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Journal of Experimental Biology
Year: 2009  |  Volume: 212  |  Issue: 12  |  Page No.: 1840 - 1848

Plasmatocyte-spreading peptide (PSP) plays a central role in insect cellular immune defenses against bacterial infection

I Eleftherianos, M Xu, H Yadi, R. H ffrench Constant and S. E. Reynolds    

Abstract: I. Eleftherianos, M. Xu, H. Yadi, R. H. ffrench-Constant, and S. E. Reynolds

Insect hemocytes (blood cells) are a central part of the insect's cellular response to bacterial pathogens, and these specialist cells can both recognize and engulf bacteria. During this process, hemocytes undergo poorly characterized changes in adhesiveness. Previously, a peptide termed plasmatocyte-spreading peptide (PSP), which induces the adhesion and spreading of plasmatocytes on foreign surfaces, has been identified in lepidopteran insects. Here, we investigate the function of this peptide in the moth Manduca sexta using RNA interference (RNAi) to prevent expression of the precursor protein proPSP. We show that infection with the insect-specific bacterial pathogen Photorhabdus luminescens and non-pathogenic Escherichia coli induces proPSP mRNA transcription in the insect fat body but not in hemocytes; subsequently, proPSP protein can be detected in cell-free hemolymph. We used RNAi to silence this upregulation of proPSP and found that the knock-down insects succumbed faster to infection with P. luminescens, but not E. coli. RNAi-treated insects infected with E. coli showed a reduction in the number of circulating hemocytes and higher bacterial...

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