TNFα has long stood as a hallmark feature of both inflammatory bowel disease (IBD) and arthritis with its therapeutic potential demonstrated in neutralizing monoclonal antibody treatments such as Infliximab. Due to the high global burden of latent Mycobacterium tuberculosis (TB) infections, prior to receiving anti-TNF therapy, patients testing positive for latent TB are given prophylactic treatment with anti-tuberculoid medications including the first described TB-selective antibiotic, Isoniazid. While this is common clinical practice to prevent the emergence of TB, little is known about whether Isoniazid modifies intestinal inflammation alone. The aim of this study therefore, was to determine whether Isoniazid presents a novel TB-independent therapeutic option for the treatment of CD-like ileitis and uncover new mechanisms predisposing the host to intestinal inflammation.
The transgenic TNFΔARE mouse model of Crohn’s-like terminal ileitis was used. The impact of Isoniazid administration (10mg/kg/day dosed in drinking water) on disease development was monitored between 8 and 12 weeks of age using a variety of behavioural and serological assays. Behavioural and motor functions were assessed using the LABORAS automated monitoring system while systemic and local tissue inflammation were determined at experimental termination using multiplex cytokine analysis. Whole mount tissue immunofluorescence and fluorescent in situ hybridization (FISH) was used to qualify changes within the host as well as the microbial compartment of the ileum and associated mesentery. Proposed cellular mechanisms of altered cytokine decay were performed on isolated primary splenocytes in vitro using selective pharmacological agents.
Compared to age-matched WT littermates, TNFΔARE mice display prominent progressive sickness behaviours from 8 through 12 weeks of age indicated by reduced movement, climbing, and rearing. Prophylactic administration of Isoniazid (10mg/kg/day) is effectively able to protect TNFΔARE mice from this loss of function during the same period. Analysis revealed that Isoniazid was able to significantly reduce both systemic and intestinal inflammation compared to untreated vehicle controls impacting the epithelial colonization of known pathobiont segmented filamentous bacteria (SFB). Reduction in terminal ileal inflammation was also associated to the diminished formation of precursor-tertiary lymphoid organs within the associated ileal mesentery which were found to be associated with endospores derived SFB itself. Finally, we reveal that due to their genetic manipulation, TNFΔARE mice display accelerated post-transcriptional decay of IL-22 mRNA resulting in diminished IL-22 protein production and associated downstream antimicrobial peptide production.
Isoniazid protects against the development of intestinal and systemic inflammation in the TNFΔARE model of terminal ileitis by limiting the expansion of mucosal-SFB and progression of the associated microbial-driven inflammation. This work highlights a possible mycobacterial-independent function of Isoniazid in limiting CD-pathophysiology through limiting the mucosal establishment of pathobionts such as SFB and the association of such microbe-derived endospores linked to the formation of ectopic tertiary lymphoid organs seen commonly in patients.

© The Author(s) 2025. Published by Oxford University Press on behalf of European Crohn’s and Colitis Organisation.