Chronic obstructive pulmonary disease (COPD) is a condition characterised by progressive lung function limitation. COPD is associated with airway inflammation and high numbers of inflammatory cells. Alveolar macrophages are the major phagocytic cell of the lung and control levels of pathogens through phagocytosis. Despite an increase in cell numbers in COPD subjects, there is evidence of bacterial colonisation possibly due to reduced phagocytosis. Reduced clearance of bacteria extends to fungal spores and apoptotic cells, suggesting defective phagocytosis of pathogens could contribute to colonisation, inflammation and disease progression.
This thesis examines mechanisms underpinning defective bacterial phagocytosis. Monocyte-derived macrophages (MDM) from non-smokers, smokers and COPD subjects differentiated in GM-CSF were used to explore the role of the motor protein dynein in the context of defective phagocytosis in COPD.
Defective bacterial phagocytosis of H. influenzae and S. pneumoniae was confirmed in COPD MDM, compared to non-smoker MDM and was associated with reduced trafficking of dynein. Inhibiting the movement of dynein in healthy cells also led to defective phagocytic uptake. To understand if these results were due to differences in cell signalling, leading to alterations in cytoskeletal rearrangements in COPD, the phosphorylation profile of MDM from COPD patients and controls in the absence or presence of H. influenzae was analysed. Analysis showed differential phosphorylation of several cytoskeletal associated proteins, including ezrin. Further analysis of ezrin suggested that reduced activation is linked to a reduction in phagocytosis in MDM, suggesting ezrin is important in this process. Changes to its expression or activity could contribute to defective phagocytosis, through its effect on microtubule instability, leading to reduced receptor recycling and early satiety.
Cytoskeletal changes could be contributing to defective phagocytosis by COPD MDM. Investigations into defective phagocytosis aim to find an appropriate target for therapeutic modification, thereby restoring phagocytic capability, reducing bacterial load and diminishing inflammation.