Cloning of an interleukin-3 receptor gene: a member of a distinct receptor gene family

Interleukin-3 (IL-3) binds to its receptor with high and low affinities, induces tyrosine phosphorylation, and promotes the proliferation and differentiation of hematopoietic cells. A binding component of the IL-3 receptor was cloned. Fibroblasts transfected with the complementary DNA bound IL-3 with a low affinity [dissociation constant (Kd) of 17.9 +/- 3.6 nM]. No consensus sequence for a tyrosine kinase was present in the cytoplasmic domain. Thus, additional components are required for a functional high affinity IL-3 receptor. A sequence comparison of the IL-3 receptor with other cytokine receptors (erythropoietin, IL-4, IL-6, and the beta chain IL-2 receptor) revealed a common motif of a distinct receptor gene family.     

The structure, function, and expression of interleukin-2 receptors on normal and malignant lymphocytes

Antigen or mitogen-induced activation of resting T cells induces the synthesis of interleukin-2 (IL-2) as well as the expression of specific cell surface receptors for this lymphokine. Failure of the production of either IL-2 or its receptor results in a failure of the T-cell immune response. The receptor is composed of a 33,000-dalton (251-amino acid) peptide precursor that is post-translationally glycosylated into the mature 55,000-dalton form. In contrast to resting T cells, human T-cell lymphotrophic virus I (HTLV-I)-associated adult T-cell leukemia cells constitutively express large numbers of IL-2 receptors. Because IL-2 receptors are present on the malignant T cells but not on normal resting cells, clinical trials have been initiated in which patients with adult T-cell leukemia are treated with a monoclonal antibody that binds to the IL-2 receptor.     

Structure and functional expression of a human interleukin-8 receptor

Interleukin-8 (IL-8) is a member of a family of pro-inflammatory cytokines. Although the best characterized activities of IL-8 include the chemoattraction and activation of neutrophils, other members of this family have a wide range of specific actions including the chemotaxis and activation of monocytes, the selective chemotaxis of memory T cells, the inhibition of hematopoietic stem cell proliferation, and the induction of neutrophil infiltration in vivo. A complementary DNA encoding the IL-8 receptor from human neutrophils has now been isolated. The amino acid sequence shows that the receptor is a member of the superfamily of receptors that couple to guanine nucleotide binding proteins (G proteins). The sequence is 29% identical to that of receptors for the other neutrophil chemoattractants, fMet-Leu-Phe and C5a. Mammalian cells transfected with the IL-8 receptor cDNA clone bind IL-8 with high affinity and respond specifically to IL-8 by transiently mobilizing calcium. The IL-8 receptor may be part of a subfamily of related G protein-coupled receptors that transduce signals for the IL-8 family of pro-inflammatory cytokines.     

COOH-terminal-modified interleukin-3 is retained intracellularly and stimulates autocrine growth

Autocrine growth due to dysregulated growth factor production may have a role in the development of neoplasia. Whether autocrine growth is stimulated by growth factor secretion in an autocrine loop or by intracellular binding of the growth factor to a receptor has been unclear. The carboxyl-terminus coding sequence for murine interleukin-3 (IL-3) was extended with an oligonucleotide encoding a four-amino acid endoplasmic reticulum retention signal. IL-3-dependent hematopoietic cells became growth factor-independent when the modified IL-3 gene was introduced by retroviral gene transfer, despite lack of secretion of the modified IL-3. Hence autocrine growth can occur as a result of the intracellular action of a growth factor and this mechanism may be important in neoplastic and normal cells.     

