Enhancement of release of granulocyte- and granulocyte-macrophage colony-stimulating factors from phytohemagglutinin-stimulated sorted subsets of human T lymphocytes by recombinant human tumor necrosis factor-alpha. Synergism with recombinant human IFN-gamma

The influence of purified recombinant human TNF-alpha (rhuTNF-alpha) was assessed, alone and in combination with purified recombinant human IFN-gamma (rhuIFN-gamma), for its effects on enhancing release from human T lymphocytes of activities that stimulate colony formation by granulocyte-macrophage, erythroid, and multipotential progenitor cells. rhuTNF-alpha or rhuIFN-gamma enhanced the release of CSF, which were determined to be granulocyte-CSF and granulocyte-macrophage-CSF by human bone marrow colony assays, morphologic assessment of colony types, and neutralization studies with rabbit anti-human granulocyte-CSF and monoclonal mouse anti-human granulocyte-macrophage-CSF. The CSF were released only when PHA was used, whether or not rhuTNF-alpha and/or rhuIFN-gamma were present while the lymphocytes conditioned the medium. T lymphocytes were sorted into subsets by using three-color immunofluorescence and a dye laser flow cytometry system with cells incubated with biotin anti-Leu-4 labeled with Texas Red, FITC-conjugated anti-Leu-3a, and phycoerythrin-conjugated anti-Leu-2a. Both the Leu-4+3a+2a- and the Leu-4+2a+3a- cells released CSF in response to PHA, but the release of CSF from PHA-stimulated lymphocytes was enhanced by rhuTNF-alpha and rhuIFN-gamma only from the Leu-4+3a+2a- subset of cells. Use of the three-color cell sorting made it highly unlikely that NK cells were involved, because both sorted subsets were positive for Leu-4. rhuTNF-alpha and rhuIFN-gamma synergized to enhance release of CSF such that low concentrations of each molecule, which were inactive when used alone, were active when the two molecules were used together. These studies suggest a role, at least in vitro, for TNF-alpha and IFN-gamma in the release of CSF from subsets of T lymphocytes stimulated with PHA.