Background Failure to treat autoimmune diseases with leukocyte-targeted therapies, candidates locally residing stromal cells as possible therapeutic target in chronic disease. Phenotypical and functional changes associated with the acquisition of lymphoid-like features have been described in the stroma during tertiary lymphoid organ (TLO) formation. Our group has demonstrated that IL-22 regulates pathogenic stromal cell expansion, development of germinal centres and humoral response in TLOs. However, to date the mechanisms responsible for initiating stromal cell activation are still unclear. IL-4R signalling has been described to regulate, upon injury, mesenchyme differentiation in muscle or adipose tissue.
Objectives We hypothesise that this same pathway regulates the transition from of normal/quiescent stromal to lymphoid like/pathological mesenchyme.
Methods Adult mesenchymal adipose-derived stem cells (ADSC) were treated in vitro with inflammatory cytokines to evaluate their potential to induce stromal cell activation. An inducible mouse model of TLO formation by retrograde cannulation of the salivary glands with a replication deficient adenovirus was used to assess the role of IL-13 and IL-4 in vivo. Salivary glands of C57BL/6 mice wild type and knockout mice (IL-4Ra–/–, IL-4–/–, IL-13–/–) were cannulated and sacrificed at different time points post cannulation (p.c.). Immunofluorescence, flow cytometry and RT-PCR were used to evaluate the dynamic of acquisition of lymphoid features and stromal cell activation.
Results We observed that treatment of ADSC with IL-13 and/or IL-4 together with LTαβ and/or TNFα significantly influenced the ability of ADSC to acquire a lymphoid-like pathogenic phenotype. These data were confirmed in an in vivo model of TLO formation where we demonstrated that in absence of IL-4R mediated signalling (IL-4Ra–/– mice) stromal cell activation does not occur and stromal cell fail to up regulate gp38, ICAM1 and VCAM1. Absence of lymphoid stromal cell markers is associated with abrogated chemokine expression and defective TLO formation. Similar phenotype was observed in IL-13–/– mice but not IL-4–/– mice where normal induction of TLO occurs. Investigation of IL-13GFP and IL-4GFP reporter mice as well as WT mice showed a high level of IL-13 but not IL-4 expression in the salivary gland at early time-points after TLO induction, thus suggesting that IL-13 but not IL-4 is responsible for stromal cell transition to a pathogenic phenotype. Surprisingly, investigation of bone-marrow chimeric mice demonstrated that the source of IL-13 was represented not only by haematopoietic cells but also by epithelial and stromal cells. Interestingly, administration of recombinant IL-13 in absence of virus was sufficient to cause stromal cell activation in absence of viral insult.
Conclusions All together these results demonstrate that activation of quiescent tissue-resident stromal cells at site of TLO formation and chronic inflammation is mediated by engagement of IL4-R on resident stroma. Therapeutic intervention aimed to block this signalling in autoimmune conditions is currently under development.
Disclosure of Interest : None declared