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.