The pre-activated immune response induced by LPS protects host from leptospirosis

Leptospirosis is an important global zoonosis caused by pathogenic Leptospira. It is estimated that more than 1 million people are infected by Leptospira each year, and the death toll is about 60,000. Some studies showed that delayed immune response was associated with severe leptospirosis, and TLR4 was very important in the control of leptospirosis. In this study, we aimed to explore the effect of the classical activator (LPS) of TLR4 on leptospirosis in susceptible and resistant hosts. The results showed that LPS pretreatment increased the survival rate of hamsters to 80%. And LPS pre-treatment also significantly reduced the leptospiral load and alleviated the pathological injury in organs of hamsters and mice. The result detected by ELISA in mice showed that the levels of TNF-α and IL-1β were increased in the LPS-treated group compared to the control group before infection. However, two days after infection, the level of cytokines in LPS group was down-regulated compared with that in control group. In addition, in vitro results showed that LPS pre-treatment enhanced the phagocytosis and bactericidal ability of macrophages on Leptospira. Collectively, our results indicated that the pre-activated immune response induced by LPS enhanced the ability of host against leptospirosis.