Trained Immunity in Anopheles gambiae: Antibacterial Immunity Is Enhanced by Priming via Sugar Meal Supplemented With a Single Gut Symbiotic Bacterial Strain

Abstract

Mosquitoes have evolved an effective innate immune system. The mosquito gut accommodates various microbes, which play a crucial role in shaping the mosquito immune system during evolution. The resident bacteria in the gut microbiota play an essential role in priming basal immunity. In this study, we show that antibacterial immunity in Anopheles gambiae can be enhanced by priming via a sugar meal supplemented with bacteria. Serratia fonticola S1 and Enterobacter sp. Ag1 are gut bacteria in mosquitoes. The intrathoracic injection of the two bacteria can result in an acute hemocoelic infection in the naïve mosquitoes with mortality of ∼40% at 24 h post-infection. However, the Enterobacter orSerratia primed mosquitoes showed a better 24 h survival upon the bacterial challenge. The priming confers the protection with a certain degree of specificity, the Enterobacter primed mosquitoes had a better survival upon the Enterobacter but not Serratia challenge, and the Serratia primed mosquitoes had a better survival upon the Serratia but not Enterobacter challenge. To understand the priming-mediated immune enhancement, the transcriptomes were characterized in the mosquitoes of priming as well as priming plus challenges. The RNA-seq was conducted to profile 10 transcriptomes including three samples of priming conditions (native microbiota, Serratia priming, and Enterobacter priming), six samples of priming plus challenges with the two bacteria, and one sample of injury control. The three priming regimes resulted in distinctive transcriptomic profiles with about 60% of genes affected by both bacteria. Upon challenges, different primed mosquitoes displayed different transcriptomic patterns in response to different bacteria. When a primed cohort was challenged with a heterogenous bacterium, more responsive genes were observed than when challenged with a homogenous bacterium. As expected, many canonical immune genes were responsive to the priming and challenge, but much more non-immune genes with various functions were also responsive in the contexts, which implies that the prior priming triggers a delicately coordinated systemic regulation that results in an enhanced immunity against the subsequent challenge. Besides the participation of typical immune pathways, the transcriptome data suggest the involvement of lysosome and metabolism in the context. Overall, this study demonstrated a trained immunity via priming with bacteria in diet.

Aryl hydrocarbon receptor and Krüppel like factor 10 mediate a transcriptional axis modulating immune homeostasis in mosquitoes

“…The bacterial culture at OD 600nm = 1 was diluted 1000 times with sterile H 2 O, and approximately 100 nl of this bacterial solution yielded approximately 100 colony-forming units (CFU) per mosquito. As we have shown in a previous study 13 , the injection of this bacterial amount causes an acute bacterial infection, all mosquitoes die within three days post injections; thus, the 24 h-survival percent is the most informative data point to measure the infection outcome and the effects of treatments as well 13 . In this study, on day 3 after AhR activity was manipulated as described above, the mosquitoes were challenged with the bacteria, survival at 24 h post-infection was documented to examine the effects of AhR manipulation on the infection outcomes.…”

“…Recently we have shown that the bacterium Serratia fonticola S1 strain, once injected into the hemocoel intrathoracically, can cause acute hemocoel infection and trigger an immune response. Survival at 24 h post-injection is an informative measure of infection and immune outcomes 13 . Kynurenine (Kyn) is an endogenous AhR ligand 14 , which is an intermediate metabolite of tryptophan oxidation catalyzed by tryptophan-2,3-dioxygenase (TDO) in mosquitoes 15 .…”

Pre-exposure to Candida albicans induce trans-generational immune priming and gene expression of Musca domestica

“…Recent studies indicated that there were certain differences in the gene expression during immune priming of insects to different pathogens. The most identified genes during immune priming were a variety of PRRs and immune effectors ( Zhao et al, 2013 ; Greenwood et al, 2017 ; Tate et al, 2017 ; Yi et al, 2019 ; Kulkarni et al, 2021 ; Maya-Maldonado et al, 2021 ). To explore the molecular mechanism of TGIP of the housefly to C. albicans , RNA-seq was performed to detect the gene expression after immune priming.…”

“…Gram-negative bacteria-binding proteins (GNBPs) can recognize the glucan of fungi and initiate immune responses ( Matskevich et al, 2010 ). Recent studies indicated that the expression of GNBPs was changed during immune priming of Anopheles gambiae and T. castaneum ( Tate et al, 2017 ; Kulkarni et al, 2021 ). Collectively, the above PRRs might play important roles in the process of TGIP of the housefly.…”

“…Many transcriptomic studies have found that multiple immune genes and signaling pathways were involved in the process of immune priming, such as pattern recognition receptors (PRRs), AMPs, and Toll signaling pathway ( Pham et al, 2007 ). However, there were differences in gene expression between different hosts to different pathogens ( Zhao et al, 2013 ; Pinaud et al, 2016 ; Yi et al, 2019 ; Kulkarni et al, 2021 ; Sheehan et al, 2021 ). Therefore, the mechanism of invertebrate immune priming deserves further study.…”