Fig 2.

In genetically predisposed individual, environmental factors like diet, infections and smoking can cause dysbiosis in the gut microbiota resulting in expansion of contraction of certain species of a genus. This dysbiosis may be related to production of some metabolites as well as NFkB activation and Th17 cytokine production, compromising the integrity of the gut epithelial layer and causing a leaky gut and disease conditions. On the other hand a healthy individual will maintain homeostasis in the gut so that the local and systemic immune systems stay healthy.