Human diseases caused by protozoan parasites are renowned for their high rates of morbidity and mortality worldwide. Some examples include African trypanosomiasis or sleeping sickness, American trypanosomiasis or Chagas disease,... more
Human diseases caused by protozoan parasites are renowned for their high rates of morbidity and mortality worldwide. Some examples include African trypanosomiasis or sleeping sickness, American trypanosomiasis or Chagas disease, leishmaniases, malaria and babesiosis. These infections tend to follow a chronic rather than an acute course with lifelong persistence of parasites. Regulatory T cells (Treg), in particular the CD4+CD25+ cell subset, appear to control the immune competence of host response triggered by the presence of parasites, promoting homeostasis and protecting the host from collateral tissue damage whilst allowing parasite persistence. To date, there is still considerable controversy on the characteristics and function of these cells when induced during different protozoan infections, evidencing the need of further research. Therefore, this review aims to provide a comprehensive overview about Treg cells development, phenotype determination and general functions. The above pathologies were used as selected examples to discuss the role of Treg cells during protozoan infections. Understanding of the mechanisms that contribute towards homeostasis and the survival of the host, and simultaneously allow the persistence of the pathogen, may yield important insights for new strategies of prophylaxis and therapy.
Leishmania infantum is the causative agent of zoonotic visceral leishmaniasis (ZVL), a disease frequently characterized by specific impairment of cell-mediated immune responses and uncontrolled parasitization. Regulatory T cells (Treg)... more
Leishmania infantum is the causative agent of zoonotic visceral leishmaniasis (ZVL), a disease frequently characterized by specific impairment of cell-mediated immune responses and uncontrolled parasitization. Regulatory T cells (Treg) have been shown to be involved in the direct ...
This work aims to study the influence of H-2 locus in the control of Leishmania infantum infection by evaluating whether cytokine responses by host macrophages of different H-2 haplotype are differentially regulated, either induced or... more
This work aims to study the influence of H-2 locus in the control of Leishmania infantum infection by evaluating whether cytokine responses by host macrophages of different H-2 haplotype are differentially regulated, either induced or actively impaired during parasite growth and ...
Malaria cysteine proteases have been shown to be immunogenic and are being exploited as serodiagnostic markers, drug and vaccine targets. Several Plasmodium spp. cysteine proteases have been described and the best characterized of these... more
Malaria cysteine proteases have been shown to be immunogenic and are being exploited as serodiagnostic markers, drug and vaccine targets. Several Plasmodium spp. cysteine proteases have been described and the best characterized of these are the falcipains, a family of papain-family enzymes. Falcipain-2 and falcipain-3 act in concert with other proteases to hydrolyze host erythrocyte hemoglobin in the parasite food vacuole. Falcipain-1 has less similarity to the other falcipains and its physiological role in parasite asexual blood stage still remains uncertain. Immunolocalization studies using an antibody developed against the Plasmodium chabaudi recombinant chabaupain-1, the falcipain-1 ortholog, were performed confirming its cellular localization in both erythrocyte and mosquito ookinete stage. Immunostaining of chabaupain-1 preferentially in apical portion of parasite ookinete suggests that this protease may be related with parasite egression from mosquito midgut. Immune responses to chabaupain-1 were evaluated using two different adjuvants, chitosan nanoparticles and hydroxide aluminum. Mice immunized with the recombinant protein alone or in association with nanoparticles were challenged with P. chabaudi showing that immunization with the recombinant protein confers partial protection to blood stage infection in BALB/c animal model.
