Intrapulmonary Administration of Leukotriene B4Enhances Pulmonary Host Defense against Pneumococcal Pneumonia

Abstract

Leukotriene B₄(LTB₄) is a potent lipid mediator of inflammation formed by the 5-lipoxygenase (5-LO)-catalyzed oxidation of arachidonic acid. We have previously shown that (i) LTB₄is generated during infection, (ii) its biosynthesis is essential for optimal antimicrobial host defense, (iii) LT deficiency is associated with clinical states of immunocompromise, and (iv) exogenous LTB₄augments antimicrobial functions in phagocytes. Here, we sought to determine whether the administration of LTB₄has therapeutic potential in a mouse model of pneumonia. Wild-type and 5-LO knockout mice were challenged withStreptococcus pneumoniaevia the intranasal route, and bacterial burdens, leukocyte counts, and cytokine levels were determined. LTB₄was administered via the intraperitoneal, intravenous, and intranasal routes prior to pneumococcal infection and by aerosol 24 h following infection. Leukocytes recovered from mice givenS. pneumoniaeand treated with aerosolized LTB₄were evaluated for expression levels of the p47phox subunit of NADPH oxidase. Intrapulmonary but not systemic pretreatment with LTB₄significantly reduced the lungS. pneumoniaeburden in wild-type mice. Aerosolized LTB₄was effective at improving lung bacterial clearance when administered postinoculation in animals with established infection and exhibited greater potency in 5-LO knockout animals, which also exhibited greater baseline susceptibility. Augmented bacterial clearance in response to LTB₄was associated with enhanced monocyte recruitment and leukocyte expression of p47phox. The results of the current study in an animal model serve as a proof of concept for the potential utility of treatment with aerosolized LTB₄as an immunostimulatory strategy in patients with bacterial pneumonia.