AUTHOR=Novak Andreja , Pupo Elder , van’t Veld Esther , Rutten Victor P. M. G. , Broere Femke , Sloots Arjen 

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

JOURNAL=Frontiers in Immunology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2022.823058

DOI=10.3389/fimmu.2022.823058

ISSN=1664-3224

ABSTRACT=<p>Canine <italic>Leptospira</italic> vaccines contain inactivated strains of pathogenic <italic>Leptospira</italic>, the causative agents of leptospirosis. For an effective response to vaccination, activation of the innate immune system <italic>via</italic> pattern recognition receptors such as TLRs is crucial. However, it is not known which TLRs are activated by <italic>Leptospira</italic> in dogs. To investigate the involvement of canine TLR2, TLR4, and TLR5 in the recognition of <italic>Leptospira</italic>, we stimulated canine moDC and reporter cells expressing canine TLR2 with either whole-inactivated bacteria or purified LPS of <italic>Leptospira</italic> strains, representing the serogroups generally used in canine leptospirosis vaccines. Using the endotoxin neutralizing reagent polymyxin B and TLR4 antagonist RS-LPS, we demonstrate that <italic>Leptospira</italic> LPS and canine TLR4 are involved in IL-1β production as well as in the uptake of inactivated <italic>Leptospira</italic> in canine moDC. Furthermore, polymyxin B only partially inhibited IL-1β production induced by inactivated <italic>Leptospira</italic>, suggesting that next to TLR4, also other TLRs may be involved. The observed activation of canine TLR2-expressing reporter cells by inactivated <italic>Leptospira</italic> strains indicates that TLR2 could be one of these TLRs. Next, we analyzed TLR2 and TLR4 activating capabilities by the same <italic>Leptospira</italic> strains using human and mouse TLR-expressing reporter cells. Inactivated <italic>Leptospira</italic> and leptospiral LPS activated not only mouse, but also human TLR4 and this activation was shown to be LPS dependent in both cases. Additionally, inactivated <italic>Leptospira</italic> activated mouse and human TLR2-expressing reporter cell lines. In our study, we could not identify significant species differences in the recognition of <italic>Leptospira</italic> by TLR2 and TLR4 between dog, human and mouse. Lastly, we show that these inactivated <italic>Leptospira</italic> strains 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 of <italic>Leptospira</italic> strains used in the production of canine <italic>Leptospira</italic> vaccines. This study contributes to the understanding of <italic>Leptospira</italic>-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 against <italic>Leptospira</italic>.</p>