Bordetella intracellular survival encompasses host cell defense gene regulation

VALDEZ, HUGO; LAMBERTI, YANINA; RODRIGUEZ, MARIA EUGENIA

Ouro Preto

Simposio; The innate Immune response in the pathogenesis of Infectious disease; 2013

Keystone Symposia on MOlecular and Cellular Biology

Bordetella pertussis, the causative agent of whooping cough, is a highly human pathogen that has persisted within the population despite decades of vaccination. Historically regarded as an extracellular pathogen we recently reported evidence indicating that this bacterium can survive and replicate inside human macrophages. The replication appears around 24 h post-infection. IFN-mediated immunity is vital for intracellular pathogens clearing. As many other successful intracellular pathogens, B. pertussis seems to counteract the effect of IFN. We had previously observed that B. pertussis interferes with HLA-DR up regulation in response to IFN. We now observed that the presence of IFN (150 U/ml during the whole experiment) does not affect B. pertussis survival inside the cell. Given the potential importance of this immune evasion strategy, in this study we investigated whether infection of human macrophages is facilitated by B. pertussis interference of IFNsignaling. To this end we used a combination of quantitative RT-PCR and flow cytometry. Our results indicate that the response of the IFN-inducible chemokines IP-10/CXCL10 and MIG/CXCL9 to IFNwas not inhibited in infected macrophages at early time points but was drastically down regulated at later time points, concurring with the start of bacterial intracellular growing. IFNreceptor expression was then quantified by RT-PCR. We also used flow cytometry which enabled the discrimination between total and surface exposed receptor. IFN receptor expression was found unchanged over the time of infection and similar to uninfected cells. In the presence of IFN, both infected and uninfected macrophages showed a similar down regulation of IFN receptor expression, except 48 hours post infection at which a deep gene repression was observed in infected cells. Finally, we investigated SOCS1 and SOCS3 protein expression. Both proteins are involved in the negative feedback mechanism to limit IFN mediated inflammatory response, and are usually used by intracellular pathogens to inhibit the macrophage activation. A significant up regulation of SOCS1 and SOCS3 mRNA expression was seen already at early time points after infection and increased over the time. The presence of IFN enhanced the expression of SOCS1 and SOCS3 in infected macrophages as compared with uninfected cells. Taken together these results suggest that B. pertussis manage to turn defense cells into suitable hosts for bacterial propagation by manipulating the expression of key signaling molecules which might eventually allow the pathogen to survive until local inflammation has been modulated.