The role of human pentraxins in the Leishmania-vector lifecycle

Leishmaniasis is a disease caused by the protozoan parasite species Leishmania and is spread by the phlebotomine sand fly vector. Leishmaniasis has an array of clinical forms with varying severity, of which some can lead to organ failure and death. The WHO have estimated there are over 600,000 new cases every year and over one billion people living in endemic areas.

In order to complete its lifecycle and be transmitted to a new host, the Leishmania parasite must resist being defecated by the sand fly by attaching to the sand fly gut. However, the mechanism of this attachment differs depending on the species of Leishmania and sand fly. Some sand fly species only allow the survival and maturation of a few particular Leishmania species (restrictive vector). An attachment mechanism for one of these sand fly species has already been published with a sand fly midgut receptor interacting with specific sugars presented on a Leishmania surface molecule called LPG. Other sand fly species can support the maturation of a range of Leishmania species (permissive vector) but the mechanism of attachment for these sand flies is still unclear and it is thought to be LPG-independent. More recently it has been suggested that some midges are vectors of Leishmania, with the midgut attachment mechanism unknown.

This project comes under the theme of global infectious health and will look at the role of the human serum components pentraxins, to see if they cross-link the Leishmania parasite to the sand fly and midge midgut. It will also look at alternative Leishmania-midgut binding mechanisms and different roles for pentraxins within the vector, with the hope of eventually blocking parasite binding.

One part of this project has been to learn how to carry out midgut attachment assays. Midgut attachment assays involve the vector midgut being removed and opened longitudinally with parasites then being placed on top to see how binding differs under a range of conditions. Vectors infected with parasites can also be used. Using this technique allows us to study whole organism physiology. I have gained a lot of experience with these assays in the past couple of years. I have also spent time reviewing the literature, comparing studies which use this method. Results of different protocols and conditions can be compared using the appropriate statistical tests allowing us to quantify our data. Fly infections have been carried out to look at the effects of anti-pentraxin antibodies and compounds.

Bioinformatics will also be used to look for vector receptor candidates and to see if Leishmania or the vectors have a similar component to that found in human serum. I have been able to expand my knowledge in bioinformatics by attending a module ran at LSHTM.

Biacore surface plasmon resonance, western blots and ELISAs are being used to learn about the binding interaction of parasites and sand flies with the human serum components. Western blots and ELISAs allow us to see what parts of the Leishmania parasite or vector midgut the human serum components are binding to. The Biacore surface plasmon resonance system allows more information to be learnt about a binding interaction, for example we can find out about binding strength as well as rates of association/dissociation. I have limited experience in this technique, however my co-supervisor is an expert meaning I have the opportunity to learn a great deal and expand my interdisciplinary skill set.

Confocal microscopy is also being used in this study to look at the binding of these human serum components to parasite and midgut surfaces. I have been able to learn how to use the confocal microscope through the imaging unit at LSHTM.

I have attended four MSc modules at LSHTM and a range of the transferable skills courses. I was recently able to present a poster of my work at the WorldLeish7 conference in Cartagena, Colombia.