Lipid Motif of a Bacterial Antigen Mediates Immune Responses via TLR2 Signaling

Abstract

The cross-talk between the innate and the adaptive immune system is facilitated by the initial interaction of antigen with dendritic cells. As DCs express a large array of TLRs, evidence has accumulated that engagement of these molecules contributes to the activation of adaptive immunity. We have evaluated the immunostimulatory role of the highly-conserved outer membrane lipoprotein P6 from non-typeable Haemophilus influenzae (NTHI) to determine whether the presence of the lipid motif plays a critical role on its immunogenicity. We undertook a systematic analysis of the role that the lipid motif plays in the activation of DCs and the subsequent stimulation of antigen-specific T and B cells. To facilitate our studies, recombinant P6 protein that lacked the lipid motif was generated. Mice immunized with non-lipidated rP6 were unable to elicit high titers of anti-P6 Ig. Expression of the lipid motif on P6 was also required for proliferation and cytokine secretion by antigen-specific T cells. Upregulation of T cell costimulatory molecules was abrogated in DCs exposed to non-lipidated rP6 and in TLR2−/− DCs exposed to native P6, thereby resulting in diminished adaptive immune responses. Absence of either the lipid motif on the antigen or TLR2 expression resulted in diminished cytokine production from stimulated DCs. Collectively; our data suggest that the lipid motif of the lipoprotein antigen is essential for triggering TLR2 signaling and effective stimulation of APCs. Our studies establish the pivotal role of a bacterial lipid motif on activating both innate and adaptive immune responses to an otherwise poorly immunogenic protein antigen.

Changes in pathogenicity and immunogenicity of Mycoplasma mycoides subsp. mycoides strains revealed by comparative genomics analysis

“…Essentially all the lipids of mycoplasmas are located in the cell membrane 32 . As a part of lipoprotein, the mycoplasma lipid moiety was the main component recognized by the innate immune system through Toll-like receptors (TLR) 2 and 6 33 34 . So we further investigated whether continuous passage caused gene variation affected biosynthetic pathways of Mycoplasma lipids.…”

Cigarette Smoke Exposure Exacerbates Lung Inflammation and Compromises Immunity to Bacterial Infection

“…Here, we evaluated a candidate vaccine antigen selected based on our previous work describing the immunogenic and protective potential of the lipoprotein P6 (26). Although anti-P6 responses were diminished in the cigarette smoke exposed mice, the vaccine was still protective, and conferred immunity similar to that of unimmunized mice never exposed to smoke.…”

“…We have previously demonstrated that T cell responses to P6 are associated with relative protection against NTHI infection in adults with COPD (24). The immunogenic nature of this highly conserved lipoprotein makes P6 a promising vaccine candidate for NTHI (25,26). The expectation would be that vaccine-induced immunity would minimize NTHI-mediated lung damage during COPD exacerbations.…”

Hyaluronan Is Not a Ligand but a Regulator of Toll-Like Receptor Signaling in Mesangial Cells: Role of Extracellular Matrix in Innate Immunity

“…HA consists of D-glucuronate and D-N-acetylglucosamine in an alternating sequence [ 3 ], lacking additional binding sites in larger molecules. The LPS binding of TLR4 [ 40 ] and between TLR2 and its ligand lipoprotein [ 41 ] is based on their lipophilic binding sites, and the binding activates the signalling cascade. HA as a hydrophilic molecule should not be able to bind directly to any of these lipophilic receptors, at least not to the same binding sites as the named ligands.…”