AHR and immune system disorder: In a study on human umbilical cord mesenchymal stem cells (HUMSC) treatment in rats with collagen-induced arthritis (CIA), it was found that HUMSC could regulate the interactions between host immunity and gut microbiota through the AhR, affecting B-cell differentiation, increasing the proportion of B-cells in the Peyer’s Patches (PP) and Lamina Propria Lymphocytes (LPL), and partially reversing arthritis-induced immune disorders (Li et al. 2020b).