Activated B cells steer fibroblasts towards a proinflammatory phenotype in giant cell arteritis
Shuang Xu, William F Jiemy, Nanthicha Inrueangsri, YouBeen Ko, Wayel H Abdulahad, Ellen Verschoor, Yannick van Sleen, Jacoba C Graver, Kornelis S M van der Geest, Gwenny M Verstappen, Elisabeth Brouwer, Peter Heeringa, Annemieke M H Boots, Maria SandoviciAbstract
Objectives
Giant cell arteritis (GCA) is characterized by chronic large-vessel inflammation and remodelling. Within affected arteries, especially in aorta, organized B cell clusters are mainly localized in adventitia, where fibroblasts represent the dominant stromal population. This study aims to investigate fibroblast heterogeneity within these clusters and B cell–fibroblast interactions in vitro as possible contributors to disease chronicity in GCA.
Methods
Fibroblast phenotypes in CD20+ B cell clusters in GCA and atherosclerotic aortic tissues were characterized using immunohistochemistry for fibroblast markers (CD90, podoplanin [PDPN], fibroblast activation protein [FAP], CD248, α-smooth muscle actin [α-SMA]) and cytokine expression (IL-6, GM-CSF, B-cell activating factor [BAFF]). In vitro, peripheral blood B cells from treatment-naïve GCA patients and healthy donors were stimulated and cocultured with human aortic adventitial fibroblasts (HAoAFs) using either direct cell coculture or transwell systems. To identify relevant molecular pathways for B cell–fibroblast interaction, HAoAFs were pre-treated with infliximab, tocilizumab, baricitinib or upadacitinib, followed by exposure to activated B cell conditioned medium. Protein secretion was assessed by ELISA, Luminex and Olink; mRNA expression was determined by qPCR.
Results
CD90+PDPN+ immunofibroblasts mainly localized centrally, whereas CD90+FAP+ and CD90+CD248+ fibroblasts mostly located at the border of the clusters. Fibroblasts in or around clusters co-expressed IL-6, GM-CSF and BAFF. In vitro, HAoAFs cocultured with activated B cells or supernatants thereof upregulated IL-6, GM-CSF, PDPN and FAP mRNA, and actively secreted IL-6, GM-CSF and BAFF, while type I collagen expression was suppressed. Janus kinase–signal transducer and activator of transcription (JAK–STAT) inhibition abrogated these pro-inflammatory effects, whereas TNF-α and IL-6 receptor blockade did not.
Conclusion
Activated B cells drive fibroblasts toward a pro-inflammatory phenotype, potentially sustaining chronic inflammation and disease progression in GCA. JAK–STAT signalling appears central to this effect, highlighting its therapeutic potency at the vascular level in GCA.