection status, although only ELISA with promastigote-coated plates and, particularly, western blotting (WB) allowed an early diagnosis. Prominent antigens were identified by mass peptide fingerprinting. Chaperonin HSP60, 32 and 30 KDa antigens were recognized by all dogs on week 10 post infection. This suggests that these antigens may be valuable for early diagnosis. Advanced infection showed, in addition, reactivity to HSP83 and HSP70. Disease outcome did not show a clear relationship with ELISA or IFAT titers. Correlation between the clinical status and the combined reactivity to some antigens sustains their use for diagnosis and follow-up.

Biomarkers Associated With Leishmania infantum Exposure, Infection, and Disease in Dogs

Canine leishmaniosis (CanL) is a vector-borne disease caused by the protozoan Leishmania (Leishmania) infantum species [syn. L. (L.) infantum chagasi species in the Americas] which is transmitted by the bite of a female phlebotomine sand fly. This parasitosis is endemic and affect millions of dogs in Asia, the Americas and the Mediterranean basin. Domestic dogs are the main hosts and the main reservoir hosts for human zoonotic leishmaniosis. The outcome of infection is a consequence of intricate interactions between the protozoan and the immunological and genetic background of the host. Clinical manifestations can range from subclinical infection to very severe disease. Early detection of infected dogs, their close surveillance and treatment are essential to control the dissemination of the parasite among other dogs, being also a pivotal element for the control of human zoonotic leishmaniosis. Hence, the identification of biomarkers for the confirmation of Leishmania infection, disease and determination of an appropriate treatment would represent an important tool to assist clinicians in diagnosis, monitoring and in giving a realistic prognosis to subclinical infected and sick dogs. Here, we review the recent advances in the identification of Leishmania infantum biomarkers, focusing on those related to parasite exposure, susceptibility to infection and disease development. Markers related to the pathogenesis of the disease and to monitoring the evolution of leishmaniosis and treatment outcome are also summarized. Data emphasizes the complexity of parasite-host interactions and that a single biomarker cannot be used alone for CanL diagnosis or prognosis. Nevertheless, results are encouraging and future research to explore the potential clinical application of biomarkers is warranted.

Identification of Immunoreactive Leishmania infantum Protein Antigens to Asymptomatic Dog Sera through Combined Immunoproteomics and Bioinformatics Analysis

Leishmania infantum is the etiologic agent of zoonotic visceral leishmaniasis (VL) in countries in the Mediterranean basin, where dogs are the domestic reservoirs and represent important elements in the transmission of the disease. Since the major focal areas of human VL exhibit a high prevalence of seropositive dogs, the control of canine VL could reduce the infection rate in humans. Efforts toward this have focused on the improvement of diagnostic tools, as well as on vaccine development. The identification of parasite antigens including suitable major histocompatibility complex (MHC) class I- and/or II-restricted epitopes is very important since disease protection is characterized by strong and long-lasting CD8⁺ T and CD4⁺ Th1 cell-dominated immunity. In the present study, total protein extract from late-log phase L. infantum promastigotes was analyzed by two-dimensional western blots and probed with sera from asymptomatic and symptomatic dogs. A total of 42 protein spots were found to differentially react with IgG from asymptomatic dogs, while 17 of these identified by Coommasie stain were extracted and analyzed. Of these, 21 proteins were identified by mass spectrometry; they were mainly involved in metabolism and stress responses. An in silico analysis predicted that the chaperonin HSP60, dihydrolipoamide dehydrogenase, enolase, cyclophilin 2, cyclophilin 40, and one hypothetical protein contain promiscuous MHCI and/or MHCII epitopes. Our results suggest that the combination of immunoproteomics and bioinformatics analyses is a promising method for the identification of novel candidate antigens for vaccine development or with potential use in the development of sensitive diagnostic tests.

Relationship between clinical and pathological signs and severity of canine leishmaniasis

Canine visceral leishmaniasis (CVL) is a zoonotic disease that presents variable clinical and laboratory aspects. The aims of this study were to identify the main biochemical/hematological status of dogs naturally infected with Leishmania (Leishmania) infantum and to associate theses parameters with clinical forms of CVL. Blood samples were analyzed from 51 dogs, 15 uninfected (control group) and 36 infected, which were classified clinically in three groups: asymptomatic (n=12), oligosymptomatic (n=12) and symptomatic (n=12). All the infected dogs showed lower albumin/globulin ratios (A-G ratio) than the limit of reference. The mean values of total protein, urea, α-globulin 2, globulin and A-G ratio of infected dogs were outside the reference interval and differed significantly from those of the controls. Anemia was detected only in groups that showed clinical signs of the disease, and a statistical analysis indicated a significantly higher frequency of lower eritrogram in these groups than in the asymptomatic group. In addition, a significant association was observed between anemia and the presence of the symptoms, with dogs displaying higher erythrogram values showing better clinical conditions. These results provide additional evidence that the clinical forms of CVL may reflect on the erythrogram status.

