The balance of intestinal Foxp3+ regulatory T cells and Th17 cells and its biological significance.

Balanced mucosal immunity in the gut is critical for host homeostasis and defense. Th17 cells are a subset of IL-17-producing CD4+ T cells, which play a crucial role in clearing pathogens during host defense reactions and in inducing tissue inflammation in autoimmune diseases. CD4+CD25+ Foxp3+ regulatory T cells (Tregs) are recognized as one of the major regulatory factors in immune tolerance and inflammatory responses. Since both Tregs and Th17 cells pertain to the gut immune system, their inter-regulation and balance represent a novel mechanism for maintaining the intestinal immune and inflammatory homeostasis. Accordingly, the imbalance and dysregulation of Tregs and Th17 cells in the intestine is closely associated with intestinal autoimmune disorders like the inflammatory bowel diseases. In this review, we discuss the characteristics of gut Tregs and Th17 cells and their role in gut diseases.