Diversidade antigênica e evasão imune nos parasitos da malária

Clinical immunity against blood stage malaria is achieved only after multiple infections with the same species. A major reason for this is the extense diversity of antigens located at the parasites surface or even at the surface of the infected red blood cell. There are two sources for antigenic diversity: first, there is allelic polymorphism with the existence of different and genetically stable versions of antigen encoding genes, generated through mutations and recombination. The second source is antigenic variation, a mechanism by which different antigens are expressed successively without change of the underlying genotype (Ferreira and col., 2007). Herein, we discuss the mechanisms and origins of diversity and antigenic variationUma das principais razões do porquê a imunidade clínica contra a malária se desenvolve somente após diversas infecções pela mesma espécie de parasito se deve à extensa diversidade dos antígenos de superfície dos plasmódios e de hemácias infectadas. Existem duas origens para tal diversidade antigênica: uma é o polimorfismo alélico, com a existência de formas alternativas e estáveis de genes que codificam antígenos, gerados através de mutações e recombinações; outra é devido à variação antigênica, mecanismo pelo qual uma linhagem clonal de parasitos expressa sucessivamente formas alternativas de um antígeno sem alterações de genótipo (Ferreira e col., 2007). Aqui, os mecanismos e origens da diversidade e variação antigênica são discutido

Antibody recognition of plasmodium falciparum infected red blood cells by symptomatic and asymptomatic individuals in the brazilian Amazon

In the Amazon Region, there is a virtual absence of severe malaria and few fatal cases of naturally occurring Plasmodium falciparum infections; this presents an intriguing and underexplored area of research. In addition to the rapid access of infected persons to effective treatment, one cause of this phenomenon might be the recognition of cytoadherent variant proteins on the infected red blood cell (IRBC) surface, including the var gene encoded P. falciparum erythrocyte membrane protein 1. In order to establish a link between cytoadherence, IRBC surface antibody recognition and the presence or absence of malaria symptoms, we phenotype-selected four Amazonian P. falciparum isolates and the laboratory strain 3D7 for their cytoadherence to CD36 and ICAM1 expressed on CHO cells. We then mapped the dominantly expressed var transcripts and tested whether antibodies from symptomatic or asymptomatic infections showed a differential recognition of the IRBC surface. As controls, the 3D7 lineages expressing severe disease-associated phenotypes were used. We showed that there was no profound difference between the frequency and intensity of antibody recognition of the IRBC-exposed P. falciparum proteins in symptomatic vs. asymptomatic infections. The 3D7 lineages, which expressed severe malaria-associated phenotypes, were strongly recognised by most, but not all plasmas, meaning that the recognition of these phenotypes is frequent in asymptomatic carriers, but is not necessarily a prerequisite to staying free of symptoms.In the Amazon Region, there is a virtual absence of severe malaria and few fatal cases of naturally occurring Plasmodium falciparum infectionsthis presents an intriguing and underexplored area of research. In addition to the rapid access of infected p1095598601FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO2009/17114-3576128/2008-2To Wolfgang Fischer and Márcio Yamamoto, for sequencing of DBLα tag sequences, and to Drs Mauro Shugiro Tada and Tony Katsuragawa, for help with data and sample collection at the site

Variant surface antigens from Plasmodium falciparum-infected erythrocytes in Brazilian Amazon: adherence to endothelium receptors (CD36 and ICAM-1) and antibodies recognition.

