Immunization with 3-oxododecanoyl-l-homoserine lactone–protein conjugate protects mice from lethal Pseudomonas aeruginosa lung infection

Abstract

Quorum-sensing systems have been reported to play a critical role in the pathogenesis of several bacterial infections. Recent data have demonstrated that Pseudomonas N-3-oxododecanoyl-l-homoserine lactone (3-oxo-C12-homoserine lactone, 3-oxo-C12-HSL), but not N-butanoyl-l-homoserine lactone (C4-HSL), induces apoptosis in macrophages and neutrophils. In the present study, the effects of active immunization with 3-oxo-C12-HSL–carrier protein conjugate on acute P. aeruginosa lung infection in mice were investigated. Immunization with 3-oxo-C12-HSL–BSA conjugate (subcutaneous, four times, at 2-week intervals) elaborated significant amounts of specific antibody in serum. Control and immunized mice were intranasally challenged with approximately 3×106 c.f.u. P. aeruginosa PAO1, and survival was then compared. All control mice died by day 2 post bacterial challenge, while 36 % of immunized mice survived to day 4 (P<0.05). Interestingly, bacterial numbers in the lungs did not differ between control and immunized groups, whereas the levels of pulmonary tumour necrosis factor (TNF)-α in the immunized mice were significantly lower than those of control mice (P<0.05). Furthermore, the extractable 3-oxo-C12-HSL levels in serum and lung homogenate were also significantly diminished in the immunized mice. Immune serum completely rescued reduction of cell viability by 3-oxo-C12-HSL-mediated apoptosis in macrophages in vitro. These results demonstrated that specific antibody to 3-oxo-C12-HSL plays a protective role in acute P. aeruginosa infection, probably through blocking of host inflammatory responses, without altering lung bacterial burden. The present data identify a promising potential vaccine strategy targeting bacterial quorum-sensing molecules, including autoinducers.

The quorum quenching antibody RS2-1G9 protects macrophages from the cytotoxic effects of the Pseudomonas aeruginosa quorum sensing signalling molecule N-3-oxo-dodecanoyl-homoserine lactone

“…The antibody also prevents the activation of cellular stress kinase pathways, indicating that the sequestration of 3-oxo-C 12 -HSL is complete. Our data also suggest that the protection achieved by the active vaccination approach reported by Tateda and co-workers might be due to the elicitation of 3-oxo-C 12 -HSL-neutralizing antibodies (Miyairi et al, 2006).…”

“…An advantage of mAbs is that by scavenging soluble molecules they also neutralize the cytotoxic AHL effects on host cells, in analogy to antibodies against other bacterial toxins. Notably, an active immunization using an AHL-based hapten coupled to a carrier protein has shown promise in in vivo infection models (Miyairi et al, 2006). To gain greater insight into the molecular details of antibody-mediated protection, we investigated mAb RS2-1G9's ability to neutralize 3-oxo-C 12 -HSL and protect murine macrophages against the cytotoxic effects in vitro.…”

Exploiting Quorum Sensing To Confuse Bacterial Pathogens

“…The highest-affinity MAbs were specific for 3OC12HSL, and investigators were able to demonstrate that one of these MAbs, RS2-1G9, inhibited QS signaling and QS-regulated pyocyanin production in P. aeruginosa in vitro, suggesting therapeutic potential of antibody-mediated QSI (109). Shortly thereafter, Miyairi and colleagues demonstrated that active immunization with bovine serum albumin (BSA)-conjugated 3OC12HSL increased survival of mice following intranasal challenge with P. aeruginosa, despite having no effect on bacterial burdens in the lung (110). Experiments confirmed that immunized mice had lower levels of free 3OC12HSL in both serum and lung homogenates than nonimmunized mice, and sera from immunized mice were able to protect macrophages from the cytotoxic effects of 3OC12HSL, suggesting that antibody targeting the AHL was responsible for protection following immunization (110).…”

“…Shortly thereafter, Miyairi and colleagues demonstrated that active immunization with bovine serum albumin (BSA)-conjugated 3OC12HSL increased survival of mice following intranasal challenge with P. aeruginosa, despite having no effect on bacterial burdens in the lung (110). Experiments confirmed that immunized mice had lower levels of free 3OC12HSL in both serum and lung homogenates than nonimmunized mice, and sera from immunized mice were able to protect macrophages from the cytotoxic effects of 3OC12HSL, suggesting that antibody targeting the AHL was responsible for protection following immunization (110). The MAb RS2-1G9 was also tested for its ability to protect murine macrophages from cytotoxicity effects of 3OC12HSL, and it was demonstrated that RS2-1G9 protected macrophages from 3OC12HSL-induced apoptosis in a concentration-dependent manner (111).…”

Targeting virulence not viability in the search for future antibacterials

“…QS networks have been quenched or modulated at three points (reviewed in [49]) by (i) inhibiting signal generation (e.g. by blocking synthesis of AHL in vitro using AHL analogues [50,51]), (ii) degrading the signal molecule (AHLs can be destroyed chemically by increasing the pH [2] or by use of 'quorum quenching' enzymes [47], or inactivated with antibodies [52]) and (iii) blocking the interaction of the QS signal molecule with the receptor. The last is the most popular approach.…”