Bordetella Pertussis Toxin does not induce the release of pro-inflammatory cytokines in human whole blood

Pertussis Toxin (PTx) is one of the most important virulence factors of Bordetella pertussis, the cause of whooping cough. Therefore, the inactivated toxin is an obligatory constituent of acellular pertussis vaccines. It is described in the literature that both native PTx and recombinant Pertussis Toxin (PTg) activate human monocytes whereas others report an inhibition of mammalian monocytes during pertussis infection. B. pertussis, as a Gram-negative bacterium, harbours naturally lipopolysaccharide (LPS, also known as endotoxin), one of the strongest stimulators of monocytes. The latter is triggered via the interaction of endotoxin with inter alia the surface receptor CD14. Consequently, it is necessary to consider a potential contamination of Pertussis Toxin preparations with LPS. First, we determined the LPS content in different preparations of PTx and PTg. All preparations examined were contaminated with LPS; therefore, possible PTx- and PTg-driven monocyte activation independently of LPS was investigated. To meet these aims, we examined monocyte response to PTx and PTg while blocking the LPS receptor CD14 with a specific monoclonal antibody (anti-CD14 mAb). In addition, all toxin preparations examined underwent an LPS depletion. Our results show that it is contaminating LPS, not Pertussis Toxin, which activates human monocytes. Blocking the CD14 receptor prevents Pertussis Toxin-mediated induction of pro-inflammatory cytokines in human monocytes. The depletion of LPS from Pertussis Toxin leads to the same effect. Additionally, the PTx toxicity after LPS depletion procedure was confirmed by animal tests. In contrast, the original Pertussis Toxin preparations not treated as mentioned above generate strong monocyte activation. The results in this publication allow the conclusion that purified Pertussis Toxin preparations do not induce the release of pro-inflammatory cytokines in human whole blood.