A relativa raridade de casos graves de malária no Brasil sugere que os isolados locais de Plasmodium falciparum tenham menor virulência que os parasitas africanos e asiáticos. Este trabalho investigou os padrões de aderência de sete isolados de P. falciparum, provenientes de uma área da Amazônia brasileira em que a malária grave é rara, a dois receptores do endotélio vascular, CD36 e ICAM-1. Também analisamos a resposta de anticorpos de indivíduos locais contra oitos antígenos de superfície, incluindo isolados de campo e a cepa 3D7. Mostramos que: (a) de modo geral, os isolados locais de P. falciparum expressam VSAs capazes de aderir tanto a ICAM-1 quanto a CD36; (b) detectamos anticorpos contra antígenos apresentados por isolados de campo e pela cepa 3D7 entre moradores de uma área endêmica próxima à origem dos isolados; (c) vimos que alguns dos soros testados foram capazes de bloquear a adesão de hemácias parasitadas a ICAM-1 e CD36, in vitro; (d) detectamos uma baixa prevalência do alelo S (hemoglobina S) na população de estudo.The relative rarity of severe malaria in Brazil suggests that the local Plasmodium falciparum isolates are less virulent than African and Asian parasites. This work investigated adherence patterns to CD36 and ICAM-1, two receptors of the vascular endothelium, in P. falciparum isolates from an area of the Brazilian Amazonia, where severe malaria is rare. We also analyzed, in the same area, the antibody responses of people against eight VSAs. We found that: (a) local P. falciparum isolates express VSAs capable to adhere to both receptors, CD36 and ICAM-1; (b) we detected antibodies against VSAs in a human population exposed to malaria, expressed from local parasites and the 3D7 control; (c) we found in vitro that some sera contained naturally acquired antibodies which blocked the adherence of the parasitized RBCs to ICAM-1 and CD36; (d) we detected a low frequency of the S allele (hemoglobin S) in the study population

Análise da expressão e silenciamento de genes do trato digestivo de Anopheles aquasalis

Estudos recentes vêm elucidando a importância de uma diversidade de proteínas do intestino médio de insetos vetores, tanto nos processos de digestão como em respostas imunológicas e interações parasita-hospedeiro. Este trabalho teve como objetivo analisar a expressão de genes do intestino médio de Anopheles aquasalis, um importante vetor de malária no Brasil, a partir de clones sequenciados de bibliotecas de cDNA de machos e fêmeas alimentados apenas com sacarose. Nas fêmeas, pôde-se notar a grande predominância de serino proteases, proteínas ligantes de quitina e fatores relacionados à imunidade. Os machos também apresentaram diversos peptídeos de defesa imune, porém apenas uma protease digestiva e uma glicosidase. Alguns genes foram selecionados das bibliotecas para estudo de suas expressões durante a vida de An. aquasalis. Tripsina 1, peritrofina 1 e quinurenina 3-monooxigense tiveram seus níveis de expressão aumentados 6h após a ingestão de sangue, analisados através de qRT-PCR. No entanto, o silenciamento desses genes não resultou em alterações na longevidade de fêmeas adulta. O gene da serpina foi expresso em todas as fases do desenvolvimento do mosquito, exceto em ovos; e o gene da cecropina foi expresso em trato digestivo e carcaça de machos e fêmeas, principalmente após alimentação de açúcar ou sangue. Considerando que a ingestão de alimentos é a principal porta de entrada a microorganismos durante a vida adulta destes mosquitos, a presença de diversos produtos antimicrobianos, bem como a precoce expressão de peritrofina, outra proteína relacionada com a proteção do trato digestivo, mostrou que An. aquasalis está bem preparado imunologicamente contra esses microorganismos. Esta proteção está envolvida com o hábito alimentar desta espécie e pode também estar associada à sua baixa capacidade vetorial com relação aos plasmódios.The importance of midgut proteins of Anopheles aquasalis has been elucidated both in digestion process as in immune responses and parasite-host interactions. This project targeted to analyze the midgut genes expression from An. aquasalis, an important malaria vector in Brazil, selecting clones from midgut cDNA library of female and male mosquitoes fed only on sugar. Serine proteases were predominant in females besides chitin binding proteins and immunity factors. Male mosquitoes also showed immune defense peptides, however only one digestive protease and one glucosidase. Some genes were selected from these libraries to expression study during mosquito development stages. Trypsin 1, peritrophin 1 and kynurenine 3-monoxygenase expression were up regulated at the midgut 6h after blood feeding, analyzed by real time PCR. Nevertheless, the gene silencing did not change the survivorship of adult females. Serpin gene was expressed in all mosquito development stages but eggs; cecropin gene was expressed in midgut and carcass from male and female, mainly after sugar or blood feeding. Considering the alimentation is the main entrance way of pathogens, the presence of antimicrobial peptides as the early peritrophin expression showed that An. aquasalis is immunologically adapted against these microorganisms. This protection is involved in feeding behavior of this specie and can be also related to its low Plasmodium vector capacity.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Factors in time to malaria treatment in the Brazilian Amazon: a survival analysis

