Conventional dendritic cell 2 links the genetic causal association from allergic asthma to COVID-19: a Mendelian randomization and transcriptomic study

Abstract Recent evidence suggests that allergic asthma (AA) decreases the risk of Coronavirus Disease 2019 (COVID-19). However, the reasons remain unclear. Here, we systematically explored data from GWAS (18 cohorts with 11,071,744 samples), bulk transcriptomes (3 cohorts with 601 samples), and single-cell transcriptomes (2 cohorts with 29 samples) to reveal the immune mechanisms that connect AA and COVID-19. Two-sample Mendelian randomization (MR) analysis identified a negative causal correlation from AA to COVID-19 hospitalization (OR = 0.968, 95% CI 0.940–0.997, P = 0.031). This correlation was bridged through white cell count. Furthermore, machine learning identified dendritic cells (DCs) as the most discriminative immunocytes in AA and COVID-19. Among five DC subtypes, only conventional dendritic cell 2 (cDC2) exhibited differential expression between AA/COVID-19 and controls (P