MNDA, also known as myeloid cell nuclear differentiation antigen, is detected only in nuclei of cells of the granulocyte-monocyte lineage. This protein may act as a transcriptional activator/repressor in the myeloid lineage and plays a role in the granulocyte/monocyte cell-specific response to interferon. A 200-amino acid region of human MNDA is strikingly similar to a region in the proteins encoded by a family of interferon-inducible mouse genes, designated Ifi-201, Ifi-202, and Ifi-203, that are not regulated in a cell- or tissue-specific fashion.