Poster sessionsThorax 2012;67(Suppl 2):A1-A204 A175 students t-test) than in non-COPD (mean expression=26.74%, SD=11.12), reflecting previous findings. PD-1 expression in CD4+ T cells appeared to be lower in COPD (mean expression=39.91%, SD=13.02) than non-COPD (mean expression=50.53%, sd=13.05) but this was not significant. PD-1 expressing CD4+ cells (mean expression=2.17%, SD=1.4) and CD8+ cells (mean expression=6.02%, sd=5.73) were detected in tissue, but not in the blood of the same patients. PD-L1 was undetectable on lung epithelial cells but was expressed on macrophages (mean expression = 2.85%, SD=1.91). Methods Whole blood and sputa were collected from stable patients in the London COPD cohort. Stable COPD was defined as no symptom-defined exacerbations recorded on prospectively completed diary cards in the preceding four weeks and subsequent two weeks. Monocytes were isolated from the whole blood and cultured with GM-CSF (2 ng/ml) for 12 days to generate MDMs. MDM phagocytosis of fluorescently-labelled polystyrene beads, Haemophilus influenzae (HI) and Streptococcus pneumoniae (SP) was measured by fluorimetry. LABC was defined as detection of HI, SP or Moraxella catarrhalis (MC) in sputum using quantitative PCR. Results MDMs were cultured from 26 COPD patients. 54% were male, mean age 70.0 years (SD 8.3), FEV 1 predicted 55.3% (20.3), 46% were current smokers, median daily inhaled corticosteroid (ICS) dose was 1000 (640-2000) mcg (beclomethasone equivalent dose) and median exacerbation frequency per year was 1.8 (1.0-2.9) based on diary card events. Phagocytosis of HI was significantly less with increasing exacerbation frequency (p=0.002, r=-0.58, Figure 1), although no significant associations were demonstrated between exacerbation frequency and phagocytosis of inert beads or SP (p=0.27 and p=0.22 respectively). 13 patients (50%) with LABC did not demonstrate any significant difference in phagocytosis of either beads (p=0.29), HI (p=0.66) or SP (p=0.88) compared with non-colonised patients. There was no significant association between phagocytosis of beads, HI or SP with age, FEV 1 %predicted, smoking pack year history, ICS dose or BMI (all p>0.05). Conclusion In stable COPD patients, decreasing phagocytosis of HI was associated with increasing exacerbation frequency. Phagocytosis was not related to LABC suggesting that macrophage activity alone may not determine bacteria colonisation. Further work is needed to elucidate the mechanisms of reduced phagocytosis in COPD and its relationship to exacerbation frequency. P253described. CSE was prepared by combusting 1 Marlboro cigarette through 25 ml of media. Cell viability was determined after primary nasal epithelial cells (PNECs) were stimulated with 5% CSE for 24 h (caspase 3 levels determined after 4 h), in the presence or absence of 20 mM N-acetylcysteine (NAC). In separate experiments, cultures were stimulated with Pseudomonas aeruginosa lipopolysaccharide (PA LPS) for 24 h (0 -30 µg/ml), and the effects of pre-incubation with CSE±20 mM NAC for 4 h ev...