The biochemical basis of antimicrobial responses in Manduca sexta

Abstract

Innate immunity is essential for the wellbeing of vertebrates and invertebrates. Key components of this defense system include pattern recognition receptors that bind to infectious agents, extra–and intra–cellular proteins that relay signals, as well as molecules and cells that eliminate pathogens. We have been studying the defense mechanisms in a biochemical model insect, Manduca sexta. In this insect, hemolin, peptidoglycan recognition proteins, β‐1,3‐glucan recognition proteins and C‐type lectins detect microbial surface molecules and induce immune responses such as phagocytosis, nodulation, encapsulation, melanization and production of antimicrobial peptides. Some of these responses are mediated by extracellular serine proteinase pathways. The proteolytic activation of prophenoloxidase (proPO) yields active phenoloxidase (PO) which catalyzes the formation of quinones and melanin for wound healing and microbe killing. M. sexta hemolymph proteinase 14 (HP14) precursor interacts with peptidoglycan or β‐1,3‐glucan, autoactivates, and leads to the activation of other HPs including HP21 and proPO‐activating proteinases (PAPs). PAP‐1, ‐2 and ‐3 cut proPO to generate active PO in the presence of two serine proteinase homologs. Inhibition of the proteinases by serpins and association of the proteinase homologs with bacteria ensure a localized defense reaction. M. sexta HP1, HP6, HP8, HP17 and other proteinases may also participate in proPO activation or processing of spätzle and plasmatocyte spreading peptide.

A positive feedback mechanism in the Manduca sexta prophenoloxidase activation system

“…sexta serves as a useful biochemical model in the research on insect antimicrobial responses (Kanost et al, 2004;Jiang, 2008). Over the years, molecular probes (e.g.…”

Reconfiguration of the immune system network during food limitation in the caterpillarManduca sexta

“…1, see Jiang, 2008;Kanost and Gorman, 2008;Christen et al, 2012;Zhang et al, 2011;Cao et al, 2015;Chevignon et al, 2015). This assessment included different aspects of constitutive immunity, i.e.…”

Predator stress-induced immunosuppression: trade-off, immune redistribution or immune reconfiguration?

“…wood crickets, Nemobius sylvestris; Bucher et al, 2015), it must rely on internal mechanisms to deal with an increased predation risk. We assessed the effects of predator stress on key aspects of its immune system, including cellular immunity (haemocyte count and nodulation), humoral immunity ( phenoloxidase and lysozyme-like activity), clot formation and immune gene expression (see Jiang, 2008;Kanost and Gorman, 2008;Strand, 2008;Zhang et al, 2011;Chevignon et al, 2015). Like vertebrates, insects have both constitutive and inducible immune responses (Schmid-Hempel, 2011).…”