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Cambridge University Science Magazine
An international team of researchers, including several scientists from the Wellcome Sanger Institute, has identified a number of new immune cell types in mosquitoes, one of which could be involved in the response to malaria infection. The findings, published in Science, offer a detailed insight into the mosquito immune system at the molecular level and may prove valuable in attempts to reduce transmission of infectious diseases from mosquitoes to humans.

Malaria, a disease which infects millions and kills hundreds of thousands every year, is caused by Plasmodium parasites and transmitted to humans via bites from female mosquitoes of the Anopheles genus. A number of other life-threatening diseases are also spread by mosquitoes, including Dengue fever and Zika. Understanding the mosquito immune system, which mediates the insect’s response to parasitic or viral infection, is key to controlling the proliferation of malaria and other mosquito-borne diseases.

The researchers analysed 8,506 individual hemocytes (immune cells) from two disease-carrying mosquito species, sequencing their RNA and looking for molecular markers in order to categorise specific cell types. They found at least twice as many hemocyte types as had previously been known, and were able to observe the ways in which they reacted to infection with the Plasmodium parasite. This led to further insights, showing for example that immune cells known as granulocytes increased in number in response to infection and were able to develop into other types of immune cells.

One discovery of particular note was a rare new cell type referred to by the researchers as a ‘megacyte’. These cells were found to contain high levels of a molecule involved in a process called immune priming, in which the mosquito immune system is activated to fight the Plasmodium parasite. This is a long-lasting response akin to acquired immunity in humans, as it is triggered by initial exposure to Plasmodium and results in increased resistance to subsequent infections. An improved understanding of this process could bring immunotherapy research closer to breaking the chain of malaria transmission between mosquitoes and humans.

Dr Oliver Billker, joint senior author on the paper, said: “This is the first time a specific mosquito cell type has been implicated in regulating the control of malaria infection, and is a really exciting discovery. We now need to carry out further studies to validate this and better understand these cells and their role.”

Publication:Gianmarco Raddi and Ana Beatriz F. Barletta et al. (2020) Mosquito cellular immunity at single-cell resolution. Science.

Zak Lakota-Baldwin is a 4th year History and Philosophy of Science undergraduate, and news editor at BlueSci