D2.437 - Human memory CD4+T cells induce hyperresponsiveness in mast cells

CD4 helper T cells (T cells) infiltrate and localize in proximity to mast cells (MC) in inflammatory environments, such as the skin in chronic spontaneous urticaria and psoriasis. Emerging evidence indicates that T cells can influence the phenotypic and functional features of MCs via both soluble mediators and receptor-ligand mechanisms. Therefore, T cells have the potential to regulate MC activities and may be involved in chronic MC-mediated disorders. The functional outcomes of MC-T cell interactions, particularly involving human primary skin MCs (hMC) and pathogenic memory CD4⁺T cells (Tm), have, however, not yet been studied in detail. This study aims to assess how primary Tm influence the phenotype and function of primary hMC.

IgE-sensitized hMC were either co-cultured with activated Tm (act-Tm) or their supernatants (Tm-sup) for 18 hours. Anti-IgE induced hMC degranulation was assessed by flow cytometry and cytokines in the Tm-supernatant were measured by a multiplex assay. To assess the contribution of T cell-derived cytokines in hMC activation, hMC were primed overnight with recombinant cytokines or Tm-sup in the absence or presence of respective cytokine neutralizing antibodies. The cytokine profile of primed hMC was analyzed by multiplex assay. In parallel, short-term stimulations under identical conditions were performed to investigate intracellular signalling pathways.

act-Tm (p = 0.0011) and Tm-sup (p = 0.0056) significantly enhanced FcεRI-dependent hMC degranulation, even in sub-degranulating anti-IgE concentrations. Recombinant IFN-γ and IL-4 increased degranulation of FcεRI-activated hMC, from 43% to 58%, while blocking of IFN-γ reduced Tm-sup-induced degranulation by32%. Simultaneous neutralisation of both IL-4 and IFN-γ reduced release of GM-CSF by 40%, IL-13 by 108%, and TNF by 90%. Furthermore, Tm-sup increased phosphorylated STAT1 and PLCγ1 levels in hMC, which were both reduced following neutralisation of IFN-γ. In line with this, JAK1/2 inhibitor robustly abolished the Tm-sup-mediated enhancement on hMC activation.

Tm cells and their cytokine IFN-γ promote a hyperresponsive MC phenotype, characterized by increased degranulation and cytokine secretion. Targeting interactions between MCs and T cells or blocking T cell-derived IFN-γ, could offer a selective strategy to reduce MC activation in chronic MC-driven diseases.