AbstractsBiology & Animal Science

Tese de doutoramento, Ciências Biomédicas (Microbiologia e Parasitologia), Universidade de Lisboa, Faculdade de Medicina, 2014 Malaria and tuberculosis (TB) endemic regions overlap considerably, especially in sub-Saharan Africa. Although it is very likely that co-infections occur in these regions, not much is known about malaria-TB co-infections in humans, and how the interplay between these two infections might affect the prognosis of co-infected individuals. Furthermore, multiple Plasmodium infections will likely result in accumulation of malaria pigment (hemozoin) in host organs. Hemozoin was first thought of as an inert waste product resulting from hemoglobin digestion. However, several studies have associated the presence of hemozoin with host immunosuppression. Thus, the subject of this thesis was the study of Malaria-Tuberculosis co-infections with a particular focus on a possible role for hemozoin induced immunosuppression. For this, protocols for hemozoin production and characterization were first established. Then, in vitro studies to investigate how hemozoin ingestion affected cellular functions of human peripheral blood mononuclear cells (PBMC) were performed. For the first time hemozoin effects at the single cell level were investigated by flow-cytometry, using a novel method developed by us, which uses Side Scatter Depolarization for hemozoin detection. Following in vitro studies, we investigated hemozoin dynamics in host tissues of two murine models, post-malaria clearance. Hemozoin deposition in host organs was evaluated both by flow-cytometry, as well as by observation of histological preparations. Finally, the murine model was used to evaluate the susceptibility of Plasmodium infected mice to subsequent tuberculosis infection. Tuberculosis infection was evaluated during acute malaria, and during chronic Plasmodium infection. Results from in vitro studies suggested that hemozoin impaired cell functions and that these effects could be propagated to non-hemozoin containing cells. Hemozoin-induced impairment decreased microbicidal activity, as shown by higher mycobacterial load in these cells. Our investigation of hemozoin kinetics in host organs revealed that hemozoin is dynamic within and between host organs, with very little signs of it being eliminated over time. Malaria-tuberculosis co-infection in vivo demonstrated that mice presenting with acute malaria, have a poor prognosis when co-infected with tuberculosis. Mice infected with tuberculosis during chronic malaria did not become as sick as mice during acute infection however, they still exhibited symptoms of malaria-induced anaemia. Thus, in our model of co-infection hemozoin did not seem to contribute significantly to immunosuppression of the host nor to increased susceptibility to tuberculosis infection. Overall, we present a novel method for the detection of hemozoin that allowed functional investigation of hemozoin-containing and non-hemozoin containing leukocytes at the single cell level, in the same sample. This might be useful for…