Induction of mouse p55 interleukin-2 receptor gene expression by IL-2 and IL-4 and characterization of its transcription initiation sites

IL-4 potentiates activated T cell apoptosis via an IL-2-dependent mechanism

Activation-induced cell death (AICD) of T cells is one of the major mechanisms of peripheral tolerance. The regulation of AICD by IL-4 is poorly understood. In this study, we report that AICD in IL-4-deficient T cells is significantly reduced compared with that in wild-type T cells. This impaired AICD correlates with the failure to induce degradation of cellular FLIP. IL-4-mediated enhancement of AICD and cellular FLIP degradation requires a Janus kinase/STAT-6 signaling pathway. Unexpectedly, these effects of IL-4 could be blocked by a neutralizing anti-IL-2 Ab, and addition of rIL-2 could completely restore the defective AICD in IL-4-deficient T cells. Furthermore, IL-4 regulates the T cell thresholds for IL-2 signaling during AICD. These data suggest that IL-4 promotes AICD via an IL-2-dependent mechanism.

Signaling domains of the interleukin 2 receptor

Interleukin (IL-)2 and its receptor (IL-2R) constitute one of the most extensively studied cytokine receptor systems. IL-2 is produced primarily by activated T cells and is involved in early T cell activation as well as in maintaining homeostatic immune responses that prevent autoimmunity. This review focuses on molecular signaling pathways triggered by the IL-2/IL-2R complex, with an emphasis on how the IL-2R physically translates its interaction with IL-2 into a coherent biological outcome. The IL-2R is composed of three subunits, IL-2Ralpha, IL-2Rbeta and gammac. Although IL-2Ralpha is an important affinity modulator that is essential for proper responses in vivo, it does not contribute to signaling due a short cytoplasmic tail. In contrast, IL-2Rbeta and gammac together are necessary and sufficient for effective signal transduction, and they serve physically to connect the receptor complex to cytoplasmic signaling intermediates. Despite an absolute requirement for gammac in signaling, the majority of known pathways physically link to the receptor via IL-2Rbeta, generally through phosphorylated cytoplasmic tyrosine residues. This review highlights work performed both in cultured cells and in vivo that defines the functional contributions of specific receptor subdomains-and, by inference, the specific signaling pathways that they activate-to IL-2-dependent biological activities.

Heterogeneous effects of IL-2 on collagen-induced arthritis

IL-2 is generally considered a pro-inflammatory cytokine that exacerbates Th1-mediated disease states, such as autoimmune arthritis. Consistent with this role for IL-2, recent studies from our laboratory demonstrate that IL-2 mRNA is markedly increased during the acute stage of collagen-induced arthritis (CIA), an animal model of rheumatoid arthritis. To further define the role of IL-2 in CIA, the levels of IL-2 protein and its receptor and the effects of IL-2 administration were analyzed during CIA. IL-2 protein and IL-2R were preferentially expressed at disease onset, compared with later stages of disease. Administration of recombinant human IL-2 (rhIL-2) at, or just before, disease onset exacerbated disease; surprisingly, rhIL-2 given before disease onset inhibited CIA, associated with reduced cellular and humoral responses to type II collagen. Determination of in vivo serum levels of Th1 and Th2 cytokines in response to rhIL-2 treatment demonstrated that IFN-gamma, but not IL-4, was markedly up-regulated in response to IL-2. In mice treated with anti-IFN-gamma Ab, both early and late IL-2 administration exacerbated CIA. Thus, IL-2 can have two opposite effects on autoimmune arthritis, a direct stimulatory effect and an indirect suppressive effect that is mediated by IFN-gamma.

