Airborne particulate matter and the lung-brain axis: unraveling the neuroinflammatory cascade from alveolar irritation to microglial activation

BACKGROUND: Epidemiological evidence increasingly substantiates a correlation between chronic exposure to airborne environmental pollutants—specifically fine particulate matter (PM₂.₅) and diesel exhaust particles—and the prevalence of neurological disorders. While the respiratory consequences of these exposures are well-documented, the mechanisms by which pulmonary distress communicates pathogenic signals to the central nervous system remain complex and multifaceted. SCOPE & REVIEW: This review explores the "Lung-Brain Axis" as a critical conduit for neurotoxicity. We synthesize current findings on two primary pathways: (1) the direct translocation of ultrafine particles via the olfactory nerve and compromised blood-brain barrier (BBB), and (2) the indirect "spill-over" hypothesis, where pulmonary-derived pro-inflammatory cytokines (e.g., IL-1β, TNF-α, IL-6) and extracellular vesicles (EVs) propagate systemic inflammation that subsequently primes microglial activation in the brain. KEY MECHANISMS: We detail the molecular interplay between alveolar macrophages and the subsequent polarization of neuroimmune cells. Special attention is given to the role of the vagus nerve in sensing pulmonary inflammation and the potential involvement of lung-derived exosomes in transporting microRNAs that disrupt neuronal homeostasis. CONCLUSION: Understanding the specific molecular messengers of the lung-brain axis is essential for developing therapeutic strategies. Targeting the pulmonary inflammatory response may offer a novel prophylactic approach to mitigate the neurological burden of environmental pollution.