Neutrophil crawling in capillaries; a novel immune response to Staphylococcus aureus.

Mark Geoffrey Harding,Kunyan Zhang,Paul Kubes,John Conly,Frank R Deleo

doi:10.1371/journal.ppat.1004379

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA), particularly the USA300 strain, is a highly virulent pathogen responsible for an increasing number of skin and soft tissue infections globally. Furthermore, MRSA-induced soft tissue infections can rapidly progress into life-threatening conditions, such as sepsis and necrotizing fasciitis. The importance of neutrophils in these devastating soft tissue infections remains ambiguous, partly because of our incomplete understanding of their behaviour. Spinning disk confocal microscopy was used to visualize the behaviour of GR1-labelled neutrophils in subcutaneous tissue in response to GFP-expressing MRSA attached to a foreign particle (agarose bead). We observed significant directional neutrophil recruitment towards the S. aureus agarose bead but not a control agarose bead. A significant increase in neutrophil crawling within the capillaries surrounding the infectious nidus was noted, with impaired capillary perfusion in these vessels and increased parenchymal cell death. No neutrophils were able to emigrate from capillaries. The crawling within these capillaries was mediated by the β2 and α4 integrins and blocking these integrins 2 hours post infection eliminated neutrophil crawling, improved capillary perfusion, reduced cell death and reduced lesion size. Blocking prior to infection increased pathology. Neutrophil crawling within capillaries during MRSA soft tissue infections, while potentially contributing to walling off or preventing early dissemination of the pathogen, resulted in impaired perfusion and increased tissue injury with time.

Highlights

Staphylococcus aureus is a Gram-positive, facultatively anaerobic bacterium that poses considerable challenges to human health as a re-emerging pathogen in both hospital and community settings
We investigated the role of neutrophils in soft tissue infections, as these immune cells have been shown to be both essential for clearance of this pathogen and for increasing tissue injury associated with S. aureus infections
In addition to a profound neutrophil recruitment into the infectious nidus, significant neutrophil crawling in capillaries surrounding the region was noted, a region of vasculature which has not previously been associated with neutrophil recruitment during infection

Summary

Introduction

Staphylococcus aureus is a Gram-positive, facultatively anaerobic bacterium that poses considerable challenges to human health as a re-emerging pathogen in both hospital and community settings. S. aureus is a serious pathogen, responsible for approximately 18,500 deaths per year in the United States, more than all deaths caused by AIDS, influenza, or viral hepatitis [2]. S. aureus infections, those due to methicillin-resistant Staphylococcus aureus (MRSA) have been increasing in frequency in recent years, and account for the majority of all clinical skin and soft tissue infections in the United States [3]. These infections can cause serious complications, such as necrotizing fasciitis, necrotizing pneumonitis and sepsis [4]. A single MRSA strain, pulsotype USA300 is the dominant community acquired strain in North America [5,6,7,8]

Results

Discussion

Conclusion