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

Signaling mechanisms through cytokine receptors that share signal transducing receptor components

Most of the receptors for soluble factors functioning in immune and hematopoietic systems belong to the cytokine receptor family. These receptors often share common signal transducing receptor components with other members of the same family. Such receptors and signal transducers possess no intrinsic tyrosine kinase domain but have recently been found to be associated with members of a JAK family of cytoplasmic tyrosine kinases. The JAK kinases become activated after ligand-induced dimerization of the receptor components. This activation appears to link the cell surface receptors to the nuclear genes through tyrosine phosphorylation and activation of latent cytoplasmic transcription factors called signal transducers and activators of transcription (STATs).

Four-helix bundle growth factors and their receptors: protein-protein interactions

Many growth factors and cytokines promote receptor clustering on binding. At least three different protein-protein interaction sites are involved: cytokine-receptor I, cytokine-receptor II and receptor I-receptor II. Although structural data on these complexes are limited, recent structural and mutagenesis studies of the four-helix bundle class of cytokines are clarifying the nature of the complexes formed.

Partial inhibition of Theileria parva-infected T-cell proliferation by antisense IL2R alpha-chain RNA expression

Antisense RNA expression was used to assess the role of the interleukin 2 receptor (IL2R) alpha-chain in proliferation of T cells transformed by infection with the intracellular parasite Theileria parva. Two vectors were constructed, in which part of the bovine IL2R alpha-chain cDNA was inserted in either a sense or antisense orientation in the plasmid pHS1-CAT, which is expressed by induction of the human metallothionein IIA (hMT-IIA) with cadmium (Cd2+). A T. parva-infected T-cell line, TpM(803), known to express the IL2 and IL2R genes in a constitutive way, was permanently transfected with one of the two constructs, and the effect of antisense IL2R alpha-chain RNA expression upon proliferation of TpM(803) cells was tested. Antisense-transfected TpM(803) cells grew much more slowly than sense-transfected cells even in the absence of added Cd2+, but the addition of Cd2+ to the culture medium resulted in further inhibition. A strong reduction in IL2R alpha-chain mRNA was observed in antisense but not in sense-transfected cells. These observations confirm a role for the IL2R alpha-chain in proliferation of T. parva-infected TpM(803) cells.

Interleukin-15 and the growth of tumor derived activated T-cells

Interleukin-15 was tested to determine whether this recently discovered cytokine was capable of stimulating the growth of tumor derived activated T cells in culture (TDAC, also referred to as tumor infiltrating lymphocytes). When established cultures of IL-2 induced, IL-2 dependent TDAC were tested, IL-15 stimulated growth in a dose dependent manner, alone or in the presence of IL-2. One established TDAC was cultured with IL-15 alone for 18 passages over a 10 week period. Comparing IL-2 and IL-15 treated cultures, growth rate with IL-15 was slower. IL-15 doubled the secreted interferon alpha and granulocyte-macrophage colony stimulating factor. IL-15 and IL-2 were compared in primary TDAC cultures. IL-15 induced TDAC outgrowth in 3 of 6 cultures. IL-2 induced outgrowth in all 6. Tumor cells were eliminated as TDAC grew out in both IL-2 and IL-15 treated cultures. These results suggested that IL-15 like IL-2, is capable of stimulating the growth of TDAC with antitumor activity, but with certain distinct effects which may be of interest therapeutically.

Murine B cell development: commitment and progression from multipotential progenitors to mature B lymphocytes

B lymphocytes, the cellular source of antibody, are critical components of the immune response. They develop from multipotential stem cells, progressively acquiring the traits that allow them to function as mature B lymphocytes. This developmental program is dependent on appropriate interactions with the surrounding environment. These interactions, mediated by cell-cell and cell-matrix interactions, provide the growth and differentiation signals that promote progression along the developmental pathway. This chapter addresses the properties of developing B lineage cells and the nature of the environmental signals that support B lineage progression.

