Background Tertiary lymphoid organs (TLO) characterised by germinal centre formation and B cell proliferation represent the histological hallmark of primary Sjögren's syndrome (pSS). TLO persistence in the salivary glands is associated with systemic disease manifestations and lymphoma development in pSS patients (1).
We previously demonstrated that gp38+ stromal cells are instrumental for TLO development and provide chemokines, such as CXCL13, CCL19 and CCL21 necessary for lymphocyte recruitment and organization (2). Similarly, in the lymph node, FAP+gp38+ lymphoid stromal cells regulate lymphocyte homing and homeostasis. Accordingly, deletion of FAP+gp38+ cells results in aberrant expression of lymphoid survival factors, disrupted lymph node organization and decreased ability to mount efficient immune responses (3, 4).
Objectives To dissect the effects of FAP+gp38+ cell deletion in TLO dynamic and function in an animal model of pSS.
Methods We used a model of conditional depletion of FAP-expressing cells, in which FAP-DTR mice were treated prophylactically with Diphtheria Toxin (DTx). Following depletion, submandibular salivary glands of FAP-DTR mice and littermate controls were intra-ductally cannulated with luciferase-encoding replication-deficient adenovirus to induce TLO formation and pSS-like disease as previously described (5). A combination of immunofluorescence, quantitative RT-PCR and flow cytometry on digested salivary glands was used to address the consequences of stromal cell deletion in the TLOs.
Results We confirmed that in cannulated, inflamed wild-type salivary glands, FAP is upregulated on a population of activated stromal cells that expresses gp38 and produces lymphoid chemokines. As anticipated, analysis of DTx-treated FAP-DTR salivary glands reveals significantly decreased numbers of gp38+ stromal cells and deletion of FAP+ stromal cells leads to a significant defect in lymphoid chemokine production, decreased number of infiltrating lymphocytes and severely compromises TLO formation.
Conclusions These data demonstrate that salivary glands gp38+ activated stromal cells express FAP and are required for TLO organization and maintenance in the tissue. Deletion of activated lymphoid stroma affects lymphocyte recruitment and organization, thus providing the rational for stromal cell targeting in TLO associated autoimmune diseases.
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Disclosure of Interest None declared
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