Signal transduction through the EGF receptor transfected in IL-3-dependent hematopoietic cells

An expression vector for the epidermal growth factor (EGF) receptor was introduced into the 32D myeloid cell line, which is devoid of EGF receptors and absolutely dependent on interleukin-3 (IL-3) for its proliferation and survival. Expression of the EGF receptor conferred the ability to utilize EGF for transduction of a mitogenic signal. When the transfected cells were propagated in EGF, they exhibited a more mature myeloid phenotype than was observed under conditions of IL-3-directed growth. Moreover, exposure to EGF led to a rapid stimulation of phosphoinositide metabolism, while IL-3 had no detectable effect on phosphoinositide turnover either in control or EGF receptor-transfected 32D cells. Although the transfected cells exhibited high levels of functional EGF receptors, they remained nontumorigenic. In contrast, transfection of v-erbB, an amino-terminal truncated form of the EGF receptor with constitutive tyrosine kinase activity, not only abrogated the IL-3 growth factor requirement of 32D cells, but caused them to become tumorigenic in nude mice. These results show that a na?ve hematopoietic cell expresses all of the intracellular components of the EGF-signaling pathway necessary to evoke a mitogenic response and sustain continuous proliferation.     

Biological activity of recombinant human interleukin-2 produced in Escherichia coli

The gene for interleukin-2 was isolated from the Jurkat cell line and from normal peripheral blood lymphocytes and, when inserted in Escherichia coli, was expressed at high concentrations. This interleukin-2 was purified to apparent homogeneity and tested for biological activity in a variety of assays in vitro and in vivo. The recombinant lymphokine supports the growth of murine and human interleukin-2 dependent cell lines, enhances the generation of murine and human cytolytic cells in vitro, and generates lymphokine activated killer cells from murine and human lymphocytes. It has a serum half-life of 2 to 3 minutes in the mouse and significantly enhances the generation of cytolytic cells in vivo after alloimmunization. No functional differences between native and the recombinant interleukin-2 molecules have been detected.     

The alarmin interleukin-33 drives protective antiviral CD8⁺ T cell responses

Pathogen-associated molecular patterns decisively influence antiviral immune responses, whereas the contribution of endogenous signals of tissue damage, also known as damage-associated molecular patterns or alarmins, remains ill defined. We show that interleukin-33 (IL-33), an alarmin released from necrotic cells, is necessary for potent CD8(+) T cell (CTL) responses to replicating, prototypic RNA and DNA viruses in mice. IL-33 signaled through its receptor on activated CTLs, enhanced clonal expansion in a CTL-intrinsic fashion, determined plurifunctional effector cell differentiation, and was necessary for virus control. Moreover, recombinant IL-33 augmented vaccine-induced CTL responses. Radio-resistant cells of the splenic T cell zone produced IL-33, and efficient CTL responses required IL-33 from radio-resistant cells but not from hematopoietic cells. Thus, alarmin release by radio-resistant cells orchestrates protective antiviral CTL responses.     

Immortalization of human T lymphocytes after transfection of Epstein-Barr virus DNA

Epstein-Barr virus (EBV), a ubiquitous human herpesvirus, has the ability to transform human B lymphocytes. No other cell type has been experimentally transformed by EBV, either by intact virions or naked viral DNA and subgenomic fragments. Two immortalized human T-lymphoblastoid cell lines have now been established by transfecting cord blood lymphocytes with purified B95-8 viral DNA enclosed in fusogenic Sendai virus envelopes (RSVE) and then exposing the cells to EBV from a P3HR-1 cell subclone. One of these lines, which has been fully characterized, is termed HBD-1. This line is positive for EBV DNA and expresses surface OKT11, OKT4, and Tac receptors, but not M-1, mu immunoglobulin chains, EBV receptors, or B-1 surface markers. The cells contain fully rearranged T-cell receptor genes and germline immunoglobulin genes. The karyotype of the cells is normal, they do not require interleukin-2 for growth, and do not contain human T-lymphotropic virus type I. However, the HBD-1 cells contain incomplete EBV genomes and express several EBV-determined antigens, including the early antigen type D, membrane antigens, but not EBV-determined nuclear antigen (EBNA). This association of the EBV genome with permanently growing hematopoietic cells of non B-cell lineage should prove useful in studies on the mechanism of EBV-mediated cell transformation.     

