Distinct reactivities of four monoclonal antibodies with human interleukin 2 receptor

Hrs recognizes a hydrophobic amino acid cluster in cytokine receptors during ubiquitin-independent endosomal sorting

Hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs) is a component of the ESCRT-0 protein complex that captures ubiquitylated cargo proteins and sorts them to the lysosomal pathway. Although Hrs acts as a key transporter for ubiquitin-dependent endosomal sorting, we previously reported that Hrs is also involved in ubiquitin-independent endosomal sorting of interleukin-2 receptor β (IL-2Rβ). Here, we show direct interactions between bacterially expressed Hrs and interleukin-4 receptor α (IL-4Rα), indicating that their binding is not required for ubiquitylation of the receptors, similar to the case for IL-2Rβ. Examinations of the Hrs binding regions of the receptors reveal that a hydrophobic amino acid cluster in both IL-2Rβ and IL-4Rα is essential for the binding. Whereas the wild-type receptors are delivered to LAMP1-positive late endosomes, mutant receptors lacking the hydrophobic amino acid cluster are sorted to lysobisphosphatidic acid-positive late endosomes rather than LAMP1-positive late endosomes. We also show that the degradation of these mutant receptors is attenuated. Accordingly, Hrs functions during ubiquitin-independent endosomal sorting of the receptors by recognizing the hydrophobic amino acid cluster. These findings suggest the existence of a group of cargo proteins that have this hydrophobic amino acid cluster as a ubiquitin-independent sorting signal.

Expression of IL-2 receptor beta and gamma chains by human gingival fibroblasts and up-regulation of adhesion to neutrophils in response to IL-2

To investigate the role of human gingival fibroblasts (HGF), the major constituents of gingival tissue in periodontal inflammatory disease, the expression of interleukin-2 receptor (IL-2R) alpha, beta, and gamma chains was examined. Immunohistochemistry showed a pronounced accumulation of CD8(+) T cells in the inflamed lamina propria of gingival tissue from patients with adult periodontitis. HGF express IL-2Rbeta and IL-2Rgamma at mRNA and protein levels, but the expression of IL-2Ralpha could not be detected, as assessed by reverse transcriptase-polymerase chain reaction and flow cytometry. IL-2Rbeta, and -gamma expressed on HGF were functionally active, as addition of neutralizing anti-IL-2Rbeta and -gamma antibodies caused inhibition of the IL-2-induced production of monocyte chemoattractant protein-1 (MCP-1), and addition of IL-2 induced phosphorylation of Janus tyrosine kinase 3, which is critical in signaling through IL-2Rgamma in HGF. The IL-2-induced MCP-1 production was significantly inhibited by pretreatment with neutralizing antibody to IL-15. Addition of IL-2 also induced a marked up-regulation of the expression of intercellular adhesion molecule-1 (ICAM-1) on the surface of HGF, which in turn, significantly augmented the adhesion of human neutrophils, which were inhibited by an anti-ICAM-1 antibody. These results suggest that HGF express functional IL-2Rbetagamma, respond to IL-2 from infiltrated T cells, and actively participate in the inflammatory process in the periodontal region and that IL-15 produced by HGF sustains IL-2-mediated signaling in HGF.

Induction of OX40, a receptor of gp34, on T cells by trans-acting transcriptional activator, Tax, of human T-cell leukemia virus type I

gp34, which we had identified as a target molecule of the trans-activation by Tax of human T-cell leukemia virus type I (HTLV-I), has been found to bind OX40, a member of the tumor necrosis factor receptor family, resulting in growth stimulation of activated T cells. We here demonstrate that not only gp34 (OX40L), but also OX40 can be transcriptionally activated by Tax. Three Tax-producing human T-cell lines carrying the HTLV-I genome expressed OX40 on their surfaces. Furthermore, Tax-induced transcriptional activation of OX40 was shown in Tax-inducible JPX-9 cells. These results demonstrate that both OX40 and its ligand (gp34) are constitutively expressed on the surfaces of Tax-expressing T lymphocytes, suggesting that the OX40L/OX40 system contributes to growth stimulation of the virus-infected T cells.

