The Role of Mutants in the Spatiotemporal Progression of Inflammatory Bowel Disease: Three Classes of Permanent Form Traveling Waves

Abstract. Despite its high prevalence and impact on the lives of those affected, a complete understanding of the cause of inflammatory bowel disease (IBD) is lacking. In this paper, we investigate a novel mechanism which proposes that mutant epithelial cells are significant to the progression of IBD since they promote inflammation and are resistant to death. We develop a simple model encapsulating the propagation of mutant epithelial cells and immune cells which results from interactions with the intestinal barrier and bacteria. Motivated by the slow growth of mutant epithelial cells, and relatively slow response rate of the adaptive immune system, we use singular perturbation theory via the method of matched asymptotic expansions to determine the one-dimensional slow invariant manifold that characterizes the leading order dynamics at all times beyond a passive initial adjustment phase. The dynamics on this manifold are controlled by a bifurcation parameter [Formula: see text] which depends on the ratio of growth to decay rates of all components except mutants and determines three distinct classes of permanent-form traveling waves that describe the propagation of mutant epithelial and immune cells. These are obtained from scalar reaction-diffusion equations with the reaction being (i) a bistable nonlinearity with a cut-off, (ii) a cubic Fisher nonlinearity, and (iii) a Kolmogorov–Petrovskii–Piskunov or Fisher nonlinearity. Our results suggest that mutant epithelial cells are critical to the progression of IBD. However, their effect on the speed of progression is subdominant.