Background Tertiary lymphoid organ formation is a hallmark of many chronic inflammatory diseases such as Sjögren’s syndrome and rheumatoid arthritis. The processes underlying the persistence of inflammation in these ectopic lymphoid aggregates remain to be elucidated and, if better understood, could shed light on therapeutic targets aimed at diverting the immune response away from chronicity and towards resolution. It has previously been proposed that an excess of antigen may result in the detrimental prolongation of the local immune response and persistence of ectopic lymphoid organs within the tissue.
Objectives Here, we aim to test this hypothesis by expanding an existing novel murine model using adenovirus-infected salivary glands to address the factors influencing memory formation and contributing to the persistence of tertiary lymphoneogenesis (1).
Methods The submandibular glands of female C57BL/6 mice were cannulated via the excretory duct with 108 p.f.u. of luciferase-expressing replication-deficient adenovirus. At day 15 post-cannulation, the mice were recannulated and then culled at days 2, 5, 8 and 15 post-recannulation. Flow cytometry was carried out on collagenase-digested salivary glands to determine the dynamics of the lymphoid-like stromal cell (LLSc) (CD45-EPCAM-CD31-gp38+) response. Real-time PCR and immunofluorescence were used to quantify mRNA expression of lymphoid chemokines and visually characterise aggregate formation respectively. ELISAs were used to quantify the anti-viral response (IgG and IgM) in the serum.
Results As a result of increased initial proliferation, LLSc activation remained high at day 8 post-recannulation instead of beginning to resolve as seen in historical single cannulated control mice. Expression of lymphoid chemokines CXCL13 and CCL19 were significantly higher at days 2, 5 and 8, accompanied by higher expression of AID and vastly increased production of anti-viral IgG as compared to their single-cannulated counterparts. However, expression of B-cell survival factor BAFF was seen to be lower from day 8 onwards. Large, organised follicles were seen earlier than in primary immunisation with diffuse expression of CXCL13 at day 8.
Conclusions Persistence of inflammation underlies many chronic inflammatory pathologies. Here we show that providing an excess of antigen at the peak of the inflammatory process appears to provoke a faster, more vigorous secondary immune response, both in terms of stromal cell activation and leucocyte recruitment, resulting in the avid production of anti-viral IgG antibodies. While this remains a spontaneously resolving process, it is the first step in characterising the secondary immune response in this novel murine model and brings us closer towards deciphering the factors triggering or preventing resolution.
Bombardieri M, Barone F, Lucchesi D, Nayar S, van den Berg WB, Proctor G et al. Inducible tertiary lymphoid structures, autoimmunity, and exocrine dysfunction in a novel model of salivary gland inflammation in C57BL/6 mice. J Immunol. 2012 Oct 1;189(7):3767-76.
Disclosure of Interest None Declared