Leukotriene B4 is essential for lung host defence and alpha-defensin-1 production during Achromobacter xylosoxidans infection.

Leukotriene B4 (LTB4) is essential for host immune defence. It increases neutrophil recruitment, phagocytosis and pathogen clearance, and decreases oedema and inflammasome activation. The host response and the role of LTB4 during Achromobacter xylosoxidans infection remain unexplored. Wild-type (129sv) and LTB4 deficient (Alox5 -/-) mice were intratracheally infected with A. xylosoxidans. Wild-type 129sv infected mice survived beyond the 8th day post-infection, exhibited increased levels of LTB4 in the lung on the 1st day, while levels of PGE2 increased on the 7th day post-infection. Infected Alox5 -/- mice showed impaired bacterial clearance, increased lung inflammation, and succumbed to the infection by the 7th day. We found that exogenous LTB4 does not affect the phagocytosis of A. xylosoxidans by alveolar macrophages in vitro. However, treatment of infected animals with LTB4 protected from mortality, by reducing the bacterial load and inflammation via BLT1 signalling, the high affinity receptor for LTB4. Of importance, we uncovered that LTB4 induces gene and protein expression of α-defensin-1 during the infection. This molecule is essential for bacterial clearance and exhibits potent antimicrobial activity by disrupting A. xylosoxidans cell wall. Taken together, our data demonstrate a major role for LTB4 on the control of A. xylosoxidans infection.