IL-2 Receptor α-Chain Expression Is Independently Regulated in Primary and Secondary Lymphoid Organs

The IL-2R is composed of three chains: IL-2Rα, IL-2Rβ, and IL-2Rγ. In mice, IL-2Rα is critical and determines IL-2 binding to the tripartite IL-2R complex. To extend our previous studies, which demonstrated that IL-2 regulates IL-2Rα expression in vitro, we have analyzed expression in IL-2-deficient mice in vivo. As in control animals, CD4−CD8− thymocytes and bone marrow-derived B220+ pre-B cells were Il-2Rα positive. In contrast, activated lymph node and splenic CD4 T cells (CD4+CD69+) were found to be IL-2Rα negative, whereas ∼20% of the same cell populations from the MLR/lpr strain, which also accumulate large numbers of CD4-activated T cells in the presence of intact IL-2, retained expression. A similar pattern of IL-2Rα expression was found among splenic CD8 cells from IL-2−/− and IL-2+/− animals. These findings demonstrate that in primary lymphoid organs, IL-2 is not directly involved in IL-2Rα expression. However, at the level of mature lymphocytes, and more specifically CD4 T cells, IL-2 remains in vivo, as in vitro, the most critical cytokine controlling both IL-2Rα expression and sensitivity to IL-2.

Lack of intermediate-affinity interleukin-2 receptor in mice leads to dependence on interleukin-2 receptor alpha, beta and gamma chain expression for T cell growth

An interleukin (IL)-4 dependent mouse T cell clone 8.2 derived from an IL-2-dependent T cell line was characterized. As measured by flow cytometric analysis and Northern blotting, it expresses IL-2 receptor beta (IL-2R beta) and gamma (IL-2R gamma) chains, but has lost expression of IL-2 receptor alpha chain (IL-2R alpha). To investigate the properties of the mouse IL-2R beta gamma complex and the role of IL-2R alpha gene expression, this clone was further studied. T cell clone 8.2 has lost the capacity to bind 125I-labeled human IL-2 under experimental conditions able to detect intermediate-affinity IL-2R in human cells. Mouse IL-2 is unable to block the binding of mAb TM beta 1 to 8.2 cells. Under the same experimental conditions, mouse IL-2 blocks the binding of TM beta 1 to C30-1 cells expressing the IL-2 alpha beta gamma complex. Since TM beta 1 recognizes an epitope related to the IL-2 binding site of IL-2R beta, these results can be taken as a demonstration that mouse IL-2R beta gamma does not bind mouse IL-2. Furthermore, T cell clone 8.2 does not proliferate in response to recombinant mouse or human IL-2. On the other hand, T cell transfectant lines expressing heterospecific receptors made of the human IL-2R beta and mouse IL-2R gamma chains bind 125I-labeled human IL-2 and proliferate in response to IL-2. This establishes the difference between mouse and human IL-2R beta chains. Transfection of T cell clone 8.2 with human IL-2R alpha genes restores their capacity to proliferate in response to IL-2. In addition, all transfectants grown in IL-2 express the endogeneous mouse IL-2R alpha chain. When grown in IL-4, the endogeneous mouse IL-2R alpha gene remains silent in all these transfectants. These results show that, contrary to the human, the mouse does not express an intermediate-affinity IL-2R. Expression of the IL-2R alpha gene is therefore required for the formation of the functional IL-2R in mice.

Characterization of a monoclonal antibody directed against the NH2 terminal area of interleukin-2 (IL-2) and inhibiting specifically the binding of IL-2 to IL-2 receptor beta chain (IL-2R beta)

An anti-human IL-2 mAb (19B11/beta) was found to selectively block the binding of IL-2 to TS1 beta cells expressing the interleukin-2 receptor beta (IL-2R beta) without affecting binding to TS1 alpha cells expressing the IL-2R alpha receptor. It also specifically inhibits the IL-2 driven cell proliferation in TS1 beta cells. These observations have lead to the hypothesis that its epitope is related to an IL-2 area involved in binding with IL-2R beta chain. This epitope was identified using various peptides covering the N-terminal half (including alpha helix A) of the 133 amino acids of IL-2. MAb 19B11/beta does not recognize peptides 30-54 and 44-54 but recognizes peptides 1-22 and 1-30 with a good affinity. Furthermore, threonine in position no. 3 was found to be critical for the binding of mAb 19B11/beta. A relationship between the epitope of mAb 19B11/beta and the glycosylation of the IL-2 molecule was observed. This further demonstrates that the NH2 terminal area of IL-2 is critical for IL-2/IL-2R beta interactions. Two other mAbs were studied during the course of this work. They served as control for the study of mAb 19B11/beta and provide some additional insight concerning the question of IL-2/IL-2R structure-function. MAb 16F11/alpha selectively blocks the IL-2 binding to TS1 alpha cells. The epitope of mAb 16F11 is conformational and it was not possible to study the corresponding IL-2/IL-2R alpha region of interaction. Epitope of mAb 3H9 is localized between residues 30 and 54 and does not affect the binding of IL-2 to IL-2R alpha.

