Abstract Introduction We previously reported impaired airway macrophage (AM) phagocytosis of inhaled particulate matter in children with airway inflammation, secondary to increased airway prostaglandin-E2 (PEG2). Since recurrent respiratory infections and airway inflammation are key clinical features of bronchiectasis, and air pollution is a global health burden, we investigated the effects of PGE2 and diesel exhaust particle (DEP) on AM bacterial killing in vitro in children with bronchiectasis. Methods With informed consent (UK ethics 24/SC/0177), children with bronchiectasis and healthy controls underwent sputum induction. Sputum samples were processed to extract enriched AM using the RosetteSep monocyte enrichment cocktail. Following overnight adhesion, enriched AM were incubated with bovine serum albumin to prevent non-specific binding. AM were incubated with 6x105Pseudomonas Aeruginosa (PA01) for 1.5 h to allow phagocytosis, before addition of gentamicin to kill non-phagocytosed bacteria. AM were exposed to PGE2 and PGE2+DEP for 2 h before lysis. Lysed cells were plated on LA agar overnight. AM killing was assessed by colony-forming unit (CFU) the next day. Results Children with bronchiectasis (n = 7, mean age 8.43 years) demonstrated similar AM killing to healthy controls (n = 10, mean age 11.13 years) (mean CFU ± SEM 38.1 ± 15.4 vs 30.6 ± 9.7, p = 0.86; Figure 1A). PGE2 impaired killing in bronchiectasis AM (mean CFU ± SEM 150.7 ± 40.0, p 0.05), which was further impaired by addition of DEP (mean CFU ± SEM 228.6 ± 79.6, p 0.05; Figure 1B). Similarly, impaired AM killing in healthy controls was seen when incubated with PGE2 (mean CFU ± SEM 188.9 ± 49.5, p 0.01); and PGE2+DEP (mean CFU ± SEM 146.5 ± 47.3, p 0.05; Figure 1C). Conclusion When removed from their native airway secretion environment, AM from children with bronchiectasis and healthy controls demonstrated comparable killing capacity in vitro. Exposure to PGE2 impaired AM killing in both groups. In bronchiectasis, a synergistic enhancement of AM killing was observed with combined PGE2 and DEP exposure, whereas this synergy was absent in healthy controls, although overall killing remained impaired with PGE2+DEP. Further work is warranted to determine the mechanisms underlying the synergistic impairment of AM killing by PGE2 and DEP in bronchiectasis. This abstract is funded by: Barts Charity, UK
Liu et al. (Fri,) studied this question.