PURPOSE OF REVIEW: This review addresses recent progress in our understanding of the role of regulatory T (Treg) cells in enforcing immune tolerance and tissue homeostasis in the lung at steady state and in directing the immune response in asthmatic lung inflammation.

RECENT FINDINGS: Regulatory T cells regulate the innate and adaptive immune responses at steady state to enforce immune tolerance in lung tissues at steady state and their control of the allergic inflammatory responses induced by allergens. This regulatory function can break down in the context of chronic asthmatic airway inflammation such that the lung tissue Treg cells become skewed towards a pathogenic phenotype that aggravates and perpetuates disease. Subversion of lung tissue Treg cell function involves their upregulation of Notch4 expression, which in turn acts to amplify T helper type 2 and type 17 and innate lymphoid cell type 2 responses in the airways.

SUMMARY: A dual role for Treg cells has emerged both as immune regulators but also a potential disease effectors in asthma, with implications for disease therapy.