Insect Cytokine Paralytic Peptide (PP) Induces Cellular and Humoral Immune Responses in the Silkworm Bombyx mori

Abstract

In the blood (hemolymph) of the silkworm Bombyx mori, the insect cytokine paralytic peptide (PP) is converted from an inactive precursor to an active form in response to the cell wall components of microorganisms and contributes to silkworm resistance to infection. To investigate the molecular mechanism underlying the up-regulation of host resistance induced by PP, we performed an oligonucleotide microarray analysis on RNA of blood cells (hemocytes) and fat body tissues of silkworm larvae injected with active PP. Expression levels of a large number of immune-related genes increased rapidly within 3 h after injecting active PP, including phagocytosis-related genes such as tetraspanin E, actin A1, and ced-6 in hemocytes, and antimicrobial peptide genes cecropin A and moricin in the fat body. Active PP promoted in vitro and in vivo phagocytosis of Staphyloccocus aureus by the hemocytes. Moreover, active PP induced in vivo phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK) in the fat body. Pretreatment of silkworm larvae with ML3403, a pharmacologic p38 MAPK inhibitor, suppressed the PP-dependent induction of cecropin A and moricin genes in the fat body. Injection of active PP delayed the killing of silkworm larvae by S. aureus, whereas its effect was abolished by preinjection of the p38 MAPK inhibitor, suggesting that p38 MAPK activation is required for PP-dependent defensive responses. These findings suggest that PP acts on multiple tissues in silkworm larvae and acutely activates cellular and humoral immune responses, leading to host protection against infection.

Structural analysis of an innate immunostimulant from broccoli, <i>Brassica oleracea</i> var. <i>italica </i>

“…RH2180-5, using a silkworm model of infection (3). Injection of yeast β-glucans and bacterial peptidoglycans into the silkworm Bombyx mori induces maturation of the insect cytokine paralytic peptide, which results in muscle contraction of the larvae (4,5). We established an assay using the silkworm based on muscle contraction, which is associated with activation of innate immunity (6), and purified a polysaccharide with innate immunestimulating activity from green tea extracts (7).…”

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“…The status of Wolbachia in A. domesticus is unknown because no previous studies regarding this matter have been reported. In addition, there were also no Ishii et al (2010), have been heavily focused on specific AMPs extracted from various insects species and then tested on pathogenic agents in order to prove their significance for the regulation of antimicrobial activity. Cytryńska et al (2006) reported that eight peptides isolated and purified from Galleria mellonella were able to induce antimicrobial activity when tested against gram-negative and gram-positive bacteria, yeast, and filamentous fungi.…”

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