Simon P. Hogan

Introduction Food allergic reactions can be severe and potentially life‐threatening and the underlying immunological processes that contribute to the severity of reactions are poorly understood. The aim of this study is to integrate bulk RNA‐sequencing of human and mouse peripheral blood mononuclear cells during food allergic reactions and in vivo mouse models of food allergy to identify dysregulated immunological processes associated with severe food allergic reactions. Methods Bulk transcriptomics of whole blood from human and mouse following food allergic reactions combined with integrative differential expressed gene bivariate and module eigengene network analyses to identify the whole blood transcriptome associated with food allergy severity. In vivo validation immune cell and gene expression in mice following IgE‐mediated reaction. Results Bulk transcriptomics of whole blood from mice with different severity of food allergy identified gene ontology (GO) biological processes associated with innate and inflammatory immune responses, dysregulation of MAPK and NFkB signalling and identified 429 genes that correlated with reaction severity. Utilizing two independent human cohorts, we identified 335 genes that correlated with severity of peanut‐induced food allergic reactions. Mapping mouse food allergy severity transcriptome onto the human transcriptome revealed 11 genes significantly dysregulated and correlated with severity. Analyses of whole blood from mice undergoing an IgE‐mediated reaction revealed a rapid change in blood leukocytes particularly inflammatory monocytes (Ly6C hi Ly6G − ) and neutrophils that was associated with changes in CLEC4E, CD218A and GPR27 surface expression. Conclusions Collectively, IgE‐mediated food allergy severity is associated with a rapid innate inflammatory response associated with acute cellular stress processes and dysregulation of peripheral blood inflammatory myeloid cell frequencies.

Background Pulmonary eosinophils comprise at least two distinct populations of resident eosinophils (rEOS) and inflammatory eosinophils (iEOS), the latter recruited in response to pulmonary inflammation. Here, we determined the impact of complement activation on rEOS and iEOS trafficking and function in two models of pulmonary inflammation. Methods BALB/c wild‐type and C5ar1 −/− mice were exposed to different allergens or IL‐33. Eosinophil populations in the airways, lung, or mediastinal lymph nodes (mLN) were characterized by FACS or immunohistochemistry. rEOS and iEOS functions were determined in vivo and in vitro. Results HDM and IL‐33 exposure induced a strong accumulation of iEOS but not rEOS in the airways, lungs, and mLNs. rEOS and iEOS expressed C3/C5 and C5aR1, which were significantly higher in iEOS. Initial pulmonary trafficking of iEOS was markedly reduced in C5ar1 −/− mice and associated with less IL‐5 production from ILC2 cells. Functionally, adoptively transferred pulmonary iEOS from WT but not from C5ar1 −/− mice‐induced airway hyperresponsiveness (AHR), which was associated with significantly reduced C5ar1 −/− iEOS degranulation. Pulmonary iEOS but not rEOS were frequently associated with T cells in lung tissue. After HDM or IL‐33 exposure, iEOS but not rEOS were found in mLNs, which were significantly reduced in C5ar1 −/− mice. C5ar1 −/− iEOS expressed less costimulatory molecules, associated with a decreased potency to drive antigen‐specific T cell proliferation and differentiation into memory T cells. Conclusions We uncovered novel roles for C5aR1 in iEOS trafficking and activation, which affects key aspects of allergic inflammation such as AHR, ILC2, and T cell activation.