A critical role for IL-21 in regulating immunoglobulin production

The cytokine interleukin-21 (IL-21) is closely related to IL-2 and IL-15, and their receptors all share the common cytokine receptor gamma chain, gammac, which is mutated in humans with X-linked severe combined immunodeficiency disease (XSCID). We demonstrate that, although mice deficient in the receptor for IL-21 (IL-21R) have normal lymphoid development, after immunization, these animals have higher production of the immunoglobulin IgE, but lower IgG1, than wild-type animals. Mice lacking both IL-4 and IL-21R exhibited a significantly more pronounced phenotype, with dysgammaglobulinemia, characterized primarily by a severely impaired IgG response. Thus, IL-21 has a significant influence on the regulation of B cell function in vivo and cooperates with IL-4. This suggests that these gammac-dependent cytokines may be those whose inactivation is primarily responsible for the B cell defect in humans with XSCID.     

Mechanism of interleukin-2 signaling: mediation of different outcomes by a single receptor and transduction pathway

The T cell lymphokine, interleukin-2 (IL-2), plays a pivotal role in an immune response by stimulating antigen-activated B lymphocytes to progress through the cell cycle and to differentiate into antibody-secreting cells. An IL-2 inducible B lymphoma line, in which the growth and differentiation responses are uncoupled, provides a model system for dissecting the signaling mechanisms operating in each response. This system was used to show that both signals are initiated by IL-2 binding to a single, unifunctional receptor complex. Moreover, both signals are transduced by a pathway that does not involve any known second messenger system and that can be blocked by a second T cell lymphokine, interleukin 4. These findings suggest that the pleiotrophic effects of IL-2 are determined by different translations of the signal in the nucleus.     

Structural mutations of the T cell receptor zeta chain and its role in T cell activation

T cell hybridomas that express zeta zeta, but not zeta eta, dimers in their T cell receptors (TCRs) produce interleukin-2 (IL-2) and undergo an inhibition of spontaneous growth when activated by antigen, antibodies to the receptor, or antibodies to Thy-1. Hybridomas without zeta and eta were reconstituted with mutated zeta chains. Cytoplasmic truncations of up to 40% of the zeta molecule reconstituted normal surface assembly of TCRs, but antigen-induced IL-2 secretion and growth inhibition were lost. In contrast, cross-linking antibodies to the TCR activated these cells. A point mutation conferred the same signaling phenotype as did the truncations and caused defective antigen-induced tyrosine kinase activation. Thus zeta allows the binding of antigen/major histocompatibility complex (MHC) to alpha beta to effect TCR signaling.     

The interleukin-2 T-cell system: a new cell growth model

Synchronized interleukin-2 receptor-positive T cells, homogeneous immunoaffinity-purified interleukin-2, and a monoclonal antibody to interleukin-2 receptors were used to show that only three factors are critical for T-cell cycle progression: interleukin-2 concentration, interleukin-2 receptor density, and the duration of the interleukin-2 receptor interaction. Since the proliferative characteristics of T cells are identical to those of both prokaryotic and all other eukaryotic cells, these findings provide a new model that accounts fully for the variables that determine cell cycle progression.     

Requirement of nuclear prolactin for interleukin-2--stimulated proliferation of T lymphocytes

Prolactin (PRL) is necessary for the proliferation of cloned T lymphocytes in response to interleukin-2 (IL-2). Translocation of PRL into the nucleus occurs during IL-2--stimulated mitogenesis. Therefore, the function of intranuclear PRL in T cell proliferation was tested. Eukaryotic expression vectors were prepared to express wild-type PRL [PRL(WT)], PRL that lacks the signal sequence for translocation into the endoplasmic reticulum [PRL(ER-)], and chimeric PRL in which the signal peptide was replaced with the sequence that directs the nuclear translocation of the SV40 large T antigen [PRL(NT+)]. Expression of these constructs in a T cell line (Nb2) responsive to PRL and IL-2 resulted in localization of PRL in the extracellular milieu, cytoplasm, or nucleus, respectively. Stimulation with IL-2 alone resulted in a five- to tenfold increase in the incorporation of [3H]thymidine by cells expressing PRL(NT+) or PRL(WT) as compared to PRL(ER-) or the parental Nb2 cells. Only the PRL(NT+) clone proliferated continuously with IL-2 stimulation in the presence of antiserum to PRL. These results demonstrate that nuclear PRL is necessary for IL-2--stimulated proliferation and suggest that a peptide hormone can function in the nucleus without binding to its cell surface receptor.     

