RESUMO
Biological interactions play an important role in regulating and maintaining natural populations. Like most interactions, parasitism may be influenced by environmental conditions. Therefore, changes caused by human activity may drastically affect the equilibrium of the assemblages of parasitized organisms (hosts). Herein, we described the composition of hemoparasites of anurans from two distinct environments: forest and oil palm plantations. We identified the most frequent groups of blood parasites, and whether infections differ between habitats (forest and plantation) and between microhabitats (arboreal or terrestrial). We collected 128 anurans, of which 46 (36%) were parasitized by hemoparasites. The genus Trypanosoma spp. was found in 30% (n = 37/128) of the infected anurans in both habitats, recorded mostly in terrestrial anurans in oil palm plantations. Apicomplexa hemoprotozoans were also found in 13% (n=17/128) of the anurans, which mainly were terrestrial species collected in oil palm plantations. There was no difference in parasitism between the two assemblies and between the studied microhabitats. This is the first study that has analyzed the ecological relationship between anurans as hosts and their blood parasites, in a region under intense anthropic pressure, in the Brazilian Amazon.
Assuntos
Parasitos , Agricultura , Animais , Anuros , Ecossistema , Florestas , HumanosRESUMO
The mechanism by which protective immunity to Plasmodium is lost in the absence of continued exposure to this parasite has yet to be fully elucidated. It has been recently shown that IFN-γ produced during human and murine acute malaria primes the immune response to TLR agonists. In this study, we investigated whether IFN-γ-induced priming is important to maintain long-term protective immunity against Plasmodium chabaudi AS malaria. On day 60 postinfection, C57BL/6 mice still had chronic parasitemia and efficiently controlled homologous and heterologous (AJ strain) challenge. The spleens of chronic mice showed augmented numbers of effector/effector memory (TEM) CD4(+) cells, which is associated with increased levels of IFN-γ-induced priming (i.e., high expression of IFN-inducible genes and TLR hyperresponsiveness). After parasite elimination, IFN-γ-induced priming was no longer detected and protective immunity to heterologous challenge was mostly lost with >70% mortality. Spontaneously cured mice had high serum levels of parasite-specific IgG, but effector T/TEM cell numbers, parasite-driven CD4(+) T cell proliferation, and IFN-γ production were similar to noninfected controls. Remarkably, the priming of cured mice with low doses of IFN-γ rescued TLR hyperresponsiveness and the capacity to control heterologous challenge, increasing the TEM cell population and restoring the CD4(+) T cell responses to parasites. Contribution of TLR signaling to the CD4(+) T cell responses in chronic mice was supported by data obtained in mice lacking the MyD88 adaptor. These results indicate that IFN-γ-induced priming is required to maintain protective immunity against P. chabaudi and aid in establishing the molecular basis of strain-transcending immunity in human malaria.
Assuntos
Linfócitos T CD4-Positivos/imunologia , Interferon gama/imunologia , Malária/imunologia , Plasmodium chabaudi/imunologia , Animais , Linfócitos T CD4-Positivos/metabolismo , Proliferação de Células , Feminino , Imunoglobulina G/sangue , Contagem de Linfócitos , Malária/sangue , Malária/parasitologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Fator 88 de Diferenciação Mieloide/genética , Fator 88 de Diferenciação Mieloide/imunologia , Fator 88 de Diferenciação Mieloide/metabolismo , Parasitemia/imunologia , Parasitemia/parasitologia , Transdução de Sinais/imunologiaRESUMO
Plasmodium chabaudi infection induces a rapid and intense splenic CD4(+) T cell response that contributes to both disease pathogenesis and the control of acute parasitemia. The subsequent development of clinical immunity to disease occurs concomitantly with the persistence of low levels of chronic parasitemia. The suppressive activity of regulatory T (T(reg)) cells has been implicated in both development of clinical immunity and parasite persistence. To evaluate whether IL-2 is required to induce and to sustain the suppressive activity of T(reg) cells in malaria, we examined in detail the effects of anti-IL-2 treatment with JES6-1 monoclonal antibody (mAb) on the splenic CD4(+) T cell response during acute and chronic P. chabaudi AS infection in C57BL/6 mice. JES6-1 treatment on days 0, 2 and 4 of infection partially inhibits the expansion of the CD4(+)CD25(+)Foxp3(+) cell population during acute malaria. Despite the concomitant secretion of IL-2 and expression of high affinity IL-2 receptor by large CD4(+) T cells, JES6-1 treatment does not impair effector CD4(+) T cell activation and IFN-γ production. However, at the chronic phase of the disease, an enhancement of cellular and humoral responses occurs in JES6-1-treated mice, with increased production of TNF-α and parasite-specific IgG2a antibodies. Furthermore, JES6-1 mAb completely blocked the in vitro proliferation of CD4(+) T cells from non-treated chronic mice, while it further increased the response of CD4(+) T cells from JES6-1-treated chronic mice. We conclude that JES6-1 treatment impairs the expansion of T(reg) cell population during early P. chabaudi malaria and enhances the Th1 cell response in the late phase of the disease.
