Abstract
CD4 T helper (Th) cells play critical roles in adaptive immune responses. They recruit and activate other immune cells including B cells, CD8 T cells, macrophages, mast cells, neutrophils, eosinophils and basophils. Based on their functions, their pattern of cytokine secretion and their expression of specific transcription factors, Th cells, differentiated from naïve CD4 T cells, are classified into four major lineages, Th1, Th2, Th17 and T regulatory (Treg) cells, although other Th lineages may exist. Subsets of the same lineage may express different effector cytokines, reside at different locations or give rise to cells with different fates, whereas cells from different lineages may secrete common cytokines, such as IL-2, IL-9 and IL-10, resulting in massive heterogeneity of the Th cell population. In addition, the pattern of cytokine secretion may switch from that of one lineage toward another under certain circumstances, suggesting that Th cells are plastic. Tregs are also more heterogeneous and plastic than were originally thought. In this review, we summarize recent reports on heterogeneity and plasticity of Th cells, and discuss potential mechanisms and implications of such features that Th cells display
Contents
1. Introduction of T helper (Th) cell types and their functions
2. Th ‘lineages’ other than Th1/Th2/Th17/Treg?
3. Heterogeneity among Th1/Th2/Th17 cells
4. Heterogeneity of regulatory T cells
5. Plasticity of Th1/Th2 cells
6. Plasticity of Th17/Treg cells
7. Relationship between heterogeneity and plasticity
8. What heterogeneity and plasticity mean to immune modulation
9. References