Maarten Cozijnsen

Abstract Background Infliximab treatment results in endoscopic remission in a relative high proportion of pediatric Crohn’s disease (CD) patients. Still, the underlying immune mechanisms by which infliximab treatment restores homeostasis are largely unknown. Prednisolone treatment on the other hand, while able to establish clinical remission, less often result in endoscopic remission – a finding well accepted among pediatric gastroenterologists, but never demonstrated in a prospective comparative trial. A comparative analysis of the immune responses during either treatment may reveal the immune mechanisms targeted by infliximab and may uncover immune pathways that drive endoscopic remission. Objective To study differences in the immune responses of newly diagnosed pediatric CD patients to infliximab or prednisolone treatment. Design In a randomized open-label trial, 11 newly diagnosed pediatric CD patients were treated with either infliximab (plus azathioprine) or prednisolone (plus azathioprine). Endoscopic disease activity was assessed at week 0 and 10, and samples were taken for measurement of peripheral blood RNA expression and serum inflammatory protein measurement. RNA expression was measured using whole-genome micro-array analysis, and serum proteomics with the Olink proseek Inflammation panel was performed. Data were analyzed pairwise and corrected for multiple testing. Results Infliximab treatment more often resulted in endoscopic remission than prednisolone treatment, while clinical remission rates were comparable. Infliximab treatment lowered the number of circulating neutrophils and monocytes, and significantly altered mRNA expression and serum protein concentrations. We identified three dominant pathways that associate with infliximab treatment and endoscopic remission. Firstly, infliximab treatment down regulated mRNA expression of Th1 related genes in peripheral blood leukocytes and reduced concentrations of Th1 related serum proteins. Secondly, it reduced transcription of S100 calcium-binding proteins – dominantly expressed in neutrophils – and lowered concentrations of chemo attractants that recruit neutrophils to inflamed tissue. Lastly, infliximab treatment down regulated transcription of genes involved in tissue remodeling and reduced concentrations of tissue remodeling proteins in sera of CD patients. Prednisolone treatment, on the other hand, did not significantly alter mRNA expression or protein concentrations in blood of CD patients in this pilot analysis. Conclusion Infliximab treatment had a strong effect on mRNA expression and protein concentrations. It reduced Th1 and neutrophil signatures, and tissue remodeling proteins. These effects were not seen in CD patients treated with prednisolone. Our findings provide insight into the effect of infliximab treatment and may help unravel the underlying immune mechanisms by which infliximab treatment restores homeostasis.