Stability and commitment in T helper cell development

Specialized effector activities that are required to eliminate various pathogens involve cytokines produced by specialized CD4⁺ T cells subsets, dogmatically termed Th1 and Th2 cells. Despite some oversimplifications, this paradigm is useful for organizing the complex pathways that control forward and backward movements along the road of T cell differentiation. Effective immune memory relies, in part, on the maintenance of the T helper phenotype. This review will address basic issues that relate to the maintenance or reversibility of Th1/Th2 states within the CD4⁺ T cell lineage.