T-cell switch

The reciprocal expression of the two co-receptors CD4 and CD8 define two major subsets of T lymphocytes in the peripheral immune system, namely helper and cytotoxic T cells. In the July 11 Nature, Chi et al. define a role for the SWI/SNF-like BAF chromatin-remodelling complexes in regulating the expression of the CD4 and CD8 genes (Nature 2002, 418:195-199). Chi et al. created transgenic mice expressing mutant forms of the HMG protein BAF57 that disrupt the function of the BAF complex; they found that disruption of BAF function impaired both CD4 silencing and CD8 activation in the thymus. Crossing the BAF mutant mice with mice lacking the Brg gene, encoding a catalytic subunit of the BAF complex, enhanced the CD8 expression defects without affecting CD4 silencing. Chi et al. go on to show that the BAF complex binds to the characterized CD4 silencer element. Thus, mammalian SWI/SNF complexes appear to be functionally linked to lineage differentiation and T-cell development.