Immunoglobulin subclass distribution and diagnostic value of Leishmania donovani antigen-specific immunoglobulin G3 in Indian kala-azar patients

Detection of Leishmania (Mundinia) macropodum (Kinetoplastida: Trypanosomatidae) and heterologous Leishmania species antibodies among blood donors in a region of Australia with marsupial Leishmania endemicity

OBJECTIVES

The Australian Leishmania (Mundinia) macropodum parasite causes cutaneous leishmaniasis among marsupial species. Although cutaneous leishmaniasis is a major public health burden worldwide, it is not clear if humans are naturally exposed to the unique L. macropodum. To assess whether humans have an immunoglobulin (Ig) G response to L. macropodum, we examined anti-Leishmania antibodies among humans residing in a region of marsupial Leishmania endemicity in Australia.

METHODS

Using a serological enzyme-linked immunosorbent assay, we characterized Leishmania-specific IgG and IgG subclass responses to soluble Leishmania antigen from L. macropodum, and other Leishmania species (L. donovani, L. major, and L. mexicana) in 282 blood donor samples.

RESULTS

We found that 20.57% of individuals demonstrated a positive total IgG response to L. macropodum. For individuals with antibodies to soluble Leishmania antigen from one Leishmania species, there was no increased likelihood of recognition to other Leishmania species. For samples with detectable L. macropodum IgG, IgG1 and IgG2 were the prevalent subclasses detected.

CONCLUSION

It is not yet clear whether the IgG antibody detection in this study reflects exposure to Leishmania parasites or a cross-reactive immune response that was induced against an unrelated immunogen. Future studies should investigate whether L. macropodum can result in a viable infection in humans.

An Insight Into Systemic Immune Response in Leishmania donovani Mediated Atypical Cutaneous Leishmaniasis in the New Endemic State of Himachal Pradesh, India

Leishmaniasis continues to afflict known and newer endemic sites despite global efforts towards its control and elimination. In this regard, the emergence of newer endemic sites with unusual disease formats is recognized wherein Leishmania donovani complex classically known to cause visceral disease is demonstrated to cause cutaneous manifestation. In this context, atypical cutaneous leishmaniasis (CL) cases caused by L. donovani genetic variants from the newer endemic state of Himachal Pradesh (HP) in India are beginning to be understood in terms of parasite determinants. The atypical CL manifestation further needs to be explored to define host immune correlates with a possible role in driving the unusual disease progression. In the given study, we performed comprehensive systemic-immune profiling of the atypical CL patients from the study area in HP, India, in comparison with the classical visceral leishmaniasis (VL) patients from the northeast region of India. The systemic immune response was studied using ELISA-based assessment of Th1, Th2, Th17, Treg, and Th22 specific plasma cytokine expression pattern and parasite-specific total serum IgG/IgG subclasses. The specified immune correlates are known to exhibit heterogeneous association with the different infecting parasite species, infection load, and co-lateral host immunopathology in classical CL and VL. In the atypical CL patient group, altered expression of IL-10 emerged as the key finding that could potentially fine-tune the Th1/Th17/Th22 effector cytokine axis towards a localized cutaneous manifestation. A reduced expression of IL-10 along with a high IFN-γ/IL-10 ratio as a readout of effective parasite killing defined atypical cutaneous outcome. In contrast, high circulatory IL-10 levels and a depressed IFN-γ/IL-10 ratio were seen in classical VL patients in line with an ineffective parasite-killing cytokine response. Overall, the study highlights new knowledge on host immune correlates in terms of cytokine expression pattern and IgG subclasses that underline atypical disease manifestation such that L. donovani, a generally visceralizing parasite species cause skin localized cutaneous lesions.

Potential biomarkers of immune protection in human leishmaniasis

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

Molecular Tracking of the Leishmania Parasite

With the Visceral Leishmaniasis/Kala-azar Elimination Program in South Asia in its consolidation phase, the focus is mainly on case detection, vector control, and identifying potential sources of infection. Accordingly, emphasis is presently on curbing transmission, which is potentially achievable by identification and elimination of potential reservoirs. The strongest contenders for being the disease reservoir are cases of Post Kala-azar Dermal Leishmaniasis (PKDL) which occurs in a minor proportion of individuals apparently cured of Visceral Leishmaniasis (VL). The demonstration of parasites in tissue aspirates despite being a risky and invasive process is the gold standard for diagnosis of VL, but is now being replaced by serological tests e.g., rK39 strip test and direct agglutination test. However, these antibody based tests are limited in their ability to diagnose relapses, detect cases of PKDL, and monitor effectiveness of treatment. Accordingly, detection of antigen or nucleic acids by polymerase chain reaction has been successfully applied for monitoring of parasite kinetics. This review article provides updated information on recent developments regarding the available antibody or antigen/nucleic acid based biomarkers for longitudinal monitoring of patients with VL or PKDL and emphasizes the need for availability of studies pertaining to quantification of treatment response or relapse.

