The reliability of an in vitro pyrogen test system based on proinflammatory cytokine release from human monocytic cells was assessed by comparison with a test system based on a human whole blood culture as well as with the conventional rabbit pyrogen test. The human cells used as the pyrogen indicator cells were newly selected by subcloning of a human monocytic cell line, Mono-Mac-6. The selected cells, named MM6-CA8, responded to various pyrogens, including endotoxin, peptidoglycan (PG), Staphylococcus aureus Cowan 1 (SAC), and poly(I · C), with a high sensitivity and produced proinflammatory cytokines, such as interleukin 1 (IL-1), IL-6, and tumor necrosis factor alpha. Among these cytokines, IL-6 was produced most sensitively in response to traces of the pyrogens and detected in the largest quantities in the culture medium. The cytokineproducing responses of MM6-CA8 cells correlated significantly with the responses of cultured human whole blood, which represents an ex vivo culture test system reproducing pyrogen-induced cytokine production in the human body. In terms of cytokine inducibility, the pyrogens were ranked in the order endotoxin > PG > poly (I · C) > SAC in both culture systems, a ranking which almost agreed with the ranking of their pyrogenicity as assessed by the rabbit pyrogen test. These results suggest that the in vitro responsiveness of MM6-CA8 cells to various pyrogens is highly relevant for human pyrogenic reactions. Therefore, the in vitro test system is useful and reliable for detecting the presence of materials that are pyrogenic for humans.

Interleukin-1 (IL-1) inhibits the growth of A375S2 human melanoma cells by arresting them at G 1 and G 2 phases of the cell cycle. The arrests are preceded by a rapid decrease in kinase activities of cyclin E-Cdk2 and cyclin B1-Cdc2, which are critical for G 1 -S and G 2 -M progression, respectively. IL-1 quickly enhances the protein expression of the CDK inhibitor p21cip1 . The induced p21 binds preferentially to cyclin E-Cdk2, and the increase in p21 binding parallels the decrease in cyclin E-Cdk2 activity. Thus, p21 is likely to be responsible for the inhibition of cyclin E-Cdk2 activity and G 1 arrest. Coinciding with the decrease in cyclin B1-Cdc2 activity, there is an increase in tyrosine phosphorylation of Cdc2, suggesting that an increase in the inactive Tyr-15-phosphorylated form of Cdc2 is involved in the decrease in cyclin B1-Cdc2 activity and G 2 arrest. Furthermore, we found that IL-1 causes rapid dephosphorylation of p107, but not of pRb or p130, while the total protein levels of p130 are increased. Thus, IL-1 may exert its growtharresting effects via p107 and p130 pathways rather than through pRb.Interleukin-1 ␤ (IL-1), 1 originally defined as a monocytederived factor mitogenic for thymocytes, is now known to affect many biological activities, including the ability to alter immunologic, inflammatory, hematopoietic, and homeostatic responses in the host system. In vitro, IL-1 has been shown to inhibit the growth of certain tumor cells (1-3). A role for IL-1 in host defense against tumors has been further suggested by its ability to augment natural killer cell activity (4), monocytemediated tumor cytotoxicity (5), and T-and B-cell responses (6) and to induce tumor regression in mice (7). These properties have made IL-1 an attractive candidate for potential application for certain solid tumors (8 -12), although several problems including various adverse effects such as fever and hypotension remain unresolved. Elucidation of the molecular mechanisms that mediate the antiproliferative effect of IL-1 on tumor cells would not only be of help in resolving these problems; it would also provide valuable information on how cell proliferation is regulated negatively by extracellular signals.In cell culture, various types of tumor cells, such as melanoma (4, 13-19), breast carcinoma (20), myeloid leukemia (21, 22), ovarian carcinoma (23), and lung adenocarcinoma (24) cells, have been shown to be susceptible to the antiproliferative action of IL-1. A highly susceptible human melanoma cell line, A375-C6, is commonly used to study the mechanism of the IL-1-mediated growth arrest. The action of IL-1 in A375-C6 cells has been documented to be mediated through specific cell surface receptors (25). The binding of IL-1 to its receptor results in activation of a variety of second-messenger signaling pathways (reviewed in Ref. 13) and a unique primary gene expression program characterized by the induction of a composite set of immediate early genes such as gro-␣, gro-␤, c-jun, nur77/NGF1-B/NAK1, 17,19). IL-1 action in A...