Farm-Dust Mediated Protection of Childhood Asthma: Mass Cytometry Reveals Novel Cellular Regulation

This study examined the immune mechanisms responsible for the protective association of farm dust exposure on asthma development by using peripheral blood at the single-cell level.The study included 20 children aged 4 to 17 years enrolled in the CLARA/CLAUS cohort, 10 healthy controls, and 10 with mild to moderate physician-diagnosed asthma symptoms, serum-specific immunoglobulin E greater than 35 kU/L, and significant reversible airflow on spirometry.Farm dust was collected from classical cow farming using electrostatic dust collectors resting in the shed of a German farm for 4 weeks. Farm dust was extracted using a standardized cold sodium chloride extraction method. In vitro cells from children with and without allergic asthma and with and without farm dust stimulation had single-cell protein expression measured using mass cytometry. The proportions of innate and adaptive immune cells were analyzed using linear regression, and T-cell proliferation was examined. Functional marker expression was evaluated using Earth Mover’s Distance and its significance was measured using the Monte Carlo permutation test.In vitro farm dust stimulation induced downregulated innate immune cell populations (monocytes/dendritic cells [P < .001] and natural killer [NK] cells [P < .05]), upregulated adaptive immune cell populations (B cells [P < .05] and CD4+ T cells [P < .05]), reduced CD4+ CD25− T- cell proliferation, and increased activation (CD25) of T cells and NK cells in both groups after multiple testing correction. Markers of cytotoxicity (GZMB) and inflammation (pERK1/2 and pp38) were decreased in the allergic asthma group. Markers associated with asthma (Th2 GATA3, Th17 RORγ, and antigen presenting HLA-DR) were decreased in the allergic asthma group and unchanged or increased in the healthy controls. B cells showed an increase in functional markers in both groups, with greater effects among healthy controls.Farm dust exposure induced cellular activation in the healthy control and allergic asthma groups and reduced expression of asthma-associated markers of cytotoxicity, inflammation, and antigen presentation in the allergic asthma group.This study enhances our understanding of the immune mechanisms associated with the lower prevalence of asthma among children exposed to traditional farming environments. Future studies exploring the changes in regulation of immune cells with farm dust exposure and possible strategies to prevent pediatric asthma would benefit from the examination of functional marker expression in immune cells of the airways and mucous membranes, a larger sample size, and replication in vivo.