Paralytic Peptide: An Insect Cytokine That Mediates Innate Immunity

Abstract

Host animals combat invading pathogens by activating various immune responses. Modulation of the immune pathways by cytokines is critical for efficient pathogen elimination. Insects and mammals possess common innate immune systems, and individual immune pathways have been intensively studied over the last two decades. Relatively less attention, however, has been focused on the functions of cytokines in insect innate immunity. Here, we summarize our recent findings from studies of the insect cytokine, paralytic peptide, in the silkworm Bombyx mori. The content of this report was presented at the First Asian Invertebrate Immunity Symposium. Acute activation of paralytic peptide occurs via proteolysis after stimulation with the cell wall components of pathogens, leading to the induction of a wide range of cellular and humoral immune responses. The pathogenic bacterium Serratia marcescens suppresses paralytic peptide-dependent immune activation, which impairs host resistance. Studies of insect cytokines will broaden our understanding of the basic mechanisms underlying the interaction between host innate immunity and pathogenic agents.

Advantages of the Silkworm As an Animal Model for Developing Novel Antimicrobial Agents

“…We previously reported the activation of innate immunity in silkworm during pathogen invasion and found that a cytokine-like paralytic peptide induced humoral and cellular responses and played an important role in silkworm immunity. Further, we found that the paralytic peptide promoted the engulfment of bacteria and induced nitric oxide (NO) production, that is required for both p38 and MAPK activation (Ishii et al, 2013, 2015a). …”

Serine protease Bm-SP142 was differentially expressed in resistant and susceptible Bombyx mori strains, involving in the defence response to viral infection

“…In insects, pathogens are recognized as “nonself” and further removed by the synergistic action of both humoral and cellular responses [11, 22], and proteins such as defensin, moricin and lectin were reported to participate in the regulation of immune responses [23–25]. Evidence suggests that serine proteases may be involved in resistance to pathogenic invasion in insects.…”

Using silkworms as a laboratory animal to evaluate medicines and foods

“…Determining whether or not immunity is activated in humans and other mammals is usually difficult. We found that stimulating innate immunity in silkworms causes muscle contractions (10,11). Activation of cells responsible for innate immunity in silkworms leads to enhancement of immune cells that results in the activation of a cytokine that has the pharmacologic capacity to induce muscle contractions.…”