Liposomal Formulation of ChimeraT, a Multiple T-Cell Epitope-Containing Recombinant Protein, Is a Candidate Vaccine for Human Visceral Leishmaniasis

Background: Leishmaniases are neglected diseases caused by infection with Leishmania parasites and there are no human vaccines in use routinely. The purpose of this study was to examine the immunogenicity of ChimeraT, a novel synthetic recombinant vaccine against visceral leishmaniasis (VL), incorporated into a human-compatible liposome formulation. Methods: BALB/c mice were immunized subcutaneously with ChimeraT/liposome vaccine, ChimeraT/saponin adjuvant, or ChimeraT/saline and immune responses examined in vitro and in vivo. Results: Immunization with the ChimeraT/liposome formulation induced a polarized Th1-type response and significant protection against L. infantum infection. ChimeraT/liposome vaccine stimulated significantly high levels of interferon (IFN)-γ, interleukin (IL)-12, and granulocyte macrophage-colony stimulating factor (GM-CSF) cytokines by both CD4 and CD8 T-cells, with correspondingly lower levels of IL-4 and IL-10 cytokines. Induced antibodies were predominantly IgG2a isotype, and homologous antigen-stimulated spleen cells produced significant nitrite as a proxy for nitric oxide (NO). Furthermore, we examined a small number of treated VL patients and found higher levels of circulating anti-ChimeraT protein IgG2 antibodies, compared to IgG1 levels. Conclusions: Overall, the liposomal formulation of ChimeraT induced a protective Th1-type immune response and thus could be considered in future studies as a vaccine candidate against human VL.

F1 Domain of the Leishmania (Leishmania) donovani Nucleoside Hydrolase Promotes a Th1 Response in Leishmania (Leishmania) infantum Cured Patients and in Asymptomatic Individuals Living in an Endemic Area of Leishmaniasis

The Leishmania (Leishmania) donovani nucleoside hydrolase NH36 is the main antigen of the Leishmune® vaccine and one of the promising candidates for vaccination against visceral leishmaniasis. The antigenicity of the N-terminal (F1), the central (F2), or the C-terminal recombinant domain (F3) of NH36 was evaluated using peripheral blood mononuclear cells (PBMC) from individuals infected with L. (L.) infantum from an endemic area of visceral leishmaniasis of Spain. Both NH36 and F1 domains significantly increased the PBMC proliferation stimulation index of cured patients and infected asymptomatic individuals compared to healthy controls. Moreover, F1 induced a 19% higher proliferative response than NH36 in asymptomatic exposed subjects. In addition, in patients cured from visceral leishmaniasis, proliferation in response to NH36 and F1 was accompanied by a significant increase of IFN-γ and TNF-α secretion, which was 42-43% higher, in response to F1 than to NH36. The interleukin 17 (IL-17) secretion was stronger in asymptomatic subjects, in response to F1, as well as in cured cutaneous leishmaniasis after NH36 stimulation. While no IL-10 secretion was determined by F1, a granzyme B increase was detected in supernatants from cured patients after stimulation with either NH36 or F1. These data demonstrate that F1 is the domain of NH36 that induces a recall cellular response in individuals with acquired resistance to the infection by L. (L.) infantum. In addition, F1 and NH36 discriminated the IgG3 humoral response in patients with active visceral leishmaniasis due to L. (L.) donovani (Ethiopia) and L. (L.) infantum (Spain) from that of endemic and non-endemic area controls. NH36 showed higher reactivity with sera from L. (L.) donovani-infected individuals, indicating species specificity. We conclude that the F1 domain, previously characterized as an inducer of the Th1 and Th17 responses in cured/exposed patients infected with L. (L.) infantum chagasi, may also be involved in the generation of a protective response against L. (L.) infantum and represents a potential vaccine candidate for the control of human leishmaniasis alone, or in combination with other HLA epitopes/antigens.

In vitro activity and in vivo efficacy of a combination therapy of diminazene and chloroquine against murine visceral leishmaniasis

The present study evaluated the in vitro activity and in vivo efficacy of diminazene combined with chloroquine as a potential drug against Leishmania donovani. Amphotericin B was used as a positive control drug. In vitro activity involved incubation of various drug concentrations with promastigotes or vero cells in culture before determination of parasite growth inhibition or cell death while in vivo evaluations involved infection of various mice groups with virulent L. donovani parasites and treatment with test drug compounds following disease establishment. Weight changes in experimental mice were also evaluated before infection and throughout the experiment. The results indicated that the diminazene–chloroquine combination was at least nine times more efficacious than individual drugs in killing promastigotes in culture. The diminazene–chloroquine combination was safer (Ld₅₀ = 0.03±0.04) than Amphotericin B (Ld₅₀ = 0.02±0.01). Body weight in infected mice increased significantly (P = 0.0007) from day 7 to day 37 following infection (P = 0.026). However, body weight remained comparable in all mice groups during treatment (P = 0.16). The diminazene–chloroquine combination significantly reduced splenic parasite numbers as compared to individual drug therapies (P = 0.0001) although Amphotericin B was still more efficacious than any other treatment (P = 0.0001). Amongst the test compounds, the diminazene–chloroquine combination showed the lowest level of IgG antibody responses with results indicating significant negative correlation between antileishmanial antibody responses and protection against disease. These findings demonstrate the positive advantage and the potential use of a combined therapy of diminazene–chloroquine over the constituent drugs. Further evaluation is recommended to determine the most efficacious combination ratio of the two compounds.

