[Suppression of myeloperoxidase gene expression by gamma-interferon]

The gene expression of myeloperoxidase (MPO) in HL60 cells, as tested by Northern blot analysis with a MPO gene probe, was markedly suppressed by treatment with gamma interferon (IFN-gamma)(200U/ml) for 9hr, whereas cytochemically detected MPO activity, cell surface antigen expression, and cell morphology remained unchanged even at 48hr after the treatment. IFN-gamma of 50U/ml was sufficient for the suppression at 24hr. When the HL60 cells treated with IFN-gamma (200U/ml) for 24hr were cultured in the absence of IFN-gamma for another 24hr, the transcript of MPO gene reverted to a level comparable to that of the HL60 cells cultured thoroughly in the absence of IFN-gamma, indicating the reversibility of the suppression. The suppression of MPO expression at RNA level, possibly independent of differentiation, is one of the biological activities exerted by IFN-gamma, which has not been previously reported.