Chapter 46 : Biomarkers of Gastrointestinal Host Responses to Microbial Infections

Abstract:

The gastrointestinal (GI) environment is a complex ecosystem, where the host lives in complete homeostasis with its microbiota, with the two generally maintaining a delicate balance (1, 2). An immune tolerance exists between the host and its microflora and is acquired soon after birth, preventing harmful inflammation in the setting of a normal microbiota (3–5). When an infection disturbs this stability, the host response is targeted towards rebuilding the equilibrium as quickly as possible. The initial barrier between this internal environment and the outside is the intestinal epithelial cell, which not only plays a role as a physical barrier and nutrient provider, but also protects its local milieu by initiating the immune response sequence (6, 7). The microbiota is also thought to play an important role in the immune response and regulation; this has been referred to as “host-commensal mutualism” (2, 3, 8, 9). The innate response, depending on the infection, may lead to activation of pro- or anti-inflammatory signaling pathways, producing cytokines and chemokines that protect the host from this invasion. However, in some instances, this response may become deleterious to the host and exacerbate the damage.