Transcriptomics highlight eosinophils and TH2 as disease-driving cells in AR
We assessed whole blood gene expression comparing AR and non-AR individuals from our previously described SSIC cohort using whole transcriptomic sequencing (Supplementary Table 2A ). A total of 1160 unique probes associated to 1095 unique genes were differentially expressed at a nominal significance level of 0.05. A total of 23 probes representing 20 unique gene transcripts were robust after stringent correction for multiple testing at a false discovery rate (FDR) p-value of 0.05, with all transcripts upregulated in AR (Table 1A ). Given that atopy is well known to be associated with eosinophil levels, sensitivity analysis with adjustment for eosinophil counts was performed, with all identified differentially expressed genes (DEGs) remaining significant post adjustment. To account for ethnicity and environmental influences on atopic gene expression, we validated our findings in BAMSE population-based cohort comprising of Swedish adolescents (Table 1B ). Out of 20 DEGs identified in the SSIC cohort, 11 DEGs were replicated and reached significance in BAMSE, confirming the transferability of our findings irrespective of ethnicity and environmental differences (Table 1B ).
For top DEGs that reached nominal significance in the SSIC cohort, we interrogated for biological function and performed Ingenuity Pathway Analysis (IPA). In the disease and disorders category, hypersensitivity and inflammatory responses were significantly associated with nominal AR-related DEGs (Table 2A ). Top pathways enriched for hypersensitivity and inflammatory responses included cell-to-cell signalling and haematological system and cell-mediated immune response (Table 2B, C ). Importantly, we observed strong functional enrichment for eosinophils, along with basophils and mast cells, in hypersensitivity responses associated with AR (Table 2B ). Similarly, functional activation of TH2 and myeloid cells were highlighted to drive inflammatory responses in AR (Table 2C) . Consistent with current understanding, transcriptomic findings emphasise eosinophils and TH2 cells as key drivers of AR.