Systematic review of biomarkers to monitor therapeutic response in leishmaniasis

Recently, there has been a renewed interest in the development of new drugs for the treatment of leishmaniasis. This has spurred the need for pharmacodynamic markers to monitor and compare therapies specifically for visceral leishmaniasis, in which the primary recrudescence of parasites is a particularly long-term event that remains difficult to predict. We performed a systematic review of studies evaluating biomarkers in human patients with visceral, cutaneous, and post-kala-azar dermal leishmaniasis, which yielded a total of 170 studies in which 53 potential pharmacodynamic biomarkers were identified. In conclusion, the large majority of these biomarkers constituted universal indirect markers of activation and subsequent waning of cellular immunity and therefore lacked specificity. Macrophage-related markers demonstrate favorable sensitivity and times to normalcy, but more evidence is required to establish a link between these markers and clinical outcome. Most promising are the markers directly related to the parasite burden, but future effort should be focused on optimization of molecular or antigenic targets to increase the sensitivity of these markers. In general, future research should focus on the longitudinal evaluation of the pharmacodynamic biomarkers during treatment, with an emphasis on the correlation of studied biomarkers and clinical parameters.

IgG1 as a potential biomarker of post-chemotherapeutic relapse in visceral leishmaniasis, and adaptation to a rapid diagnostic test

Background

Visceral leishmaniasis (VL), caused by protozoa of the Leishmania donovani complex, is a widespread parasitic disease of great public health importance; without effective chemotherapy symptomatic VL is usually fatal. Distinction of asymptomatic carriage from progressive disease and the prediction of relapse following treatment are hampered by the lack of prognostic biomarkers for use at point of care.

Methodology/Principal Findings

All IgG subclass and IgG isotype antibody levels were determined using unpaired serum samples from Indian and Sudanese patients with differing clinical status of VL, which included pre-treatment active VL, post-treatment cured, post-treatment relapsed, and post kala-azar dermal leishmaniasis (PKDL), as well as seropositive (DAT and/or rK39) endemic healthy controls (EHCs) and seronegative EHCs. L. donovani antigen-specific IgG1 levels were significantly elevated in relapsed versus cured VL patients (p<0.0001). Using paired Indian VL sera, consistent with the known IgG1 half-life, IgG1 levels had not decreased significantly at day 30 after the start of treatment (p = 0.8304), but were dramatically decreased by 6 months compared to day 0 (p = 0.0032) or day 15 (p<0.0001) after start of treatment. Similarly, Sudanese sera taken soon after treatment did not show a significant change in the IgG1 levels (p = 0.3939). Two prototype lateral flow immunochromatographic rapid diagnostic tests (RDTs) were developed to detect IgG1 levels following VL treatment: more than 80% of the relapsed VL patients were IgG1 positive; at least 80% of the cured VL patients were IgG1 negative (p<0.0001).

Conclusions/Significance

Six months after treatment of active VL, elevated levels of specific IgG1 were associated with treatment failure and relapse, whereas no IgG1 or low levels were detected in cured VL patients. A lateral flow RDT was successfully developed to detect anti-Leishmania IgG1 as a potential biomarker of post-chemotherapeutic relapse.

Visceral leishmaniasis (VL) is a systemic disease with highest prevalence in South Asia, East Africa, and Brazil. VL is caused by protozoan (unicellular) parasites of the Leishmania donovani complex, transmitted to humans when an infected sandfly takes a bloodmeal. Within the human host, the parasites replicate within cells, particularly of bone marrow and spleen. Without effective treatment, symptomatic VL is usually fatal. As outlined in a recent World Health Organisation report, the development of new diagnostic tools to test for successful cure after chemotherapy is a research priority. In this work we investigated the association of clinical status of VL patients (active pre-treatment, and those deemed cured or relapsed post-treatment) with subclasses of the IgG antibody response made to L. donovani infection. We show that high levels of subclass IgG1 are found in pre-treatment and relapsed patients, but are very much lower in patients deemed to be cured. We further show that the decrease in IgG1 is detectable in patients 6 months after successful treatment, and that this detection method can be adapted to a rapid diagnostic test format requiring minimal technical expertise. Thus we believe that IgG1 levels are potentially a biomarker of post-chemotherapeutic monitoring.

