| Popis: |
Erythropoietin can be released from bone marrow-derived macrophages grown in culture. Evidence is presented to show that, when unseparated and unstimulated mouse bone marrow cells are incubated on hydrophobic PTE foils for 14 days under reduced oxygen tensions, a 98% pure population of macrophages results. The cells develop as a result of production of low GM-CSF concentrations by the macrophages themselves. Using phenotypic and functional markers such as the Ia antigen, 5’-nucleotidase, plasminogen activator, Interleukin-1 and lactoferrin, it is possible to classify these cells as belonging to a “resident” rather than an “inflammatory” macrophage population. It is from this population that erythropoietin can be detected in the extracellular medium. The erythropoietin activity is dependent on the prevailing physiological oxygen tension under which the cells are grown, the optimal being 3.5% O2. This erythropoietin activity can be neutralized by an anti-erythropoietin antiserum. Furthermore,addition of macrophages, derived from these cultures and grown under 2%, 3.5% or 5% oxygen tension, can stimulate bone marrow CFU-E to various degrees in the absence of exogenous erythropoietin. That the macrophage can actually produce erythropoietin is shown by the combined expression of the erythropoietin gene as detected by in situ hybridization and the binding of the monoclonal antibody directed against the mouse macrophage-specific F4/80 antigen. Because not all macrophages in the culture demonstrate in situ hybridization as detected using either a 35S- or biotin-labeled erythropoietin probe, it is possible that only a subpopulation of macrophages possess the capacity of expressing the erythropoietin gene. |