Serological diagnosis of canine leishmaniosis: comparison of three commercial ELISA tests (Leiscan, ID Screen and Leishmania 96), a rapid test (Speed Leish K) and an in-house IFAT

Background

Speed Leish K^® is used as a serological screening test for Leishmania infection prior to vaccination. Limited comparative serological studies with Speed Leish K^® have been performed. The aim of this study was to evaluate the diagnostic performance of four commercially available serologic tests including ELISAs (Leiscan^®, ID Screen^® and Leishmania 96^®), a rapid test (Speed Leish K^®) and an in-house IFAT for the detection of specific antibodies against Leishmania infantum antigen in dogs in different states of infection.

Methods

Sick infected dogs (n = 36), healthy infected dogs (n = 18), L. infantum seropositive dogs with low to high levels of antibodies (n = 53), dogs seropositive to other pathogens (to evaluate cross reaction) (n = 14) and uninfected dogs from a non-endemic area (n = 50) and from an endemic area (n = 32) were analysed by the serological methods mentioned above.

Results

The sensitivity was as follows: ID Screen^® (0.953), Leiscan^® and Leishmania 96^® (0.925), IFAT (0.869) and Speed Leish K^® (0.636). The maximum specificity (1.000) was attained for all diagnostic tests except the Leishmania 96^® (0.896) and IFAT (0.917). The accuracy was as follows: ID Screen^® (0.975), Leiscan^® (0.961), Leishmania 96^® (0.911), IFAT (0.892) and Speed Leish K^® (0.808). In relation to the area under the ROC curve (AUC-ROC), the maximum value was attained with the ID Screen^® (0.993) closely followed by Leiscan^® (0.990), then, Leishmania 96^® (0.962), IFAT (0.926) and Speed Leish K^® (0.818). For the Kappa index, the best result was obtained by the ID Screen^® (0.951) followed by Leiscan^® (0.921), Leishmania 96^® (0.822), IFAT (0.783) and Speed Leish K^® (0.622). Statistically significant differences were found between the AUC-ROC of quantitative serological tests and the only qualitative rapid test evaluated. There were also statistically significant differences between AUC-ROC of the ELISAs (ID Screen^® and Leiscan^®) and IFAT.

Conclusions

Leiscan^® and ID Screen^® had superior diagnostic performance measures than IFAT and all quantitative serological tests were superior when compared to Speed Leish K^®. Thus, Speed Leish K^® may be considered a less valuable screening test prior to vaccination as it may result in vaccination of seropositive dogs and in some cases seropositive sick dogs.

DL. Improvement in clinical signs and cellular immunity of dogs with visceral leishmaniasis using the immunomodulator P-MAPA

This study investigated the immunotherapeutic potential of the protein aggregate magnesium-ammonium phospholinoleate-palmitoleate anhydride immuno-modulator (P-MAPA) on canine visceral leishmaniasis. Twenty mongrel dogs presenting clinical symptoms compatible with leishmaniasis and diagnosis confirmed by the detection of anti-leishmania antibodies were studied. Ten dogs received 15 doses of the immunomodulator (2.0 mg/kg) intramuscularly, and 10 received saline as a placebo. Skin and peripheral blood samples were collected following administration of the immunomodulator. The groups were followed to observe for clinical signals of remission; parasite load in the skin biopsies using real-time PCR, the cytokines IL-2, IL-10 and IFN-γ in the supernatant of peripheral blood mononuclear cells stimulated in vitro with either total promastigote antigen or phytohemagglutinin measured by capture ELISA, and changes in CD4⁺ and CD8⁺ T cell subpopulations evaluated by flow cytometry. Comparison between the groups showed that treatment with the immunomodulator promoted improvement in clinical signs and a significant reduction in parasite load in the skin. In peripheral blood mononuclear cell cultures, supernatants showed a decrease in IL-10 levels and an increase in IL-2 and IFN-γ. An increase in CD8⁺ T cells was observed in peripheral blood. In addition, the in vitro leishmanicidal action of P-MAPA was investigated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and no leishmanicidal activity was detected. These findings suggest that P-MAPA has potential as an immunotherapeutic drug in canine visceral leishmaniasis, since it assists in reestablishing partial immunocompetence of infected dogs.

