Higher blood monocyte numbers in people with clinically confirmed pulmonary fibrosis are linked to poor prognosis. It’s unclear whether they play a role in developing and evolving interstitial lung abnormalities (ILA) in people. The researchers examined the relationships between blood monocyte count and various immune cell types, ILA, high attenuation areas (HAA), and forced vital capacity (FVC) in four separate cohorts. Participants in the Multi-Ethnic Study of Atherosclerosis (MESA, n=484), Age/Gene-Environment Susceptibility Study (AGES-Reykjavik, n=3,547), Genetic Epidemiology of COPD (COPDGene, n=2,719), and Evaluation of COPD Longitudinally to Identify Predictive Surrogate End-points (ECLIPSE, n=646) with measured monocyte counts and CT.

After controlling for variables, a 1-SD increase in blood monocyte count was linked to ILA in MESA (odds ratio (OR) 1.3, 95% CI 1.0-1.8), AGES-Reykjavik (OR 1.2, 95% CI 1.1-1.3), COPDGene (OR 1.3, 95% CI 1.2-1.4), and ECLIPSE (OR 1.2, 95% CI 1.0-1.4). In the AGES-Reykjavik study, a higher monocyte count was linked to ILA progression over 5 years (OR 1.2, 95% CI 1.0-1.3). In MESA, participants with ILA had a larger percentage of activated monocytes than those without ILA. In MESA and COPDGene, a higher monocyte count was linked to a higher HAA and a worse FVC. Other immune cell types had less consistent associations. The presence and progression of interstitial lung abnormalities and a lower FVC were linked to higher blood monocyte counts.