A cytokine was identified that stimulated the proliferation of T lymphocytes, and a complementary DNA clone encoding this new T cell growth factor was isolated. The cytokine, designated interleukin-15 (IL-15), is produced by a wide variety of cells and tissues and shares many biological properties with IL-2. Monoclonal antibodies to the beta chain of the IL-2 receptor inhibited the biological activity of IL-15, and IL-15 competed for binding with IL-2, indicating that IL-15 uses components of the IL-2 receptor.

Suml'l'lary A significant proportion of previously activated human T cells undergo apoptosis when triggered through the CD3/T cell receptor complex, a process termed activation-induced cell death (AICD). Ligation of Fas on activated T cells by either Fas antibodies or recombinant human Fas-ligand (Fas-L) also results in cytolysis. We demonstrate that these two pathways of apoptosis are causally related. Stimulation of previously activated T ceils resulted in the expression of Fas-L mILNA and lysis of Fas-positive target cells. Fas-L antagonists inhibited AICD of T cell clones and staphylococcus enterotoxin B (SEB)-specific T cell lines. The data indicate AICD in previously stimulated T ceils is mediated by Fas/Fas-L interactions. Mature peripheral T cells generally undergo activation . and proliferation when stimulated through the CD3/ TCR complex. Under certain circumstances, however, thymocytes, T cell hybridomas, and both CD4 + and CD8 + T cell clones (TCC) 1 undergo cell death when stimulated through the TCR with CD3 antibody in the absence of APC (1-6). This process is rapid and exhibits classic characteristics of apoptosis such as membrane blebbing, chromatin condensation, and the formation of DNA fragments of ",,200 bp. Deletion of T cells by apoptosis appears to be important not only in regulating autoreactive T cells in the thymus, but also in regulating the peripheral T cell pool (7,8). Little is known, however, about the mechanism that mediates the lytic process that has been termed activation-induced cell death (AICD).Fas/APO-1 (CD95) is a protein expressed on the surface of a variety of transformed cell lines and chronically stimulated T cells that can mediate apoptosis after ligation with a Fas-specific antibody (9-12). Under appropriate conditions Fas also transduces a stimulatory signal to certain B cell lines (13) and to .freshly isolated human peripheral blood T cells and thymocytes (14). To investigate a possible relationship between CD3-stimulated AICD and Fas-mediated T cell apoptosis, we have used a mAb directed against human Fas (Fas M3). Immobilized Fas M3 mAb is able to lyse Fas-expressing tumor cell lines in a manner analogous to Fas-ligand (Fas-L) or the prototypic Fas mAb, CH-11, whereas soluble Fas M3 blocks Fas-mediated killing (15).1 Abbreviations used in this paper: AICD, activation-induced cell death; Fas-L, Fas-ligand; SEB, staphylococcal enterotoxin B; TCC, T cell done, Materials and MethodsT Cell Lines and Clones. The alloreactive TCC used in this study were generated by establishing MLC in bulk culture for 7 d followed by limit dilution cloning in 96-well round-bottomed plates in the presence of 10 s irradiated allogeneic PBMC and 10 ng/mt of Ib2. TCC were maintained by stimulation with irradiated PBMC and soluble CD3 antibody (10 ng/ml) approximately every 2 wk and maintenance in IL-2 (10 ng/ml) between stimulations. Shortterm staphylococcal enterotoxin B (SEB)-specific T cell lines were established by stimulation of PBMC (106) with 5 /~g/ml SEB (Sigma Chemical Co., St. Loui...

One of the earliest cell surface antigens expressed by T cells following activation is CD69, which is detectable within one h of ligation of the T cell receptor/CD3 complex. Once expressed, CD69 acts as a costimulatory molecule for T cell activation and proliferation. In addition to mature T cells, CD69 is inducibly expressed by immature thymocytes, B cells, natural killer (NK) cells, monocytes, neutrophils and eosinophils, and is constitutively expressed by mature thymocytes and platelets. Recently, cDNA clones encoding human and mouse CD69 were isolated and showed CD69 to be a member of the C-type lectin superfamily. Gene mapping studies have placed CD69 on distal mouse chromosome 6 and human chromosome 12p13, close to, if not in, the NK gene complex. The structure, chromosomal localization, expression and function of CD69 suggest that it is likely a pleiotropic immune regulator, potentially important not only in NK cell function but also in the activation and differentiation of a wide variety of hematopoietic cells.

