Inflammatory bowel diseases (IBDs) are thought to develop as a result of complex interactions between host genetics, the immune system and the environment including the gut microbiome. Although an improved knowledge of the immunopathogenesis of IBDs has led to great advances in therapy such as the highly effective anti-tumor necrosis factor class of medications, a significant proportion of patients with Crohn's disease and ulcerative colitis do not respond to anti-tumor necrosis factor antibodies. Further understanding of the different immune pathways involved in the genesis of chronic intestinal inflammation is required to help find effective treatments for IBDs. In this review, the role of the mucosal innate and adaptive immune system in IBD is summarized, highlighting new areas of discovery which may hold the key to identifying novel predictive or prognostic biomarkers and new avenues of therapeutic discovery.

BackgroundInfliximab is an effective salvage therapy in acute severe ulcerative colitis; however, the optimal dosing strategy is unknown. We performed a systematic review and meta-analysis to examine the impact of infliximab dosage and intensification on colectomy-free survival in acute severe ulcerative colitis.MethodsStudies reporting outcomes of hospitalized steroid-refractory acute severe ulcerative colitis treated with infliximab salvage were identified. Infliximab use was categorized by dose, dose number, and schedule. The primary outcome was colectomy-free survival at 3 months. Pooled proportions and odds ratios with 95% confidence intervals were reported.ResultsForty-one cohorts (n = 2158 cases) were included. Overall colectomy-free survival with infliximab salvage was 79.7% (95% confidence interval [CI], 75.48% to 83.6%) at 3 months and 69.8% (95% CI, 65.7% to 73.7%) at 12 months. Colectomy-free survival at 3 months was superior with 5-mg/kg multiple (≥2) doses compared with single-dose induction (odds ratio [OR], 4.24; 95% CI, 2.44 to 7.36; P < 0.001). However, dose intensification with either high-dose or accelerated strategies was not significantly different to 5-mg/kg standard induction at 3 months (OR, 0.70; 95% CI, 0.39 to 1.27; P = 0.24) despite being utilized in patients with a significantly higher mean C-reactive protein and lower albumin levels.ConclusionsIn acute severe ulcerative colitis, multiple 5-mg/kg infliximab doses are superior to single-dose salvage. Dose-intensified induction outcomes were not significantly different compared to standard induction and were more often used in patients with increased disease severity, which may have confounded the results. This meta-analysis highlights the marked variability in the management of infliximab salvage therapy and the need for further studies to determine the optimal dose strategy.