Mechanisms of Immunomodulation by Probiotics in Inflammatory Bowel Disease

Abstract

Inflammatory bowel disease (IBD) is an intestinal inflammatory disease with a poorly understood multifactorial pathogenesis. The two main types of IBD, Crohn’s disease (CD) and ulcerative colitis (UC), are distinct disease forms with differences in genetic risk factors, involved immune cells, and affected parts of the gastrointestinal (GI) tract. Additionally, environmental factors and the intestinal microbiome also contribute to CD and UC pathogenesis. CD and UC are both characterized by chronic, relapsing inflammation of the GI tract. Currently, treatment consists of untargeted immunomodulatory therapies, targeted biologic therapies, and surgery. Despite the variety of treatment options available, curative treatment of IBD is not (yet) possible. Because the intestinal microbiome and immunological factors contribute to IBD pathogenesis, probiotics are being investigated for their therapeutic potential. Probiotics are live microorganisms that, upon administration, can provide a health benefit to the host. One of the mechanisms of action of probiotics is immunomodulation. In this literature review, the mechanisms of immunomodulation by probiotics in IBD patients and disease models are discussed. The immunomodulatory effects of probiotics on immune cells involved in IBD pathogenesis are reviewed individually, which includes the effects on intestinal epithelial cells (IECs), neutrophils, macrophages, dendritic cells (DCs), T cells, and B cells. It is discussed that probiotics can affect cytokine production, cell signaling, gene expression, cell differentiation, immune cell infiltration, number of pro-inflammatory and immunoregulatory cells, and/or the production of immunoglobulins in IBD patients and disease models. Furthermore, recommendations for future studies on probiotics in IBD treatment are discussed.