Host Immunosuppression Induced by Steinernema feltiae, an Entomopathogenic Nematode, through Inhibition of Eicosanoid Biosynthesis

Abstract

Steinernema feltiae K1 (Filipjev) (Nematode: Steinernematidae), an entomopathogenic nematode, was isolated and identified based on its morphological and molecular diagnostic characteristics. Its infective juveniles (IJs) were highly pathogenic to three lepidopteran (LC50 = 23.7–25.0 IJs/larva) and one coleopteran (LC50 = 39.3 IJs/larva) insect species. Infected larvae of the diamondback moth, Plutella xylostella (L.) (Insecta: Lepidoptera), exhibited significant reduction in phospholipase A2 (PLA2) activity in their plasma. The decrease of PLA2 activity was followed by significant septicemia of the larvae infected with S. feltiae. Insecticidal activity induced by S. feltiae was explained by significant immunosuppression in cellular immune responses measured by hemocyte nodule formation and total hemocyte count (THC). Although S. feltiae infection suppressed nodule formation and THC in the larvae, an addition of arachidonic acid (AA, a catalytic product of PLA2) rescued these larvae from fatal immunosuppression. In contrast, an addition of dexamethasone (a specific PLA2 inhibitor) enhanced the nematode’s pathogenicity in a dose-dependent manner. To discriminate the immunosuppressive activity of a symbiotic bacterium (Xenorhabdus bovienii (Proteobacteria: Enterobacterales)) from the nematode, kanamycin was applied to after nematode infection. It significantly inhibited the bacterial growth in the hemolymph. Compared to nematode treatment alone, the addition of antibiotics to nematode infection partially rescued the immunosuppression measured by phenol oxidase activity. Consequently, treatment with antibiotics significantly rescued the larvae from the insecticidal activity of S. feltiae. These results suggest that immunosuppression induced by infection of S. feltiae depends on its symbiotic bacteria by inhibiting eicosanoid biosynthesis, resulting in significant insect mortality. However, the addition of antibiotics or AA could not completely rescue the virulence of the nematode, suggesting that the nematode itself also plays a role in its insecticidal activity.

Parasitic nematode fatty acid- and retinol-binding proteins compromise host immunity by interfering with host lipid signaling pathways

“…We hypothesize that FARs bind to lipids that function as signaling molecules for a diverse range of functions including inflammation, immunity, homeostasis and reproduction. It has been proposed that most terrestrial insects lack free long-chain polyunsaturated fatty acids (LC-PUFAs) including arachidonic acid (AA), due to its role in oxidative stress (Chandra Roy et al, 2019; Stanley and Kim, 2018). Insects have high levels of reactive oxygen species (ROS), such as the superoxide anion (O 2 − ), due to their significant production of ATP in the mitochondrial electron transport chain.…”

Special Issue: Insects, Nematodes, and Their Symbiotic Bacteria

“…In pioneering work, Kim and co-workers showed that eicosanoid signaling is targeted by EPNs and their bacteria (summarized in [ 4 ]). This has now been confirmed for Steinernema feltiae and—after using antibiotic treatment—partly attributed to their bacteria, although nematodes seem to be contributing too [ 5 ]. In addition to a reduction in cellular immunity, the activation of prophenoloxidase is used in this article as a readout for immune competence.…”

Introduction of Varroa destructor has not altered honey bee queen mating success in the Hawaiian archipelago

“…Because the queens were shipped live but the workers were preserved in ethanol, we only analyzed the queens for pathogens. Using established protocols 37 – 39 , we extracted RNA from each queen’s eviscerated body (head, thorax, and remaining abdomen) using a bead beater by first crushing each sample in individual microcentrifuge tubes, then adding 600 μL Trizol (Thermo Fisher Scientific, HQ in Waltham, MA, USA). We then extracted the RNA following the Trizol protocol (Thermo Fisher Scientific, HQ in Waltham, MA, USA).…”

“…Following protocols outlined in Lee et al 37 , the spermathecae from each queen was placed into 1000 µl of saline buffer, ruptured with forceps to release sperm, gently mixed with forceps, and transferred via glass Pasteur pipet into an amber chromatography vial containing 10 µL of Syber 14 (Invitrogen Live/Dead sperm staining kit #L7011; 1 mM in DMSO) diluted 1:500 into Dimethylsulfoxide (99.8%) and 10 µL propidium iodide solution (2.4 mM in water). The vial was gently vortexed for 2 s at 2000 rpm to homogenize and mix.…”