Farm‐dust mediated protection of childhood asthma: Mass cytometry reveals novel cellular regulation

Abstract Background Farm‐dust mediated asthma protection in childhood was replicated in numerous epidemiological studies. Central immune mechanisms are not fully understood. This exploratory study aimed to disentangle underlying immunological regulation of farm‐dust mediated protection in peripheral blood on a single‐cell level. Methods Single‐cell protein expression of in vitro farm‐dust stimulated and unstimulated cells from allergic asthmatics and healthy controls were measured using mass cytometry. Analysis of innate and adaptive cellular proportions (linear regression) and T‐cell proliferation was performed. Functional marker intensity was investigated using Earth Mover's Distance and the Monte Carlo permutation test. Results Farm‐dust stimulation induced cell type‐specific regulation: Key‐features of farm‐dust stimulation comprised opposing regulation of immune‐cell frequencies (downregulated innate cell populations (monocytes/DCs ( p < .001), NK‐cells ( p < .05)) and upregulated adaptive populations (B‐cells, CD4 + T‐cells (both p < .05)), reduced CD4 + CD25 − T‐cell proliferation, and differential cell type‐specific functional marker expression. Following stimulation, functional marker analysis revealed induced activation (CD25) in T‐cells and NK‐T‐cells in both phenotypes even after correction for multiple testing. Cytotoxicity (GZMB) and inflammation (pERK1/2, pp38) related markers were reduced in T‐cells exclusively in asthmatic children. Asthma‐associated markers (Gata3, RORγ, and HLA‐DR) were reduced in T‐ and innate‐ cell populations of asthmatics following stimulation. B‐cells displayed a phenotypically independent increase of diverse functional markers upon farm‐dust stimulation. Conclusions This study mimicking in vivo environmental exposure identified a novel profile of immune‐regulatory markers using mass cytometry demonstrating decreased asthma‐associated markers following farm‐dust stimulation. These findings may be key for further studies on asthma prevention in childhood.