Characterization of the humoral immune response against Gnathostoma binucleatum in patients clinically diagnosed with gnathostomiasis

Gnathostomiasis is an emerging systemic parasitic disease acquired by consuming raw or uncooked fresh-water fish infected with the advanced third-stage larvae of Gnathostoma spp. This disease is endemic to the Pacific region of Mexico, and one of its etiologic agents has been identified as Gnathostoma binucleatum. We characterized the humoral immune response of patients clinically diagnosed with gnathostomiasis by detecting total IgM, IgE, and IgG class and subclasses against a crude extract of the parasite by Western blotting. Our results do not show differences in the antigens recognized by IgM and IgE. However, we found that the specific humoral immune response is caused mainly by IgG, specifically IgG4. We found that 43%, 65.2%, 54.1%, and 26.3% of the patients recognize the 37-kD, 33-kD, 31-kD, and 24-kDa antigens, suggesting that the 33-kD antigen is the immunodominant antigen of G. binucleatum.

Immunobiology of visceral leishmaniasis

Visceral leishmaniasis (VL), commonly known as kala-azar, is caused by Leishmania donovani and Leishmania infantum (Leishmania chagasi in the Americas). These Leishmania species infect macrophages throughout the viscera, and parasites are typically found in the spleen, liver, and bone marrow. Patients with active disease typically exhibit marked immunosuppression, lack reactivity to the Leishmania skin test (LST), a delayed type hypersensitivity test, and their peripheral blood mononuclear cells (PBMC) fail to respond when stimulated with leishmanial antigens in vitro. However, most people infected with visceralizing species of Leishmania never develop disease. Understanding immune failure and the underlying immune mechanism that lead to disease as well as control of infection are key questions for research in this field. In this review, we discuss immunological events described in human and experimental VL and how these can affect the outcome of infection.

Vaccine Development Against Leishmania donovani

Visceral leishmaniasis (VL) caused by Leishmania donovani and Leishmania infantum/chagasi represents the second most challenging infectious disease worldwide, leading to nearly 500,000 new cases and 60,000 deaths annually. Zoonotic VL caused by L. infantum is a re-emergent canid zoonoses which represents a complex epidemiological cycle in the New world where domestic dogs serve as a reservoir host responsible for potentially fatal human infection and where dog culling is the only measure for reservoir control. Life-long immunity to VL has motivated development of prophylactic vaccines against the disease but very few have progressed beyond the experimental stage. No licensed vaccine is available till date against any form of leishmaniasis. High toxicity and increasing resistance to the current chemotherapeutic regimens have further complicated the situation in VL endemic regions of the world. Advances in vaccinology, including recombinant proteins, novel antigen-delivery systems/adjuvants, heterologous prime-boost regimens and strategies for intracellular antigen presentation, have contributed to recent advances in vaccine development against VL. Attempts to develop an effective vaccine for use in domestic dogs in areas of canine VL should be pursued for preventing human infection. Studies in animal models and human patients have revealed the pathogenic mechanisms of disease progression and features of protective immunity. This review will summarize the accumulated knowledge of pathogenesis, immune response, and prerequisites for protective immunity against human VL. Authors will discuss promising vaccine candidates, their developmental status and future prospects in a quest for rational vaccine development against the disease. In addition, several challenges such as safety issues, renewed and coordinated commitment to basic research, preclinical studies and trial design will be addressed to overcome the problems faced in developing prophylactic strategies for protection against this lethal infection.

Significance of persistence of antibodies against Leishmania infantum in Sicilian patients affected by acute visceral leishmaniasis

The background of this article is as follows: Few data are available about the persistence of serum-specific IgG antibodies to L. infantum after acute VL. The objective of this article is to evaluate the persistence of antibodies against L. infantum in patients healed from acute VL, and the kinetic of the same antibodies observed in 2 cases of VL relapse and 2 cases of resistance to therapy. The methods which we used to obtain our objective are the following: 55 apparently immunocompetent, HIV-negative patients were examined for antibodies to L. infantum by IFAT over 14 years period, and we got the following results: Serum-specific IgG antibodies titers decrease slowly, but constantly. In the patients with a diagnosis of VL relapse, the kinetic of antibodies was characterized by an initial reduction, and a subsequent antibody levels rapidly increase, while in the patients with a clinical and parasitological diagnosis of VL not responding to specific therapy, we demonstrated persistent high level of antibodies to L. infantum. Finally, we conclude that specific antibodies to L. infantum might persist for many years, and decrease slowly, but steadily. The persistence of these specific antibodies is not related to poor therapeutic response or prognosis, but an acute increase in their levels might be a sentinel of a VL relapse, while persistence of high antibody levels could suggest a resistance to therapy.

