Cloning of a T cell growth factor that interacts with the beta chain of the interleukin-2 receptor

Human herpesvirus-6 enhances natural killer cell cytotoxicity via IL-15

The marked tropism of human herpesvirus-6 (HHV-6) for natural killer (NK) cells and T lymphocytes has led us to investigate the effect of HHV-6 on cellular cytotoxicity. We describe here how HHV-6 infection of peripheral blood mononuclear cells (PBMC) leads to upregulation of their NK cell cytotoxicity. The induction of NK cell activity by HHV-6 was abrogated by monoclonal antibodies (mAbs) to IL-15 but not by mAbs to other cytokines (IFN-alpha, IFN-gamma, TNF-alpha, TNF-beta, IL-2, IL-12) suggesting that IL-15 secreted in response to viral infection was responsible for the observed effect. Furthermore, NK activation by HHV-6 was blocked with mAb to CD122, as well as by human anti-HHV-6 neutralizing antibodies. Using RT-PCR, we were able to detect IL-15 mRNA upregulation in purified monocyte and NK cell preparations. IL-15 protein synthesis was increased in response to HHV-6. Finally, addition of IL-15 to PBMC cultures was found to severely curtail HHV-6 expression. Taken together, our data suggest that enhanced NK activity in response to viral infection represent a natural anti-viral defense mechanism aimed at rapidly eliminating virus-infected cells.

Immunity at the surface: homeostatic mechanisms of the skin immune system

The coordinated function of multiple epidermal and dermal cell populations allows the skin immune system to respond rapidly and effectively to a wide variety of insults occurring at the interface of the organism and its environment. Keratinocytes are the first line of defense in the skin immune system, and keratinocyte-derived cytokines are pivotal in mobilizing leukocytes from blood and signaling other cutaneous cells. Cytokine-mediated cellular communication also enables dermal fibroblasts and endothelial cells lining the cutaneous vasculature to participate in immune and inflammatory responses. Skin is an important site for antigen presentation, and both epidermal Langerhans cells and dermal dendritic cells play pivotal roles in T cell-mediated immune responses to antigens encountered in skin. Proinflammatory signaling pathways are necessarily balanced by a variety of regulatory pathways that help maintain the homeostatic functioning of the skin immune system.

The role of interleukin-15 in T-cell migration and activation in rheumatoid arthritis

Interleukin 15 (IL-15) is a novel cytokine with interleukin-2-like activity. It is also a potent T-lymphocyte chemoattractant. Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by the presence of activated T lymphocytes, macrophages and synoviocytes in the synovial membrane. The mechanisms of T-cell activation in RA are currently unclear. We report the presence of high concentrations of IL-15 in rheumatoid arthritis (RA) synovial fluid and have demonstrated its expression in the synovial membrane lining layer by immunohistochemistry. RA synovial fluids were found to contain chemotactic activity, which was attributable in part to the presence of IL-15. Moreover, in a murine model, injection of recombinant IL-15 was found to induce a local tissue inflammatory infiltrate consisting predominantly of T lymphocytes. Synovial fluid T lymphocytes proliferate in response to IL-15, demonstrating that continued responsiveness to IL-15 is a feature of T cells after entry into the synovial compartment. These data suggest that IL-15 can recruit and activate T lymphocytes in the synovial membrane, thereby contributing to RA pathogenesis.

Interleukin-15 expression by human endothelial cells: up-regulation by ultraviolet B and psoralen plus ultraviolet A treatment

The purposes of the present study were to determine whether endothelial cells express IL-15 and to evaluate effects of ultraviolet B (UVB) and 8-methoxypsoralens plus UVA (PUVA) on such expression. Cultured human endothelial cells derived from dermis or umbilical veins were subjected to reverse transcriptase-polymerase chain reaction (RT-PCR) and immunoblot analyses for the detection of IL-15 mRNA and protein, respectively. Both dermal and umbilical vein endothelial cells were shown to express IL-15 mRNA and protein, and these markers were upregulated following UVB or PUVA treatment (but not by UVA or 8-methoxypsoralens alone). Also using RT-PCR, dermal and umbilical vein endothelial cells were shown to express IL-2R gamma c mRNA. These results expand the sources of IL-15 in skin to include keratinocytes, dermal fibroblasts, and now endothelial cells. That IL-15 from all three skin cells can be upregulated by UV treatment suggests a role for this cytokine in photosensitive disorders. Finally, the possibility of an autocrine effect of IL-15 on endothelial cells is raised by the expression of IL-2R gamma c in these cells.

CD40/CD40 ligand interactions are required for T cell-dependent production of interleukin-12 by mouse macrophages

We have previously shown that T cell receptor-activated mouse T helper (Th)1 clones induce the production of interleukin (IL)-12 by splenic antigen-presenting cells (APC). Here, we show that the expression of CD40L by activated T cells is critical for T cell-dependent IL-12 production by mouse macrophages. IL-12 was produced in cultures containing alloreactive Th1 clones stimulated with allogeneic peritoneal macrophages, or in cultures of splenocytes stimulated with anti-CD3. Anti-CD40L monoclonal antibodies (mAb) inhibited the production of IL-12, but not IL-2, in these cultures by approximately 90% and had dramatic inhibitory effects on antigen-dependent proliferation of Th1 clones. In addition, both activated T cells and a Th1 clone derived from CD40L knockout mice failed to induce IL-12 production from splenic APC or peritoneal macrophages. Finally, macrophages cultured in the absence of T cells produced IL-12 upon stimulation with soluble recombinant CD40L in combination with either supernatants from activated Th1 clones or with interferon-gamma and granulocyte/macrophage colony-stimulating factor. Thus, both CD40L-dependent and cytokine-mediated signals from activated T cells are required to induce the production of IL-12 by macrophages. A blockade at the level of IL-12 production may explain, at least in part, the dramatic ability of anti-CD40L mAb to inhibit disease in animal models that are dependent upon the generation of a cell-mediated immune response. Moreover, a defect in T cell-dependent induction of IL-12 may contribute to the immune status of humans that lack functional CD40L.

Interleukin-2 receptor common gamma-chain signaling cytokines regulate activated T cell apoptosis in response to growth factor withdrawal: selective induction of anti-apoptotic (bcl-2, bcl-xL) but not pro-apoptotic (bax, bcl-xS) gene expression

Cytokine deprivation from activated T cells leads to apoptosis associated with down-regulation of the bcl-2 gene product. It is not clear, however, how cytokines other than interleukin-2 (IL-2) may affect this process and regulate the involvement of other apoptosis-modulating genes. We show that a group of cytokines including IL-2 (IL-2R gamma), prevent the apoptosis of IL-2-deprived activated T cells. This rescue involves the induction of the anti-apoptosis genes bcl-2 and bcl-xL), but causes little change in expression of bax and bcl-xS, which promote apoptosis. Furthermore, the prevention of apoptosis and induction of proliferation by the common gamma chain cytokines can be dissociated. Thus, when proliferation is blocked, the common gamma chain cytokines still induce up-regulation of bcl-2 relative to bax and retard apoptosis. These cytokines can thus regulate the persistence or removal of effector T cells by coordinating the balance between genes which promote and those which inhibit apoptosis, events which are probably mediated at least in part by signals through the common gamma chain. These data also implicate inappropriate T cell apoptosis resulting from a dysfunctional common gamma-chain as part of the pathophysiological defect in patients with X-linked severe-combined immunodeficiency (SCID).