T lymphocyte-mediated antiviral immune responses in mice are diminished by treatment with monoclonal antibody directed against the interleukin-2 receptor

Blocking the interleukin-2 receptor's alpha-chain in lymphocytic choriomeningitis virus-infected mice by treatment with monoclonal antibodies diminished the increase of numbers of CD8+ T lymphocytes in spleens and prevented CD8+ T lymphocyte-mediated virus clearance from organs as well as generation of virus-specific cytotoxic T lymphocytes. Also, the CD8+ T cell-mediated early phase of the delayed-type hypersensitivity footpad swelling reaction was decreased. The same treatment had no effect on the number of CD4+ spleen T lymphocytes, which, however, did not enlarge during infection, but these cells' heightened DNA synthesis and cytokine production were reduced by antibody treatment; yet the generation of antiviral antibodies remained unaffected, and the CD4+ T lymphocyte-mediated second part of the footpad reaction was somewhat augmented. We conclude that blocking of the interleukin-2 receptor by antibody in lymphocytic choriomeningitis virus-infected mice diminishes both CD8+ and CD4+ T cell-mediated antiviral immune responses, the former more than the latter.

Prevention of T cell anergy by signaling through the gamma c chain of the IL-2 receptor

When stimulated through their antigen receptor without requisite costimulation, T cells enter a state of antigen-specific unresponsiveness termed anergy. In this study, signaling through the common gamma chain of the interleukin-2 (IL-2), IL-4, and IL-7 receptors in the presence of antigen was found to be sufficient to prevent the induction of anergy. After culture with IL-2, IL-4, or IL-7, Jak3 kinase was tyrosine-phosphorylated, which correlated with the prevention of anergy. Therefore, a signal through the common gamma chain may regulate the decision of T cells to either clonally expand or enter a state of anergy.

Erythropoietin and interleukin-2 activate distinct JAK kinase family members

The erythropoietin (EPO) receptor and the interleukin-2 (IL-2) receptor beta-chain subunit are members of the cytokine receptor superfamily. They have conserved primary amino acid sequences in their cytoplasmic domains and activate phosphorylation of common substrates, suggesting common biochemical signaling mechanisms. We have generated a cell line, CTLL-EPO-R, that contains functional cell surface receptors for both EPO and IL-2. CTLL-EPO-R cells demonstrated similar growth kinetics in EPO and IL-2. Stimulation with EPO resulted in the rapid, dose-dependent tyrosine phosphorylation of JAK2. In contrast, stimulation with IL-2 or the related cytokine IL-4 resulted in the rapid, dose-dependent tyrosine phosphorylation of JAK1 and an additional 116-kDa protein. This 116-kDa protein was itself immunoreactive with a polyclonal antiserum raised against JAK2 and appears to be a novel member of the JAK kinase family. Immune complex kinase assays confirmed that IL-2 and IL-4 activated JAK1 and EPO activated JAK2. These results demonstrate that multiple biochemical pathways are capable of conferring a mitogenic signal in CTLL-EPO-R cells and that the EPO and IL-2 receptors interact with distinct JAK kinase family members within the same cellular background.

Interleukin-12 regulates the proliferation of Th1, but not Th2 or Th0, clones

Our results indicate that interleukin (IL)-12 is an important costimulator of antigen-dependent proliferation of murine Th1 clones. In addition, we demonstrate that IL-10 inhibits splenic antigen-presenting cell (APC)-dependent proliferation of Th1 clones, at least in part, via down-regulation of APC-derived IL-12. Moreover, the failure of activated B cells to provide costimulation via IL-12 accounts for their inability to support optimal proliferative responses of Th1 clones. We also show that IL-12 regulates the ability of Th1 clones to respond to IL-4 and enhances their proliferation in response to IL-2, IL-7, or IL-15. In contrast, Th2 and Th0 clones appear refractory to the effects of IL-12, on antigen-dependent or growth factor-induced proliferation.

