Análises dos mecanismos imunopatológicos e moleculares envolvidos no processo de citoaderência de Plasmodium vivax

Author(s)

Catarina Baeta da Luz Bourgard

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
• Defense date: 2019-03-01

Examining board members

Fabio Trindade Maranhão Costa; Cristiana Ferreira Alves de Brito; Fernanda Janku Cabral; Gerhard Wunderlich; Danilo Ciccone Miguel

• Advisor: Letusa Albrecht; Fabio Trindade Maranhão Costa

Abstract

Plasmodium vivax is the most prevalent, widespread and neglected human malaria parasite, currently placing billions of people at risk of infection, thus imposing major health and economic burdens. Worldwide, anti-malarial drug resistance emergence and severe clinical complications are of great concern. The mechanisms underlying the pathobiology of the neglected P. vivax are still little known. The lack of a reliable in vitro P. vivax long-term culture restricts its biology study in place and time, relegating researchers to work in malaria endemic field conditions, where successful omics applications are very challenging. The capacity of P. vivax to remodel host reticulocyte membrane and promote adhesivity has been demonstrated, which is an important mechanism for host immune evasion. Functional studies have already reported that adhesion of P. vivax infected red blood cells (PvIRBCs) to the host endothelial cells, although in considerably lower rates, is as strong and stable as the verified for P. falciparum infections. Also, it has been reported adhesion of normocytes to the PvIRBCs is strong and results in stable rosette formation, which shows higher rates in vivax compared to falciparum malaria. More recently, it was reported that there is a correlation between rosette formation and altered membrane deformability of PvIRBCs, where the rosette-forming PvIRBCs are significantly more stiff and rigid than their non-rosetting equals. Mature staged parasites (schizonts) show a higher capacity for adherence than other asexual parasite stages both in cytoadherence and rosetting. The lower proportion of schizonts observed on the peripheral blood circulation of patients suggests that parasites could be sequestered on the host vascular endothelium. Rosette-forming PvIRBCs may also be the cause for this lower rate of schizonts in the patients’ blood, contributing for parasite sequestration phenomena in the host microvasculature and/or spleen, and consequently, the rheopathological characteristics present in vivax malaria disease. Vivax malaria patient autopsies have shown accumulation of PvIRBCs in the lungs, spleen, liver and bone marrow. Additionally, it has been demonstrated that parasitemia underestimates total parasite biomass, which is greater in severe vivax malaria patients, and thus, capable of mediating systemic inflammatory pathology. In this study, we aimed to understand the molecular mechanisms behind adherence phenotypes by identifying proteins, especially parasitic ligands, which might be important in P. vivax adhesion capacity. Using RNA-seq coupled with parasite field sample enrichment, ex vivo maturation and cytoadherence assays, we have sequenced the whole transcriptome of parasite populations with distinct adhesive characteristics. Our expression profiles brings out the importance of membrane and membrane-associated proteins, with adhesin or adhesin-like properties, such as Plasmodium Interspersed repeats (PIR) and Plasmodium Helical Interspersed SubTelomeric (PHIST) proteins, which might pay a role in adherence phenotypes. Within those protein groups, we found a percentage of differentially expressed genes that traditionally are more expressed in sexual rather than asexual parasite stages, suggesting the relevance of rosette formation by P. vivax gametocytes. Importantly, we found host immune-related differentially expressed genes, of which several are associated with the human phagocytosis pathways. These data strongly suggest that rosetting can hamper leukocyte phagocytosis host immune response, as an effective mechanism of P. vivax immune evasion adaptation. Our results reflect the pathobiology of circulating Brazilian P. vivax populations, principally concerning its adhesive capacity as a possible source of the severe clinical manifestations reported. Furthermore, we hope that such achievements will further enable the investigations on the biology of P. vivax apicomplexan parasite, impacting considerably in vaccine and drug design, ultimately helping us achieve the future elimination of vivax malaria. (AU)

• FAPESP's process: 13/20509-5 - Analyses of the immunopathological and molecular mechanisms involved in cytoadherence of Plasmodium vivax
• Grantee: Catarina Baeta da Luz Bourgard
• Support Opportunities: Scholarships in Brazil - Doctorate