Immune-modulatory effects of low dose γ-radiation on wax moth (Galleria mellonella) larvae

Abstract

Larvae of the greater wax moth Galleria mellonella are common pests of beehives and commercial apiaries, and in more applied settings, these insects act as alternative in vivo bioassays to rodents for studying microbial virulence, antibiotic development, and toxicology. In the current study, our overall aim was to assess the putative adverse effects of background gamma radiation levels on G. mellonella. To achieve this, we exposed larvae to low (0.014 mGy/h), medium (0.056 mGy/h), and high (1.33 mGy/h) doses of caesium-137 and measured larval pupation events, weight, faecal discharge, susceptibility to bacterial and fungal challenges, immune cell counts, activity, and viability (i.e., haemocyte encapsulation) and melanisation levels. The effects of low and medium levels of radiation were distinguishable from the highest dose rates used - the latter insects weighed the least and pupated earlier. In general, radiation exposure modulated cellular and humoral immunity over time, with larvae showing heighted encapsulation/melanisation levels at the higher dose rates but were more susceptible to bacterial (Photorhabdus luminescens) infection. There were few signs of radiation impacts after 7 days exposure, whereas marked changes were recorded between 14 and 28 days. Our data suggest that G. mellonella demonstrates plasticity at the whole organism and cellular levels when irradiated and offers insight into how such animals may cope in radiologically contaminated environments.

Effect of acute ultraviolet radiation onGalleria mellonellahealth and immunity

“…Again, this is consistent with data from human studies which showed that UVB irradiation of the human body led to decreases in both phagocytic, chemotactic and adhesion activities of neutrophils, largely due to decreased expression of receptors involved in such processes (Lundin et al, 1990;Leino et al, 1999;Hart and Norval, 2021). This further establishes the synonymy of cellular innate immunity in G. mellonella and mammals, and that the former is a candidate model for reducing our reliance on mammals for such studies (Browne et al 2013;Kay et al 2019;Krachler et al, 2021;Lim et al, 2022). Therefore, while more haemocytes remain in larvae exposed to UVA, they were functionally compromised, whereas UVBradiated larvae had fewer haemocytes which was also compromised -which UVB is more potent an antagonist -as reflected in larval health, and expedited mortality when infected, in addition to compromised haemocyte functionality.…”

“…The copyright holder for this preprint this version posted December 2, 2022. ; https://doi.org/10.1101/2022.12.02.517514 doi: bioRxiv preprint Kay et al 2019;Krachler et al, 2021;Lim et al, 2022). Therefore, while more haemocytes remain in larvae exposed to UVA, they were functionally compromised, whereas UVBradiated larvae had fewer haemocytes which was also compromised -which UVB is more potent an antagonist -as reflected in larval health, and expedited mortality when infected, in addition to compromised haemocyte functionality.…”

“…Implants were imaged -at both ends -using an upright (light) microscope (CX31, Olympus) with an eyepiece camera (BF960, Swift Optical Instruments Ltd). Percentage of nylon thread covered by capsule formation was determined by measuring capsular area using ImageJ software (National Institutes of Health) and related to the entire thread as visualised (Lim et al, 2022). Sample sizes included 6 larvae per condition across two independent experiments.…”

“…Previously, larvae exposed to Cs-137 ionising radiation led to increased faecal load over time (Lim et al, 2022). To determine what effect non-ionising radiation had on the insect gut and its bacterial flora, larvae were irradiated, incubated for 3 days and were monitored for changes in faecal discharge.…”

“…To understand the influence that UV radiation exposure has on the innate immune system, we used insect larvae from the Greater wax moth, Galleria mellonella. Wax moth larvae are ethically more acceptable than vertebrates for experimentation (i.e., rodents) and larger than traditional invertebrate models like Drosophilids and nematodes; requiring neither specialist equipment nor training (Mather, 2001;Mylonakis, 2008;Lionakis, 2011;Coates et al, 2019;Emery et al, 2019Emery et al, , 2021Lim et al, 2022). Galleria mellonella possesses an innate immune system -lacking the ability to produce clonal immunoglobulins or long-term immune memory (adaptive immunity) -thereby permitting a targeted assessment of UV exposure on frontline immune defences.…”