Previous research by the lab

The research on this page has been completed and is recorded here for archive purposes. We are not accepting PhD proposals based on this research.

Specificity of the insect immune system

The insect immune system is important for human health and well being. Insects spread a large number of human diseases, think of malaria and mosquitoes. Where the insects immune system comes in, is that malaria is also a parasite of the mosquito, it doesn't just passively carry the parasite. Some mosquitoes are better than others at fighting off the infection. The more we understand about the insect immune response here the better. Insects also act as pollinators to some of our most important crop species. As has been reported in the news, people are worried about insects', especially bees' decline. Part of the cause of this decline is disease. Again the more we know about the insect immune response here the better.

Yet insect immunity still holds many mysteries, chief among them, its unexpected specificity. Insect immune recognition molecules are thought to bind only to broad categories of parasites, such as bacteria or fungi. They are therefore non-specific compared to the vertebrate immune systems that have the ability to differentiate subtle differences between different strains of the same disease using antibodies. However, there is a large amount of ecological evidence in invertebrates suggesting they are indeed capable of responding specifically to even different strains of the same parasite. The bumblebee/Crithidia system is possibly the best-studied example of specific interaction between an insect host and its parasite. It has been consistently shown that different bumblebee colonies are infected differentially by different strains of Crithidia, a trypanosome that lives in the bumblebee's gut. Recently we demonstrated that this specificity is also found in the immune response itself, with the expression of antimicrobial peptides depending on which strain of Crithidia infected which colony of bumblebee. Antimicrobial peptides are proteins produced by many animals, including humans, that help them fight disease. We also showed that knocking down AMPs lead to increased Crithidia infection.

Given that the model of how an insect immune system works says bees shouldn't be able to differentiate between Crithidia strains, but they most certainly can, the aim of current work is to elucidate the molecular basis of this immune response specificity. Currently we are carrying out an RNA-Seq experiment to discover more genes and networks involved in this immune specificity.

As well as the previously mentioned importance of understanding the insect immune system, looking at specificity from the parasite end is also of value. Emerging diseases will be one of the key challenges of the environmental change, we are currently living through. Emerging diseases account for 12% of all human pathogens. Emerging diseases arise when previously unimportant pathogens find a new way of making a living (technically called a niche) due to the disruption of the environment. The most important trait of emerging diseases is that they are general rather than specific. Understanding the role of specificity will therefore be of importance in dealing with these new challenges.

The effect of the immune system on learning in insects

In vertebrates, it is well established that there are many intricate interactions between the immune system and the nervous system, and vice versa. Regarding insects, until now little has been known about the link between these two systems. I found behavioural evidence indicating a link between the immune system and the nervous system in insects. Otherwise non-infected honeybees whose immune systems are challenged by a non-pathogenic immunogenic elicitor lipopolysaccharide (LPS) have reduced abilities to associate an odour with sugar reward in a classical conditioning paradigm. The cost of an immune response therefore not only affects survival of the host, as previously shown, but also everyday behaviour and memory formation.

We extended this work to show the same effects in harnessed and free-flying bumblebees. We showed that it was protein dependent. It seems that this physiological trade-off does not equate to an evolutionary one. Recently we showed that these same immune-memory interactions are found in Drosophila and are mediated by sleep.

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