The effect of calcium on the production of interleukin 1 (IL 1) and the expression of IL 1 receptors (R) of adult T-cell leukemia (ATL) cells was studied in vitro. ATL cells freshly obtained from patients and ATL cell lines produced limited amounts of IL 1 by culturing in a low-calcium concentration of medium (<0.01 mm). However, the production of IL 1 was enhanced by the addition of calcium chloride to the medium in a concentration-dependent manner and reached the maximum at the higher calcium concentration (3–4 mm) than at the standard calcium concentration of medium (1.26 mm). The production of IL 1 from ATL cells was further enhanced by calcium ionophore. Furthermore, the expression of IL 1R on ATL cells was augmented in proportion to the extracellular calcium concentration and calcium ionophore. In accordance with the change of the extracellular calcium concentration, the intracellular calcium concentration of ATL cells detected by Fura 2 was changed. However, this calcium dependency was not observed in the human T-cell leukemia virus I-negative acute T-cell leukemia cells. These results suggest that calcium plays a critical role in the regulation of the production of IL 1 and the expression of IL 1R on ATL cells.

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This work was supported in part by Grants-in-Aid for scientific research from the Ministry of Education, Science, and Culture of Japan and for cancer research from the Ministry of Health and Welfare of Japan (1–33) and by funds from Fukuoka Cancer Society.

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