Regulation of expression of IL-4 alleles: Analysis using a chimeric GFP/IL-4 gene

CD4 cells from mice heterozygous for an IL-4 and a GFP/IL-4 gene frequently express a single allele. Analysis of IL-4 or GFP production by cells from recently primed Th2 cells indicates that essentially all are competent to t ranscribe either allele but have a low probability of doing so. By contrast , long-term Th2 clones show distinct and heritable ratios in the proportion of cells that express IL-4 or GFP. We conclude that in the course of Th2 p riming an early efficient event renders both alleles capable of being ineff iciently transcribed; a second, less frequent event occurs that renders one allele more competent, accounting for the differential expression of IL-4 and GFP in different clones.