An autocrine role for urokinase in phorbol ester-mediated differentiation of myeloid cell lines.

The human myeloid cell line HL60 secretes urokinase-type plasminogen activator (uPA) and expresses its receptor. When stimulated with phorbol myristate acetate (PMA), both secretion of uPA and the expression of its receptor are up-regulated, and these cells differentiate to an adherent phenotype. This adhesive response is markedly reduced in the presence of uPA antibodies. The PMA response is restored by the addition of native uPA, an amino-terminal fragment of uPA (residues 1-143) devoid of proteolytic activity, or a synthetic peptide (residues 12-32) from the uPA growth factor domain known to mediate receptor binding. In contrast, the addition of catalytically active low molecular weight uPA, which is missing the growth factor domain, or a peptide from the catalytic domain (residues 247-266) is ineffective. The influence of uPA antibodies on a second marker of macrophage differentiation, cysteine proteinase activity, was also examined. Cysteine proteinase activity of HL60 cells is increased in PMA-treated cells after 24 h but it fails to increase in the presence of anti-uPA. This increase in cathepsin B-like activity is also restored by exogenous uPA. These experiments indicate that an autocrine interaction of the growth factor domain of uPA with its receptor mediates an essential step in PMA-mediated myeloid cell differentiation.

Alveolar macrophage urokinase receptors localize enzyme activity to the cell surface.

Human alveolar macrophages are known to synthesize urokinase (uPA) and a specific plasminogen activator inhibitor, PAI-2. In this study we have identified a uPA receptor expressed by these cells and defined the influence of PAI-2 on the interaction of uPA with its receptor. Alveolar macrophages from four normal volunteers were incubated with 55 kDa 125I-labeled uPA (0.24-8 nM) in the presence or absence of excess unlabeled uPA. Specific and saturable binding was demonstrable in all cases. Scatchard plots were linear; regression analysis revealed a mean Kd of 5.25 nM (range 3.2-6.7) and mean Bmax of 30.7 femtomoles/10(5) cells (range 21.5-34.5). The structure of the uPA receptor was defined by electroblotting membrane fractions of macrophages and sequentially exposing filters to uPA and uPA antibodies. Membranes from macrophages demonstrated binding of either uPA or a 15-kDa amino-terminal fragment of uPA to a 55- to 60-kDa glycosylated membrane protein. Binding of uPA to filters was blocked by a synthetic oligopeptide containing the known receptor binding region of native uPA. Preincubation of 125I-uPA with PAI-2 dramatically reduced the rate of association of uPA with macrophage uPA receptor. Conversely, receptor-bound uPA activity was less susceptible to inhibition by PAI-2 than soluble uPA activity. These data indicate that normal alveolar macrophages express uPA receptors. The receptor preferentially binds and protects free uPA over complexed enzyme, indicating that one function of the receptor is to allow the cells to express active uPA in an inhibitor-rich environment.

Widespread intradermal accumulation of mononuclear leukocytes in lepromatous leprosy patients treated systemically with recombinant interferon gamma.

Intradermal administration of recombinant interferon gamma (rIFN-gamma) to lepromatous leprosy patients has converted the local histology toward a tuberculoid pattern. However, such changes have been confined to the site of injection. In contrast, in the present study, marked, intradermal accumulation of CD3+, CD4+, CD8+, and CD1a+ T cells and Leu-M5+ mononuclear phagocytes was induced at a distance from the sites of administration, in a dose-dependent manner, by 10 daily intramuscular injections of 10-30 micrograms rIFN-gamma/m2. Mononuclear cell infiltration began within 3 d of onset of rIFN-gamma therapy and persisted at least 8 wk. Intramuscular administration of rIFN-gamma to lepromatous patients receiving concurrent chemotherapy can safely induce widespread histologic features of an upgrading reaction.

Properties of isolated red pulp macrophages from mouse spleen.

Dense monolayers of large, adherent macrophages were prepared from the red pulp of mouse spleen. These sinus-lining phagocytes resembled liver Kupffer cells in morphology, as well as expression of F4/80 and class II MHC antigens and receptors for IgG. C3-coated red cells attached at low levels to spleen macrophages, but attachment and endocytosis were enhanced on fibronectin-coated surfaces. The ionophore A23187 induced spleen macrophages to synthesize prostaglandin E2, but like Kupffer cells, spleen macrophages did not synthesize leukotrienes and made relatively small amounts of HETE and 12-hydroxyheptadecanoic acid. Resident spleen macrophages did not produce H2O2, but splenic inflammatory cells, induced by infection of animals with Listeria monocytogenes, actively released H2O2. We conclude that the functional properties of resident, sinusoidal-lining macrophages in liver and spleen are similar to one another but distinct from other pools of phagocytes.