EVALUATING THE IMPACT OF PLASMODIUM FALCIPARUM MEDIUM SIZED EXTRACELLULAR VESICLES ON HOST IMMUNITY

Abstract

Severe malaria is caused by Plasmodium falciparum, which causes two-thirds of malaria infections in sub-Saharan Africa with children under the age of 5 and pregnant women being the most affected. The mechanisms underlying malaria pathogenesis have been linked to the sequestration of infected red blood cells, immune activation, and inflammation. However, the full range of parasite factors that are involved in malaria pathogenesis is yet to be understood. One possible way of parasite-host interactions leading to inflammation is through released extracellular vesicles (EVs), which contain in them bioactive material that could be nucleic acids, proteins, lipids or other metabolites. Previous studies have been able to establish the interaction between the parasite-released EVs and host cells by using either mouse model malaria or long-term culture maintained parasite isolates which had recently not been into the host immune environment. I, therefore, used a short-term culture-adapted and ex-vivo matured clinical isolates as these isolates are still well adapted to survive within the host. I, particularly, evaluated the upregulation of surface activation markers CD25, CD69, and PD-1 on T cells, B cells, and monocytes following co-culture with medium-sized extracellular vesicles, and went further to determine the immune cell subsets that preferentially interact with the mEVs. I did this by co-culturing P. falciparum medium EVs with PBMCs for 18 hours, harvested the cells, stained them with antibodies conjugated to certain fluorochromes and analysed through flow cytometry. The results show that the mEVs from the short-term culture-adapted isolates induced expression of the activation marker CD69 on T cells, B cells and monocytes and CD25 on monocytes. However, the mEVs from the ex vivo matured isolates induced the expression of the activation marker CD25 on monocytes only. Further, mEVs have been identified to preferentially interact with monocytes and B cells. Overall, P. falciparum mEVs seem to preferentially interact and activate monocytes and the mEVs from the ex vivo isolates seem to have less impact on PBMCs as compared to culture-adapted isolates. The fact that the investigated PfmEVs activated T cells, B cells and monocytes to express costimulatory molecules CD69 and CD25 implies that mEVs may have a role in inducing inflammation during vi malaria infection. CD69 and CD25 are expressed on the surfaces of immune cells (T cells, B cells and monocytes) and are involved in the process of cells activation and the subsequent release of pro- and anti-inflammatory molecules. When the released inflammatory molecules fail to balance, then severe malaria normally results. Besides pathogenesis, the observation that mEVs from ex vivo clinical parasite isolates have a less impact on the immune cells compared to the mEVs from the short term lab adapted parasite isolate requires an investigation to test if the observed difference is due to a difference in the EV content in relation to the different adaptations in culture.