Vaccines for canine leishmaniasis

Leishmaniasis is the third most important vector-borne disease worldwide. Visceral leishmaniasis (VL) is a severe and frequently lethal protozoan disease of increasing incidence and severity due to infected human and dog migration, new geographical distribution of the insect due to global warming, coinfection with immunosuppressive diseases, and poverty. The disease is an anthroponosis in India and Central Africa and a canid zoonosis (ZVL) in the Americas, the Middle East, Central Asia, China, and the Mediterranean. The ZVL epidemic has been controlled by one or more measures including the culling of infected dogs, treatment of human cases, and insecticidal treatment of homes and dogs. However, the use of vaccines is considered the most cost-effective control tool for human and canine disease. Since the severity of the disease is related to the generation of T-cell immunosuppression, effective vaccines should be capable of sustaining or enhancing the T-cell immunity. In this review we summarize the clinical and parasitological characteristics of ZVL with special focus on the cellular and humoral canine immune response and review state-of-the-art vaccine development against human and canine VL. Experimental vaccination against leishmaniasis has evolved from the practice of leishmanization with living parasites to vaccination with crude lysates, native parasite extracts to recombinant and DNA vaccination. Although more than 30 defined vaccines have been studied in laboratory models no human formulation has been licensed so far; however three second-generation canine vaccines have already been registered. As expected for a zoonotic disease, the recent preventive vaccination of dogs in Brazil has led to a reduction in the incidence of canine and human disease. The recent identification of several Leishmania proteins with T-cell epitopes anticipates development of a multiprotein vaccine that will be capable of protecting both humans and dogs against VL.

Relationship of Leishmania-specific IgG levels and IgG avidity with parasite density and clinical signs in canine leishmaniasis

The clinical status and tissue parasite burden of the skin and spleen of 40 dogs naturally infected with Leishmania chagasi (syn. Leishmania infantum), together with 5 uninfected control dogs, were assessed. On the basis of the clinical evaluation, infected dogs were classified as asymptomatic (AD) or symptomatic (SD). Infected animals were also grouped according to their parasite load as exhibiting low (LP), medium (MP) and high (HP) parasitism. The results indicated a high parasite load in the skin samples of SD animals in relation to the AD group. The serum immunoglobin isotype profiles of the studied animals revealed increased levels of IgG(1) in the AD and LP dogs, whereas high levels of IgG(2) were correlated with SD and HP dogs. The avidity index (AI) of IgG(total) in the SD group was high in comparison of that of the AD group. Moreover, animals with a larger parasite burden either in the spleen or skin showed higher AI values than animals with lower parasitism. Based on these findings, it is suggested that CVL commences with an asymptomatic clinical form with low parasitism, high production of IgG(1) and low affinity of IgG(total) molecules, and evolves into a symptomatic clinical form with higher parasitism intensity, higher IgG(2) levels, and high affinity of IgG(total).

IgG subclass profile of serum antibodies to Leishmania chagasi in naturally infected and vaccinated dogs

Leishmaniosis is a zoonotic disease that is caused by Leishmania chagasi and transmitted by sandflies. In Brazil, canine visceral leishmaniosis (CVL) is an emerging disease in urban areas and dogs are the main reservoir host. The aim of the present study was to analyze IgG seroconversion of dogs to L. chagasi and to determine whether there was dominance of any particular IgG subclasses in this immune response. Antibody detection was performed by ELISA with 120 sera from confirmed seropositive dogs (obtained from epidemiological surveys), 24 samples from naturally infected dogs with clinical signs of the disease, and 40 sera from animals immunized with a commercially available vaccine. Ninety percent of seropositive survey population samples had detectable levels of anti-Leishmania total IgG by ELISA, compared with 70% of samples from symptomatic animals and only 13% of samples from the immunized dogs. The serological response in each group displayed a distinct bias in IgG subclass usage as detected by application of a panel of monoclonal antibodies specific for canine IgG1-IgG4. The survey population, which comprised predominantly asymptomatic dogs, had a dominant IgG1 response, while symptomatic dogs had a mixed pattern of IgG subclass usage. In contrast, sera from vaccinated animals had high titres of IgG2 Leishmania antibody. These distinctive IgG subclass profiles may be related to the infection status of the dogs. Moreover, detection of antigen-specific IgG subclasses may provide a valuable diagnostic tool for predicting the clinical outcome of visceral leishmaniasis, as well as differentiating infected dogs from vaccinated animals.