Insights on the pathogenicity of human T-lymphotropic/leukemia virus types I and II

Human T-lymphotropic/leukemia virus types I and II (HTLV-I and HTLV-II) are phylogenetically and immunologically related viruses that differ in their pathogenicity in vivo. HTLV-I is the etiologic agent of adult T-cell leukemia/lymphoma, as well as a chronic progressive myelopathy, HTLV-I-associated myelopathy/tropical spastic paraparesis. In contrast, HTLV-II has not been conclusively associated with specific diseases. Both HTLV-I and HTLV-II transform CD4+ T-cells in vitro, but their in vivo target cells appear to differ. HTLV-I is found mainly in CD4+ cells, whereas HTLV-II has been demonstrated mainly in CD8+ cells. Clearly the definition of the viral genetic determinants responsible for the different tropism and pathogenicity in vivo may provide the basis of our understanding of the HTLV-I oncogenicity. In this short review we emphasize two aspects of viral infection of T cells: (1) the influence of viral infection on the major proteins involved in the G0-G1 phase of the cell cycle and (2) the effect of viral infection on the S phase of the cell cycle, i.e., the interleukin-2 receptor pathway.

Functional characterization of the human interleukin-15 receptor alpha chain and close linkage of IL15RA and IL2RA genes

Interleukins-2 and -15 (IL-2 and IL-15) are cytokines with overlapping but distinct biological effects. Their receptors share two subunits (the IL-2R beta and -gamma chains) that are essential for signal transduction. The IL-2 receptor requires an additional IL-2-specific alpha subunit for high affinity IL-2 binding. Recently, a murine IL-15-specific alpha subunit was identified, cloned, and shown to be structurally related to IL-2R alpha. However, the murine IL-15R alpha alone bound IL-15 with a 1000-fold higher affinity than that seen with IL-2R alpha and IL-2. We now extend these studies into the human system with the isolation of three differentially spliced human IL-15R alpha variants that are all capable of high affinity binding of IL-15. The cytoplasmic domain of IL-15R alpha, like that of IL-2R alpha, is dispensable for mitogenic signaling, suggesting that the primary role of the alpha chains is to confer high affinity binding. At high concentrations, IL-15, like IL-2, is able to signal through a complex of IL-2R beta and -gamma in the absence of the alpha subunit. Furthermore, the IL15RA and IL2RA genes have a similar intron-exon organization and are closely linked in both human and murine genomes. However, the distribution of expression of the IL-15R alpha is much wider than that of the IL-2R alpha, suggesting a broader range of cellular targets for IL-15.

Interleukin (IL)-15 promotes the growth of murine epidermal gamma delta T cells by a mechanism involving the beta- and gamma c-chains of the IL-2 receptor

Dendritic epidermal T cells (DETC) are skin-specific members of the epithelial gamma delta T-cell family in mice. We have reported previously that the growth of DETC is promoted by interleukin (IL)-2 in an autocrine fashion, or by IL-7, which is secreted by neighboring keratinocytes. Here we report that DETC growth is promoted by IL-15, a newly discovered T-cell growth factor that is produced in lymphoid as well as nonlymphoid tissues. Recombinant IL-15 promoted the growth of the 7-17 DETC line in a time- and dose-dependent fashion. Using monoclonal antibodies against alpha-, beta-, or gamma c-chains of the IL-2 receptor complex, we observed that the combination of anti-beta chain and anti-gamma c chain antibodies blocked IL-15 responsiveness completely, whereas anti-alpha chain had no effect. These results indicate that this gamma delta T-cell line uses the beta/gamma c heterodimer for proliferative responses to IL-15. Antibodies against IL-2 or IL-7 did not block IL-15-driven proliferation of 7-17 DETC, indicating that IL-15 promotes their growth in an IL-2- and IL-7-independent manner. Both the surface expression of beta/gamma c heterodimers and the IL-15 responsiveness of 7-17 DETC were highest 1 to 8 days after concanavalin A stimulation, and both declined substantially 21 days after stimulation, illustrating regulation by the state of cell activation. Working with epidermal cells that were freshly procured from CBA mice, we noted that IL-15 promoted conavalin-A-triggered growth of Thy-1+ cells (i.e., DETC), but not of the Thy-1- cells. The gamma c-chain was not expressed by freshly procured DETC, becoming detectable within 48 h after concanavalin A stimulation. We propose that IL-15 facilitates the growth of epithelial gamma delta T cells by a beta/gamma c receptor-dependent mechanism.

Recombinant proteins for medical use: the attractions and challenges

Recombinant proteins that have survived the challenges of process development and clinical trials are becoming blockbuster medical products. Growth factors, enzymes and antibodies are being improved by mutational approaches, fused with other proteins, and even chemically modified in vitro. Drug development and testing approaches have advanced, and proteins produced in transgenic animals are new becoming available. Future protein products might include cancer vaccines and therapies for a variety of genetic diseases, but alternative treatments involving gene therapy or small synthetic compounds will provide competition.

Interleukins 2, 4, 7, and 15 stimulate tyrosine phosphorylation of insulin receptor substrates 1 and 2 in T cells. Potential role of JAK kinases

The signaling molecules insulin receptor substrate (IRS)-1 and the newly described IRS-2 (4PS) molecule are major insulin and interleukin 4 (IL-4)-dependent phosphoproteins. We report here that IL-2, IL-7, and IL-15, as well as IL-4, rapidly stimulate the tyrosine phosphorylation of IRS-1 and IRS-2 in human peripheral blood T cells, NK cells, and in lymphoid cell lines. In addition, we show that the Janus kinases, JAK1 and JAK3, associate with IRS-1 and IRS-2 in T cells. Coexpression studies demonstrate that these kinases can tyrosine-phosphorylate IRS-2, suggesting a possible mechanism by which cytokine receptors may induce the tyrosine phosphorylation of IRS-1 and IRS-2. We further demonstrate that the p85 subunit of phosphoinositol 3-kinase associates with IRS-1 in response to IL-2 and IL-4 in T cells. Therefore, these data indicate that IRS-1 and IRS-2 may have important roles in T lymphocyte activation not only in response to IL-4, but also in response to IL-2, IL-7, and IL-15.

