Insights Into the Antiviral Pathways of the Silkworm Bombyx mori

Abstract

The lepidopteran model silkworm, Bombyx mori, is an important economic insect. Viruses cause serious economic losses in sericulture; thus, the economic importance of these viruses heightens the need to understand the antiviral pathways of silkworm to develop antiviral strategies. Insect innate immunity pathways play a critical role in the outcome of infection. The RNA interference (RNAi), NF-kB-mediated, immune deficiency (Imd), and stimulator of interferon gene (STING) pathways, and Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway are the major antiviral defense mechanisms, and these have been shown to play important roles in the antiviral immunity of silkworms. In contrast, viruses can modulate the prophenol oxidase (PPO), phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt), and the extracellular signal-regulated kinase (ERK) signaling pathways of the host to elevate their proliferation in silkworms. In this review, we present an overview of the current understanding of the main immune pathways in response to viruses and the signaling pathways modulated by viruses in silkworms. Elucidation of these pathways involved in the antiviral mechanism of silkworms furnishes a theoretical basis for the enhancement of virus resistance in economic insects, such as upregulating antiviral immune pathways through transgenic overexpression, RNAi of virus genes, and targeting these virus-modulated pathways by gene editing or inhibitors.

The Intestinal Immune Defense System in Insects

“…The pathway is conserved throughout biological evolution and plays an important role in insect innate immunity [ 141 , 142 ]. Numerous studies have revealed its involvement in intestinal immune responses, such as resistance to viral infections [ 143 , 144 , 145 , 146 ] and resistance to fungal and bacterial infections [ 147 , 148 ].…”

The Role of Mosquito Hemocytes in Viral Infections

“…However, a single-cell RNA-sequencing study of BmNPV-infected hemocytes in B. mori has shown suppression of the RNAi pathway by the virus [ 61 ]. These studies highlight the role of the RNAi pathway in B. mori hemocytes; however, its direct involvement in the antiviral defense remains unclear [ 62 ].…”

Precocious Metamorphosis of Silkworm Larvae Infected by BmNPV in the Latter Half of the Fifth Instar

“…The alkalinity of the silkworm midgut triggers the dissolution of OBs and the release of ODV in the midgut lumen. The ODV is responsible for the primary infection through oral transmission of the virus among silkworm larvae, while the BV is responsible for the secondary infection, causing systemic spreading all over the host within the infected silkworm larvae ( Jiang, 2021 ).…”

“…Bombyx mori is a model organism, and BmNPV is a typical baculovirus ( Gomi et al, 1999 ; Mita et al, 2004 ; Xia et al, 2004 ), and together, they present an important model to assess host–baculovirus interactions ( Jiang and Xia, 2014 ). Insights from previous host studies revealed that innate antiviral immunity in lepidopteran insects plays important roles in host–baculovirus interactions ( Jiang, 2021 ). Antiviral proteins, including red fluorescent proteins (RFPs) ( Sunagar et al, 2011 ; Manjunatha et al, 2018 ), Bmlipase (Bmlipase-1 and Bmlipase member H-A) ( Ponnuvel et al, 2003 ; Zhang S. Z. et al, 2020 ), serine proteases (SPs), and serine protease homologs (SPHs) ( Nakazawa et al, 2004 ; Ponnuvel et al, 2012 ), show strong antiviral activity in the digestive juice of the silkworm.…”