Th1 and Th2 subsets: paradigms lost?

The T helper 1 (Th1)/Th2 model has provided a valuable framework to investigate and explain many immune reactions and now pervades current thinking on the regulatory role of T cells. However, individual T cells and clones display remarkable diversity in their cytokine profiles, collectively forming a continuous spectrum in which Th1 and Th2 cells may be only two of the possible extreme phenotypes. For these reasons, Anne Kelso argues that cytokine-producing T cells cannot be classified into discrete subsets.