Endogenous production of interleukin 15 by activated human monocytes is critical for optimal production of interferon-gamma by natural killer cells in vitro

Natural killer (NK) cells are large granular lymphocytes that constitutively express functional IL-2 receptors. We have shown that recombinant human IL-15 uses the IL-2 receptor to activate human NK cells and can synergize with recombinant human IL-12 to stimulate NK cell production of IFN-gamma in vitro. IFN-gamma production by NK cells is critical in the prevention of overwhelming infection by obligate intracellular microbial pathogens in several experimental animal models. Herein, we demonstrate that human monocytes produce IL-15 protein within 5 h of activation with LPS. Using an IL-15-neutralizing antiserum in a coculture of LPS-activated monocytes and NK cells, we demonstrate that monocyte-derived IL-15 is critical for optimal NK cell production of IFN-gamma. Endogenous IL-15 activates NK cells through the IL-2 receptor, and with endogenous IL-12, regulates NK cell IFN-gamma after monocyte activation by LPS. These in vitro studies are the first to characterize a function for endogenous IL-15, and as such, suggest an important role for IL-15 during the innate immune response. IL-15 may be an important ligand for the NK cell IL-2 receptor in vivo.

Role of the common cytokine receptor gamma chain in cytokine signaling and lymphoid development

To examine the role of gamma c in lymphoid development, we have analyzed mice in which the gamma c gene was specifically inactivated by homologous recombination. These mice also serve as an animal model of human X-linked severe combined immunodeficiency (XSCID). Interestingly, gamma c knockout mice exhibited a somewhat different phenotype than humans with XSCID. Absolute T-cell numbers are greatly diminished in young gamma c-/Y mice, but accumulate with age. gamma delta T cells and NK cells are absent in gamma c-/Y mice and conventional B cells are greatly diminished, yet substantial numbers of peritoneal B-1 cells are present. Since humans with XSCID have essentially no mature T cells, it is especially striking that T cells are readily apparent in gamma c-/Y mice. This observation indicates that in these mice, the gamma c-dependent block in T cell development is less severe than it is in humans. It is possible but unproven that thymic stromal derived lymphopoietin, TSLP, contributes to thymocyte development in these mice. Since B-cell numbers are normal in humans with XSCID, it is also striking that gamma c-/Y mice paradoxically exhibit greatly diminished numbers of B cells. This likely indicates that IL-7 signaling plays a critical role in pre-B cell maturation in mice but is less important in humans. Thus, the abnormalities observed in gamma c-/Y mice have provided clues to assist in dissecting the role of cytokines and their receptors in lymphoid development and have also identified interesting differences in the regulation of this process in mice and humans.

Effects of TH1 and TH2 cytokines on CD8+ cell response against human immunodeficiency virus: implications for long-term survival

CD8+ cells from long-term survivors [LTS; infected with human immunodeficiency virus (HIV) for 10 or more years and having CD4+ cell counts of > or = 500 cells per microliters] have a 3-fold greater ability to suppress HIV replication than do CD8+ cells from patients who have progressed to disease (progressors) during the same time period. A change in the pattern of cytokines produced in the host from those that typically favor cell-mediated immunity (T helper 1, TH1 or type 1) to those that down-regulate it (T helper 2, TH2 or type 2) was investigated as a cause of this reduced CD8+ cell anti-HIV function. Treatment of CD8+ cells from LTS with the TH1 cytokine interleukin (IL)-2 enhanced their anti-HIV activity, whereas exposure of these cells to TH2 cytokines IL-4 or IL-10 reduced their ability to suppress HIV replication and to produce IL-2. IL-2 could prevent and reverse the inhibitory effects of IL-4 and IL-10. Moreover, prolonged exposure of CD8+ cells from some progressors to IL-2 improved the ability of these cells to suppress HIV replication. These observations support previous findings suggesting that strong CD8+ cell responses play an important role in maintaining an asymptomatic state in HIV infection. The data suggest that the loss of CD8+ cell suppression of HIV replication associated with disease progression results from a shift in cytokine production within the infected host from a TH1 to a TH2 pattern. Modulation of these cytokines could provide benefit to HIV-infected individuals by improving their CD8+ cell anti-HIV activity.

Interleukin-2 as a neuroregulatory cytokine

Interleukin-2 (IL-2), the cytokine also known as T-cell growth factor, has multiple immunoregulatory functions and biological properties not only related to T-cells. In the past decade, substantial evidence accumulated to suggest that IL-2 is also a modulator of neural and neuroendocrine functions. First, extremely potent effects of IL-2 on neural cells were discovered, including activities related to cell growth and survival, transmitter and hormone release and the modulation of bioelectric activities. IL-2 may be involved in the regulation of sleep and arousal, memory function, locomotion and the modulation of the neuroendocrine axis. Second, the concept that IL-2 could act as a neuroregulatory cytokine has been supported by reports on the presence in rodent and human brain tissues of IL-2-like bioactivity, IL-2-like immunoreactivity, IL-2-like mRNA, IL-2 binding sites, IL-2 receptor (IL-2R alpha) and beta chain mRNA and IL-2R immunoreactivity. IL-2 and/or IL-2R molecules mainly localize to the frontal cortex, septum, striatum, hippocampal formation, hypothalamus, locus coeruleus, cerebellum, the pituitary and fiber tracts, such as the corpus callosum, where they are likely expressed by both neuronal and glial cells. Although the molecular biology of the brain IL-2/IL-2R system (including its relation to IL-15/IL-15R alpha) is not yet fully established by cloning and complete sequencing of all respective components, similarities (and to some extent differences) to peripheral counterparts are now apparent. The ability of IL-2 to readily penetrate the blood-brain barrier further suggests that this cytokine could regulate interactions between peripheral tissues and the central nervous system. Taken together, these data suggest that IL-2 of either immune and CNS origin can have access to functional IL-2R molecules on neurons and glia under normal conditions. Additionally, dysregulation of the IL-2/IL-2 receptor system could lead or contribute to functional and pathological alterations in the brain as in the immune system. Understanding the neurobiology of the IL-2/IL-2 receptor system should also help to explain neurologic, neuropsychiatric and neuroendocrine side effects occurring during IL-2 treatment of peripheral and brain tumors. Immunopharmacological manipulation either aiming at the activation or suppression of IL-2 signaling should consider functional interference with constitutive and inducible IL-2 receptors on brain cells in order to fulfil the high expectations associated with the use of this cytokine as a promising agent in immunotherapies, especially of brain tumors.

