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

BAROLI, CARLOS; GORGOJO, JUAN PABLO; CARRICA, MARIELA; VALDEZ, HUGO; RODRIGUEZ, MARÍA EUGENIA

Brussels

Simposio; 12th International Symposium on Bordetella; 2019

B. parapertussis (Bpp) incidence increased after replacement of whole cell vaccines by acellular vaccines and it is thought to contribute to the reemergence of whooping cough. Current 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, neutrophils might be in presence of priming cytokines, like gamma-interferon (IFN-γ), eventually improving 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-y at 150 U/ml for 30 min prior to addition of an activating stimulus, is enough to enhance neutrophil bactericidal mechanisms. However, IFN-γ-primed neutrophils did not show improved phagocytosis or intracellular killing of Bpp as determined by fluorescence microscopy and Polymyxin B protection assays, respectively. Accordingly, there was no activation of primed neutrophils during Bpp encounter, as demonstrated by the absence of reactive oxygen species (ROS) production. Similarly, neutrophil extracellular traps (NETs), an extracellular microbicidal mechanism, was not induced by Bpp in IFN-γ-primed neutrophils, as determined by fluorescence microscopy. Adenylate cyclase toxin (CyaA) activity proved not required to avoid any of these bactericidal activities but was found involved in inhibiting neutrophil activation if the cells are subjected to a second chemical (PMA) or bacterial (P. aureginose) stimulus. Together with previous results, this later results seems to indicate that in the absence of opsonic antibodies Bpp is able to survive the encounter with this aggressive immune cell, probably through the action of different virulence factors, even in a pro-inflamatory cell-activating environment like the one it could face during infection.