Th9: A New Player in Asthma Pathogenesis?

Abstract

CD4⁺ T helper (Th) cells act as important regulators of the mammalian adaptive immune response. CD4⁺ Th cells were originally characterized as either Th1 or Th2 types, based on the cytokines they produce. Over the past two decades, however, we have attained a much more detailed understanding of CD4⁺ T-cell differentiation, functions, and gene expression profiles, which led to the identification of additional types, such as the Th17 and induced regulatory T cells. Recently, researchers have characterized yet another novel and distinct population that exists among these immune-modulatory cells. The ‘Th9’ cells were first identified as a Th2 subpopulation that produced exceptionally large quantities of the Th2-specific cytokine interleukin 9. However, experimental analysis revealed that Th9 cells had divergent regulatory capabilities and were critically involved in different immune processes. In particular, we now know that Th9 acts as a major contributor to the onset and progression of allergies, especially asthma. Here, we will review the heterogeneity and biology of CD4⁺ Th cells and summarize the characteristics known to date of interleukin 9 and Th9 cells to build a framework for better understanding of their roles in disease processes, especially in allergy-induced asthma.

• Th9
• IL-9
• PU.1
• allergic asthma
• autoimmune diseases

Acknowledgment

Dr. Jennifer C. van Velkinburgh, who works for the van Velkinburgh Initiative for Collaborative BioMedical Research, has provided substantial writing assistance for this manuscript.

Declaration of Interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper. This work was supported by the Major State Basic Research Development Program of China (973 Program) (Nos. 2007CB512401 and 2007CB512805), the General Program of the National Natural Science Foundation of China (No. 30771950), and CSTC (2008BB5033).