Identification of highly specific and cross-reactive antigens of Leishmania species by antibodies from Leishmania (Leishmania) chagasi naturally infected dogs

The Leishmania species present a genetic homology that ranges from 69 to 90%. Because of this homology, heterologous antigens have been used in the immunodiagnosis and vaccine development against Leishmania infections. In the current work, we describe the identification of species-specific and cross-reactive antigens among several New World Leishmania species, using symptomatic and asymptomatic naturally Leishmania chagasi-infected dog sera. Soluble antigens from five strains of New World Leishmania were separated by electrophoresis in SDS-PAGE and immunoblotted. Different proteins were uniquely recognized in the L. chagasi panel by either symptomatic or asymptomatic dog sera suggesting their use as markers for the progression of disease and diagnosis of the initial (sub-clinical) phase of the infection. Cross-reactive antigens were identified using heterologous antigenic panels (L. amazonensis strains PH8 and BH6, L. guyanensis and L. braziliensis). L. guyanensis panel showed the highest cross-reactivity against L. chagasi specific antibodies, suggesting that proteins from this extract might be suitable for the diagnosis of visceral canine leishmaniasis. Interestingly, the 51 and 97 kDa proteins of Leishmania were widely recognized (77.8% to 100%) among all antigenic panels tested, supporting their potential use for immunodiagnosis. Finally, we identified several leishmanial antigens that might be useful for routine diagnosis and seroepidemiological studies of the visceral canine leishmaniasis.

FML vaccine against canine visceral leishmaniasis: from second-generation to synthetic vaccine

The Leishmania donovani glycoprotein fraction, known as FML, successfully underwent preclinical and clinical (Phase I-III) vaccine trials against canine visceral leishmaniasis (92-95% of protection and 76-80% of vaccine efficacy) when formulated with a QS21 saponin-containing adjuvant. It became the licensed Leishmune vaccine for canine prophylaxis in Brazil. The immune response raised by the vaccine is long lasting, immunotherapeutic and reduces dog infectivity blocking the transmission of the disease, as revealed by an in vivo assay. The preliminary epidemiological control data of vaccinated areas in Brazil indicate that, in spite of the still low vaccine coverage, there was a significant decrease in the incidence of the human and canine disease. A 36-kDa glycoprotein, in the FML complex, is the human marker of the disease, which was protective in mice as native recombinant protein or DNA vaccine. The DNA vaccine is now being tested against the canine disease. This review resumes the development of the second-generation FML-saponin-Leishmune vaccine, its adjuvant and of the NH36 DNA vaccine, toward the identification of its major epitopes that might be included in a possible future synthetic vaccine.

Methods for diagnosis of canine leishmaniasis and immune response to infection

Canine leishmaniasis (CanL) caused by Leishmania infantum (syn. L. chagasi, in Latin America), which is transmitted by the bite of phlebotomine sand flies, is endemic and affects millions of dogs in Europe, Asia, North Africa and South America. It is an emergent disease in North America. Early detection and treatment of infected animals may be critical in controlling the spread of the disease and is an essential part of human zoonotic visceral leishmaniasis control. The laboratory diagnosis of CanL still poses a challenge, despite progress made in the development of several direct and indirect methods. An effective diagnosis test, apart of being able to confirm a clinical suspicion in a single patient as well as to detect infection in asymptomatic dogs, should have high sensitivity, specificity and reproducibility; it must be simple, easy to perform, non-expensive, feasible in regional laboratories or adaptable for field conditions. Ideally, it should detect all Leishmania-infected dogs, preferentially using non-invasive collection of biological samples. In this paper we review the advantages and shortcomings of the available procedures for CanL diagnosis in the different phases, e.g. pre-patent and patent period of the infection and methods to determine the related immune response.

