Biophysical properties of blood-stage Plasmodium falciparum malaria: from single-cell host-pathogen interactions to human protective polymorphisms

Malaria is a mosquito-borne infectious disease responsible for half a million deaths every year and long-term economic stagnation in many countries where it is endemic. All symptoms and pathology of malaria are caused by Plasmodium falciparum parasite, and are initiated when parasites invade human red blood cells, then mature and multiply inside them in approximately 48 hours. The invasion process is completed in less than a minute and is one of the most crucial, yet least understood, phases of malaria infection. It also represents a brief window in which the parasites are extracellular and hence exposed to the host immune system, therefore representing a potential target for vaccines and treatments. The work described in this thesis firstly includes the optimisation of a real-time live microscopy platform for recording parasite egress-invasion sequences under controlled conditions, and to investigate their morphology and kinetics. This set-up was employed to address the role of calcium in mediating successful invasion by observing the invasion process simultaneously in bright-field and fluorescence. Elevated calcium signal was found to be absent during the early steps of the process, implying that calcium does not trigger invasion, and an alternative invasion mechanism was suggested. To investigate whether parasite and host cell physical parameters were actively involved in invasion, adhesion forces between parasites and red cells were measured with optical tweezers, while the biophysical properties of the red blood cells such as bending modulus, tension, radius, and viscosity were assessed by analysing their plasma membrane fluctuations. In particular, cells from the Dantu blood group, a rare blood variant found mainly in East Africa that provides up to 70% protection against malaria, and from Beta-thalassaemia individuals, were studied. A general correlation between red blood cell membrane tension, invasion efficiency and dynamics was established, determining a protective tension threshold above which cells are less likely to be invaded. Finally, mature parasites have the ability to bind to the endothelium of peripheral blood vessels, causing impair flow that can lead to a range of fatal conditions. To study malaria cytoadherence to endothelial cells, a microfluidic device was designed to produce an in vitro physiologically relevant model of human circulation. Increasing cytoadhesion was experimentally associated with endothelial glycocalyx disruption as initial factor for malaria pathogenesis. Live imaging methods and techniques adopted in this study highlight mechanisms crucial for malaria infection, and represent an innovative and complementary study of this disease with respect to purely biological approaches. These findings show how changes in red blood cell biophysics can be linked to human evolutionary response against malaria with tangible effects on the population.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2020

Author dc:creator

• Introini, Viola

Advisor dc:contributor.advisor

• Cicuta, Pietro

• Plasmodium falciparum malaria
• Calcium
• Biophysics
• Dantu red blood cells
• Beta thalassaemia
• Cytoadherence
• Glycocalyx

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/6bcc61cd-193e-45d5-ac7f-bbc428802d89/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

Author Identifier

0000-0001-9012-4696

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/305576