Anti-Leishmania chagasi immunoglobulin G3 detected by flow cytometry for early cure assessment in American visceral leishmaniasis

We have previously reported a novel flow cytometric based methodology to access the reactivity of seric anti-live (FC-ALPA) and fixed (FC-AFPA) L. chagasi IgG antibodies applicable for cure assessment after specific therapy of VL. Both, FC-ALPA-IgG and FC-AFPA-IgG are promising targets to be used for early cure assessment. However, our finding suggested that further refinements were still required to improve the performance of FC-AFPA IgG for early cure assessment in VL. In the present investigation, we have established and evaluated the performance of FC-AFPA-IgG1/IgG2/IgG3/IgG4 aiming to increase the performance index of the previously reported for FC-AFPA-IgG. The data was expressed as percentage of fluorescent positive parasites after incubation of pre-fixed L. chagasi promastigotes with the test sera samples and addition of second-step FITC-labeled anti-human IgG subclasses conjugates. The analysis of anti-L. chagasi IgG reactivity in polled sera samples from VL patients demonstrated that, before the etiological treatment, the IgG subclass profile was characterized by IgG1>IgG3 with the absence of IgG2 and IgG4 at the specific sera dilution tested. Following the establishment of specific PPFP cut-off-edges to segregate negative and positive results (PPFP of 50% for FC-AFPA-IgG1 and PPFP of 40% for FC-AFPA-IgG3), the analysis of IgG1 and IgG3 reactivity demonstrated good performance for early cure assessment in VL. The analysis of individual samples indicated that despite at 2 mAT, most treated VL patients (81%) still displayed positive results in FC-AFPA-IGg1 analysis, an increased fraction of treated patients (76%) presented negative in FC-AFPA-IgG1 analysis at 6 mAT. Interestingly, the data from FC-AFPA-IgG3 demonstrated an outstanding performance of this method to early cure assessment in VL with increased frequency of treated patients displaying negative results at 2 mAT (90.5%) as well as at 6 mAT (95.2%). The analysis of likelihood ratio (LR) further confirmed the remarkable performance of FC-AFPA-IgG3 as an early complementary biomarker useful to monitor the post-therapeutic cure in human VL.

Tracing immunity to human leishmaniasis

People who have recovered from leishmaniasis are believed to have long-lasting protection against subsequent infection. Understanding the immunological changes that are associated with protection from cure of and susceptibility to the disease are fundamental to both designing and evaluating vaccine candidates against the leishmaniases. In the quest for a vaccine against leishmaniasis, appropriate surrogate markers of immunity would be valuable and cost effective. Biomarkers would ease screening and selection of potentially efficient vaccine candidates. Moreover, biomarkers of disease may be used to monitor disease and aid therapeutic prognosis. This would be useful in the evaluation of both existing and new drugs, making invasive post-treatment evaluation redundant. Biomarkers may also be indicative of the severity of the disease and may be able to predict the outcome of an infection and indicate whether the patient will spontaneously recover, exhibit mild symptoms or if the disease is disseminating and will be severe. In this article we discuss the immunological changes associated with different forms of human leishmaniasis and the value of appropriate immunological biomarkers in finding an effective vaccine and an evaluation of therapies against leishmanial disease will be given.

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.

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.

IL-10- and TGF-beta-mediated susceptibility in kala-azar and post-kala-azar dermal leishmaniasis: the significance of amphotericin B in the control of Leishmania donovani infection in India

Visceral leishmaniasis (VL) or kala-azar is known to be associated with a mixed Th1-Th2 response, and effective host defense requires the induction of IFN-gamma and IL-12. We address the role of the differential decline of IL-10 and TGF-beta in response to sodium antimony gluconate (SAG) and amphotericin B (AmB), the therapeutic success of SAG and AmB in Indian VL, and the significance of IL-10 and TGF-beta in the development and progression of post-kazla-azar dermal leishmaniasis (PKDL). In the active disease, PBMC from VL patients showed suppressed Ag-specific lymphoproliferation, IFN-gamma and IL-12 production, and elevation of IL-10 and TGF-beta. Cure corresponded with an elevation in IFN-gamma and IL-12 production and down-regulation of IL-10 and TGF-beta. Both CD4(+) and CD8(+) T cells were involved in IFN-gamma and IL-10 production. Interestingly, the retention and maintenance of residual IL-10 and TGF-beta in some SAG-treated individuals and the elevation of IL-10 and TGF-beta in PKDL, a sequel to kala-azar, probably reflects the role of these cytokines in reactivation of the disease in the form of PKDL. Contrastingly, AmB treatment of VL resulted in negligible TGF-beta levels and absolute elimination of IL-10, reflecting the better therapeutic activity of AmB and its probable role in the recent decline in PKDL occurrences in India. Moreover, elucidation of immune responses in Indian PKDL patients revealed a spectral pattern of disease progression where disease severity could be correlated inversely with lymphoproliferation and directly with TGF-beta, IL-10, and Ab production. In addition, the enhancement of CD4(+)CD25(+) T cells in active VL, their decline at cure, and reactivation in PKDL suggest their probable immunosuppressive role in these disease forms.

