Priming the prophenoloxidase system of Artemia franciscana by heat shock proteins protects against Vibrio campbellii challenge

Like other invertebrates, the brine shrimp Artemia franciscana relies solely on innate immunity, which by definition lacks adaptive characteristics, to combat against invading pathogens. One of the innate mechanisms is melanisation of bacteria mediated by the activation of the prophenoloxidase (proPO) system. The 70 kDa heat shock proteins (Hsp70) derived from either prokaryote (Escherichia coli) or eukaryote (Artemia), well conserved and immune-dominant molecules, protect Artemia against Vibrio campbellii. However, the molecular mechanisms by which these proteins protect Artemia against Vibrio campbellii infection are unknown. Here we demonstrated that feeding gnotobiotically grown Artemia with either Artemia Hsp70 or the E. coli Hsp70 equivalent DnaK, each overproduced in E. coli, followed by V. campbellii challenge enhanced the proPO system, at both mRNA and protein activity levels. Additionally, the Artemia fed with these proteins survived well in a Vibrio challenge assay. These results indicated that Hsp70s derived from either prokaryotic or eukaryotic sources generate protective immunity in the crustacean Artemia against V. campbellii infection by priming the proPO system. This is apparently the first in vivo report on priming activity of Hsp70 in an invertebrate.