IT

he ability of T lymphocytes to divide and differentiate in response to spe-cific antigen is critical to the immune defense of vertebrates. A major remodeling of gene and protein expression accompanies T cell activation. The latter is shaped not only by the turning on and off of dozens of genes but also by changes in the splicing of precursor messenger RNA (mRNA), which produces a shift in the mRNA and protein isoforms that are expressed (1). The alter-ation of alternative splicing in the trans-membrane protein CD45 has been widely used to distinguish naïve T cells from recently activated cells and their descen