IgG and IgG subclass antibodies in patients with active cutaneous leishmaniasis

This research was planned to detect IgG and IgG subclasses in sera of patients with active cutaneous leishmaniasis (CL). Sera from 30 patients with active CL aged between 10 and 50 years and from 30 healthy controls aged between 8 and 50 years were included in the study. Levels of IgG and its subclasses were measured by a nephelometer. Levels of IgG, IgG1 and IgG3 in the CL patients were higher than in the controls. In addition, IgG and IgG1, and IgG and IgG3 levels showed a significant positive correlation. These results showed that IgG subclasses could possibly be used as a helpful diagnostic marker in CL.

Isotype patterns of immunoglobulins: hallmarks for clinical status and tissue parasite density in Brazilian dogs naturally infected by Leishmania (Leishmania) chagasi

The role of anti-leishmanial immune response underlying the susceptibility/resistance during canine visceral leishmaniasis (CVL) has been recognized throughout ex vivo and in vitro investigations. Recently, we demonstrated that immunoglobulin levels (Igs), as well as the parasite load are relevant hallmarks of distinct clinical status of CVL. To further characterize and upgrade the background on this issue, herein, we have evaluated, in Leishmania (Leishmania) chagasi naturally infected dogs, the relationship between tissue parasitism (skin, bone marrow, spleen, liver and lymph node), the CVL clinical status (asymptomatic (AD), with no suggestive signs of the disease; oligosymptomatic (OD), with maximum three clinical signs-opaque bristles; localized alopecia and moderate loss of weight; symptomatic (SD), serologically positive with severe clinical signs of visceral leishmaniasis), and the humoral immunological profile of anti-Leishmania immunoglobulins (IgG, IgG1, IgG2, IgM, IgA and IgE). Our major statistically significant findings revealed distinct patterns of tissue parasite density within L. chagasi-infected dogs despite their clinical status, pointing out the spleen and skin as the most relevant sites of high parasitism during ongoing CVL. Parasite density of bone marrow and spleen were the most reliable parasitological markers to decode the clinical status of CVL. Moreover, the parasite density of bone marrow better correlates with most anti-Leishmania Igs reactivity. Additionally, a prognostic hallmark for canine visceral leishmaniasis was found, highlighting strong correlation between IgG1 and asymptomatic disease, but with IgA, IgE and IgG2 displaying better association with symptomatic disease. The new aspects of this study highlighted pioneer findings that correlated the degree of tissue parasite density (low (LP), medium (MP) and high (HP) parasitism) with distinct patterns of anti-Leishmania Igs reactivity. In this scope, our data re-enforce the anti-Leishmania IgG but with IgA reactivity as the better marker for overall tissue parasitism. The association between clinical status, Ig profile and the tissue parasitism support a novel investigation on the impact of humoral immune response and susceptibility/resistance mechanism during ongoing CVL.

Estudo comparativo de anticorpos IgG e IgE antileishmania como marcadores de infecção e doença em indivíduos de área endêmica de leishmaniose visceral, em São Luis, MA

Estudo comparativo de anticorpos IgG e IgE antileishmania como marcadores de infecção e doença em área endêmica de leishmaniose visceral na ilha de São Luis, MA no período de maio de 1999 a maio de 2000. A casuística foi composta de 1.016 menores de 16 anos. Destes, foram randomizados 85 para dosagem de IgE antileishmania pelo ELISA. A prevalência de soropositividade por IgG foi de 17,1% (174 menores) e 0,4% da população evoluiu para leishmaniose visceral doença. A positividade para IgE antileishmania, foi de 43,5% dos 85 indivíduos estudados. Dos 7 casos de calazar no passado analisados, observou-se que todos apresentavam positividade para IgG e 4 (57,14%) permaneciam positivos para IgE, mesmo 7 anos após a cura. Os 3 menores com leishmaniose visceral doença, apresentaram positividade para IgG e IgE antileishmania. A detecção de IgE antileishmania demonstrou ser marcador de infecção para Leishmania chagasi em área endêmica, não sendo entretanto, marcador de doença.

Balance of IL-10 and interferon-gamma plasma levels in human visceral leishmaniasis: implications in the pathogenesis

BACKGROUND

Leishmaniasis remains a serious public health problem in several parts of the developing world. Effective prophylactic measurements are hampered by imprecise comprehension of different aspects of the disease, including its immunoregulation. A better comprehension of immunoregulation in human VL may be useful both for designing and evaluating immunoprophylaxis.

METHODS

To explore immunoregulatory mechanisms, 20 visceral leishmaniasis (VL) patients were evaluated during active disease and at different periods up to one year after treatment determining their plasma cytokine levels, clinical parameters (palpable spleen and liver) and antibody levels.

