Background/Purpose:  T cell-dependent activation of B lymphocytes is a key effector arm of the adaptive immune system, resulting in protective antibody responses and long-lived humoral immunity. Such B cell responses often occur in germinal centers (GCs); specialized anatomical locations within secondary lymphoid organs. Similar GC-like structures can also be found in involved tissue in various autoimmune diseases, including the salivary glands of primary Sjögren’s syndrome (pSS) patients. Previous work has implicated CD40-CD154 pathway-dependent processes in regulating B cell survival and function in GCs, and we wanted to investigate whether this costimulatory pathway might be linked to ELS formation and function in pSS

Methods:  Histological analysis of minor salivary gland biopsies from pSS patients revealed evidence of CD40 and CD154 expression on ELS-resident B and T cells respectively, co-locating receptor and ligand positive cells in affected tissue. These results suggested that there might be ongoing T-B cell collaboration in these ELS and we therefore wanted to examine whether there was evidence of CD40 pathway activation in situ. To do this we first generated a CD40-pathway gene signature in primary human B cells following recombinant CD154 stimulation in vitro

Results:  Using a published microarray dataset generated using parotid gland biopsies we could demonstrate upregulation of a portion of the B cell CD40 gene signature in biopsies from pSS patients but not from healthy donors or individuals with Sicca symptoms, suggesting that CD40 pathway activation was occurring within disease-relevant tissue in lymphocytes implicated in disease pathology. To better understand the role of CD40-CD154 interactions in ELS, we examined salivary glands in CD40 knockout NOD mice. Wild-type NOD mice develop sialadenitis, anti-SSA/SSB autoantibodies, and display evidence of ELS in salivary glands. In contrast, there was no evidence of ELS, sialadenitis or autoantibodies in CD40 deficient NOD mice up to one year of age. Further, anti-CD154 treatment resulted in disaggregation in splenic GCs as well as established ELS in NOD mice and resulted in decreased levels of IgG secreting cells in salivary glands

Conclusion:  Collectively our data indicate that CD40 pathway signalling is essential for formation and maintenance of salivary gland ELS and suggest that CD40 pathway signalling is active in established ELS from pSS patients, supporting the notion that blockade of CD40-CD154 interactions may provide therapeutic benefit in patients suffering from this autoimmune exocrinopathy

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/cd40-pathway-activation-in-ectopic-lymphoid-structure-els-resident-b-cells-contributes-to-disease-pathology-in-primary-sjogrens-syndrome/