Selective elimination of HIV-1-infected cells with an interleukin-2 receptor-specific cytotoxin

Infection by human immunodeficiency virus type 1 (HIV-1) is associated with cellular activation and expression of the interleukin-2 (IL-2) receptor. A genetically engineered fusion toxin, DAB486 IL-2, that contains the enzymatic site and translocation domain of diphtheria toxin and the receptor binding domain of IL-2 specifically kills cells that express high-affinity IL-2 receptors. This toxin selectively eliminated the HIV-1-infected cells from mixed cultures of infected and uninfected cells and inhibited production of viral proteins and infectious virus. Thus, cellular activation antigens present a target for early antiviral intervention.     

Downregulation of L3T4+ cytotoxic T lymphocytes by interleukin-2

Proliferation of activated cytotoxic T lymphocytes (CTLs) that recognize foreign histocompatibility antigens is induced by interleukin-2, a potent immunoregulatory molecule originally described as T cell growth factor. Interleukin-2 (IL-2) is widely used to isolate and induce clonal expansion of CTLs for functional studies in vitro and in vivo. However, in studies with CTLs specific for class I and class II histocompatibility antigens, IL-2 rapidly downregulated the lytic activity of some class II-specific CTLs in a time- and dose-dependent manner. Lytic activity of L3T4+ CTLs specific for the murine class II antigen I-Ek was repeatedly up- and downregulated in vitro by alternate exposure to specific (alloantigen) and nonspecific (recombinant IL-2) signals, respectively. These results demonstrate that some CTLs modulate their functional property (cytolysis) while undergoing IL-2-driven cell proliferation without loss of antigen specificity or ability to revert to a lytic phenotype.     

EGF receptor and erbB-2 tyrosine kinase domains confer cell specificity for mitogenic signaling

The epidermal growth factor (EGF) receptor (EGFR) can efficiently couple with mitogenic signaling pathways when it is transfected into interleukin-3 (IL-3)-dependent 32D hematopoietic cells. When expression vectors for erbB-2, which is structurally related to EGFR, or its truncated counterpart, delta NerbB-2, were introduced into 32D cells, neither was capable of inducing proliferation. This was despite overexpression and constitutive tyrosine kinase activity of their products at levels associated with potent transformation of fibroblast target cells. Thus, EGFR and erbB-2 couple with distinct mitogenic signaling pathways. The region responsible for the specificity of intracellular signal transduction was localized to a 270-amino acid stretch encompassing their respective tyrosine kinase domains. Thus, tissue- or cell-specific regulation of growth factor receptor signaling can occur at a point after the initial interaction of growth factor with receptor. Such specificity in signal transduction may account for the selection of certain oncogenes in some malignancies.     

Cytotoxicity of human pI 7 interleukin-1 for pancreatic islets of Langerhans

Activated mononuclear cells appear to be important effector cells in autoimmune beta cell destruction leading to insulin-dependent (type 1) diabetes mellitus. Conditioned medium from activated mononuclear cells (from human blood) is cytotoxic to isolated rat and human islets of Langerhans. This cytotoxic activity was eliminated from crude cytokine preparations by adsorption with immobilized, purified antibody to interleukin-1 (IL-1). The islet-inhibitory activity and the IL-1 activity (determined by its comitogenic effect on thymocytes) were recovered by acid wash. Purified natural IL-1 and recombinant IL-1 derived from the predominant pI 7 form of human IL-1, consistently inhibited the insulin response. The pI 6 and pI 5 forms of natural IL-1 were ineffective. Natural and recombinant IL-1 exhibited similar dose responses in their islet-inhibitory effect and their thymocyte-stimulatory activity. Concentrations of IL-1 that inhibited islet activity were in the picomolar range. Hence, monocyte-derived pI 7 IL-1 may contribute to islet cell damage and therefore to the development of insulin-dependent diabetes mellitus.