CHARACTERIZATION OF A NEW MONOCLONAL-ANTIBODY (PG-M3) DIRECTED AGAINST THE AMINOTERMINAL PORTION OF THE PML GENE-PRODUCT - IMMUNOCYTOCHEMICAL EVIDENCE FOR HIGH EXPRESSION OF PML PROTEINS ON ACTIVATED MACROPHAGES, ENDOTHELIAL-CELLS, AND EPITHELIA

PG-M3 is a new monoclonal antibody (MoAb) specifically directed agains t a peptide sequence located in the aminoterminal region of the human PML protein. PML gene fuses with the retinoic acid receptor alpha (RAR alpha) gene during the t(15;17) chromosomal translocation of acute pr omyelocytic leukemia (APL). The epitope recognized by PG-MS is species -specific acid fixative-resistant and is shared by most PML isoforms a nd PML/RAR alpha fusion proteins. PML is consistently located within t he nucleus, although a minority of cells (about 20%), both in vitro an d in vivo, show positivity for PML also in the cytoplasm. The nuclear staining pattern of PG-M3 varies from speckled (cells other than APL) to micro-punctate (APL cells). Although two physiologically expressed PML isoforms are detectable by immunocytochemistry only or predominant ly in the cytoplasm of transfected cells, the cytoplasmic localization of PML is a property also shared by the PML isoforms that predominant ly localize to the nuclei. Immunohistologic analysis of normal human t issues with the PG-MB MoAb showed variable PML expression, with the hi ghest levels of the protein in postmitotic, differentiated cell types, such as endothelial cells, epithelia, and tissue macrophages, especia lly activated ones. In keeping with this in vivo finding. PML appears strongly upregulated in the U937 promonocyte cell line after exposure to agents that induce monocyte/macrophage activation (interferon gamma ) or maturation (vitamin D3 and transforming growth factor beta 1). (C ) 1995 by The American Society of Hematology.