Vaccines for leishmaniasis in the fore coming 25 years

Human vaccination against leishmaniasis using live Leishmania was used in Middle East and Russia (1941-1980). First-generation vaccines, composed by killed parasites induce low efficacies (54%) and were tested in humans and dogs Phase III trials in Asia and South America since 1940. Second-generation vaccines using live genetically modified parasites, or bacteria or viruses containing Leishmania genes, recombinant or native fractions are known since the 1990s. Due to the loss of PAMPs, the use of adjuvants increased vaccine efficacies of the purified antigens to 82%, in Phase III dog trials. Recombinant second-generation vaccines and third-generation DNA vaccines showed average values of parasite load reduction of 68% and 59% in laboratory animal models, respectively, but their success in field trials had not yet been reported. This review is focused on vaccine candidates that show any efficacy against leishmaniasis and that are already in different phase trials. A lot of interest though was generated in recent years, by the studies going on in experimental models. The promising candidates may find a place in the forth coming years. Among them most probably are the multiple-gene DNA vaccines that are stable and do not require cold-chain transportation. In the mean time, second-generation vaccines with native antigens and effective adjuvants are likely to be licensed and used in Public Health control programs in the fore coming 25 years. To date, only three vaccines have been licensed for use: one live vaccine for humans in Uzbekistan, one killed vaccine for human immunotherapy in Brazil and a second-generation vaccine for dog prophylaxis in Brazil.

A comparison of the immune parameters of dogs infected with visceral leishmaniasis using Western blot and neutralization techniques

The Western blot technique was used to demonstrate the presence of antibodies in the blood of dogs that presented canine visceral leishmaniasis. This technique was used against some specific molecules present in the lysate of the promastigote form of Leshmania chagasi. Through the association of the results of the Western blot technique with the morphological alterations seen as a result of the serum neutralization technique performed in McCoy cells (which mimetizes the macrophage) it was possible to observe the role of some molecules of great relevance in determining the disease in symptomatic dogs as well as that of some other molecules associated with asymptomatic infected dogs that may become transmitters as well as differentiating them as asymptomatic resistant dogs. In the sera analyses carried out during the immunobloting a variation of 9 to 27 immunoreacting bands was observed, which were then compared using Dice's similarity coefficient. In the dendrogram constructed on the basis of the coefficient, 50% similarity was observed among the total number of reagent bands with the promastigote lysate, thus creating five groups. The main difference observed related to the clinical condition of the dogs: symptomatic and asymptomatic dogs were found in separate groups. The asymptomatic group of dogs was distributed in two different places in the dendrogram because they presented two different behavior patterns regarding the cellular morphology in the serum neutralization reaction: the presence or absence of cellular lysis. According to this analysis it is possible to evaluate the immune status and associate it with specific markers observed in the reaction found in the Western blot strips.

Idiotype expression of IgG1 and IgG2 in dogs naturally infected with Leishmania infantum

Here we analyzed, by Western blot analysis, the idiotype expression of IgG1 and IgG2 in 109 canine sera corresponding to 50 dogs from endemic areas of leishmaniosis in order to detect markers related to Leishmania infantum infection and clinical condition (asymptomatic or symptomatic). Twenty-four dogs from an area free of leishmaniosis were used as controls. IgG1 and IgG2 responses in symptomatic and asymptomatic L. infantum infections differed mainly in subclass production (ELISA values), with higher IgG2 production occurring particularly in symptomatic dogs. Nevertheless, we observed little difference in the idiotype expression of these IgG subclasses, which, in general, recognized the same antigenic fractions. While early L. infantum infection was characterized by recognition of polypeptide fractions of low molecular weight, mainly fractions of 14, 16 and 18 kDa by IgG1 and 14 and 16 kDa by IgG2, symptomatology was associated with recognition by both IgG subclasses of a 24 kDa fraction and other antigens belonging to the AG24 family.

Immunoglobulin G subclass distribution in canine leishmaniosis: A review and analysis of pitfalls in interpretation

Infection with Leishmania may have different outcomes in genetically distinct individuals and the course of infection is determined by the nature of the host innate and adaptive immune response. Thus in experimentally infected mice, and in naturally infected dogs or humans, the protective (self-healing or asymptomatic) phenotype is associated with the induction of Th1-regulated cell-mediated immunity. By contrast, a Th2-regulated humoral immune response is associated with severe symptomatic disease. In the murine model system there is strong correlation between clinicopathological phenotype and the nature of the antigen-specific humoral immune response. Symptomatic infection and Th2-regulation is associated with elevation in antigen-specific IgG1 and IgE, whereas asymptomatic infection with Th1-regulation is linked with IgG2a production. IgG subclass restriction is less clear in human disease with only some clinical forms being correlated to a specific serological profile. Although numerous studies have questioned whether infected dogs develop skewed IgG subclass usage, the results of these have been conflicting-suggesting bias towards IgG1 or IgG2 or neither subclass in different investigations. This confusion could relate to the specificity of the commercially available polyclonal antisera used to detect the canine IgG1 and IgG2 subclasses. More meaningful results might be obtained by the use of the panel of monoclonal antibodies with well-validated specificity for all four canine IgG subclasses.