UVB-dependent modulation of epidermal cytokine network: roles in UVB-induced depletion of Langerhans cells and dendritic epidermal T cells

The epidermis of mice consists of three cellular components, i.e., keratinocytes, Langerhans cells (LC), and dendritic epidermal T cells (DETC). Each epidermal subpopulation produces a different set of cytokines, thereby forming a unique cytokine milieu. These cytokines, in turn, support the survival and growth of LC and DETC and regulate their immunological functions. LC and DETC play important, but distinct, effector roles in protective immunity against antigens that are generated in or penetrate into the epidermis. Acute or chronic exposure of mice to ultraviolet B (UVB) radiation is known to impair this cutaneous immunity, as evidenced by the failure to induce T cell-mediated immune reactions, by the generation of antigen-specific immunological unresponsiveness, and by the development of skin cancers. Importantly, these changes are associated with reduced densities of LC and DETC in UVB-exposed skin, suggesting that the deficiency in these epidermal leukocytes may account for some of the deleterious influences of UVB radiation on skin. Here I will review the recent advance in our understanding of the mechanisms by which UVB radiation may deplete LC and DETC from epidermis. More specifically, I will discuss the following possibilities: a) UVB-mediated suppression of the production of relevant growth factors for LC and DETC, b) UVB-induced abrogation of surface expression of growth factor receptors, and c) UVB-triggered apoptotic cell death in epidermal leukocytes.

Interleukin (IL) 4, in the absence of antigen stimulation, induces an anergy-like state in differentiated CD8+ TC1 cells: loss of IL-2 synthesis and autonomous proliferation but retention of cytotoxicity and synthesis of other cytokines

Naive T cells in the periphery mainly secrete interleukin (IL) 2 upon activation. After stimulation in the presence of appropriate costimulators, both CD4+ and CD8+ T cells differentiate into effector cells secreting distinct T helper (Th) 1- and Th2-like cytokine patterns. Subsequent to differentiation, both CD4+ (Th1 and Th2) and CD8+ (TC1 and TC2) cells are stable and cannot be induced to differentiate into the opposite pattern or revert to the naive cytokine secretion pattern. We now show that IL-4 caused committed TC1 bulk populations or clones to lose the ability to synthesize IL-2. The cells retained the ability to secrete interferon (IFN) gamma, granulocyte/macrophage colony-stimulating factor, and tumor necrosis factor, did not synthesize any Th2 cytokines, and did not alter cell surface marker expression. IL-4 rapidly inhibited IL-2-synthesizing ability in the absence or presence of antigen-presenting cells, thus demonstrating that IL-4 acted directly on TC1 cells. The defect in IL-2 synthesis could not be reversed by subsequent stimulation with potent antigen-presenting cells in the presence of IL-2 and anti-IL-4, or with anti-CD3 plus anti-CD28 antibodies. Both IL-2+ and IL-2- TC1 cells were strongly cytotoxic toward allogeneic but not syngeneic targets. However, IL-2- TC1 cells were unable to proliferate unless exogenous IL-2 was provided. TC1 cells that lose IL-2 synthesis but retain IFN-gamma synthesis and cytotoxicity may be similar to the "anergic" cells induced by stimulation of CD4+ or CD8+ cells in the absence of costimulators. These results suggest that during a mixed type 1/type 2 response in vivo, IL-4 may induce the IL-2+ TC1-->IL-2-TC1 conversion, and thus curtail the expansion of the TC1 response without impairing short-term effector function.

Cytokines and transplantation: Th1/Th2 regulation of the immune response to solid organ transplants in the adult

It has been very tempting to accept the suggestion that the route to rejection or tolerance of organ transplants is determined by T-helper type 1 and type 2 cells, respectively. Much of the data used to support this idea, however, is indirect and therefore cannot be used to imply a causal role for either population as suggested. Recent experiments have been aimed at further expanding knowledge in this area and conclude that the expansion of neither population alone inevitably results in graft damage or tolerance.

Interleukin-2 receptor alpha chain regulates the size and content of the peripheral lymphoid compartment

Interleukin-2 receptor alpha chain (IL-2R alpha) expression occurs at specific stages of early T and B lymphocyte development and is induced upon activation of mature lymphocytes. Young mice that lack IL-2R alpha have phenotypically normal development of T and B cells. However, as adults, these mice develop massive enlargement of peripheral lymphoid organs associated with polyclonal T and B cell expansion, which, for T cells, is correlated with impaired activation-induced cell death in vivo. Older IL-2R alpha-deficient mice also develop autoimmune disorders, including hemolytic anemia and inflammatory bowel disease. Thus, IL-2R alpha is essential for regulation of both the size and content of the peripheral lymphoid compartment, probably by influencing the balance between clonal expansion and cell death following lymphocyte activation.

Cytokine interactions in human immunodeficiency virus-infected individuals: roles of interleukin (IL)-2, IL-12, and IL-15

Cytokines have been shown to be powerful regulators of the immune response. In this study, we analyze the effect that the newly recognized cytokine interleukin (IL)-15 has on proliferation and cytokine induction using peripheral blood mononuclear cells (PBMCs) and purified CD4+ T cells from patients infected with human immunodeficiency virus (HIV) who are at various stages in their disease. We observed that IL-15 enhances the proliferative response in a dose-dependent manner from PBMCs of HIV-infected individuals when stimulated by polyclonal mitogen, tetanus toxoid, or HIV-specific antigen. The effects of exogenous IL-15 are substantially diminished by adding a neutralizing antibody to the beta chain of the IL-2 receptor. Moreover, the ability of IL-15 to increase proliferation is enhanced by the presence of endogenous IL-2 produced in the cultures. The effect that exogenous IL-15 had on IL-2, IL-4, and interferon (IFN)-gamma induction from PBMC's or CD4+ T cells in response to mitogen or tetanus toxoid was also examined. This was compared to the effect that exogenous IL-2 and IL-12 had under the same conditions. Addition of IL-2 or IL-15 to short-term in vitro cultures of either PBMCs or CD4+ T cells had little effect on IL-2, IL-4, or IFN-gamma production. By contrast, IL-12 caused substantial enhancement of both IL-2 and IFN-gamma production from these cultures. The role that endogenous cytokines have on IFN-gamma induction was also studied. Addition of a neutralizing antibody to the alpha chain of the IL-2 receptor or IL-12 to antigen stimulated cultures caused a striking decrease in IFN-gamma production. Neutralization of endogenous IL-15 also resulted in diminished IFN-gamma production from cultures stimulated with mitogen. IL-4 and IFN-gamma protein production by PBMCs and CD4+ T cells stimulated with mitogen was assessed to see if we could detect a specific bias of cytokine production. Small amounts of IL-4 were detected from CD4+ T cells but not PBMCs from most individuals tested. IFN-gamma and IL-2, however, were also produced from these same cultures. These results further elucidate the mechanism of cytokine regulation in HIV-infected individuals, and they provide evidence that IL-15 may be a useful immune modulator.

