Xuan, Keh Min
(2021)
Assessment of phagocytosis and
cytokine secretions by monocytes in
the presence of plasmodium falciparum.
Masters thesis, Universiti Sains Malaysia.
Abstract
Malaria remains one of the most common human infections worldwide. In
endemic areas, malaria is a leading cause of morbidity and mortality and it causes
significant socioeconomic burdens to the affected people. Monocytes are part of the
immune system to control parasite burden and to protect host against malaria
infection. Monocytes play their protective roles against malaria via phagocytosis,
cytokine production and antigen presentation. Though monocytes are crucial for
clearance of malaria infection, they also have been shown to cause adverse clinical
outcomes. The objective of this study was to determine the morphology of P.
falciparum, to assess phagocytic capability of infected red blood cells by human
monocytes and further measure the cytokine secretions of monocytes following
phagocytosis by using ELISA. In this study, monocytes were isolated from whole
blood collected from healthy individuals while Plasmodium falciparum (3D7) was
cultured under optimal conditions. Phagocytotic activity and cytokine production by
the monocytes following malaria infection were assessed in vitro by co-culturing the
monocytes and P. falciparum-infected red blood cells for 1 and 2 hours. The present
study demonstrated that the monocytes phagocytosed the P. falciparum-infected red
blood cells and the phagocytosis index increased with longer incubation time, from 8.2% at 1 hour incubation time to 10.4% (p<0.05) at 2 hours incubation time.
Following phagocytosis, the monocytes produced TNF-α, initiating innate immune
response to help in the clearance of parasite. The data have shown that monocytes
cultured alone expressed the highest level of TNF-α during 0 and 1 hour of incubation, while co-culture of monocytes with P. falciparum-infected red blood
cells produced the highest level of TNF-α after 2 hours of incubation. Comparing the
trend among monocyte control, parasite control and co-culture, all showed an
increase in the level of TNF-α produced in the first hour, but the concentration
decreased significantly in the second hour. As a conclusion, these findings suggest
that monocytes play an important role in malaria infection by phagocytosing the
parasites and producing TNF-α for the removal of parasites, thereby initiating an
immune response for malaria eradication.
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