Constitutive activation of cellular immunity underlies the evolution of resistance to infection

Abstract

Organisms rely on inducible and constitutive immune defences to 1 combat infection. Constitutive immunity enables a rapid response to infection 2 but may carry a cost for uninfected individuals, leading to the prediction that it 3 will be favoured when infection rates are high. When we exposed populations of 4Drosophila melanogaster to intense parasitism by the parasitoid wasp 5Leptopilina boulardi, they evolved resistance by developing a more reactive 6 cellular immune response. Using single-cell RNA sequencing, we found that 7 immune-inducible genes had become constitutively upregulated. This was the 8 result of resistant larvae differentiating precursors of specialized immune cells 9 called lamellocytes that were previously only produced after infection. 10

Differential activation of JAK-STAT signaling reveals functional compartmentalization in Drosophila blood progenitors

“…Several studies show that parasitoid wasps exert a selective pressure on Drosophila larvae in order to overcome infection (Kraaijeveld et al, 2001, Leitao et al, 2020, McGonigle et al, 2017. Exposing Drosophila larvae to L.boulardi and selecting flies that survive parasitism over generations, leads to constitutive upregulation of immune-inducible genes (including Drs) in such selected populations (Leitao et al, 2020). It would be interesting to know whether PP contribute to the heightened immune response in such resistant Drosophila populations.…”