Mechanisms Underlying Lineage Commitment and Plasticity of Helper CD4 + T Cells

Critical Mediators Helper T cells are the immune system's ringmasters, having a multiplicity of functions that mediate the body's immune responses to infections. Depending on the type of infection, CD4 + helper T cells respond by secreting specific patterns of cytokines, which provide important cues to other subsets of immune cells. CD4 + T cells with distinct cytokine profiles have been viewed classically as separate lineages; however, there is mounting evidence that these cells may not be terminally differentiated but are in fact quite plastic. O'Shea and Paul (p. 1098 ) review the current understanding of CD4 + T cell subset differentiation and the underlying mechanisms that drive cell-lineage commitment.