Growth signal transduction by the human interleukin-2 receptor requires cytoplasmic tyrosines of the beta chain and non-tyrosine residues of the gamma c chain

To evaluate the possible role for receptor-based tyrosine phosphorylation in growth signaling induced by interleukin-2 (IL-2), a series of substitution tyrosine mutants of the IL-2 receptor beta and gamma c chains was prepared and analyzed. Concurrent mutation of all six of the cytoplasmic tyrosines present in the beta chain markedly inhibited IL-2-induced growth signaling in both pro-B and T cell lines. Growth signaling in a pro-B cell line was substantially reconstituted when either of the two distal tyrosines (Tyr-392, Tyr-510) was selectively restored in the tyrosine-negative beta mutant, whereas reconstitution of the proximal tyrosines (Tyr-338, Tyr-355, Tyr-358, Tyr-361) did not restore this signaling function. Furthermore, at least one of the two cytoplasmic tyrosines that is required for beta chain function was found to serve as a phosphate acceptor site upon induction with IL-2. Studies employing a chimeric receptor system revealed that tyrosine residues of the beta chain likewise were important for growth signaling in T cells. In contrast, although the gamma c subunits is a target for tyrosine phosphorylation in vivo, concurrent substitution of all four cytoplasmic tyrosines of this chain produced no significant effect on growth signaling by chimeric IL-2 receptors. However, deletion of either the Box 1, Box 2, or intervening (V-Box) regions of gamma c abrogated receptor function. Therefore, tyrosine residues of beta but not of gamma c appear to play a pivotal role in regulating growth signal transduction through the IL-2 receptor, either by influencing cytoplasmic domain folding or by serving as sites for phosphorylation and subsequent association with signaling intermediates. These findings thus highlight a fundamental difference in the structural requirements for IL-2R beta and gamma c in receptor-mediated signal transduction.

Tyrosine phosphorylation and activation of STAT5, STAT3, and Janus kinases by interleukins 2 and 15

The cytokines interleukin 2 (IL-2) and IL-15 have similar biological effects on T cells and bind common hematopoietin receptor subunits. Pathways that involve Janus kinases (JAKs) and signal transducers and activators of transcription (STATs) have been shown to be important for hematopoietin receptor signaling. In this study we identify the STAT proteins activated by IL-2 and IL-15 in human T cells. IL-2 and IL-15 rapidly induced the tyrosine phosphorylation of STAT3 and STAT5, and DNA-binding complexes containing STAT3 and STAT5 were rapidly activated by these cytokines in T cells. IL-4 induced tyrosine phosphorylation and activation of STAT3 but not STAT5. JAK1 and JAK3 were tyrosine-phosphorylated in response to IL-2 and IL-15. Hence, the JAK and STAT molecules that are activated in response to IL-2 and IL-15 are similar but differ from those induced by IL-4. These observations identify the STAT proteins activated by IL-2 and IL-15 and therefore define signaling pathways by which these T-cell growth factors may regulate gene transcription.

Constitutive activation of different Jak tyrosine kinases in human T cell leukemia virus type 1 (HTLV-1) tax protein or virus-transformed cells

HTLV-1 infection causes an adult T cell leukemia in humans. The viral encoded protein tax, is thought to play an important role in oncogenesis. Our previous data obtained from a tax transgenic mouse model revealed that tax transforms mouse fibroblasts but not thymocytes, despite comparable levels of tax expression in both tissues. Constitutive tyrosine phosphorylation of a 130-kD protein(s) was observed in the tax transformed fibroblast B line and in HTLV-1 transformed human lymphoid lines, but not in thymocytes from Thy-tax transgenic mice. Phosphotyrosine immunoprecipitation followed by Western blot analysis with a set of Jak kinase specific antibodies, identified p130 as Jak2 in the tax transformed mouse fibroblastic cell line and Jak3 in HTLV-1 transformed human T cell lines. Phosphorylation of Jak2 in tax transformed cells resulted from high expression of IL-6. Tyrosine phosphorylation of this protein could also be induced in Balb/c3T3 cells using a supernatant from the B line, which was associated with induction of cell proliferation. Both phosphorylation and proliferation were inhibited by IL-6 neutralizing antibodies. Constitutive phosphorylation of Jak kinases may facilitate tumor growth in both HTLV-1 infected human T cells and the transgenic mouse model.

Antiviral immune responses in mice deficient for both interleukin-2 and interleukin-4

Antiviral immune responses of mice lacking interleukin-2 (IL-2) or IL-4 or both IL-2 and IL-4 (IL-2/4) were compared by using different viruses. Primary cytotoxic T-lymphocyte (CTL) responses against lymphocytic choriomeningitis virus (LCMV) were only moderately reduced in mice lacking IL-2 and were normal in mice lacking IL-4. Mice deficient in both interleukins exhibited variable and more strongly reduced but nevertheless in vivo protective LCMV-specific CTL responses. Similar results were obtained with vaccinia virus. Upon virus-specific restimulation in vitro, spleen cells from IL-2- and IL-2/4-deficient mice failed to generate CTL responses against virus-infected target cells, whereas the response of mice deficient in only IL-4 was comparable to that of control mice. The addition of IL-2 during in vitro restimulation completely restored the responses of both IL-2 and IL-2/4-deficient mice. T-helper-cell-independent immunoglobulin M and T-helper-cell-dependent immunoglobulin G antibody responses against vesicular stomatitis virus glycoprotein were within normal ranges for the various mutant mice. After LCMV infection, specific antibody responses against LCMV nucleoprotein were reduced four- to eightfold. These results show that mice lacking IL-2/4 have an overall tendency to exhibit more severely reduced CTL responses than IL-2- or IL-4-deficient mice. Nevertheless, and surprisingly, in vivo protective immune responses were mounted in the absence of IL-2/4, suggesting that besides a minor contribution from IL-4, other interleukins compensate in vivo for the lack of IL-2 in IL-2-deficient mice.

Molecular cloning of IL-2R alpha, IL-2R beta, and IL-2R gamma cDNAs from a human oligodendroglioma cell line: presence of IL-2R mRNAs in the human central nervous system

In the present study, we analyzed human adult brain, fetal spinal cord, and an interleukin-2 (IL-2)-responsive human oligodendroglioma subclone, TC620.6A2, for the presence of mRNAs for the alpha, beta, and gamma chains of the interleukin-2 receptor (IL-2R alpha, IL-2R beta, and IL-2R gamma). IL-2R beta mRNA, but not IL-2R alpha or IL-2R gamma was detectable by Northern blot analysis in adult human brain tissues. Northern blot analysis of TC620.6A2 and human fetal tissues revealed mRNAs of 1.5 kb and 1.3 kb that hybridized to the IL-2R alpha cDNA at low to medium stringency. Reverse transcriptase-polymerase chain reaction (RT-PCR) experiments were done on the TC620.6A2 cell line utilizing primers to IL-2R alpha, IL-2R beta, and IL-2R gamma. Southern blot analysis of the TC620.6A2 RT-PCR reactions detected products identical in size to the peripheral blood lymphocyte (PBL) positive controls at high stringency. Several of the TC620.6A2 IL-2R alpha, IL-2R beta, and IL-2R gamma cDNAs were cloned and sequenced. The sequences were found to be identical to the known IL-2R sequences. To our knowledge, these experiments are the first to demonstrate the presence of authentic IL-2R mRNAs in a human oligodendrocyte-like cell line. Demonstration of mRNA for IL-2R beta in human adult brain, IL-2R alpha in fetal brain, and IL-2R alpha, IL-2R beta, and IL-2R gamma in a malignant neural cell line suggests the possibility of a role for IL-2/IL-2R interactions in development and disease.