RESULTS

Elevated plasma levels of IFN-gamma and of IL-12 p40 were observed during active disease, significantly decreasing after treatment whereas in vitro Leishmania antigen-stimulated IFN-gamma production by PBMC exhibited an inverse pattern being low during disease and increasing steadily thereafter. Absence of IFN-gamma activity is a hallmark of VL. The main candidate for blunting IFN-gamma activity is IL-10, a cytokine highly elevated in plasma with sharp decrease after treatment. Activity of IL-10 is inferred by high levels of anti-Leishmania specific IgG1 and IgG3. TGF-beta had elevated total, but not of active, levels lessening the likelihood of being the IFN-gamma counterpart. Spleen or liver size presented a steady decrease but return to normal values at only 120 days after treatment. Anti-Leishmania IgG (total and subclasses) levels and DTH or Leishmania-stimulated lymphocyte proliferation conversion to positive also present a slow decrease after treatment. IL-6 plasma levels were elevated in only a few patients.

CONCLUSION

Taken together our results suggest that IFN-gamma and IL-10 are the molecules most likely involved in determining fate of disease. After treatment, there is a long delay before the immune profile returns to normal what precludes using plasma cytokine levels as criteria of cure as simpler clinical evaluations, as a palpable spleen or liver, can be used.

Leishmania promastigote membrane antigen-based enzyme-linked immunosorbent assay and immunoblotting for differential diagnosis of Indian post-kala-azar dermal leishmaniasis

Diagnosis of post-kala-azar dermal leishmaniasis (PKDL), caused by Leishmania donovani, is difficult, as the dermal lesions are of several types and resemble those caused by other skin diseases, especially leprosy. Since the disease generally appears very late after the clinical cure of kala-azar in India, it is also difficult to correlate PKDL with a previous exposure to L. donovani. Very few attempts have been made so far to diagnose PKDL serologically, and the diagnostic methods vary in their sensitivities and specificities. Diagnosis of PKDL through sophisticated PCR methods, although highly sensitive, has limited practical use. We have developed a serodiagnostic method using an enzyme-linked immunosorbent assay to detect specific immunoglobulin (Ig) isotypes and IgG subclass antibodies in the sera of Indian PKDL patients. Our assay, which uses L. donovani promastigote membrane antigens, was 100% sensitive for the detection of IgG and 96.7% specific for the detection of IgG and IgG1. Optical density values for individual patients, however, demonstrated wide variations. Western blot analysis based on IgG reactivity could differentiate patients with PKDL from control subjects, which included patients with leprosy, patients from areas where kala-azar is endemic, and healthy subjects, by the detection of polypeptides of 67, 72, and 120 kDa. The recognition patterns of the majority of serum samples from patients with PKDL were also distinct from those of the serum samples from patients with visceral leishmaniasis (VL), at least for a 31-kDa polypeptide. To further differentiate patients with PKDL from those with active and cured VL, we analyzed the specific titers of the Ig isotypes and IgG subclasses. High levels of IgG, IgG1, IgG2, and IgG3 antibodies significantly differentiated patients with PKDL from patients cured of VL. The absence of antileishmanial IgE and IgG4 in patients with PKDL differentiated these patients from those with active VL. These results imply intrinsic differences in the antibodies generated in the sera from patients with PKDL and VL.

Immunoglobulin G and E responses in various stages of canine leishmaniosis

Pathogenesis in visceral leishmaniosis is associated with depressed cellular immunity and a significant rise of antileishmanial antibodies. We assessed the relative levels of immunoglobulin E anti-Leishmania infantum, together with those of IgG, IgG1 and IgG2, using the enzyme-linked immunosorbent assay (ELISA) test, in non-infected and infected dogs with or without symptoms, and their association with symptoms to differentiate the stages of the infection. The expression of all immunoglobulins (IgG, IgG1, IgG2 and IgE) was higher in symptomatic dogs than in all other categories. IgG and IgG2 expression was higher in the infected asymptomatic group than in the non-infected group, whereas IgG1 and IgE expression was only higher in symptomatic animals. This correlation between the expression of IgG1 and IgE and the pathology of leishmaniosis points to their potential role as markers of the active disease.

Characterization of immunoglobulin G and its subclass response to Indian kala-azar infection before and after chemotherapy