Assuntos
Anticorpos Monoclonais/imunologia , Interleucina-2/imunologia , Malária/imunologia , Linfócitos T Reguladores/imunologia , Células Th1/imunologia , Animais , Anticorpos Monoclonais/farmacologia , Linfócitos T CD4-Positivos/imunologia , Linfócitos T CD4-Positivos/metabolismo , Proliferação de Células/efeitos dos fármacos , Células Cultivadas , Doença Crônica , Feminino , Citometria de Fluxo , Fatores de Transcrição Forkhead/imunologia , Fatores de Transcrição Forkhead/metabolismo , Imunofenotipagem , Interferon gama/imunologia , Interferon gama/metabolismo , Interleucina-2/metabolismo , Subunidade alfa de Receptor de Interleucina-2/imunologia , Subunidade alfa de Receptor de Interleucina-2/metabolismo , Subunidade beta de Receptor de Interleucina-2/imunologia , Subunidade beta de Receptor de Interleucina-2/metabolismo , Ativação Linfocitária/efeitos dos fármacos , Ativação Linfocitária/imunologia , Malária/tratamento farmacológico , Malária/parasitologia , Camundongos , Camundongos Endogâmicos C57BL , Parasitemia/tratamento farmacológico , Parasitemia/imunologia , Parasitemia/parasitologia , Plasmodium chabaudi/efeitos dos fármacos , Plasmodium chabaudi/imunologia , Baço/citologia , Baço/imunologia , Baço/metabolismo , Linfócitos T Reguladores/metabolismo , Células Th1/metabolismoRESUMO
The pivotal role of spleen CD4(+) T cells in the development of both malaria pathogenesis and protective immunity makes necessary a profound comprehension of the mechanisms involved in their activation and regulation during Plasmodium infection. Herein, we examined in detail the behaviour of non-conventional and conventional splenic CD4(+) T cells during P. chabaudi malaria. We took advantage of the fact that a great proportion of CD4(+) T cells generated in CD1d(-/-) mice are I-A(b)-restricted (conventional cells), while their counterparts in I-A(b-/-) mice are restricted by CD1d and other class IB major histocompatibility complex (MHC) molecules (non-conventional cells). We found that conventional CD4(+) T cells are the main protagonists of the immune response to infection, which develops in two consecutive phases concomitant with acute and chronic parasitaemias. The early phase of the conventional CD4(+) T cell response is intense and short lasting, rapidly providing large amounts of proinflammatory cytokines and helping follicular and marginal zone B cells to secrete polyclonal immunoglobulin. Both TNF-α and IFN-γ production depend mostly on conventional CD4(+) T cells. IFN-γ is produced simultaneously by non-conventional and conventional CD4(+) T cells. The early phase of the response finishes after a week of infection, with the elimination of a large proportion of CD4(+) T cells, which then gives opportunity to the development of acquired immunity. Unexpectedly, the major contribution of CD1d-restricted CD4(+) T cells occurs at the beginning of the second phase of the response, but not earlier, helping both IFN-γ and parasite-specific antibody production. We concluded that conventional CD4(+) T cells have a central role from the onset of P. chabaudi malaria, acting in parallel with non-conventional CD4(+) T cells as a link between innate and acquired immunity. This study contributes to the understanding of malaria immunology and opens a perspective for future studies designed to decipher the molecular mechanisms behind immune responses to Plasmodium infection.
Assuntos
Antígenos CD1d/fisiologia , Linfócitos T CD4-Positivos/imunologia , Malária/imunologia , Parasitemia/imunologia , Plasmodium chabaudi/imunologia , Baço/imunologia , Animais , Anticorpos Antiprotozoários/sangue , Linfócitos T CD4-Positivos/patologia , Citocinas/metabolismo , Ensaio de Imunoadsorção Enzimática , Feminino , Interferon gama/metabolismo , Complexo Principal de Histocompatibilidade/imunologia , Malária/parasitologia , Malária/patologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Parasitemia/patologia , Baço/patologia , Fator de Necrose Tumoral alfa/metabolismoRESUMO
The NK1.1 molecule participates in NK, NKT, and T-cell activation, contributing to IFN-gamma production and cytotoxicity. To characterize the early immune response to Plasmodium chabaudi AS, spleen NK1.1(+) and NK1.1(-) T cells were compared in acutely infected C57BL/6 mice. The first parasitemia peak in C57BL/6 mice correlated with increase in CD4(+)NK1.1(+)TCR-alphabeta(+), CD8(+)NK1.1(+)TCR-alphabeta(+), and CD4(+)NK1.1(-)TCR-alphabeta(+) cell numbers per spleen, where a higher increment was observed for NK1.1(+) T cells compared to NK1.1(-) T cells. According to the ability to recognize the CD1d-alpha-GalCer tetramer, CD4(+)NK1.1(+) cells in 7-day infected mice were not predominantly invariant NKT cells. At that time, nearly all NK1.1(+) T cells and around 30% of NK1.1(-) T cells showed an experienced/activated (CD44(HI)CD69(HI)CD122(HI)) cell phenotype, with high expression of Fas and PD-L1 correlating with their low proliferative capacity. Moreover, whereas IFN-gamma production by CD4(+)NK1.1(+) cells peaked at day 4 p.i., the IFN-gamma response of CD4(+)NK1.1(-) cells continued to increase at day 5 of infection. We also observed, at day 7 p.i., 2-fold higher percentages of perforin(+) cells in CD8(+)NK1.1(+) cells compared to CD8(+)NK1.1(-) cells. These results indicate that spleen NK1.1(+) and NK1.1(-) T cells respond to acute P. chabaudi malaria with different kinetics in terms of activation, proliferation, and IFN-gamma production.