Signaling through the interleukin 2 receptor beta chain activates a STAT-5-like DNA-binding activity

To explore the possible involvement of STAT factors ("signal transducers and activators of transcription") in the interleukin 2 receptor (IL-2R) signaling cascade, murine HT-2 cells expressing chimeric receptors composed of the extracellular domain of the erythropoietin receptor fused to the cytoplasmic domains of the IL-2R beta or -gamma c chains were prepared. Erythropoietin or IL-2 activation of these cells resulted in rapid nuclear expression of a DNA-binding activity that reacted with select STAT response elements. Based on reactivity with specific anti-STAT antibodies, this DNA-binding activity was identified as a murine homologue of STAT-5. Induction of nuclear expression of this STAT-5-like factor was blocked by the addition of herbimycin A, a tyrosine kinase inhibitor, but not by rapamycin, an immunophilin-binding antagonist of IL-2-induced proliferation. The IL-2R beta chain appeared critical for IL-2-induced activation of STAT-5, since a mutant beta chain lacking all cytoplasmic tyrosine residues was incapable of inducing this DNA binding. In contrast, a gamma c mutant lacking all of its cytoplasmic tyrosine residues proved fully competent for the induction of STAT-5. Physical binding of STAT-5 to functionally important tyrosine residues within IL-2R beta was supported by the finding that phosphorylated, but not nonphosphorylated, peptides corresponding to sequences spanning Y392 and Y510 of the IL-2R beta tail specifically inhibited STAT-5 DNA binding.

Identification and cloning of a novel IL-15 binding protein that is structurally related to the alpha chain of the IL-2 receptor

Interleukin-15 (IL-15) is a novel cytokine of the four-helix bundle family which shares many biological activities with IL-2, probably due to its interaction with the IL-2 receptor beta and gamma (IL-2R beta and gamma c) chains. We report here the characterization and molecular cloning of a distinct murine IL-15R alpha chain. IL-15R alpha alone displays an affinity of binding for IL-15 equivalent to that of the heterotrimeric IL-2R for IL-2. A biologically functional heteromeric IL-15 receptor complex capable of mediating IL-15 responses was generated through reconstruction experiments in a murine myeloid cell line. IL-15R alpha is structurally similar to IL-2R alpha; together they define a new cytokine receptor family. The distribution of IL-15 and IL-15R alpha mRNA suggests that IL-15 may have biological activities distinct from IL-2.

Solution assembly of a soluble, heteromeric, high affinity interleukin-2 receptor complex

In this study, we report the use of coiled-coil (leucine zipper) molecular recognition for the solution assembly of stable, high affinity, heteromeric interleukin-2 receptor complexes. Co-expression of interleukin-2 receptor alpha and beta extracellular domains (ectodomains), each fused to seven coiled-coil heptad repeats, resulted in the formation of heteromeric complexes that bound interleukin-2 in a cooperative fashion and with much higher affinity than similar homomeric complexes. The dissociation constants for these solution complexes are within the range of values reported for the comparable cell surface "pseudo high affinity" interleukin-2 receptor. Ligand-induced cross-linking of homomeric or heteromeric receptor subunits is the common signal transmission mechanism employed by hematopoietin receptors. Individual receptor ectodomains, however, often do not bind ligand with measurable affinity. This is the first study to demonstrate the feasibility of coiled-coil mediated preassembly of cytokine receptor complexes.

Lymphocytic choriomeningitis virus infection is associated with long-standing perturbation of LFA-1 expression on CD8+ T cells

Flow cytometric analysis of splenocytes from mice infected with lymphocytic choriomeningitis virus revealed marked and long-standing up-regulation of LFA-1 expression on CD8+, but not on CD4+ T cells. Appearance of CD8+ T cells with a changed expression of adhesion molecules reflected polyclonal activation and expansion which was demonstrated not to depend on CD4+ T cells or their products. Cell sorting experiments defined virus-specific CTL to be included in this population (LFA-1hiMEL-14lo), but since about 80% of splenic CD8+ T cells have a changed phenotype, extensive bystander activation must take place; this is indicated also by the finding that CD8+LFA-1hi cells transiently express several markers of cellular activation, e.g. transferrin receptor, IL-2R alpha and beta. Analysis of cells from the cerebrospinal fluid of mice infected intracerebrally showed that virtually all T cells present belonged to the CD8+LFA-1hi subset and, correspondingly, the ligand ICAM-1 was found to be up-regulated on endothelial cells in the inflamed meninges. Preincubation of LCMV-primed donor splenocytes with anti-LFA-1 markedly inhibited the transfer of virus-specific delayed-type hypersensitivity to naive recipients. Together, these findings indicate that up-regulation of LFA-1 expression is a critical factor involved in directing activated CD8+ T cells to sites of viral infection.

Deregulated T cell activation and autoimmunity in mice lacking interleukin-2 receptor beta

In mice lacking the interleukin-2 receptor beta chain (IL-2R beta), T cells were shown to be spontaneously activated, resulting in exhaustive differentiation of B cells into plasma cells and the appearance of high serum concentrations of immunoglobulins G1 and E as well as autoantibodies that cause hemolytic anemia. Marked infiltrative granulocytopoiesis was also apparent, and the animals died after about 12 weeks. Depletion of CD4+ T cells in mutant mice rescued B cells without reversion of granulocyte abnormalities. T cells did not proliferate in response to polyclonal activators, nor could antigen-specific immune responses be elicited. Thus, IL-2R beta is required to keep the activation programs of T cells under control, to maintain homeostasis, and to prevent autoimmunity.

Activation of Stat5 by interleukin 2 requires a carboxyl-terminal region of the interleukin 2 receptor beta chain but is not essential for the proliferative signal transmission

The high-affinity interleukin 2 (IL-2) receptor (IL-2R) consists of three subunits: the IL-2R alpha, IL-2R beta c, and IL-2R gamma c chains. Two members of the Janus kinase family, Jak1 and Jak3, are associated with IL-2R beta c and IL-2R gamma c, respectively, and they are activated upon IL-2 stimulation. The cytokine-mediated Jak kinase activation usually results in the activation of a family of latent transcription factors termed Stat (signal transducer and activator of transcription) proteins. Recently, the IL-2-induced Stat protein was purified from human lymphocytes and found to be the homologue of sheep Stat5/mammary gland factor. We demonstrate that the human Stat5 is activated by IL-2 and that Jak3 is required for the efficient activation. The cytoplasmic region of the IL-2R beta c chain required for activation of Stat5 is mapped within the carboxyl-terminal 147 amino acids. On the other hand, this region is not essential for IL-2-induced cell proliferation.