Leishmania-specific isotype levels and their relationship with specific cell-mediated immunity parameters in canine leishmaniasis

In the current retrospective study, Leishmania infantum-specific IgG, IgA and IgM levels were determined by ELISA in 106 untreated dogs with clinically-patent leishmaniasis (Sx) and in 171 clinically healthy dogs (Asx) from Spain to investigate the relationship between these Ig isotypes and clinical status. In addition, we studied if different Leishmania-specific humoral pattern exists between Asx dogs with and without cellular mediated immunity (CMI). Fifty-six dogs were assessed by means of lymphoproliferation assay (LPA), interferon production (IFN) and leishmanin skin test (LST), 71 dogs by means of both LPA and IFN and 44 only by LST. Both Sx and Asx dogs produced Leishmania-specific IgG, IgA and IgM antibodies, however the levels and proportion of positive dogs for each Ig isotype were significantly higher in Sx than in Asx ones (P<0.001). Analysis of immunological profiles determined for each cellular technique (positive and negative cellular response for each technique combined with positive or negative specific humoral response) showed that Asx dogs constituted a high heterogeneous group. No correlations were observed between CMI tests and specific IgG or IgM levels. However, a significant inverse correlation was demonstrated between specific IgA levels and LPA response (Spearman's r=-0.220; P=0.035). In general, the low correlation detected between CMI tests and isotype levels might indicate that the immune response is not strongly polarized in the majority of Asx dogs. Additionally, this study suggests that dogs developing T-cell response are probably able to avoid the dissemination of the parasite at least to mucosal surfaces and, as a consequence, to produce low or background specific IgA levels. Further studies are needed to investigate the relationship between specific IgA and parasite load, especially at mucosal site.

Setting new immunobiological parameters in the hamster model of visceral leishmaniasis for in vivo testing of antileishmanial compounds

To establish suitable immunobiological parameters for in vivo testing of new antileishmanial compounds in the golden hamster model of visceral leishmaniasis, two groups of 8 animals were infected each with 10(5) or 10(7) stationary promastigotes by the intracardiac route and the clinical and immunoparasitological features were monitored up to day 155 after infection. All animals became infected at both doses, although significant differences were observed between parasite burdens in liver and spleen. The mean number of parasites in animals infected with 10(7) promastigotes increased by 9.5 times in liver and by 43.1 times in spleen compared with those infected with 10(5) promastigotes. In animals given the higher dose, the outcome of the disease occurred between days 75 and 90 after infection, whereas no signs of disease were apparent in those given the lower infecting dose. Positive antibody (IgG) responses were detected earlier (week 5-7 after infection) in animals infected with the higher dose than in those infected with the lower dose (week 8-10 after infection), but these responses did not correlate with individual parasitological loads in liver and spleen. An inverse correlation was observed between infecting doses and in vitro spleen lymphocyte proliferation against mitogens (ConA). The proportion of CD4(+) and CD19(+) spleen cell increased in animals given the higher infection, whereas it decreased in those given the lower infection compared to naive controls.

Canine visceral leishmaniasis: relationships between clinical status, humoral immune response, haematology and Lutzomyia (Lutzomyia) longipalpis infectivity

The main source of Leishmania infantum infection in humans is a naturally infected dog. This study reports on the infectivity to phlebotomine sandflies (Lutzomyia longipalpis) of serologically positive mongrel dogs that differed in clinical status, haematology and humoral responses to immunoglobulin (Ig) G_T (total anti-Leishmania IgG), IgG₁ and IgG₂ subclasses of antibody to crude antigen of L. infantum. Forty-five female L. longipalpis were allowed to feed directly on the ears of dogs classified as asymptomatic, oligosymptomatic or symptomatic before being dissected five days later. Promastigotes were detected in 88% of the dissected sandflies. The highest rate of infectivity to sandflies was found in symptomatic dogs, followed by oligosymptomatic and asymptomatic animals. The results suggest that dogs naturally infected with L. infantum with higher total IgG and IgG₂ concentrations and lower haematocrit levels were able to infect the highest proportion of L. longipalpis. No correlation was observed between anaemia and the intensity of clinical signs. Symptomatic dogs presented the highest infection rate and intensity of infection.

