Bacterial HSP70 (DnaK) is an efficient immune stimulator in Litopenaeus vannamei

There is increasing evidence suggesting that heat shock proteins (HSPs), especially the conserved HSP70, are able to activate the immune response. In our research, we aimed at verifying the role of DnaK (the bacterial HSP70 homologue) as an immune activator in specific-pathogen-free (SPF) Litopenaeus vannamei either by injecting them with recombinant full length DnaK or a chemically synthetic 50 amino acid fragment peptide which is part of the peptide binding domain of DnaK (DnaK442-491). The expressions of two types of immune-related genes (transglutaminases and prophenoloxidases) were monitored via quantitative real time PCR (qPCR). The results showed that DnaK and DnaK442-491 are able to significantly up-regulate transglutaminase-1 (TGase-1) and prophenoloxidase-2 (proPO-2) expressions within 12 h post injection. The synthetic peptide DnaK442-491 is free of lipopolysaccharide (LPS) or any other bacterial components potentially contaminating a recombinant DnaK preparation. Hence the data suggested that DnaK, as such, stimulates the immune system of L. vannamei in a specific way (proPO-2, TGase-1). These findings indicate that DnaK is an efficient immune stimulator in L. vannamei immunity. It could be explored to modulate the expression of immune-related genes of L. vannamei potentially involved in mounting a response against infectious disease.