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The 'yin-yang' icon is a symbol of balance and harmony between two opposing forces. These forces are pervasive in our immune system, where the balance between regulatory T cells and reactive cells is important in maintaining homeostasis. This month we focus on the biology and function of regulatory T cells with a series of specially commissioned articles. The content and additional features are free online (www.nature.com/ni/focus/regulatory_tcells) during April 2005. Cover by Lewis Long.
Double-positive thymocytes are selected into the CD4 or CD8 lineage on the basis of their T cell receptor specificity. The transcription factor cKrox has been identified as being both required and sufficient to direct thymocytes undergoing positive selection to the CD4 lineage.
Different peptide antigens induce T cell repertoires of very different diversity. An analysis of the effect on T cell receptor usage of re-engineering peptide features indicates that a lack of prominent side chains presented for recognition limits the T cell repertoire.
Inflammatory signals must be resolved to avoid excessive tissue damage. The D6 chemokine receptor acts in this process by 'mopping up' proinflammatory β-chemokines.
The MAP kinase p38 is normally regulated by the MAPKKK-MAPKK pathway in mammalian cells. However, analysis of T cell signaling shows an alternative pathway for p38 activation exists.