Investigating naturally occurring regulation of human IgE-mediated hypersensitivity using hookworm-schistosome co-infection

Hookworms are some of the most prevalent infections on earth, estimated to infect between 576 and 740 million people worldwide. A scourge in endemic regions, there is little evidence that naturally occurring immunity develops against them. Through secreted products hookworms potently modulate the immune system, providing them with longevity within the human host. This occurs even though they have tissue damaging interactions with the human host's gut while they feed. The mechanisms by which the immune system is modulated can be specific to hookworms or non-specific; the latter resulting in bystander effects, in which the response to other triggers of the immune system are down regulated. These bystander effects are one of the likely reasons for the very low incidence of allergic disease in communities where hookworm infection is endemic, and although attempts have been made to decipher the modulation exerted by hookworm on allergic responses, these are often hindered by the scarcity of individuals with allergic disease in hookworm endemic areas.

Responses to another prevalent worm infection, Schistosoma mansoni, can be under tight regulation. This is particularly true of the response to eggs which are deposited in their hundreds every day, a substantial number becoming trapped in the host tissue, exposing the host to molecules that initiate an immune response. Thus regulation of the response to these molecules prevents development of severe immune driven pathology. In contrast, the blood-dwelling adult schistosome worms immune evade, with cryptic triggers of the immune system only intermittently being exposed to the host upon worm death. This intermittent exposure allows the development of IgE mediated immunity; the same immune mechanism that causes allergic reactions, and indeed these IgE-assocatiated mechanisms observed in response to dying adult worms share many features with those observed in allergic diseases.

In Mayuge District, Uganda, where for the last decade we have been conducting research on the immune response to human worm infections, the burden of both hookworm and S. mansoni infection has remained high despite regular rounds of mass drug treatment. During our studies we have observed that the immune modulation of allergy associated responses by hookworm also encompasses the IgE mediated responses that are triggered during the development of immunity to S. mansoni infection. Here we propose to study the modulation of the anti-schistosome immune response by hookworm, investigating the targets of this modulation and the potential mechanisms by which hookworms exert their effects. This modulation by hookworm has major implications for the populations who are infected with these two worms, particularly in the context of drug administration schedules of the control programme. It may be that hookworm treatment needs to be administered prior to schistosome treatment, if the immune boosting treatment effects of anti-schistosome treatment are to be fully realised. Through the shared features with allergy, the study will also provide insight into how hookworm may modulate allergic responses, beneficial knowledge for developing treatments for the hundreds of million individuals currently estimated to have their daily lives adversely affected by allergic disease. This knowledge is critical as the number of individuals affected by allergy is constantly growing as our western lifestyle of urbanisation and development expands across the globe.

From our previous immunological observations among schistosome and hookworm co-infected populations in Uganda, we hypothesis that human hookworm infection modulates the IgE effector mechanisms triggered by exposure to schistosome adult worm antigen.

We propose to conduct population based parasitological screens for selection of an adult case-control cohort of S. mansoni mono-infected controls and S. mansoni and hookworm co-infected cases for immunological analysis of IgE effector and regulatory immune mechanisms. The project aims to inform research into type-2 associated diseases by identifying potential targets of modulation, and the mechanism by which these responses are regulated.

To determine IgE effector mechanisms regulated in those with hookworm infection, a dual approach of ex vivo and in vivo responsiveness to worm derived antigens will be taken. Ex vivo we will examine control of basophil reactivity at the cellular and serological levels. We will use treatment with praziquantel, which disrupts the adults worm integrity, to examine in vivo responses, through read outs of the type-2 cytokine responses and eosinophil migration known to occur in the 24-hours following treatment. These assays will be combined with flow-cytometry analysis of the activation state of basophils, and eosinophils, both key effector cells in the type-2 immune response. B cell modulation of IgE production through cell surface and circulating soluble levels of its low affinity receptor CD23 will also be addressed.

Flow cytometry will also be used to address the second objective of identifying increases in regulatory cells and molecules that may confer type-2 response modulation in those infected with hookworm. Treg, Tr1 and Breg cell numbers will be being analysed, along with co-inhibitory signals, CTLA-4 and PD-1. These results will be analysed along side plasma measurements of the regulatory cytokine IL-10 and humoral IgG4 blocking responses.

The most immediate beneficiaries of the proposed research are the participating communities. They will receive treatment for schistosomiasis and hookworm, and other common ailments, providing them with immediate health benefits. The wider community will also benefit, as through the explanation of the research to be conducted, comes an education and greater understanding of the parasites, their health consequences and the need for regular treatment. We have observed in our previous study villages, with whom communication is maintained, that the mass-treatment programmes are seen as a positive intervention. For the duration of the study, the research team at VCD-Uganda, will administer treatment on behalf of the National control programme, ensuring that the populations within the study villages receive treatment.

The data on infection levels of two parasites obtained from the parasitological screen, coupled with our previously collected questionnaire data on social economic status, treatment uptake and perception of the mass-treatment programme, will constitute data invaluable for assessment of the mass-control programme within this area highly endemic for the two parasites. We propose to run a workshop in which the scientific researchers involved in this research will discuss the translatable findings with public health practitioners working within the National control programme. Our collaborator Dr Edridah Tukahebwa is the current director of the Ugandan national control programme for neglected tropical diseases, ensuring that our results will be available to those working at the highest levels of the control programme within Uganda.

Uganda is not unique in carrying a burden of schistosome and hookworm co-infection. If established that hookworm is modulating schistosome specific IgE effector mechanisms, mechanisms associated with immunity and thought to inducible through repeated praziquantel treatment, the results of this study will be pertinent throughout the areas of the developing world where these two parasites co-exist; for the design of mass-treatment programmes for neglected tropical diseases is to administer drugs for a number of diseases over the course of a few days. It may be essential that albandazole is administered prior to praziquantel for the extended benefits of the latter to be fully realised.

The Principle Investigator, Prof David Dunne is the director of Cambridge-Africa and the Wellcome Trust Cambridge Centre for Global Health, a strategic operation by the University of Cambridge to invest in African researchers within Africa. Prof Dunne and the co-investigator, Dr Shona Wilson, mentor PhD students, registered at African Universities. They also undertake teaching on research orientated capacity building courses held within African countries, and will during the course of the project, extend this teaching to include interactive lectures integrated into African University MSc programmes. They will continue to stay at the forefront of these strategies throughout the duration of the project.

The investigators will carry out public engagement about the research. In these times of ring-fencing of aid money, including an increase in funding by the Department of International Development for treatment of neglected tropical diseases, it is of vital importance that the public is hearing not only from those directly involved in the control programmes but also from the researchers who are helping to elucidate the impact of these diseases on the health of millions.

Due the growing global importance of allergic diseases, allergy therapeutics is a huge area of investment for biotechnology and pharmaceutical companies. By publishing the results of the proposed work in internationally renowned scientific journals, the identified targets of modulation within the IgE effector pathways will be available to the research and development sectors of these commercial companies.