Activation of Canine, Mouse and Human TLR2 and TLR4 by Inactivated Leptospira Vaccine Strains

Abstract

CanineLeptospiravaccines contain inactivated strains of pathogenicLeptospira, the causative agents of leptospirosis. For an effective response to vaccination, activation of the innate immune systemviapattern recognition receptors such as TLRs is crucial. However, it is not known which TLRs are activated byLeptospirain dogs. To investigate the involvement of canine TLR2, TLR4, and TLR5 in the recognition ofLeptospira, we stimulated canine moDC and reporter cells expressing canine TLR2 with either whole-inactivated bacteria or purified LPS ofLeptospirastrains, representing the serogroups generally used in canine leptospirosis vaccines. Using the endotoxin neutralizing reagent polymyxin B and TLR4 antagonist RS-LPS, we demonstrate thatLeptospiraLPS and canine TLR4 are involved in IL-1β production as well as in the uptake of inactivatedLeptospirain canine moDC. Furthermore, polymyxin B only partially inhibited IL-1β production induced by inactivatedLeptospira, suggesting that next to TLR4, also other TLRs may be involved. The observed activation of canine TLR2-expressing reporter cells by inactivatedLeptospirastrains indicates that TLR2 could be one of these TLRs. Next, we analyzed TLR2 and TLR4 activating capabilities by the sameLeptospirastrains using human and mouse TLR-expressing reporter cells. InactivatedLeptospiraand leptospiral LPS activated not only mouse, but also human TLR4 and this activation was shown to be LPS dependent in both cases. Additionally, inactivatedLeptospiraactivated mouse and human TLR2-expressing reporter cell lines. In our study, we could not identify significant species differences in the recognition ofLeptospiraby TLR2 and TLR4 between dog, human and mouse. Lastly, we show that these inactivatedLeptospirastrains are recognized by both mouse and human TLR5 reporter cells only after exposure to additional heat-treatment. Unfortunately, we were not able to confirm this in the canine system. Our data show that TLR2 and TLR4 are involved in the recognition ofLeptospirastrains used in the production of canineLeptospiravaccines. This study contributes to the understanding ofLeptospira-induced innate immune responses in dogs, humans, and mice. Future studies are needed to further explore the role of canine TLR2, TLR4 and TLR5 in the induction of vaccine-mediated immunity againstLeptospira.