Our data suggest that XLA might result in part from genetic inflammasome deficiency and that NLRP3 inflammasome-linked inflammation could potentially be targeted pharmacologically through BTK.

Although Staphylococcus aureus is not a classical intracellular pathogen, it can survive within phagocytes and many other cell types. However, the pathogen is also able to escape from cells by mechanisms that are only partially understood. We analysed a series of isogenic S. aureus mutants of the USA300 derivative JE2 for their capacity to destroy human macrophages from within. Intracellular S. aureus JE2 caused severe cell damage in human macrophages and could efficiently escape from within the cells. To obtain this full escape phenotype including an intermittent residency in the cytoplasm, the combined action of the regulatory systems Sae and Agr is required. Mutants in Sae or mutants deficient in the Sae target genes lukAB and pvl remained in high numbers within the macrophages causing reduced cell damage. Mutants in the regulatory system Agr or in the Agr target gene psmα were largely similar to wild-type bacteria concerning cell damage and escape efficiency. However, these strains were rarely detectable in the cytoplasm, emphasizing the role of phenol-soluble modulins (PSMs) for phagosomal escape. Thus, Sae-regulated toxins largely determine damage and escape from within macrophages, whereas PSMs are mainly responsible for the escape from the phagosome into the cytoplasm. Damage of macrophages induced by intracellular bacteria was linked neither to activation of apoptosis-related caspase 3, 7 or 8 nor to NLRP3-dependent inflammasome activation.

The human pathogen Staphylococcus aureus is considered mainly an extracellular, opportunistic pathogen, yet the bacterium is able to survive within and escape from host cells, including macrophages. An agr/ sae mutant of strain USA300 is unable to escape from human macrophages but can replicate and survive within macrophages. We questioned whether such “„non-toxic“” S. aureus resembles the less pathogenic coagulase-negative Staphylococcal species (CoNS) like S. carnosus, S. lugdunensis, S. capitis, S. warneri or S. pettenkoferi. We show that in contrast to the “„non-toxic“” S. aureus strains, the CoNS species are efficiently killed within 24 h post-infection in the macrophage-like THP-1 cells or in human primary macrophages. Bacterial persistence of “„non-toxic“” S . aureus or CoNS induced IL-1ß release but no cell-death. Mutations in genes coding for katalase, copprer transport or the regulatory system GraRS or SigB did not impact bacterial survival in THP-1 cells. Deletion of the superoxide dismutases sodA and sodM impaired S. aureus survival in human primary macrophages but not in THP-1 cells. However, expression of the S. aureus specific sodM in S. epidermidis was not sufficient to protect this species from being killed in THP-1 cells. Thus, at least in those cells better bacterial survival of S. aureus could not be linked to higher protection from ROS. However, “„non-toxic“” S. aureus was found to be insensitive to pH, whereas S. epidermidis was protected when phagosomal acidification was inhibited. Thus, species differences seem to be linked to different sensitivity to acidification.