Macrophage-derived LTB4 promotes abscess formation and clearance of Staphylococcus aureus skin infection in mice

Abstract

The early events that shape the innate immune response to restrain pathogens during skin infections remain elusive. Methicillin-resistant Staphylococcus aureus (MRSA) infection engages phagocyte chemotaxis, abscess formation, and microbial clearance. Upon infection, neutrophils and monocytes find a gradient of chemoattractants that influence both phagocyte direction and microbial clearance. The bioactive lipid leukotriene B4 (LTB4) is quickly (seconds to minutes) produced by 5-lipoxygenase (5-LO) and signals through the G protein-coupled receptors LTB4R1 (BLT1) or BLT2 in phagocytes and structural cells. Although it is known that LTB4 enhances antimicrobial effector functions in vitro, whether prompt LTB4 production is required for bacterial clearance and development of an inflammatory milieu necessary for abscess formation to restrain pathogen dissemination is unknown. We found that LTB4 is produced in areas near the abscess and BLT1 deficient mice are unable to form an abscess, elicit neutrophil chemotaxis, generation of neutrophil and monocyte chemokines, as well as reactive oxygen species-dependent bacterial clearance. We also found that an ointment containing LTB4 synergizes with antibiotics to eliminate MRSA potently. Here, we uncovered a heretofore unknown role of macrophage-derived LTB4 in orchestrating the chemoattractant gradient required for abscess formation, while amplifying antimicrobial effector functions.

Redundant and Cooperative Roles for Yersinia pestis Yop Effectors in the Inhibition of Human Neutrophil Exocytic Responses Revealed by Gain-of-Function Approach

“…Importantly, LTB 4 production is not dependent on transcriptional regulation (29). Therefore, LTB 4 is produced more rapidly than other chemoattractants, such as IL-8, and it is pivotal in mounting a swift inflammatory response (26,28,(30)(31)(32). Moreover, release of LTB 4 is independent of degranulation (33), suggesting that regulation of LTB 4 release also differs from degranulation.…”

Leukotriene B4licenses inflammasome activation to enhance skin host defense

“…We and others have shown that enhances microbial clearance by controlling the generation of reactive oxygen and nitrogen species, as well as antimicrobial peptides in vivo (16)(17)(18)(19). We also have shown that the treatment of mice with a topical ointment containing LTB4 enhances S. aureus clearance, production of inflammatory mediators, and abscess formation (20). Whether LTB4 enhances skin host defense directly or by indirectly increasing production of proinflammatory mediators remains to be determined.…”

“…Here, we measured Il1b transcripts and protein by ELISA in skin biopsy homogenates from uninfected and MRSA-infected mice. Skin biopsies from WT mice treated topically with LTB4 or the BLT1 antagonist U-75302 (20), as well as Ltb4r1 -/mice collected from uninfected skin and day 1 post-MRSA infection revealed that topical LTB4 increased IL-1β and that both BLT1 antagonist treatment and Ltb4r1 -/showed decreased IL-1β protein and Il1b mRNA transcripts during infection compared to WT mice ( Figure 1A and B). These data suggest that exogenous LTB4 (treated topically) enhances inflammasome-dependent IL-1β and endogenously produced LTB4 during skin infection is required for optimal IL-1β generation.…”

“…Murine resident peritoneal macrophages were isolated using ice-cold phosphate-buffered saline (PBS) as previously described (15,25). To isolate neutrophils, bone marrow from both tibias and femurs were flushed with phosphate-buffered saline (PBS) (20)…”

From the Cradle to the Grave of an Infection: Host‐Pathogen Interaction Visualized by Intravital Microscopy

“…Ecb, a complement inhibitor produced by S. aureus , was shown to diminish PMN recruitment to the site of infection. Conversely, the leukocyte factor LTB4 is accountable for neutrophil swarming and the formation of abscesses in infections with S. aureus , as well as Pseudomonas aeruginosa , an opportunistic gram‐negative bacterium causing acute and chronic infection of lung and soft tissues in predisposed individuals .…”