Tumour necrosis factor (tumour necrosis factor-alpha/cachectin) plays a critical role in certain physiological defensive responses but causes severe damage to the host organism when produced in excess. There are two forms of tumour necrosis factor, a type II membrane protein of relative molecular mass 26,000 (26K) and a soluble, 17K form generated from the cell-bound protein by proteolytic cleavage. The two forms of tumour necrosis factor and lymphotoxin-alpha (tumour necrosis factor-beta/lymphotoxin), a related protein, have similar but apparently not identical biological activities. A therapeutic agent which inhibited the release of tumour necrosis factor, but did not reduce the cell-associated activity or the level of lymphotoxin-alpha, might preserve the benefits of these cytokines while preventing tumour necrosis factor-induced damage. Here we describe a potent inhibitor of tumour necrosis factor processing and report that it protects mice from a lethal dose of endotoxin.

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SummaryCD40 is a member of the tumor necrosis factor (TNF) receptor family of cell surface proteins and was originally described as a B cell restricted antigen. Treatment of primary human monocytes with granulocyte/macrophage colony-stimulating factor (GM-CSF), interleukin 3 (IL-3), or interferon 3' (IFN-3') resulted in the induction of CD40 mRNA and enhancement of cell surface protein expression. CD40 was found to mediate monocyte adhesion to cells expressing recombinant CD40 ligand. CD40 ligand-transfected cells provided a potent costimulus for monocyte TNF-ot and IL-6 production in the presence of GM-CSF, IL-3, or IFN-3', and enhanced IL-8 production stimulated by GM-CSF or IL-3. In addition, CD40 ligand-transfected cells acting in the absence of a costimulus induced monocytes to become tumoricidal against a human mdanoma cell target. Collectively, these data indicate that CD40 ligand is pleiotropic with potent biological activity on monocytes.C D40 is a 50-kD molecule expressed on B cells, dendritic cells, some carcinoma cell lines, and human thymic epithelium (1-3). Abs specific for CD40 exhibit stimulatory effects on IL-4 activated B cells, including the induction of B cell growth, IgE secretion, and expression of CD23 (4-7). Human and murine forms of a ligand for CD40 (CD40L) 1 were recently cloned and demonstrated to be type II integral membrane proteins expressed primarily on activated CD4 + T cells (8)(9)(10)(11). CD40L provides a strong stimulatory signal to B cells from both species (8-10), however little is known about the regulation of expression of CD40 and the effects of CD40L on other cell types.Monocytes express a variety of cell surface proteins that are thought to play an important role in antigen presentation and the cell contact-dependent interaction of monocytes with other leukocytes. The expression of many of these proteins on monocytes can be regulated by a variety of cytokines, including GM-CSF, IL-3, IL-4, IFN-3", and . In this paper, we demonstrate that GM-CSF, IL-3, and IFN-'r enhance expression of CD40 by normal human monocytes. In addition, culture of monocytes with CD40L resulted in the stimulation or costimulation of cytokine production and in the induction of monocyte tumoricidal activity. Thus, CD40L is involved in the regulation of several critical aspects 1 Abbreviation used in this paper: L, ligand. of the immune response, and may be important in the cell contact-dependent activation of both T cells and monocytes during antigen presentation. Materials and MethodsMonocyte Purification and Culture. Monocytes were purified from normal donor PBMC by countercurrent elutriation (17) and were ~95 % pure by microscopic examination of Giemsa-stained cytocentrifuge preparations. Cells were cultured in RPMI 1640 medium containing 10% low endotoxin FBS, 50 U/ml penicillin, 50/zg/ml streptomycin, and 5 x 10 -s M 2-ME. Monocytes were cultured in polypropylene tubes (Falcon; Becton Dickinson Labware, Lincoln Park, NJ) for flow cytometry and mRNA analysis, in 24-well plates (Costar Corp., C...

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Two receptors for the proinflammatory cytokine interleukin 1 (IL-1) have been cloned and characterized biochemically. While it has been well established that the type I (80-kDa) IL There are two known receptors for IL-1, which differ in both size and tissue distribution (2-4). The ligand-binding portions of the two receptors are similar, but whereas the cytoplasmic region of the type I (-80-kDa) receptor contains -215 amino acids, that of the type II (=60-kDa) receptor is only 29 amino acids long. It is well established that the type I receptor is capable of mediating biological responses (5, 6). In studies reported elsewhere, it has also been clearly shown that the type I and type II receptors are not subunits of a multimeric receptor complex but instead bind IL-1 independently of one another (7). This raises the possibility that each receptor might couple to different signal transduction pathways. In the studies reported here, however, we have been unable to find any evidence that the type II receptor signals at all.