This study reports isoenzyme polymorphism of Leishmania strains isolated in different regions of Portugal between 1982 and 2005. A total of 213 strains were obtained from cases of visceral and cutaneous leishmaniasis isolated from... more
This study reports isoenzyme polymorphism of Leishmania strains isolated in different regions of Portugal between 1982 and 2005. A total of 213 strains were obtained from cases of visceral and cutaneous leishmaniasis isolated from immunocompetent patients (adults and children) and immunocompromised adults, as well as from dogs and sandflies. Four zymodemes were identified: MON-1, MON-24, MON-29 and MON-80. Zymodeme MON-1 was identified in 96.7% of the strains, predominating in both immunocompetent and immunocompromised human patients, and it was the only zymodeme isolated from dogs. Isoenzyme diversity in HIV-infected patients was higher than in the immunocompetent group, in which all the strains from visceral leishmaniasis were MON-1. The domestic dog was confirmed as the reservoir host of zoonotic leishmaniasis in Portugal and Phlebotomus perniciosus and Phlebotomus ariasi as vectors. The overall low enzyme polymorphism observed in the Portuguese foci contrasts with the neighbouring foci in Spain.Cette étude rapporte le polymorphisme d'isoenzyme de souches Leishmania isolées dans différentes régions du Portugal entre 1982 et 2005. Un total de 213 souches a été obtenu de cas de leishmaniose viscérale et cutanée, chez des patients adultes et enfants immunocompétents et chez des adultes immunodéprimés ainsi que chez des chiens et des mouches du sable. Quatre zymodèmes ont été identifiés: MON-1, MON-24, MON-29 et MON-80. Le zymodème MON-1 a été identifié chez 96.7% des souches avec la même prévalence chez les patients immunocompétents et chez les immunodéprimés et c’était le seul zymodème retrouvé chez les chiens. La diversité des isoenzymes chez les patients infectés par le VIH était plus élevée que chez les patients immunocompétents chez qui toutes les souches de leishmaniose viscérales isolées étaient MON- 1. Les chiens domestiques ont été confirmés comme étant l'hôte réservoir pour la leishmaniose zoonotique au Portugal; P. pernicious et P. ariasiétant les vecteurs. Le polymorphisme peu étendu en général dans les foyers portugais contraste avec les observations faites dans le foyer espagnol voisin.Este estudio reporta el polimorfismo enzimático de cepas de Leishmania aisladas en diferentes regiones de Portugal entre 1982 y 2005. Se obtuvieron 213 cepas de casos de leishmaniasis visceral y cutánea aisladas de pacientes inmunocompetentes (adultos y niños) y adultos inmunocomprometidos, así como de perros y moscas de la arena. Se identificaron cuatro zymodemos: MON-1, MON-24, MON-29 y MON-80. El zymodemo MON-1 se identificó en 96.7% de las cepas, predominando tanto en pacientes humanos inmunocompetentes como inmunocomprometidos, y fue el único zymodemo aislado de perros. La diversidad isoenzimática en pacientes infectados con VIH fue más alta que en el grupo inmunocompetente, en el cual toda las cepas de leishmaniasis visceral eran MON-1. Se confirmó al perro doméstico como hospedero reservorio de la leishmaniasis zoonótica en Portugal y a P. perniciosus y P. Ariasi como vectores. El bajo polimorfismo enzimático global observado en el foco portugués, contrasta con el del foco vecino en España.
The objective of this study was to analyse hepatic cellular immune response of mice with... more
The objective of this study was to analyse hepatic cellular immune response of mice with "cure" and "non-cure" phenotypes to Leishmania infantum infection. During infection establishment, elevated TGF-beta levels and absence of a Th1 response may have contributed to parasite multiplication and to similar hepatic parasitic loads. Later in infection, an increase in the number and activation levels of CD8+ cells was observed simultaneously with parasite elimination, but only significant in "cure" strain. During this recovering phase, "non-cure" animals showed low Th2 cytokine levels, while TGF-beta production was higher than in "cure" mice. These results point out to a role for CD8+ T cells in liver acquired immune response and to TGF-beta regulation of "cure" and…
This work aims to study the influence of H-2 locus in the control of Leishmania infantum infection by evaluating whether cytokine responses by host macrophages of different H-2 haplotype are differentially regulated, either induced or... more
This work aims to study the influence of H-2 locus in the control of Leishmania infantum infection by evaluating whether cytokine responses by host macrophages of different H-2 haplotype are differentially regulated, either induced or actively impaired during parasite growth and replication. This study shows that macrophages of "non-cure" phenotype (H-2(d)) are more susceptible to infection with virulent L. infantum promastigotes. Virulent parasites lead to impaired IL-12 and inhibited TNF-alpha expression. The degree of parasite virulence is an important contributing factor to differences detected in cytokine expression. Virulent parasites also induced TGF-beta, a deactivating cytokine that is known to suppress Th-1 type responses, thus allowing the parasite to subvert antimicrobial activity and increase its chances of survival. Depending on specific host haplotype, cells differentially respond to infection since TNF-alpha expression is inhibited and TGF-beta is enhanced by macrophages of "non-cure" phenotype, thus perhaps determining their degree of susceptibility in this strain of mice.
The aim of this study was to investigate whether treatment against canine leishmaniasis reduced the presence of Leishmania in the healthy skin of dogs, affecting the capacity of parasite transmission. A total of 37 dogs from an endemic... more
The aim of this study was to investigate whether treatment against canine leishmaniasis reduced the presence of Leishmania in the healthy skin of dogs, affecting the capacity of parasite transmission. A total of 37 dogs from an endemic region of leishmaniasis were studied. Thirteen symptomatic animals revealed parasites in the bone marrow and eight had also in the skin. Five of the 22 dogs that had been treated with meglumine antimoniate alone, meglumine antimoniate or trifluralin followed by allopurinol or just with allopurinol had the parasite in bone marrow but none showed Leishmania in the skin. One dog that was treated only with aminosidine was polisymptomatic and had parasites in bone marrow and skin. The different treatments used in this study did not completely eliminate the parasite allowing relapses to occur when the treatment is discontinued, but the use of meglumine antimoniate or allopurinol, alone or combined may improve dogs clinical condition and reduce or eliminate ...
