Immunological enhancement action of endotoxin-free tilapia heat shock protein 70 against Streptococcus iniae

• tHsp70 helped Streptococcus iniae to increase lymphocytes and macrophages proliferations.
• tHsp70 significantly increased NO release and macrophage phagocytotic ability.
• tHsp70 significantly enhanced levels of immune related genes of tilapia.
• tHsp70 assisted S. iniae antigen to enhance the vaccine-induced protection.
• Our study highlights immunological enhancement of Hsp70 in teleost immunity.

The immunological effects of heat shock proteins (HSPs) had been found in humans and mice, but scarce data of endotoxin-free Hsp70 were reported in tilapia. In the current study, we reported that tHsp70 alone and antigen-tHsp70 compound increased the proliferations of lymphocytes and macrophages, significantly increased the NO release and phagocytotic ability of macrophages (p < 0.05), and enhanced the levels of immune-related genes in lymphocytes and macrophages in a dose- and/or time-dependent manner. On the other hand, tHsp70 not only helped to reduce the proliferation inhibitions induced by the ECP treatment, but also assisted antigens to enhance the vaccine-induced protection against Streptococcus iniae (p < 0.05). We described, for the first time, a critical role of endotoxin-free tHsp70 on activation of tilapia lymphocytes and macrophages post S. iniae exposure and its up-regulation effects on vaccine-induced protection. Our research highlights the immunological enhancement action of Hsp70 in teleost immunity.