Alternative activation of mast cells by CD4+ T helper cells
Effector CD4+ T lymphocytes (Teff) infiltrate sites of inflammation and orchestrate the immune response by instructing local leukocytes. Mast cells (MCs) are tissue sentinel cells strategically located near blood vessels and T cell rich areas. MC/Teff cells interactions shape Teff cell responses but in turn, Teff cell action on MC is still poorly understood.  Here, we analyzed the human MC/Teff cells interplay through the application of RNAseq and functional assays and showed that activated Teff cells induced a specific transcriptomic program in MCs driving them toward an inflammatory phenotype. Teff cells affected key MC immune functions as they induced prostaglandin, inflammatory cytokines and chemokines production and fostered FceRI-dependent degranulation. Moreover, Teff cell induced in MCs the capacity to regulate T cell responses through a wide-range of dedicated soluble and membrane ligands. Cell-Cell communication inference based on transcriptomic data indicated that IFN-g, IL-21, IL-27 and IL-1b were the main driver of MC differentiation program. Overall design: To analyze the effects of activated CD4+ Teff cells on MCs, freshly isolated human effector/memory CD4+ T cells were cocultured with primary human MCs for 24 hours with or without anti-CD3/CD28 coated beads. In parallel experiments, MCs were stimulated with two typical well-known MC stimuli (IL-33 and IgE/Ag) as points of comparison. MCs were then FACS-sorted and processed to mRNA deep sequencing (RNAseq). We then performed gene expression profiling analysis of RNA-seq data for MCs (from 4 different donors : MC186, MC187, MC188, MC189) stimulated with 5 different conditions (unstimulated, cocultured with unstimulated Teff cells, cocultured with anti-CD3/28 bead-stimulated Teff cells, stimulated with IgE/Ag, stimulated with IL-33)