T helper cell
The characterisation of another novel T helper subtype, T helper 17 cells (Th17) has cast further doubt on the basic Th1/Th2 model. These IL-17 producing cells were initially described as a pathogenic population implicated in autoimmunity but are now thought to have their own distinct effector and regulatory functions. Of note, recent evidence suggest that functional plasticity is an intrinsic capacity of T helper cells. Indeed, a study in mice demonstrated that Th17 cells transform into Th1 cells "in vivo". A subsequent study furthermore showed that extensive T helper cell plasticity is also prominent in man.