IL-18, a potent IFN-γ-inducing cytokine, is expressed by various nonimmune cells as well as macrophages, suggesting that it has important physiological and immunological roles. The present study focused on the mechanism of active IL-18 induction from human oral epithelial cells. The epithelial cells and the cell lines constitutively express IL-18 mRNA and the 24-kDa precursor form of IL-18. Bioactive IL-18 exhibiting IFN-γ-inducing activity was detected in the supernatant of the cells on costimulation with neutrophil proteinase 3 (PR3) and LPS for 24 h after IFN-γ-priming for 3 days. An active 18-kDa form of IL-18 was detected in lysate and supernatant of the cells only after the above treatment and the induction was inhibited by cycloheximide and by serine proteinase inhibitors. After the treatment, lactate dehydrogenase activity was not detected in the cell culture supernatant, and PR3 was detected only in the membrane and not in cytoplasm fractions of the cells. Caspase-1 was not detected in the cells even after the treatment and the IL-18 induction was not inhibited by a caspase-1 inhibitor. These results suggest that the PR3-mediated induction of bioactive IL-18 secretion from oral epithelial cells in combination with LPS after IFN-γ-priming occurred via a caspase-1-independent pathway, and provide new insight into the possible involvement of a neutrophil proteinase in the induction of bioactive IL-18 in oral inflammation such as periodontitis.

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Experiments were performed on 12-wk-old nonobese diabetic (NOD) mice to investigate the immunologic background of the condition, using ICR mice as controls. The results indicate the following: (1) absolute decreases in number of T lymphocytes, (2) depression of natural killer activity, (3) normal responsiveness in delayed type hypersensitivity and functional depression of killer T cells against allogeneic tumors, (4) diminished resistance to herpes virus infection, and (5) enhanced production of polyclonal antibodies to T cell-dependent antigens. These features are similar to those noted in other autoimmune diseases of man and in their experimental models in laboratory animals. Elucidation of the pathogenetic mechanism of autoimmune diabetes mellitus in NOD mice, therefore, may contribute to the diagnosis, treatment, and prevention of a wide variety of autoimmune diseases.

SummaryMRL-Ipr/lpr mice develop a severe autoimmune disease that resembles systemic lupus erythematosis in humans . The predominant immunological feature in these mice is the development of peripheral lymphadenopathy due to the expansion of an unusual T cell subset (TCR ct//3+5CD3+4 -8-B220+), which may be related to the onset of their autoimmunity. However, it is unknown whether such abnormal lymphocytes proliferate in the specific organs or not . We demonstrated in the present study that the number of liver nonparenchymal mononuclear cells (MNC) in the diseased MRL-Ipr/Ipr mice was 10 times greater than that ofcontrol MRL-+/+ mice. Moreover, the freshlyisolated liver MNC of MRL-Ipr/lpr mice vigorously proliferated in vitro and consisted of abnormal CD3+4-8-lymphocytes. Such in vitro proliferation was not observed in the MNC of other peripheral lymphoid organs . A potent natural cytotoxicity was also confined to the liver MNC in MRL-1pr/1pr mice. In vivo injection of [3H]TdR demonstrated that liver MNC incorporated [3H]TdR; such incorporation showed a peak on day 1, and the MNC-incorporated [3H]TdR appeared in the lymph nodes as late as day 5 after the injection . These results suggest that the liver is a possible site for the proliferation of abnormal lymphocytes, which may migrate thereafter into the peripheral organs in MRL-Ipr/lpr mice.

SummaryWe demonstrated in the present study that with bacterial stimulation, an increased number of a/g T cells proliferated in the liver of mice and that even T cells bearing self-reactive T cell receptor (TCR) (or forbidden T cell clones), as estimated by antiV(3 monoclonal antibodies in conjunction with immunofluorescence tests, appeared in the liver and, to some extent, in the periphery. The majority (>80%) of forbidden clones induced had double-negative CD4-8-phenotype. In a syngeneic mixed lymphocyte reaction, these T cells appear to be self-reactive . Such forbidden clones and normal T cells in the liver showed a two-peak pattern of TCR expression, which consisted of u/(3 TCR dull and bright positive cells, as seen in the thymus. A systematic analysis of TCR staining patterns in the various organs was then carried out . T cells from not only the thymus but also the liver had the two-peak pattern of a/a TCR, whereas all of the other peripheral lymphoid organs had a single-peak pattern of TCR . However, T cells in the liver were not comprised of double-positive CD4 *8+ cells, which predominantly reside in the thymus. The present results therefore suggest that T cell proliferation in the liver might reflect a major extrathymic pathway for T cell differentiation and that this hepatic pathway has the ability to produce T cells bearing self-reactive TCR under bacterial stimulation, probably due to the lack of a double-positive stage for negative selection.I t is generally accepted that T lymphocytes differentiate in the thymus and go through a process of positive or negative selection to form the repertoires of mature T cells (1-4) . In earlier studies, several investigators proposed the existence of an extrathymic differentiation pathway of T cells, especially in experiments using congenitally athymic nude mice and in vitro culture systems (5-8) . However, investigators have not reached a consensus, since there is no definite information yet as to where such T cells differentiate outside the thymus. In recent studies, we have shown that both a/(3 and y/b T cells with double-negative (DN) t CD4 -8 -phenotype proliferate in the liver of humans and mice, especially under conditions of autoimmune diseases (9), malignancies (10, 11), and aging (12). These results have led us to consider the possibility that the liver might be a major site for extrathymic differentiation of certain T cells.In the present study, we have applied a recently described ' Abbreviations used in this paper. DN, double negative; DP, double positive, MMC, mitomycin ; MNC, mononuclear cells. 417system for identification of oligoclonal T cells expressing particular VQ of cx/0 TCRs by using mAbs (13,14) to demonstrate the hepatic pathway for cell differentiation . The present results support the possibility that the liver is a major site of extrathymic T cell differentiation and reveal that the hepatic pathway has several unique properties distinct from the intrathymic pathway for T cell differentiation . Materials and MethodsMice and Bacterial ...