This construct was created by fusing in frame a 170-bp fragment from the 5' end of IL-5 cDNA with the remaining portion of the genomic IL-5 gene. This minigene has no upstream flanking sequences but has all of the introns of the gene as well as 1 .2 kb of downstream flanking sequence. To drive expression of the transgene in T cells, a promoter and tissue-specific enhancer derived from the murine CD3d gene was included upstream. Three founding lines (NJ.759, NJ.1638, NJ.1643) were created with one chosen for further studies. High levels of circulating IL-5 were detected in the sera of transgenic mice but not in wild-type mice.