Isolation of two new members of the NF-AT gene family and functional characterization of the NF-AT proteins

The activation of cytokine genes in response to antigenic stimulation of T cells is mediated by NF-AT proteins. Previous studies have identified two NF-AT proteins, NF-ATp and NF-ATc, that are homologous within a 290 aa domain distantly related to the Rel domain. We have isolated two additional members of this gene family, NF-AT3 and NF-AT4, which encode proteins 65% identical to the other NF-AT proteins within the Rel domain. The four NF-AT genes are transcribed in different sets of tissues that included many sites of expression outside the immune system. The Rel homology domain is sufficient for DNA recognition and cooperative binding interactions with AP-1. Although other members of the Rel family bind DNA as dimers, NF-AT proteins are monomers in solution or bound to DNA. Transfection assays indicate that each of the four NF-AT proteins can activate the IL-2 promoter in T cells.

Interleukin-2 secretion by human B lymphocytes occurs as a late event and requires additional stimulation after CD40 cross-linking

While Epstein-Barr virus (EBV)-immortalized B cell lines have been shown to secrete interleukin (IL)-2 after stimulation with either teleocidin or phorbol myristate acetate (PMA) and ionomycin, experimental conditions leading to IL-2 production by normal human B cells have not been reported. In the present study we investigated various B cell activating conditions, including--by analogy to EBV-immortalized B lymphocytes--stimulation of B cells that are already proliferating (in cultures with IL-4 and immobilized anti-CD40 monoclonal antibody; the anti-CD40 system). This approach showed that B lymphocytes secreted IL-2 in the culture medium, but only if they were first activated for more than 24 h in the anti-CD40 system before exposure to PMA plus ionomycin. The production rate of IL-2 by B lymphocytes reached a maximum after 6 days of priming in such cultures followed by 48 h of stimulation with PMA plus ionomycin, corresponding to 7% or 15% of that of fresh CD4+ T cells activated, respectively, with phytohemagglutinin plus PMA, or with PMA plus ionomycin for 48 h. This IL-2 production could not be attributed to T cell contamination nor to EBV-infected B cells according to flow cytometric and reverse transcriptase-polymerase chain reaction analysis of cultured B cells. Lower IL-2 expression (detected only as mRNA synthesis) was also induced in the cultured B lymphocytes after incubation with cross-linking anti-IgM antibodies instead of PMA plus ionomycin. The appearance of IL-13 mRNA, but not IL-4 mRNA, was detected under the same stimulation conditions as for IL-2 mRNA. These results show that the production of IL-2 by normal B lymphocytes occurs as a late event relative to their activation and proliferation, and is in this respect subject to regulation different to that found in T lymphocytes.

Cytokine signaling through nonreceptor protein tyrosine kinases

Cytokines are a family of soluble mediators of cell-to-cell communication that includes interleukins, interferons, and colony-stimulating factors. The characteristic features of cytokines lie in their functional redundancy and pleiotropy. Most of the cytokine receptors that constitute distinct superfamilies do not possess intrinsic protein tyrosine kinase (PTK) domains, yet receptor stimulation usually invokes rapid tyrosine phosphorylation of intracellular proteins, including the receptors themselves. It is now clear that these receptors are capable of recruiting or activating (or both) a variety of nonreceptor PTKs to induce downstream signaling pathways. Thus, the intracytoplasmic structure of cytokine receptors has evolved so as to allow the combined action of different PTK family members expressed in different cell types, which may ultimately determine the activity of cytokines.

The effect of in vivo IL-7 deprivation on T cell maturation

A number of previous studies have suggested a key role for interleukin 7 (IL-7) in the maturation of T lymphocytes. To better assess the function of IL-7 in lymphopoiesis, we have deprived mice of IL-7 in vivo by long-term administration of a neutralizing anti-IL-7 antibody. In a previous report (Grabstein, K. H., T. J. Waldschmidt, F. D. Finkelman, B. W. Hess, A. R. Alpert, N. E. Boiani, A. E. Namen, and P. J. Morrissey. 1993. J. Exp. Med. 178:257-264), we used this system to demonstrate the critical role of IL-7 in B cell maturation. After a brief period of anti-IL-7 treatment, most of the pro-B cells and all of the pre-B and immature B cells were depleted from the bone marrow. In the present report, we have injected anti-IL-7 antibody for periods of up to 12 wk to determine the effect of in vivo IL-7 deprivation on the thymus. The results demonstrate a > 99% reduction in thymic cellularity after extended periods of antibody administration. Examination of thymic CD4- and CD8- defined subsets revealed that, on a proportional basis, the CD4+, CD8+ subset was most depleted, the CD4 and CD8 single positive cells remained essentially unchanged, and the CD4-, CD8- compartment actually increased to approximately 50% of the thymus. Further examination of the double negative thymocytes demonstrated that IL-7 deprivation did, indeed, deplete the CD3-, CD4-, CD8- precursors, with expansion of this subset being interupted at the CD44+, CD25+ stage. The proportional increase in the CD4-, CD8- compartment was found to be due to an accumulation of CD3+, T cell receptor alpha, beta + double negative T cells. Additional analysis revealed that anti-IL-7 treatment suppressed the audition/selection process of T cells, as shown by a significant reduction of single positive cells expressing CD69 and heat stable antigen. Finally, the effects of IL-7 deprivation on the thymus were found to be reversible, with a normal pattern of thymic subsets returning 4 wk after cessation of treatment. The present results thus indicate a central role for IL-7 in the maturation of thymic-derived T cells.

Pathways from hematopoietic stem cells to thymocytes

A long-standing debate has been whether commitment to the T cell lineage occurs exclusively following thymus colonization, or whether prethymic T lineage restricted progenitors exist. Recently, the analysis of murine fetal blood for the presence of hematopoietic progenitor cells has led to the identification of a T lineage committed precursor population (designated prothymocytes). Fetal blood prothymocytes lack multipotent progenitor potential as shown by the fact that they fail to reconstitute B lymphocyte, myeloid and erythroid lineages. In addition to prothymocytes, fetal blood also contains a phenotypically distinct, pluripotent progenitor population which can reconstitute both T and B lymphocytes as well as myeloid and erythroid lineages. The identification of a circulating, T lineage restricted precursor population, which is also found in the blood of fetal athymic mice, provides strong evidence that T lineage commitment can precede thymus colonization. The thymus is not, however, exclusively colonized by prothymocytes. Under appropriate developmental conditions, multipotent precursor activity for non-T lineages such as B lymphocytes and thymic dendritic cells can be revealed within the intrathymic precursor pool. Moreover, evidence has been accumulated for a common progenitor for T cells and natural killer cells which may be distinct from multipotent intrathymic progenitors.

