Background Tertiary lymphoid structures (TLS) are leukocytes aggregates forming in non-lymphoid tissues in response to chronic inflammation. Salivary glands (SG) of patients with Sjögren’s syndrome (SS) develop TLS characterised by B/T cell compartmentalization, specialised vasculature (HEV), functional B cell activation and local differentiation of autoreactive plasma cells. Although TLS presence in SS SG associates with an aggressive disease progression, the mechanisms triggering their formation in SS are largely unknown. We recently developed a model of inducible TLS formation, breach of self-tolerance and salivary hypofunction upon delivery of a replication­deficient adenovirus­5 (AdV5) into C57BL/6 mice SG. In this model, 3 weeks after infection, we observed fully formed and functional TLS, breach of self-tolerance and loss of salivary function.

Here we characterised the presence, function and relevance in TLS formation of the myeloid compartment in the first month post-infection.

Materials and methods A luciferase-encoding AdV5 was delivered to the SG, glands were collected between 1 and 4 weeks post-cannulation (WPC), embedded for immunofluorescence staining and/or digested for FACS analysis, and stained for various markers. Sorted myeloid cells were analysed my Q-PCR. Infiltration and differentiation of monocytes was followed via adoptive transfer.

Results During the first WPC, innate cells infiltrated the gland in sequential waves, as shown by FACS. Neutrophils and eosinophils were rapidly recruited to the SG and likely contributed to the histological damage observed. Inflammatory monocytes were recruited from the periphery and progressively differentiated into macrophages in-situ. NK and pDC also increased in number in response to viral infection. Gene expression analysis of sorted myeloid cells showed early upregulation of inflammatory mediators (eg, CCL5, IFNg) and a later production of lymphoneogenetic signals (eg, Lt-b, CXCL13) mRNA.

Conclusions In our model of inducible ialadenitis, innate immune cells not only mediate early inflammation in the SG, but also take part in driving the lymphocytic infiltration, thus playing a pivotal role in tertiary lymphoid formation.