A lymphocyte blastogenesis inhibitory factor (LBIF) has been characterized as an immunoregulatory molecule, especially on the T-lymphocyte proliferation. Using fast protein liquid chromatography-purified LBIF, we examined the effect of LBIF on the proliferation of various 18 tumor cell lines in vitro in comparison with those of interferon-α, interferon-γ, tumor necrosis factor-α, transforming growth factor-β1, or interleukin 1α/β. We showed here that LBIF strongly inhibited the proliferation of various tumor cell lines irrespective of cell lineage or species. LBIF was effective on a wider spectrum of tumor cell lines than other cytokines tested here. The inhibition resulted from cytotoxic or cytostatic effects, depending on individual characteristics of tumor cell lines. Five cell lines showed insensitivity against LBIF activity, suggesting a plausible involvement of LBIF receptor molecules to transduce LBIF signals. These results suggest that LBIF may play important roles in regulating cell growth.

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Supported by Grants-in-Aid for Cancer Research from the Japanese Ministry of Education, Science and Culture; from the Japanese Ministry of Health and Welfare for Comprehensive 10-Year Strategy for Cancer Control; from the Japanese Ministry of Education, Science and Culture for Scientific Research and for Developmental Scientific Research (No. 62870023); and from the Japanese Ministry of Education, Science and Culture for Scientific Research. It is also supported by the Osaka Foundation for Promotion of Clinical Immunology; by Yamanouchi Foundation for Research on Metabolic Disorders; by a Grant-in-Aid for Special Project Research from Hokkaido University; by Grants-in-aid from the Mochida Memorial Foundation for Medical and Pharmaceutical Research, and also by the Akiyama Foundation.

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