IL-2 signaling: recruitment and activation of multiple protein tyrosine kinases by the components of the IL-2 receptor

Cytokine receptors transduce signals to the cell interior upon binding of their cognate ligands, eventually leading to cellular responses such as cellular proliferation, differentiation and other effector functions. Most of the cytokine receptors, including the interleukin (IL)-2 receptor, consist of two or more distinct subunits, yet none possess any known catalytic activity such as protein tyrosine kinase activity. Significant advances have recently been made in identifying the multiple signaling molecules, including protein tyrosine kinases, that couple with the cytoplasmic regions of the IL-2 receptor, although their exact roles in cytokine signaling are still not fully understood. Another important development in the understanding of IL-2 signaling is the identification of the target genes, including nuclear proto-oncogenes. Furthermore, structure-function analyses of the components of the IL-2 receptor have enabled the dissection of multiple intracellular signaling pathways that lead to the induction of the respective target genes.

Biosynthetic and glycosylation events of the IL-6 receptor beta-subunit, gp130

It is now recognized that the beta-subunit of the interleukin-6 (IL-6) receptor, also known as gp130, is a common signal transducer shared by other cytokines, including ciliary neurotrophic factor, leukemia inhibitor factor, oncostatin M, and IL-11. In this study, the biosynthesis and glycosylation of hepatic gp130 were investigated using a specific polyclonal antibody to the 287 amino acid cytoplasmic domain of gp130. Immunoprecipitation and metabolic labeling experiments demonstrate, in addition to a mature surface expressed gp130, the presence of a major immature form of the molecule within the cell. The immature form can shift to become a functional gp130 only after being terminally glycosylated. The kinetics of gp130 maturation and surface expression were determined. When both forms of gp130 are deglycosylated the resulting core peptides migrate to identical positions in a denatured protein gel, indicating that the principal difference between the two forms resides in the extent of their glycosylation. IL-6 and other members of this cytokine family activate only the mature form, demonstrating its location at the membrane surface. Protein and mRNA turnover studies reveal gp130 to be a stable, slowly renewing population under nonstimulated conditions. These findings provide novel information on the intracellular events leading to the expression of this critically important signal transducing protein.

Endocytosis of interleukin 2 receptors in human T lymphocytes: distinct intracellular localization and fate of the receptor alpha, beta, and gamma chains

Members of the cytokine receptor family are composed of several noncovalently linked chains with sequence and structure homologies in their extracellular domain. Receptor subfamily members share at least one component: thus the receptors for interleukin (IL) 2 and IL15 have common beta and gamma chains, while those for IL2, 4, 7, and 9 have a common gamma chain. The intracellular pathway followed by IL2 receptors after ligand binding and endocytosis was analyzed by immunofluorescence and confocal microscopy in a human T lymphocytic cell line. Surprisingly, the alpha, beta, and gamma chains had different intracellular localizations after being endocytosed together. The alpha chain was always in transferrin-positive compartments (early/recycling endosomes), both at early and late internalization times, but was never detected in rab7-positive compartments (late endosomes). On the other hand, at late internalization times, the beta and gamma chains were excluded from transferrin-positive organelles and did not colocalize with alpha. Furthermore, beta could be found in rab7-positive vesicles. These differences suggest that the alpha chain recycles to the plasma membrane, while the beta and gamma chains are sorted towards the degradation pathway. The half-lives of these three chains on the cell surface also reflect their different intracellular fates after endocytosis. The beta and gamma chains are very short-lived polypeptides since their half-life on the surface is only approximately 1 h, whereas alpha is a much more stable surface protein. This shows for the first time that components of a multimeric receptor can be sorted separately along the endocytic pathway.

Direct evidence of a heterotrimeric complex of human interleukin-4 with its receptors

The mode of binding of interleukin-4 (IL-4) to its two known receptors, specific receptor IL-4R and a shared receptor gamma c, was investigated using gel filtration and gel electrophoresis. A ternary complex between IL-4 and the soluble domains of the two receptors was shown to exist in solution. The association constant between gamma c and the stable complex of IL-4/sIL-4R is in the millimolar range, making the ternary complex a feasible target for crystallization studies.

Chemoattraction of human blood T lymphocytes by interleukin-15

Recombinant interleukin (IL)-15, derived from a simian kidney epithelial cell line, is a chemoattractant for human blood T lymphocytes judged by its ability to increase the proportion of cells in polarized morphology, to stimulate invasion of collagen gels containing IL-15, and to increase the proportion of locomotor cells observed by time-lapse videorecording. The ability of lymphocytes to respond was partly, but not completely, inhibited by pretreatment with anti-IL-2 receptor beta-chain. The activity of IL-15 was completely abolished by preincubation with aIL-15 but unaffected by preincubation with aIL-2. No response of monocytes, neutrophils, or B lymphocytes to IL-15 was observed.

Insights into lymphocyte development from X-linked immune deficiencies

The genetic immune deficiencies have drawn the attention of physicians and immunologists for more than 40 years. The selectivity of these deficiencies brings into focus the contribution of the response of each arm of the immune system to specific pathogens. Recently, the genes underlying four X-linked defects in immune development in humans have been identified by either positional cloning or candidate-gene cloning techniques. Remarkably, these genetic defects reveal a microcosm of lymphocyte developmental controls involving cell-cell interactions, combinatorial cell surface receptor specificity and lineage-specific signal transduction.

Host response to Sendai virus in mice lacking class II major histocompatibility complex glycoproteins

The development of Sendai virus-specific cytotoxic T-lymphocyte (CTL) effectors and precursors (CTLp) has been compared for mice that are homozygous (-/-) for a disruption of the H-2I-Ab class II major histocompatibility complex glycoprotein and for normal (+/+) controls. The generation of CD8+ CTLp was not diminished in the -/- mice, though they failed to make virus-specific immunoglobulin G class antibodies. While the cellularity of the regional lymph nodes was decreased, the inflammatory process assayed by bronchoalveolar lavage (BAL) of the pneumonic lung was not modified, and potent CTL effectors were present in BAL populations recovered from both groups at day 10 after infection. There was little effect on virus clearance. Production of interleukin-2 by both freshly isolated BAL inflammatory cells and cultured lymph node cells was greatly diminished, though the -/- mice still made substantial levels of gamma interferon. However, treating the mice with a single dose of a monoclonal antibody to this cytokine, at least some of which is made by CD8+ T cells, did not decrease CTLp frequencies. As found previously with CD4-depleted H-2b mice, the development of Sendai virus-specific CD8+ T-cell-mediated immunity is not compromised by the absence of a concurrent class II major histocompatibility complex-restricted response.

Chromosomal assignment and genomic structure of Il15

Interleukin-15 (IL-15) is a novel cytokine whose effects on T-cell activation and proliferation are similar to those of interleukin-2 (IL-2), presumably because IL-15 utilizes the beta and gamma chains of the IL-2 receptor. Murine IL-15 cDNA and genomic clones were isolated and characterized. The murine Il15 gene was found to consist of eight exons spanning at least 34 kb and was localized to the central region of mouse chromosome 8 by interspecific backcross analysis. Intron positions in a partial human IL15 genomic clone were identical with positions of corresponding introns in the murine gene. The human IL15 gene was mapped to human chromosome 4q31 by fluorescence in situ hybridization.