Postulated Mechanisms by Which Viruses and Mycoplasma May Impair the Defense Mechanisms of the Respiratory Tract
- Reduced mucociliary clearance
- Injured epithelium enhances attachment for bacteria
- Enhanced bacterial attachment predisposes to colonization
- Decreased mucociliary clearance prolongs the resident time of bacteria favouring colonization
- Injured epithelium prevents mucociliary clearance and physical removal of bacteria
- Lack of secretory products facilitates further cell injury
- Break down the antimicrobial barrier in mucus and cells (β-defensins and anionic peptides)
- Ciliostasis caused by inflammation or by some pathogenic organisms (mycoplasmas)
- Dysfunction of pulmonary alveolar macrophages and lymphocytes
- Consolidation of the lung causes hypoxia resulting in decreased phagocytosis
- Infected macrophages fail to release chemotactic factors for other cells
- Infected macrophages fail to attach and ingest bacteria
- Lysosomes become disoriented and fail to fuse with phagosome-containing bacteria
- Intracellular killing or degradation is decreased because of biochemical dysfunction
- Altered cytokines and secretory products impair bacterial phagocytosis
- Viral-induced apoptosis of alveolar macrophages
- Altered CD4 and CD8 lymphocytes
- Toll-like receptors (TLRs) in virus-infected macrophages increase proinflammatory response to bacteria