Mouse interleukin-2 receptor alpha gene expression. Interleukin-1 and interleukin-2 control transcription via distinct cis-acting elements

We have shown that interleukin-1 (IL-1) and IL-2 control IL-2 receptor alpha (IL-2R alpha) gene transcription in CD4-CD8- murine T lymphocyte precursors. Here we map the cis-acting elements that mediate interleukin responsiveness of the mouse IL-2R alpha gene using a thymic lymphoma-derived hybridoma (PC60). The transcriptional response of the IL-2R alpha gene to stimulation by IL-1 + IL-2 is biphasic. IL-1 induces a rapid, protein synthesis-independent appearance of IL-2R alpha mRNA that is blocked by inhibitors of NF-kappa B activation. It also primes cells to become IL-2 responsive and thereby prepares the second phase, in which IL-2 induces a 100-fold further increase in IL-2R alpha transcripts. Transient transfection experiments show that several elements in the promoter-proximal region of the IL-2R alpha gene contribute to IL-1 responsiveness, most importantly an NF-kappa B site conserved in the human and mouse gene. IL-2 responsiveness, on the other hand, depends on a 78-nucleotide segment 1.3 kilobases upstream of the major transcription start site. This segment functions as an IL-2-inducible enhancer and lies within a region that becomes DNase I hypersensitive in normal T cells in which IL-2R alpha expression has been induced. IL-2 responsiveness requires three distinct elements within the enhancer. Two of these are potential binding sites for STAT proteins.

Cytokine production and responsiveness of fetal T-cell receptor V gamma 3 thymocytes

The aim of this study was to examine the cytokine production and cytokine responsiveness of the first T-cell receptor (TcR) positive cells that appear in the murine fetal thymus, namely TcR V gamma 3 cells. It is shown that IL-2-cultured fetal TcR V gamma 3 thymocytes were capable of producing IL-3, GM-CSF, TNF-alpha and IFN-gamma upon TcR triggering. IL-2, IL-4, IL-5 and IL-6 could not be detected. With regard to cytokine responsiveness, TcR V gamma 3 cells proliferated to a high extent when high concentrations of rIL-2 were added. rIL-4 or rIL-7 alone, but not rIL-1 alone, were capable of inducing a modest proliferation of TcR V gamma 3 thymocytes. When combined with low concentrations of IL-2, a synergistic effect could be observed with IL-1, IL-4 or IL-7. It is shown that the synergistic effect of IL-2 with IL-4 was mainly due to induction of IL-2 receptor expression. The synergistic effect of IL-2 and IL-7 on the proliferation of TcR V gamma 3 cells could only be partially inhibited by anti-IL-2 receptor MoAb, and this antibody had no effect on the IL-2 + IL-1 cultures. These observations can explain the extensive proliferation of TcR V gamma 3 thymocytes during fetal life and they indicate that TcR V gamma 3 thymocytes have the potential to play a functional role during fetal thymus development.

Molecular area involved in the in-vitro dimerization of the murine p55 IL-2 receptor

In order to study structure-function relationships of the M(r) 55,000 subunit of the murine IL-2R (p55 IL-2R) by epitope mapping, we have expressed the p55 IL-2R molecule in a cell-free translation system. Under these in vitro conditions, we detected the expected p55 IL-2R polypeptide initiated at Met 1 and, in addition, two internally initiated molecules at Met 64 and Met 105. In this report we describe that from such a mixture, containing three molecular species of p55 IL-2R, mAb 135D5 immunoprecipitated the polypeptide initiated at Met 105 although this N-terminally truncated form of p55 IL-2R does not contain its epitope located between amino acids 72-88. This observation can be taken as a further evidence for the formation of p55 IL-2R dimers. Finally, we identified the region implicated in the formation of p55 IL-2R dimers close to the transmembrane region of the molecule.