Immune Responses at Mucosal Surfaces

Abstract

Abstract The mucosal surfaces of the gastrointestinal or respiratory tracts form vast interfaces of the host organism with the environment and constitute major entry ports for pathogens. Strategies to defend mucosal surfaces have developed early in evolution and in mammals engage the innate as well as the adaptive arms of the immune system. This article depicts aspects of anatomy, development and function of the mucosa‐associated lymphoid tissues (MALT) with a focus on the intestinal immune system. The intestinal epithelium is continuously exposed to large amounts of foreign antigens. Thus, one of the key challenges of the intestinal immune system is to tolerate harmless food derived antigen and to keep peace with the commensal microbiota populating the gut tube, while efficiently combating pathogens and their toxins. Key Concepts: Innate and adaptive immunity synergise to protect mucosal surfaces. Adaptive immune responses at mucosal sites are initiated in Mucosa associated lymphoid tissues (MALT), such as the gut‐associated lymphoid tissue (GALT), the bronchus‐associated lymphoid tissue (BALT) and the nasal‐associated lymphoid tissue (NALT). The intestinal immune system is continuously challenged by innocuous antigen derived from food and the commensal microbiota. Interaction of the host with the commensal microbiota is required for the full maturation of the intestinal immune system whereas in turn the intestinal immune system restricts the growth and controls the composition of our commensal microbiota. Secretory IgA (SIgA) is the predominant Immunoglobulin at mucosal surfaces. Dysbiosis of the commensal microflora promotes diseases such as inflammatory bowel disease (IBD), diabetes and obesity and enhances the susceptibility to infection with enteropathogenic bacteria. Failure to induce oral tolerance towards food derived antigens manifests in allergy or coeliac disease.