Bartonella henselae

B. henselae, the causative agent of cat scratch disease and bacillary angiomatosis, is the only known bacterial pathogen causing vasculoproliferative disorders in humans (hence the name bacillary angiomatosis) [72, 73]. Gene expression analysis upon infection of epithelial HeLa cells with B. henselae revealed only 20 genes to be regulated at 6h after infection [74]. At least 14 of these genes are known to be regulated by the transcription factor HIF-1a. HIF-1a is a key transcription factor for the induction of angiogenic growth factors that adjust the vascular blood supply to tissues on metabolic demand [75, 76]. It is speculated that by this particular gene expression profile B. henselae reprograms host cells in order to create a perfect habitat for its own growth: in fact, B. henselae invades and replicates in endothelial cells [77, 78]. The signal cascade which leads to the proangiogenic gene signature is yet unknown. One interesting question in this context is why and how B. henselae provokes this specific gene expression program in host cells but prevents induction of the typical afore-mentioned proinflammatory host cell response induced by engagement of, e.g., TLRs.

The activation of the transcription factor HIF-1a by bacteria appears not to be restricted to B. henselae. There is evidence that viable as well as killed S. aureus [79] or P. aeruginosa [55] and probably many other bacteria induce activation of HIF-1a and subsequently HIF-1a-regulated genes. Future studies will need to investigate whether or not HIF-1a-mediated gene expression is a unique or specific host response in infectious diseases.

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