Assuntos
Malária/imunologia , Células T Matadoras Naturais/metabolismo , Plasmodium chabaudi/imunologia , Baço/imunologia , Subpopulações de Linfócitos T/metabolismo , Animais , Antígenos CD/biossíntese , Antígenos Ly/biossíntese , Proliferação de Células , Imunofenotipagem , Interferon gama/metabolismo , Ativação Linfocitária , Malária/patologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Subfamília B de Receptores Semelhantes a Lectina de Células NK/biossíntese , Células T Matadoras Naturais/imunologia , Células T Matadoras Naturais/parasitologia , Células T Matadoras Naturais/patologia , Plasmodium chabaudi/patogenicidade , Baço/parasitologia , Baço/patologia , Subpopulações de Linfócitos T/imunologia , Subpopulações de Linfócitos T/parasitologia , Subpopulações de Linfócitos T/patologiaRESUMO
The mechanisms responsible for the generation and maintenance of immunological memory to Plasmodium are poorly understood and the reasons why protective immunity in humans is so difficult to achieve and rapidly lost remain a matter for debate. A possible explanation for the difficulty in building up an efficient immune response against this parasite is the massive T cell apoptosis resulting from exposure to high-dose parasite Ag. To determine the immunological mechanisms required for long-term protection against P. chabaudi malaria and the consequences of high and low acute phase parasite loads for acquisition of protective immunity, we performed a detailed analysis of T and B cell compartments over a period of 200 days following untreated and drug-treated infections in female C57BL/6 mice. By comparing several immunological parameters with the capacity to control a secondary parasite challenge, we concluded that loss of full protective immunity is not determined by acute phase parasite load nor by serum levels of specific IgG2a and IgG1 Abs, but appears to be a consequence of the progressive decline in memory T cell response to parasites, which occurs similarly in untreated and drug-treated mice with time after infection. Furthermore, by analyzing adoptive transfer experiments, we confirmed the major role of CD4(+) T cells for guaranteeing long-term full protection against P. chabaudi malaria.
Assuntos
Anticorpos Antiprotozoários/sangue , Subpopulações de Linfócitos B/imunologia , Imunidade Inata , Memória Imunológica , Malária/imunologia , Malária/parasitologia , Plasmodium chabaudi/imunologia , Subpopulações de Linfócitos T/imunologia , Animais , Anticorpos Antiprotozoários/biossíntese , Subpopulações de Linfócitos B/efeitos dos fármacos , Subpopulações de Linfócitos B/parasitologia , Eritrócitos/imunologia , Eritrócitos/parasitologia , Feminino , Imunidade Inata/efeitos dos fármacos , Imunidade Inata/genética , Memória Imunológica/efeitos dos fármacos , Memória Imunológica/genética , Malária/tratamento farmacológico , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Parasitemia/tratamento farmacológico , Parasitemia/imunologia , Parasitemia/parasitologia , Plasmodium chabaudi/efeitos dos fármacos , Subpopulações de Linfócitos T/efeitos dos fármacos , Subpopulações de Linfócitos T/parasitologia , Fatores de TempoRESUMO
It is generally accepted that Plasmodium vivax, the most widely distributed human malaria, does not cytoadhere in the deep capillaries of inner organs and thus this malaria parasite must have evolved splenic evasion mechanism in addition to sequestration. The spleen is a uniquely adapted lymphoid organ whose central function is the selective clearance of cell and other particles from the blood, and microbes including malaria. Splenomegaly is a hallmark of malaria and no other disease seems to exacerbate this organ as this disease does. Besides this major selective clearance function however, the spleen is also an erythropoietic organ which, under stress conditions, can be responsible for close to 40% of the RBC populations. Data obtained in experimental infections of human patients with P. vivax showed that anaemia is associated with acute and chronic infections and it has been postulated that the continued parasitemia might have been sufficient to infect and destroy most circulating reticulocytes. We review here the basis of our current knowledge of variant genes in P. vivax and the structure and function of the spleen during malaria. Based on this data, we propose that P. vivax specifically adhere to barrier cells in the human spleen allowing the parasite to escape spleen-clearance while favouring the release of merozoites in an environment where reticulocytes, the predominant, if not exclusive, host cell of P. vivax, are stored before their release into circulation to compensate for the anaemia associated with vivax malaria.