A monoclonal antibody (MoAb), Ki-M8, that reacts specifically with cells of the monocyte/macrophage system is described. On light and electron microscopic immunohistochemistry, Ki-M8 recognizes intracytoplasmatically localized antigens of mol wt 30,000 and 32,000, increasingly expressed during differentiation of monocytes into macrophages. Ki-M8 antigen is detectable on almost all known tissue macrophages and monocyte/macrophage-related cell lines after appropriate stimulation. In functional terms Ki-M8 significantly impairs the generation of oxygen radicals during an induced respiratory burst. Applied to acute nonlymphoblastic leukemias, a clear-cut differentiation of the monocytic phenotype and differentiation is possible on the basis of Ki-M8 immunoreactivity. Ki-M8 represents a reagent specific for the monocyte/macrophage system with regard to antigen distribution in normal and neoplastic cells as well as with regard to its influence on a typical monocyte/macrophage-related function.

Total cellular RNA of highly purified normal human blood cell populations was analyzed for the expression of the protooncogene c-fos, the cellular counterpart of the transforming FBJ virus. In marked contrast to previous findings based on in vitro studies with permanent leukemic cell lines, c-fos transcription was restricted to granulocytes. Neither blood monocytes nor blood lymphocytes or alveolar macrophages revealed detectable levels of c-fos transcription. Whereas this cellular oncogene is constitutively expressed in granulocytes, the monocytic cell line U-937 showed a transient c-fos transcription only after induction of differentiation. The contradiction between the results found in vivo and in vitro is discussed.

Myelofibrosis with myeloid metaplasia (MMM) belongs to the group of myeloproliferative syndromes. It is characterized by a sustained proliferation of megakaryocytes and increased medullary reticulin fibers. Until now the cellular phase at onset of the disease has not been analyzed for clonality of the hematopoietic cells. In this study we used X-linked restriction length polymorphism (RFLP) analysis to investigate the clonality of granulocytes and bone marrow cells from the cellular phase and advanced stages of the disease. In each of 12 heterozygous females, monoclonality of granulocytes or total bone marrow cells could be demonstrated. These results show that the cellular phase represents a monoclonal, and hence a probably neoplastic, proliferation of a pluripotent stem cell. The monoclonality of granulocytes present at the onset of disease should allow analysis of DNA of these easily accessible peripheral cells for the detection of specific clonal aberrations.