Macrophage versus urinary tract infection: a help or a hindrance?

Urinary tract infections (UTIs), which are more frequently being caused by antibiotic resistant strains of uropathogenic Escherichia coli (UPEC), are common in the community and have the potential to keep reoccurring within the same individual. Combatting these infections is complicated by both the drug resistance profile of the causative bacterium and insufficient knowledge regarding the role of the adaptive immune response in the intial clearance of the pathogen as well as prevention of re-infection.

Mora-Bau et al. have recently demonstrated that a dendritic cell-mediated adaptive immune response is elicited during UTI of mice but, strikingly, does not establish sterilizing immunity in the host. Furthermore, it has already been demonstrated that both neutrophil and monocyte macrophage precursors do infiltrate the bladder during the UPEC infection process. This led Mora-Bau et al. to hypothesise that monocyte derived- and resident macrophages that are already in the bladder could be critical in the immune response to UPEC infection. Separate depletion of circulating and resident macrophages 15-18 hrs prior to UPEC infection had only a small effect on bacterial burden and, therefore, the primary infection process. However, upon challenge of mice that were depleted of resident macrophages during primary infection with UPEC, a 2 orders of magnitude drop in bacterial colony forming units was observed. This improvement was dependent upon the adaptive immune system and indicates that macrophage involvement in UPEC infection could be subverting initiation of this branch of immunity. Furthermore, in the absence of macrophages, an increased percentage of dendritic cells containing UPEC were observed. These findings suggest that development of strategies to increase bladder dendritic cell numbers could be the key to overcoming subversion of adaptive immunity by macrophages thus ensuring that patients have better protection against re-current UTIs.

Original paper: Macrophages Subvert Adaptive Immunity to Urinary Tract Infection. Gabriela Mora-Bau, Andrew M. Platt, Nico van Rooijen, Gwendalyn J. Randolph, Matthew L. Albert and Molly A. Ingersoll. PLOS Pathogens | DOI:10.1371/journal.ppat.1005044 July 16, 2015.

Image source: “Macrophage” by The original uploader was Obli at English Wikipedia – Transferred from en.wikipedia to Commons.. Licensed under CC BY-SA 2.0 via Wikimedia Commons –

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Jennifer Shepherd

A Postdoc with a passion for scientific writing and editing currently working on quality control of translation in bacteria.

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