In this study, protective effect and immune response elicited by protein fractions LiRic1 (> 75kDa) and LiRic2 (< 37kDa) released by Leishmania infantum promastigotes were analysed in challenged BALB/c mice. Viable parasites were... more
In this study, protective effect and immune response elicited by protein fractions LiRic1 (> 75kDa) and LiRic2 (< 37kDa) released by Leishmania infantum promastigotes were analysed in challenged BALB/c mice. Viable parasites were quantified in spleen and ...
The aim of the study was to assess the clinical, parasitological and immunological effect of a second inoculation of amastigotes in dogs previously inoculated with Leishmania infantum. Three dogs primarily inoculated with amastigotes... more
The aim of the study was to assess the clinical, parasitological and immunological effect of a second inoculation of amastigotes in dogs previously inoculated with Leishmania infantum. Three dogs primarily inoculated with amastigotes (Group I) and four with cultured virulent stationary phase promastigotes (Group II) were afterwards re-inoculated with 2x10(9) amastigotes per kg. Three other groups of dogs were used as controls: Group III was infected only once with amastigotes, Group IV only once with promastigotes and Group V was non infected. The animals were followed up by clinical and parasitological examinations, hematological and serum protein analysis, anti-leishmanial antibody levels and proliferative assays of specific peripheral blood mononuclear cells over a period up to 50 months. Parasites were isolated from lymph node of three animals during primary amastigote infection and in five animals (Group I and II) after re-challenge. Group I dogs presented a strong increase of the humoral immune response while Group II animals displayed no significant or significantly low antileishmanial antibodies titres, after re-challenge. The detection, only after challenge, of positive specific lymphoproliferation in two animals of Group II that had the longest primary infection interval (more than 26 months), indicates the requirement of a long time interval to obtain specific lymphocyte sensitization. A previous exposure to virulent cultured L. infantum promastigotes seems to confer some degree of resistance against an amastigote infection.
Canine visceral leishmaniasis (CanL) is an emerging disease, expanding in various parts of the world. The infection caused by Leishmania, an intracellular protozoan parasite, can show different clinical manifestations, from asymptomatic... more
Canine visceral leishmaniasis (CanL) is an emerging disease, expanding in various parts of the world. The infection caused by Leishmania, an intracellular protozoan parasite, can show different clinical manifestations, from asymptomatic or subclinical to symptomatic dogs, in which a wide spectrum of clinical signs is evident. The fact that the parasite replicates in different organs raises the hypothesis that each organ may have a specific immune response. The local immune responses should be evaluated and taken into consideration when developing prophylactic tools. Therefore, phenotypic characterization of peripheral blood, lymph node and bone marrow lymphocyte populations and the expression of class II molecules of major histocompatibility complex (MHCII) were performed in asymptomatic and symptomatic dogs and in dogs that had been diagnosed and treated for leishmaniasis. Our findings showed that blood and bone marrow lymphocytes from symptomatic dogs were highly activated. In bone marrow of asymptomatic and treated dogs, a high frequency of MHCII(+) lymphocytes was observed, as well as MHCII(+) monocytes in the treated group. These results show increased expression of MHCII molecules giving evidence for antigenic presentation mainly by lymphocytes. The symptomatic and treated dogs showed an expansion of CD4(+) T cells subpopulations in lymph nodes, revealing an important contribution of these cells in controlling local parasite replication. This study also underlines the eventual importance of CD3(+)CD4(-)CD8(-) (double negative) and CD3(+)CD4(+)CD8(+) (double positive) T cell subsets in sensing and controlling latent infections and their possible function in the immune dynamics during CanL. The specific cellular immune responses raised in different compartments where the parasite replicates seem to have variable effects on local parasite control, highlighting the complexity of the cellular immune response developed by the dog infected by Leishmania infantum.
Canine leishmaniosis, caused by Leishmania infantum, is a systemic disease with variable clinical signs and a progressive evolution. This disease is characterized by impaired T cell-mediated immune response, which has been associated with... more
Canine leishmaniosis, caused by Leishmania infantum, is a systemic disease with variable clinical signs and a progressive evolution. This disease is characterized by impaired T cell-mediated immune response, which has been associated with disease chronicity and high mortality. Protective immunity against leishmaniosis is thought to be mediated by T cell and cytokine production. The T cell activation requires a primary signal delivered by the major histocompatibility complex (MHC) molecules present on the surface of antigen presenting cells, and a non-specific signal generated by co-stimulatory molecules. To characterize canine immune responses in the presence of L. infantum parasites or their antigens, in vitro cell cultures of canine macrophages and lymphocytes were established, and the macrophages presenting MHC class II molecules were evaluated as well as the expression of IL-12 and CD80-86 co-stimulatory molecules and nitric oxide production. The results showed for the first tim...