The Role of Monocytes in the Natural History of Idiopathic Pulmonary Fibrosis: A Systematic Literature Review.

Emerging evidence suggests a significant association between monocytes and the pathophysiology and prognosis of idiopathic pulmonary fibrosis (IPF). This review aims to systematically evaluate current knowledge regarding blood monocyte counts and their relationship with the etiology, progression, and prognosis of IPF. We conducted a systematic search in the PubMed database for articles published through 17 February 2025, using the MeSH terms "lung diseases, interstitial" and "monocytes," which yielded 314 results. After filtering for full-text articles in English (n = 242), we included only studies focusing on blood monocyte counts with clinical implications in IPF. Articles relating to other cell types or non-IPF lung diseases were excluded. Our systematic search identified 12 relevant articles. Monocytes play an essential role in regulating inflammatory responses and resolution across multiple diseases, with established but incompletely understood contributions to lung fibrosis development in IPF. Correlations have been demonstrated between elevated blood monocyte counts and the following: (1) the presence and progression of interstitial lung abnormalities, (2) the progression from an indeterminate usual interstitial pneumonia (UIP) pattern on CT scans to definitive IPF, and (3) worse lung function parameters, an increased risk of acute exacerbations, and reduced overall survival in IPF patients. Monocytes serve as critical orchestrators throughout IPF's natural history-from early interstitial changes to disease progression and acute exacerbations. Targeting monocyte recruitment pathways and reprogramming their differentiation represents a promising therapeutic approach, while circulating monocyte counts offer potential as accessible biomarkers for disease progression and treatment response. Future research should characterize stage-specific monocyte phenotypes to enable precision-targeted interventions.