Serologic parameters of kala-azar were evaluated by Western blot analysis. Sera from kala-azar patients with confirmed diagnoses were screened for immunoglobulin G (IgG) and IgG subclass-specific reactivity against Leishmania donovani membrane antigen (LAg). Heterogeneous LAg-specific IgG reactivity with numerous proteins with molecular masses ranging from 18 to 190 kDa was observed. Though the individual band patterns were varied, seven polypeptides of approximately 31, 34, 51, 63, 72, 91, and 120 kDa were immunoreactive with all the sera tested from kala-azar patients. The band patterns of the immunoblots of sera from patients after treatment and clinical cure with sodium antimony gluconate revealed a decrease in the frequency of the bands. Still, recognition of the 63- and 120-kDa bands was 100%, and the 55- and 91-kDa fractions were recognized in 93% of the sera from cured individuals. Among the IgG subclasses, IgG1 reacted with the greatest number of polypeptides. The 63-kDa protein was again detected by all of the IgG subclasses of all the sera tested. Other fractions recognized by the subclasses of more than 70% of the serum samples included those of 47, 51, 55, and 78 kDa. Following treatment, 63- and 51-kDa bands were the most reactive with the IgG subclasses. LAg-associated cross-reaction with other reference human antisera revealed a mild reactivity of the 63-kDa polypeptide with some of the serum samples from leprosy, malaria, typhoid, tuberculosis, and healthy controls. Western blot analysis of LAg entrapped in liposomes, strong vaccine candidates against experimental visceral leishmaniasis, revealed a more restricted band pattern. The 63-kDa fraction revealed by all pre- and posttreatment sera showed almost negligible levels of cross-reaction with sera from patients with other diseases or from healthy controls. These observations provide insight into induced immunity during kala-azar infection for future application.

Study of specific IgG subclass antibodies for diagnosis of Gnathostoma spinigerum

Gnathostoma spinigerum infection is endemic in Thailand and many Asian countries. Current diagnosis is the skin test and enzyme-linked immunosorbent assay (ELISA) for IgG antibody against the G. spinigerum third-stage larvae (L3), but cross-reactivity is common. We evaluated the sensitivity and specificity of anti-G. spinigerum L3 IgG subclass antibodies for diagnosis of 43 patients with gnathostomiasis. The majority of patients with gnathostomiasis (91%) had eosinophilia. While the anti-G. spinigerum L3 IgG1 antibody provided the highest sensitivity (98%), the anti-G. spinigerum L3 IgG2 antibody had the highest specificity (88%). The ELISA that detected anti-G. spinigerum L3 IgG1 antibody could be a reliable laboratory screening test, while anti-G. spinigerum L3 IgG2 antibody could be used to confirm the diagnosis.

Characterization of Leishmania donovani antigens encapsulated in liposomes that induce protective immunity in BALB/c mice

Leishmania donovani promastigote membrane antigens (LAg) encapsulated in positively charged liposomes have been found to induce very significant levels of protection against experimental visceral leishmaniasis. The protectively immunized animals exhibited profound delayed-type hypersensitivity and antibody responses. The extent of protection induced by the same antigens, however, varied depending on the charge of the vesicles, with maximum induction by positively charged liposomes, followed by neutral liposomes and last negatively charged liposomes. Characterization of LAg and LAg entrapped in liposomes of different charges by Western blot analysis revealed the immunodominance of gp63 in all three vaccine preparations. The strong reactivity of antigens in a restricted antigen profile that included, in addition to gp63, 72-, 52-, 48-, 45-, 39-, and 20-kDa components in neutral and positively charged liposomes contrasted with the reactivity of a greater number of LAg components in negatively charged liposomes. Resistance to visceral leishmaniasis appears to depend on the immunity induced by gp63 and a few select antigens in association with the right liposomes. A striking similarity between the immunogenic profile of partially purified soluble antigens and that of LAg in neutral and positively charged liposomes suggests the potentiality of these antigens in future vaccine studies of L. donovani.

Differential decline in Leishmania membrane antigen-specific immunoglobulin G (IgG), IgM, IgE, and IgG subclass antibodies in Indian kala-azar patients after chemotherapy

Pathogenesis in kala-azar is associated with depressed cellular immunity and significant elevation of antileishmanial antibodies. Since these antibodies are present even after cure, analysis of the parasite-specific isotypes and immunoglobulin G (IgG) subclasses in kala-azar patients may shed new light on the immune responses during progression and resolution of infection. Using leishmanial membrane antigenic extracts, we investigated the relative levels of specific IgG, IgM, IgA, IgE, and IgG subclasses in Indian kala-azar patient sera during disease, drug resistance, and cure. Acute-phase sera showed strong stimulation of IgG, followed by IgE and IgM and lastly by IgA antibodies. IgG subclass analysis revealed expression of all of the subclasses, with a predominance of IgG1 during disease. Following sodium stibogluconate (SAG) resistance, the levels of IgG, IgM, IgE, and IgG4 remained constant, while there was a decrease in the titers of IgG2 and IgG3. In contrast, a significant (2.2-fold) increase in IgG1 was observed in these individuals. Cure, in both SAG-responsive and unresponsive patients, correlated with a decline in the levels of IgG, IgM, IgE, and all of the IgG subclasses. The stimulation of IgG1 and the persistence, most importantly, of IgE and IgG4 following drug resistance, along with a decline in IgE, IgG4, and IgG1 with cure, demonstrate the potential of these isotypes as possible markers for monitoring effective treatment in kala-azar.