Rab27a modulation reverses hemorrhage-induced neutrophil dysfunction in response to secondary respiratory challenge

Patients recovering from hemorrhage are susceptible to secondary respiratory infections, owing to dysregulated innate immune responses. Using a two-hit mouse model of hemorrhage followed by a secondary respiratory challenge with Staphylococcus aureus or lipopolysaccharide (LPS), we investigated the role of Rab27a in the neutrophil response to pulmonary inflammation and host defense. Hemorrhage followed by S. aureus infection increased surface CD63 expression on pulmonary neutrophils, indicating azurophilic granule release, and was accompanied by reduced neutrophil entry into the airspaces of the lung. Using HoxB8-conditional neutrophil progenitor (NP) transplantation to neutrophil chimeric mice, we observe that Rab27a-deficient neutrophils have enhanced recruitment into the extravascular pulmonary compartment compared with wild-type (WT) neutrophils. Furthermore, pharmacological intervention with Nexinhib20, a small-molecule inhibitor of Rab27a-JFC1 interactions, attenuated systemic and pulmonary inflammatory responses in the two-hit model, including a reduction in circulating myeloperoxidase (MPO) levels. Nexinhib20 also enhanced neutrophil-mediated S. aureus killing that was accompanied by increased intracellular MPO levels in neutrophils. Collectively, these findings implicate Rab27a-associated functions in the regulation of neutrophil trafficking and inflammatory responses following hemorrhage and secondary respiratory challenge, highlighting the potential of pharmacological targeting of Rab27a to attenuate inflammation without compromising antimicrobial host defense.