Cooperative interactions between the interleukin 2 receptor alpha and beta chains alter the interleukin 2-binding affinity of the receptor subunits

The interleukin 2 (IL-2) receptor (IL-2R) is a multisubunit receptor that includes three major IL-2 binding subunits, the IL-2R alpha, beta, and gamma chains. We have detected and analyzed cooperative interactions between the IL-2R alpha and beta chains (IL-2R alpha and IL-2R beta, respectively) in COS cells transfected with cDNAs encoding the IL-2R alpha, the IL-2R beta, or both cDNAs. We demonstrated that IL-2 F42A, an analog that fails to bind to the isolated IL-2R alpha subunit and would be predicted by the hierarchical affinity-conversion model to have impaired binding to cells expressing both chains, instead readily binds to the IL-2R alpha/beta heterodimer in COS cells. Furthermore, this binding is abolished by the antibody HIEI that separates the two IL-2R subunits. The monoclonal antibodies anti-Tac and Mik-beta 1 directed at the IL-2-binding sites on IL-2R alpha and IL-2R beta, respectively, block ligand binding to the heterodimer. This binding pattern is inconsistent with the strict hierarchical affinity-conversion model that mandates an initial binding of IL-2 to IL-2R alpha followed by binding of the IL-2/IL-2R alpha complex to IL-2R beta. Instead, our results support an alternative model of preformed complexes of IL-2R beta with other IL-2R subunits. In this alternative model, IL-2R alpha and -beta exist in part as preformed complexes in which the affinity of IL-2R beta for IL-2 is altered by the proximity of IL-2R alpha, through mechanisms that do not require the prior binding of IL-2 to IL-2R alpha.

Cloning of the gamma chain of the human IL-2 receptor

A third subunit, the gamma chain, of the human interleukin-2 receptor (IL-2R) was identified, and a complementary DNA clone encoding this member of the cytokine receptor family was isolated. The gamma chain is necessary for the formation of the high- and intermediate-affinity receptors, which consists of alpha beta gamma heterotrimers and beta gamma heterodimers, respectively. The IL-2R on murine fibroblastoid cells can be internalized after binding IL-2 only if the gamma chain is present; alpha and beta are insufficient for internalization. Thus, the gamma chain is an indispensable component of the functional IL-2R.

The interleukin 2 receptor (IL-2R): the IL-2R alpha subunit alters the function of the IL-2R beta subunit to enhance IL-2 binding and signaling by mechanisms that do not require binding of IL-2 to IL-2R alpha subunit

Interleukin 2 (IL-2)-mediated signaling through its high-affinity receptor involves a complex interrelationship between IL-2 and two IL-2-binding chains, IL-2R alpha and beta chains. Previously with the reagents available it was difficult to define functional interactions between these two IL-2R subunits involved in IL-2 binding and signal transduction. To extend our understanding of the interplay between the two binding subunits we have done studies with the monoclonal antibody HIEI, which interferes with interaction of IL-2R alpha and beta chains (IL-2R alpha and IL-2R beta, respectively). Furthermore, we used two forms of IL-2, recombinant native IL-2 and F42A, an IL-2 analog (Phe-42----Ala substitution) that binds only to IL-2R beta. Analog F42A manifested 75-100% of the bioactivity of wild-type IL-2. This observation is inconsistent with the strict hierarchical IL-2-binding affinity conversion model previously proposed by Saito and coworkers [Saito Y., Sabe, H., Suzuki, N., Kondo, S., Ogura, T., Shimizu, A. & Honjo, T. (1988) J. Exp. Med. 168, 1563-1572] that predicted an ordered sequence of events in which IL-2 must first bind to IL-2R alpha before its interaction with IL-2R beta. Previous investigations using IL-2 variants were interpreted to show that IL-2R alpha merely acts to concentrate IL-2 to the cell surface and that no other meaningful interaction occurred between IL-2R alpha and IL-2R beta. However, our data are inconsistent with this view. We draw this conclusion on the basis of our observation that antibody HIEI, which reacts with an epitope of IL-2R alpha and interferes with interaction of this chain and IL-2R beta, inhibits the IL-2-dependent proliferative effects mediated by analog F42A. Furthermore, by blocking interaction of IL-2R alpha and IL-2R beta with the antibody HIEI, a decrease in the affinity of radiolabeled analog F42A for IL-2R beta was seen. In our proposed model IL-2R alpha contributes several functions to IL-2-mediated signaling through the high-affinity IL-2R. These functions include concentration of IL-2 within the two-dimensional surface of the plasma membrane as well as alteration of the functional capacity of IL-2R beta, an effect that does not require prior binding of IL-2R to IL-2R alpha. The IL-2R alpha-mediated augmentation of IL-2R beta functions involves affinity conversion of IL-2R beta, increasing its affinity for IL-2, and may involve facilitation of Il-2-mediated signaling after binding of IL-2 to this IL-2R beta.