Kinetics and diagnostic and prognostic potential of quantitative Western blot analysis and antigen-specific enzyme-linked immunosorbent assay in experimental canine leishmaniasis

Quantitative computerized Western blot analysis of antibody responses during experimental canine Leishmania infantum infection distinguished between immunodominant and nonimmunodominant protein bands. Six infected beagles, positive by both PCR and parasite culture, were monitored over 75 weeks postinfection and during a 12-week allopurinol treatment course. All dogs were symptomatic at the time of treatment. Of 12 antigenic bands examined, the immunodominant bands (12, 14, 24, 29, 48, and 68 kDa) showed significantly increased intensities (P<0.01) and higher frequencies of recognition than the nonimmunodominant bands at all time points. Detection of the former bands at 6 weeks postinfection preceded seroconversion by enzyme-linked immunosorbent assay (ELISA) both on crude Leishmania antigen or the recombinant proteins rK39 and HSP70. Reactivity with the 14-, 48-, and 68-kDa bands signified early infection, whereas increased reactivity with the 14-, 24-, and 29-kDa bands was associated with posttreatment parasite persistence and potential unfavorable prognosis. Total lane intensity (TLI) emerged as a sensitive marker for early infection and increased as early as 4 weeks postinfection. TLI had a significantly higher (P<0.01) relative increase rate than crude Leishmania antigen or HSP70 or rK39 ELISA at all time points. These immunodominant antigens and TLI, as determined by quantitative Western blotting, will be valuable for early detection and treatment evaluation of canine leishmaniasis.

Antileishmanial antibody profile in dogs naturally infected with Leishmania chagasi

Visceral leishmaniasis (VL) presents vigorous Th2 immune response, which is mainly characterized in human by augmented expression of Il-4, polyclonal B cell activation, intense hypergammaglobulinemia and production of antileishmanial IgE antibodies. However, few aspects of this type of immune response have been demonstrated in studies of canine visceral leishmaniasis (CVL). This work investigated by ELISA and western immunoblotting the production of antileishmanial IgE antibodies (IgE Ab) in symptomatic and asymptomatic dogs naturally infected by Leishmania chagasi, and also compared this IgE immune response with those of IgG, IgG1 and IgG2 antibodies. Three groups of dogs were evaluated: 12 VL dogs with positive Leishmania biopsies (GI), 44 dogs with a positive leishmanial indirect fluorescent antibody test (IFAT), 30 of them presenting clinical signs of VL and 14 asymptomatic (GII) and 21 healthy dogs living in kennels located in leishmaniasis endemic areas (GIII), which were seronegative in the IFAT. Eighteen dogs from an area free of CVL were used as controls (GIV). Antileishmanial IgE antibodies were detected in 4 of 12 VL dogs from group I (33%) and 14 of 30 symptomatic dogs from group II (47%). While all asymptomatic dogs from group II (100%) were seronegative for antileishmanial IgE Ab, 7 of 21 healthy animals from group III (33%) had these immunoglobulins. A strong correlation was verified between antileishmanial IgG and IgG2 antibody titers in all symptomatic dogs, but only 15 of these 42 animals (36%) produced simultaneously IgE, IgG, IgG1 and IgG2 antibodies to Leishmania. IgE antibodies recognized leishmanial antigens of 12, 36, 61, 81 and 118 KDD, while a more complex pattern of immunoblotting was verified mainly for IgG and IgG2 antibodies from symptomatic animals. IgG1 and IgG2 antibodies shared the recognition of L. chagasi polypeptides of 118, 81, 61, 36, 18, 14 and 12 KDD, being more intense the immune reactions between IgG1 Ab and the leishmanial polypeptides of 61 and 36 KDD, and also between IgG2 antibodies and the antigens of 26, 21, 18, 14 and 12 KDD. Our results suggest that the polyclonal production of antileishmanial antibodies that includes IgE Ab could characterize a Th2 immune response in CVL and can help the laboratory diagnosis of this disease.