A serine proteinase homologue, SPH-3, plays a central role in insect immunity

Gabriella Felföldi, Ioannis Eleftherianos, Richard H. Ffrench-Constant, István Venekei

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22 Citations (Scopus)


Numerous vertebrate and invertebrate genes encode serine proteinase homologues (SPHs) similar to members of the serine proteinase family, but lacking one or more residues of the catalytic triad. These SPH proteins are thought to play a role in immunity, but their precise functions are poorly understood. In this study, we show that SPH-3 (an insect non-clip domain-containing SPH) is of central importance in the immune response of a model lepidopteran, Manduca sexta. We examine M. sexta infection with a virulent, insect-specific, Gram-negative bacterium Photorhabdus luminescens. RNA interference suppression of bacteriainduced SPH-3 synthesis severely compromises the insect's ability to defend itself against infection by preventing the transcription of multiple antimicrobial effector genes, but, surprisingly, not the transcription of immune recognition genes. Upregulation of the gene encoding prophenoloxidase and the activity of the phenoloxidase enzyme are among the antimicrobial responses that are severely attenuated on SPH-3 knockdown. These findings suggest the existence of two largely independent signaling pathways controlling immune recognition by the fat body, one governing effector gene transcription, and the other regulating genes encoding pattern recognition proteins.

Original languageEnglish
Pages (from-to)4828-4834
Number of pages7
JournalJournal of Immunology
Issue number8
Publication statusPublished - Apr 15 2011


ASJC Scopus subject areas

  • Immunology and Allergy
  • Immunology

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