Macrophage-derived LTB₄promotes abscess formation and clearance of Staphylococcus aureus skin infection in mice

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 LTB₄enhances antimicrobial effector functions in vitro, whether prompt LTB₄production is required for bacterial clearance and development of an inflammatory milieu necessary for abscess formation to restrain pathogen dissemination is unknown. We found that LTB₄is 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 LTB₄synergizes with antibiotics to eliminate MRSA potently. Here, we uncovered a heretofore unknown role of macrophage-derived LTB₄in orchestrating the chemoattractant gradient required for abscess formation, while amplifying antimicrobial effector functions.