Leptospira surface adhesin (Lsa21) induces Toll like receptor 2 and 4 mediated inflammatory responses in macrophages

Abstract

Leptospirosis is zoonotic and emerging infectious disease of global importance. Little is understood about Leptospira pathogenesis and host immune response. In the present work we have investigated how Leptospira modulates the host innate immune response mediated by Toll-like receptors (TLRs) via surface exposed proteins. We screened Leptospira outer membrane/surface proteins for their ability to activate/inhibit TLR2/4 signaling in HEK293 cell lines. Of these the 21 kDa Leptospira surface adhesin, Lsa21 had strong TLR2 and TLR4 activity leading to production of proinflammatory cytokines and expression of costimulatory molecules in mouse macrophages. This activity of Lsa21 on innate response was dependent on activation of mitogen activated protein kinases (MAPKs) via stimulating the rapid phosphorylation of p38, JNK and activation of transcription factor NF-κB. Additionally, neutralizing antibodies against TLR2 and TLR4 significantly inhibited cytokine secretion and attenuated Lsa21 induced phosphorylation of p38 and JNK. Furthermore, Lsa21 induced cytokine levels were significantly lower in TLR2−/− and TLR4−/− than in wild type mouse macrophage cell lines. Confocal microscopy and molecular docking confirmed that Lsa21 interacted with both TLR2 and TLR4. These results indicate that Lsa21 is a potent TLR2 and TLR4 agonist that induces strong innate response and may play important role in Leptospira pathogenesis.

A trivalent Apx-fusion protein delivered by E. coli outer membrane vesicles induce protection against Actinobacillus pleuropneumoniae of serotype 1 and 7 challenge in a murine model

“…Lymphocyte proliferation assay was performed as previously described with minor modifications [ 26 ]. Splenocytes were prepared as previously described [ 27 , 28 ]. Samples were centrifuged 5 min at 300 rpm/ min and splenocytes were suspended with RPMI incomplete medium.…”

Recent findings related to immune responses against leptospirosis and novel strategies to prevent infection

“…Recent publications show that different leptospiral proteins (hemolysins [36] and Lsa21 [37]) are TLR2 and TLR4 agonists. It is highly probable that these data are misleading since experiments were performed with recombinant proteins produced in E. coli, a bacterium expressing one of the most potent LPS.…”

Deciphering the role ofLeptospirasurface protein LigA in modulating the host innate immune response

“…It has been shown that TLR4 plays a critical role in controlling bacterial load and the development of severe leptospirosis in mice 71 .Thus, it is likely that those surface proteins and LPS which are natural ligands of these receptors and can activate macrophages and DCs, might undergo variations thereby enabling the bacteria to evade this innate recognition and adhere to the host. Several surface proteins of Leptospira have been identified as ligands of TLR2 or TLR4 that are capable of activating innate immune response and are potential vaccine candidates 34–37,72 . Lig proteins are important virulence factors and its expression during infection or loss of its expression during in vitro culture has been correlated to virulence of the infecting serovar 52,56,73 .…”