Background: Malaria continues to be one of the most relevant infectious diseases in Brazil and globally, with over 150.000 cases in 2019 alone. Due to high P. vivax prevalence and P. falciparum elimination goals, the Brazilian Malaria Elimination Program placed a high priority on timely treatment. Cases in the country are concentrated in the Legal Amazon region, with diagnosis and treatment provided for free by the government through its public health system, but many relevant questions about heterogeneity in risk and access to treatment remain. Methods: We use data from the Malaria Epidemiological Surveillance System, maintained by the Ministry of Health, from 2007-2019 to analyze factors that affect time to treatment of malaria in three distinct periods. We use Kaplan-Meier survival functions to estimate the interval between the appearance of first symptoms and beginning of treatment for several administrative, demographic, social and health variables. Results: Despite advances in malaria control over the last two decades, the program has not achieved its timely treatment goals in any of the periods analyzed. Malaria risk was highest among working-age adults, concentrated in a few high risk municipalities, autochthonously transmitted, in agriculture and domestic services, lower education, mid to low levels of parasitaemia, brown, indigenous and black populations and males. The main parasite is P. vivax and the majority of cases is still passively detected. Time-to-treatment was lower when they were detected actively, had lower levels of schooling, were not pregnant or past the 2nd trimester, between 0 and 14 years of age, worked in agriculture, had low parasite counts, were infected with P. falciparum, were indigenous people and lived in high risk municipalities. Conclusions: Differences in access to treatment were small if compared to differences in risk of acquiring malaria in the first place, but active case detection, municipal risk and race showed significant differences and potential avenues for intervention

Vector-Focused Approaches to Curb Malaria Transmission in the Brazilian Amazon: An Overview of Current and Future Challenges and Strategies

In Brazil, malaria transmission is mostly confined to the Amazon, where substantial progress has been made towards disease control in the past decade. Vector control has been historically considered a fundamental part of the main malaria control programs implemented in Brazil. However, the conventional vector-control tools have been insufficient to control or eliminate local vector populations due to the complexity of the Amazonian rainforest environment and ecological features of malaria vector species in the Amazon, especially Anopheles darlingi. Malaria elimination in Brazil and worldwide eradication will require a combination of conventional and new approaches that takes into account the regional specificities of vector populations and malaria transmission dynamics. Here we present an overview on both conventional and novel promising vector-focused tools to curb malaria transmission in the Brazilian Amazon. If well designed and employed, vector-based approaches may improve the implementation of malaria-control programs, particularly in remote or difficult-to-access areas and in regions where existing interventions have been unable to eliminate disease transmission. However, much effort still has to be put into research expanding the knowledge of neotropical malaria vectors to set the steppingstones for the optimization of conventional and development of innovative vector-control tools

Immunoproteomics of Plasmodium falciparum-infected red blood cell membrane fractions

BACKGROUND The surface of infected red blood cells (iRBCs) has been widely investigated because of the molecular complexity and pathogenesis mechanisms involved. Asymptomatic individuals are important in the field because they can perpetuate transmission as natural reservoirs and present a challenge for diagnosing malaria because of their low levels of circulating parasites. Recent studies of iRBC antibody recognition have shown that responses are quantitatively similar in symptomatic and asymptomatic infections, but no studies have characterised the plasmodial proteins targeted by this response. OBJECTIVES Our main objective was to identify Plasmodium falciparum proteins associated with iRBC ghosts recognised by antibodies in the sera of symptomatic and asymptomatic individuals in the Brazilian Amazon. METHODS We collected symptomatic and asymptomatic sera from patients residing in the Brazilian Amazon and P. falciparum iRBC ghosts to identify the proteins involved in natural antibody recognition by 2D-electrophoresis, western blotting, and highresolution mass spectrometry. FINDINGS 2D gel-based immunoproteome analysis using symptomatic and asymptomatic sera identified 11 proteins with at least one unique peptide, such as chaperones HSP70-1 and HSP70-x, which likely are components of the secretion machinery/PTEX translocon. PfEMP1 is involved in antigenic variation in symptomatic infections and we found putative membrane proteins whose functions are unknown. MAIN FINDINGS Our results suggest a potential role of old and new proteins, such as antigenic variation proteins, iRBC remodelling, and membrane proteins, with no assigned functions related to the immune response against P. falciparum, providing insights into the pathogenesis, erythrocyte remodelling, and secretion machinery important for alternative diagnosis and/or malaria therapy.publishersversionpublishe