Macrophage cell lines transformed by the malignant histiocytosis sarcoma virus: Increase of CSF receptors suggests a model for transformation

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Abstract
The malignant histiocytosis sarcoma virus (MHSV) contains Ha‐v‐ras‐related oncogenic sequences and rapidly transforms myeloid cells in vivo and in vitro. Myeloid cell lines can be derived which do not require growth factor for continued proliferation. We initiated this work to define the process of transformation leading to autonomy of cell growth in transformed myeloid cells. Five established cell lines were examined. All express macrophagespecific cell‐surface antigens and exhibit several other properties typical for mature macrophages. Growth properties, growth factor release, and growth factor receptor presentation were examined: Release of growth factors is not a consistent feature. All cell lines show cell‐density‐independent colony formation and do not release self‐stimulating factors, thus excluding autocrine stimulation as a model leading to transformation. All cell lines express unusually high levels of granulocyte‐macrophage (GM)‐and multi‐CSF receptors and, except for one M‐CSF receptors. The high increase in GM‐CSF and other growth factor receptors may be causally related to the transformed state of the cells. MHSV can be used as a tool to easily derive cell lines of the macrophage pathway as a model to study myeloid transformation, differentiation, and macrophage function.