P0117Fibroblast activation protein is selectively expressed by CD90+ fibroblasts in inflammatory bowel disease-associated intestinal fibrosis

Background Intestinal fibrosis is a common complication in inflammatory bowel disease (IBD), and diagnostic modalities to detect and determine the degree of fibrosis are limited. Fibroblast activation protein (FAP) is virtually absent in healthy tissues, but is increased in malignancies, and in immune-mediated inflammatory diseases. Here, we investigated the presence of FAP in fibrostenotic and inflamed resection specimens from Crohn’s disease (CD) and ulcerative colitis (UC) patients and defined its cellular and spatial distribution. Methods FAP mRNA (not shown) and protein levels were determined in tissue samples from CD, UC and (non-IBD) controls using quantitative polymerase chain reaction (qPCR) and immunohistochemistry (IHC). Immunohistochemical stainings (H&E and Masson’s trichrome) were performed to score for active inflammation and fibrosis as previously described1 Histological inflammation and fibrosis scores were determined by a blinded expert. Imaging Mass Cytometry (IMC) was used to identify FAP positive cells using a 20-marker panel. Results An 11.4-fold increase in FAP mRNA expression was found in fibrostenotic (median 0.02708, p = 0.0005) and a 5.9-fold increase in inflamed (median 0.01393, p = 0.0137) CD ileum compared to controls (median 0.002379). In addition, a 2.2-fold increase was observed in inflamed UC colonic specimens (median 0.006688, p = 0.0446) compared to controls (median 0.003034). In CD tissues, FAP protein expression was most abundant in the (sub)serosa and submucosa where histological signs of fibrosis were more prominent (Figure 1A). A 3.7-fold increase in FAP protein expression was seen in fibrotic CD ileum samples compared to non-inflamed CD ileum and a 2.4-fold increase in fibrostenotic (median 3.9 p = 0.0206) CD ileum samples compared to controls (median 1.6) and inflamed ileum from CD patients (median 1.6, p = 0.0469). In UC samples, FAP protein expression was mainly observed in the mucosa and submucosa. Inflamed UC colonic specimens (median 3.12) showed a 3.7-fold increase in FAP protein expression compared to controls (median 0.85, p = 0.0087, Figure 1B). Spatial phenotyping of cells expressing FAP using IMC (Figure 2) identified the majority of the FAP expressing population as CD90 positive fibroblasts in all intestinal layers, and these cells were most abundant in the subserosa. Conclusion FAP is strongly upregulated in fibrostenotic CD and inflamed intestinal tissues in UC and is predominantly expressed by CD90+ fibroblasts, showing distinct spatial distribution patterns in CD and UC. Reference: 1.Ke BJ, Abdurahiman S, Biscu F, et al. Intercellular interaction between FAP+ fibroblasts and CD150+ inflammatory monocytes mediates fibrostenosis in Crohn’s disease. J Clin Invest 2024;134. Conflict of interest: Ms. Lartey, Dalia: no COI Van Os, Bram: No conflict of interest Ke, Bo-Jun: No conflict of interest Van Wijnbergen, Kelly: No conflict of interest De Hertogh, Gert: Other: Fees to my institution KULeuven for my activities as central pathology reviewer for: Centocor and Eli Lilly Barnhoorn, Marieke: No conflicts of interest. Matteoli, Gianluca: Grant: We are recipient of the opnMe research grant from Boehringer Ingelheim. Buskens, Christianne J.: Grant: C. Buskens has received an unrestricted grant from Boehringer Ingelheim and Roche Personal Fees: C. Buskens has received consultancy fees and/or speaker’s honoraria from Tillotts, Takeda, MSD and Janssen jarmilla, van der bilt: No conflict of interest D’Haens, Geert: Grant: Pfizer, BMS, Johnson and Johnson, Abbvie, Alimentiv BV, Eli Lilly, Takeda, Prometheus Laboratories Personal Fees: Abbvie, Abivax, Agomab, Alimentiv, Anaptys Bio, AstraZeneca, Bristol Meiers Squibb, Boehringer Ingelheim, Celltrion, Eli Lilly, Exeliom Biosciences, Galapagos, Glaxo Smith Kline, Dr Falk Pharma, Pfizer, Johnson and Johnson, Merck, Mirador, Polpharma, Procise Diagnostics, Prometheus Biosciences, Sorriso Pharma, Spyre, Takeda, Ventyx Grootjans, Joep: No conflict of interest Wildenberg, Manon: Received research grant support from Hoffman-La Roche, Boehringer-Ingelheim Löwenberg, Mark: No relevant CoI to disclose