Relationship between monocyte-derived macrophage phagocytosis and airway inflammation in stable COPD

Despite increased numbers o f alveolar macrophages (mΦ) in stable COPD patients, lower airway bacterial colonisation (LABC) is often seen. We investigated the relationship between LABC status, airway inflammation & monocyte-derived mΦ (MDMs) phagocytosis. Whole blood & sputa were collected from stable COPD patients. MDMs were cultured & phagocytosis of fluorescently-labeled inert beads, or heat-killed Haemophilus influenzae (HI) & Streptococcus pneumoniae (SP) measured. Sputa were analysed by qPCR for HI, SP & Moraxella catarrhalis & airway cytokines by ELISA. Clinical characteristics are shown in Table 1. 19/40 patients had evidence of LABC on qPCR & had significantly higher levels of IL-8 and IL-1β, but not MPO, than non-LABC patients. There was a trend towards increasing airway inflammation with increasing bacterial load. Phagocytosis of HI & SP, but not beads, significantly increased with increasing airway IL-8 & IL-1β (Figure 1). There was no significant relationship between airway MPO and phagocytosis of any prey. Higher levels of airway IL-8 and IL-1β are associated with increased phagocytic response by MDMs to HI & SP but not beads. Higher bacterial loads seen in LABC patients may increase airway inflammation & this may in turn influence phagocytic ability.