Human macrophages, a cellular reservoir for Bordetella pertussis?

LAMBERTI Y; ALVAREZ HAYES, J; HARVILL ET; RODRIGUEZ ME

Congreso; 9th International Bordetella Symposium.; 2010

Previous studies had suggested that B pertussis might be able to survive the encounter with macrophages. Despite its potential importance in terms of immune subversion, the underlying mechanisms and its possible outcome under different immunity states of the host has not been studied. We here used confocal microscopy to investigate the fate of B. pertussis upon phagocytosis by human macrophages in the presence and the absence of specific antibodies. Intracellular bacterial survival was evaluated by Polymyxin B protection assays. Both in the absence and the presence of antibodies, bacterial killing within the first hours in acidic (lamp positive, lysotrack positive) compartments was observed. However, only in the absence of antibodies a significant proportion of internalized bacteria evaded this initial killing, remaining in compartments with early endosomal characteristics (Rab5 positive). Two days after infection with un-opsonised but not with opsonised bacteria, the number of intracellular viable bacteria per cell increased, suggesting the absence of antibodies enables B. pertussis trafficking to replicative compartments. Accordingly, we found B. pertussis-containing phagosomes to acquire exogenously added transferrin, indicating that intracellular bacteria have access to extracellular components and essential nutrients via the host cell recycling pathway. Interestingly, Adenylate cyclase toxin, previously described as involved in this kind of interaction, was found required for early survival but not for intracellular replication at longer times. We found that B. pertussis macrophage infection down regulates MHC class II and renders the cell unresponsive to INF. These results demonstrate that B. pertussis survives and replicates in compartments with characteristics of early-endosomes while stressing the critical role of opsonic antibodies in avoiding the establishment of bacterial reservoir potentially involved in the extraordinary ability of B. pertussis to persist within hosts and population.