Activated but not resting T cells or thymocytes express colony‐stimulating factor 1 mRNA without co‐expressing c‐fms mRNA

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Abstract
Following the observation that, besides acute myeloid leukemia cells, acute lymphoid leukemia cells of either B or T phenotype could express the transcript for the colony‐stimulating factor 1 (CSF‐1), a growth factor known to be restricted to the monocytic‐macrophage lineage, various sources of resting and/or activated T cells and thymocytes were screened for expression of this hemopoietic growth factor. We report here that the CSF‐1 transcript was rapidly (7 h) induced in T cells by a variety of stimuli, but was not detectable in either resting T cells or thymocytes. In addition, secretion of CSF‐1 was detectable in the supernatants of activated T cells by 72 h, with a peak around 92‐120 h. In contrast to activated monocytes, the transcript of the c‐fms proto‐oncogene, the product of which is the receptor for CSF‐1, was not detectable in either resting or activated T cells. This observation could be relevant to the intimate relationships between T cells and antigen‐presenting cells during immune responses.