Colony stimulating factors (CSFs) are produced by a variety of cell types, including T-lymphocytes (T cells) and mononuclear phagocytes; both cell types are known to cooperatively interact to elaborate CSFs, although the specific cellular source of CSF species and mechanisms of intercellular communications in this regard are poorly understood. In this report, we investigate the specific origin of various CSF species in peripheral blood mononuclear cells (PBMC), purified T-lymphocyte and monocyte (Mo) populations. Furthermore, we assess the conditions required for stimulation of purified cell cultures to express CSF messenger RNAs (mRNAs) and proteins. In the absence of exogenous activation stimuli, human PBMC, T cells and Mo failed to produce transcripts for CSF for macrophages (M-CSF or CSF-1), for granulocytes (G-CSF), for granulocytes/macrophages (GM-CSF), and for multilineage CSF (multi-CSF or Il-3). However, after stimulation with phorbol myristate acetate (PMA) and phytohemagglutinin (PHA), mRNAs for M-, G-, GM-CSF, and multi-CSF became detectable in PBMC as early as 6 hours after initiation of cultures. Identical culture conditions resulted in synthesis of G-, and M-CSF mRNA by Mo, whereas T-lymphocytes produced GM-CSF and multi-CSF mRNA. More physiologically, when Mo were activated with interferon (IFN)-gamma or tumor necrosis factor-alpha (TNF-alpha) and T-lymphocytes were stimulated in an Mo-independent pathway, that is via triggering of the 50 kd sheep erythrocyte receptor protein employing monoclonal antibodies (mo ab) to the Tll-2- and Tll-3- defined epitopes, similar kinetics of mRNA expression were obtained. Similarly, when interleukin-1 (Il-1) receptive T cells were stimulated with Il-1, T cells transcribed functionally active GM-CSF and multi-CSF. Maximum peak activity of GM-, G-, and M-CSF protein secretion was identical for all CSF species investigated, and occurred in culture 48-72 hours after specific induction. Constitutive expression of CSFs not found in unactivated normal hematopoietic cells was, however, frequently observed in blast cell populations of patients with acute myeloblastic leukemia. Of 49 AML samples, 15 revealed G-CSF transcripts; 11, GM-CSF mRNA; and 6 samples synthesized M-CSF mRNA. Employing specific bioassays, 12 of 15 G-CSF-mRNA-producing cell populations, 8 of 11 GM-CSF-mRNA-producing cell populations, and 1 of 6 M-CSF-mRNA-synthesizing samples, demonstrated release of the respective functionally active CSFs into their culture supernatants.(ABSTRACT TRUNCATED AT 400 WORDS)