Helper T cell diversity and plasticity.

CD4(+) helper T cells play crucial roles for host defense and immune-mediated disease by their ability to differentiate into specialized subsets. These subsets attain restricted patterns of cytokine secretion and specific expression of master transcription factors in response to microbial pathogens. Classically, the various helper CD4(+) T cell subsets have been viewed as terminally differentiated lineages with limited flexibility. However, following the recognition of new subsets, there is increased recognition of plasticity. In this review, we highlight recent advances that pertain to this topic and the mechanisms that contribute to helper CD4(+) T cell differentiation and plasticity.