Interleukin (IL) 15 is a novel cytokine that activates human natural killer cells via components of the IL-2 receptor

Interleukin 15 (IL-15) is a novel cytokine that has recently been cloned and expressed. Whereas it has no sequence homology with IL-2, IL-15 interacts with components of the IL-2 receptor (IL-2R). In the present study we performed a functional analysis of recombinant IL-15 on phenotypically and functionally distinct populations of highly purified human natural killer (NK) cells. The CD56bright subset of human NK cells constitutively expresses the high affinity IL-2R and exhibits a brisk proliferative response after the binding of picomolar amounts of IL-2. Using a proliferation assay, IL-15 demonstrated a very steep dose-response curve that was distinct from the dose-response curve for IL-2. The proliferative effects of IL-15 could be abrogated by anti-IL-2R beta (p75), but not by anti-IL-2R alpha (p55). The proliferative effects of IL-2 on CD56bright NK cells could be inhibited by both antibodies. CD56dim NK cells express the intermediate affinity IL-2R in the absence of the high affinity IL-2R. Activation of CD56dim NK cells by IL-15 was similar to that of IL-2 as measured by enhanced NK cytotoxic activity, antibody-dependent cellular cytotoxicity, and NK cell production of interferon gamma, tumor necrosis factor alpha, and granulocyte/macrophage colony-stimulating factor. The IL-15-enhanced NK cytotoxic activity could be completely blocked by anti-IL-2R beta monoclonal antibody. The binding of radiolabeled IL-2 and IL-15 to CD56dim NK cells was inhibited in the presence of anti-IL-2R beta. Scatchard analysis of radiolabeled IL-15 and IL-2 binding to NK-enriched human lymphocytes revealed the presence of high and intermediate affinity receptors for both ligands. IL-15 is a ligand that activates human NK cells through components of the IL-2R in a pattern that is similar but not identical to that of IL-2. Unlike IL-2, IL-15 is produced by activated monocytes/macrophages. The discovery of IL-15 may increase our understanding of how monocytes/macrophages participate in the regulation of NK cell function.

Erythropoietin and interleukin-2 activate distinct JAK kinase family members

The erythropoietin (EPO) receptor and the interleukin-2 (IL-2) receptor beta-chain subunit are members of the cytokine receptor superfamily. They have conserved primary amino acid sequences in their cytoplasmic domains and activate phosphorylation of common substrates, suggesting common biochemical signaling mechanisms. We have generated a cell line, CTLL-EPO-R, that contains functional cell surface receptors for both EPO and IL-2. CTLL-EPO-R cells demonstrated similar growth kinetics in EPO and IL-2. Stimulation with EPO resulted in the rapid, dose-dependent tyrosine phosphorylation of JAK2. In contrast, stimulation with IL-2 or the related cytokine IL-4 resulted in the rapid, dose-dependent tyrosine phosphorylation of JAK1 and an additional 116-kDa protein. This 116-kDa protein was itself immunoreactive with a polyclonal antiserum raised against JAK2 and appears to be a novel member of the JAK kinase family. Immune complex kinase assays confirmed that IL-2 and IL-4 activated JAK1 and EPO activated JAK2. These results demonstrate that multiple biochemical pathways are capable of conferring a mitogenic signal in CTLL-EPO-R cells and that the EPO and IL-2 receptors interact with distinct JAK kinase family members within the same cellular background.

The defective gene in X-linked severe combined immunodeficiency encodes a shared interleukin receptor subunit: implications for cytokine pleiotropy and redundancy

The interleukin-2 receptor plays a pivotal role in the regulation of the normal T cell immune response to foreign antigen. The IL-2 receptor gamma-chain is one component of this receptor, and is encoded by the gene that is defective in X-linked severe combined immunodeficiency. The clinical manifestations of this disease led to the hypothesis and subsequent confirmation that the gamma-chain was in fact a subunit shared by multiple cytokine receptors, including those for IL-2, IL-4, and IL-7.