B. parapertussis precludes neutrophil bactericidal activity under pro-inflammatory environmental conditions

BAROLI, CARLOS; HUGO A. VALDEZ; GORGOJO J. PABLO; MARÍA E. RODRIGUEZ; CARRICA MARIELA

Simposio; 12th International Symposium on Bordetella; 2019

B. parapertussis (Bpp) incidence increased after the replacement of whole cell vaccines by acellular vaccines, and it is thought to contribute to the reemergence of whooping cough. Pertussis acellular vaccines fail to induce protective antibodies against this bacterium. Our studies showed that in the absence of opsonic antibodies Bpp survives the interaction with resting neutrophils by avoiding intracellular and extracellular bactericidal mechanisms. However, during the in vivo infection, the presence of priming cytokines, like gamma-interferon (IFN-γ), might improve neutrophil control of bacterial infections. We here investigated whether IFN-γ would modify the outcome of the innate interaction of Bpp with human neutrophils. Control experiments showed that incubation with INF- at 150 U/ml for 30 min prior to addition of an activating stimulus is enough to enhance neutrophil bactericidal activity. Interestingly, our results showed that Bpp does not constitute an activating stimulus for IFN-γ-primed neutrophils as demonstrated by the absence of reactive oxygen species (ROS) production upon interaction. Accordingly, IFN-γ-primed neutrophils showed neither increased phagocytosis activity nor higher intracellular killing of Bpp compared with resting neutrophils, as determined by fluorescence microscopy and Polymyxin B protection assays, respectively. Similarly, Bpp proved unable to induce neutrophil extracellular traps (NETs), an extracellular microbicidal mechanism, in IFN-γ-primed neutrophils, as determined by fluorescence microscopy. To investigate the relevance of adenylate cyclase (CyaA), Bpp main immune-modulatory toxin, we constructed a Bpp in frame deletion mutant in the gene CyaA. We found CyaA not involved in the above-mentioned interactions but required to inhibit the activation of the Bpp infected neutrophils subjected to a second chemical (PMA) or bacterial (P. aeruginosa) stimulus. Our results reveal that in the absence of opsonic antibodies Bpp subverts neutrophil bactericidal activity, crucial for innate immunity, even under the influence of a pro-inflamatory cell-activating environment, stressing the need for specific antibodies to control Bpp infections