Cutting edge: distal regulatory elements are required to achieve selective expression of IFN-gamma in Th1/Tc1 effector cells.

Using a transgenic approach, we analyzed the contribution of introns located within the IFN-gamma gene and distal regulatory regions to IFN-gamma gene expression. Intron 1 and 3 from the IFN-gamma gene displayed strong enhancer activity. This activity appeared to be dependent upon integration into the genome but resulted in a loss of Th1 selectivity. We also found that distal regulatory elements are not required for high level expression of the human IFN-gamma gene, but rather for cell lineage-specific expression. An 8.6-kb human IFN-gamma transgene was sufficient to yield high level expression but a 191-kb IFN-gamma transgene with approximately 90 kb of flanking 5' and 3' sequence was necessary to achieve both high level and Th1 selective expression of human IFN-gamma.