Monoclonal antibodies defining distinct epitopes of the human IL-2 receptor beta chain and their differential effects on IL-2 responses

We have established and characterized five new monoclonal antibodies (mAbs) which specifically immunoprecipitate the human interleukin-2 receptor beta chain (IL-2R beta). One of them, TU30, recognizes the intracytoplasmic 'serine-rich region' of IL-2R beta that is critical for IL-2 signal transduction. The others, TU12, TU21, TU23 and TU25, completely inhibit IL-2 binding, as does the previously characterized TU27. However, reciprocal binding competition assays show that the epitopes recognized by the individual mAbs are different from each other. The mAbs inhibit the growth of IL-2-dependent cells. The magnitude of their inhibitory effects is dependent on not only the affinities of the mAbs for IL-2R beta but also upon the number of IL-2R alpha subunits expressed on IL-2-dependent cells. These mAbs should be useful in studying the structure and function of the IL-2R.

Macrophage-T cell interaction is essential for the induction of p75 interleukin 2 (IL-2) receptor and IL-2 responsiveness in human CD4+ T cells

Fresh human CD8+ T cells showed a strong proliferative response to a high concentration of interleukin 2 (IL-2) in the absence of macrophages. In contrast, CD4+ T cells revealed no significant IL-2 responsiveness in the absence of macrophages. However, if CD4+ T cells were cocultured with macrophages, they showed higher proliferative response to IL-2 than CD8+ T cells. In accordance with the magnitude of IL-2 responsiveness, freshly isolated CD8+ T cells expressed significant amounts of p75 IL-2 receptor, while fresh CD4+ T cells did not express p75 IL-2 receptor. The expression of p75 IL-2 receptor on CD4+ T cells was induced by coculture with macrophages. The macrophage-induced p75 IL-2 receptor acquisition was blocked by monoclonal antibody (mAb) against class II antigen. Moreover, the addition of anti-CD4 mAb or anti-class II mAb to the culture caused a great inhibition of IL-2 responsiveness of CD4+ T cells. These results strongly suggest that macrophage-T cell interaction through CD4 and/or class II molecules is essential for the expression of p75 IL-2 receptor and IL-2 responsiveness in human CD4+, but not CD8+ T cells.

Interleukin 2 induction of pore-forming protein gene expression in human peripheral blood CD8+ T cells

Our studies have analyzed pore-forming protein (PFP) mRNA expression in resting and stimulated human peripheral blood CD3- large granular lymphocytes (LGL), CD3+ T cells, and their CD4+ or CD8+ subsets. Signals that stimulate T cells to develop cytotoxic activity (i.e., IL-2 or OKT-3 mAb) led to the induction of PFP mRNA in T cells. The data indicated that IL-2 directly increased PFP mRNA in the CD8+ subset of T cells, in the absence of new DNA or protein synthesis. Abrogation of IL-2-induced PFP mRNA expression and cytotoxic potential of T cells by the anti-p75 IL-2 receptor mAb suggested that low numbers of p75 IL-2 receptors on CD8+ T cells were capable of transducing signals responsible for these IL-2-induced effects. The induction of T cell PFP mRNA via CD3, using OKT-3 mAb, was less rapid but greater than that caused by IL-2; however, a combination of PMA and ionomycin, which bypasses crosslinking of the TCR/CD3 complex, could not mimic this increase in PFP mRNA levels in T cells. The role of second messenger systems in regulating PFP mRNA expression remains to be determined. In contrast, high constitutive PFP mRNA expression was observed in CD3- LGL and these mRNA levels could not be enhanced by stimulation with IL-2. The cytotoxic potential of peripheral blood T cells and LGL induced in response to IL-2 correlated with IL-2-induced PFP mRNA levels in these cells and was consistent with PFP being one of several important molecules involved in the effector function of cytotoxic lymphocytes.

Activation of peripheral blood T cells via the p75 interleukin 2 receptor

By using mAb and flow cytometry, a constitutive expression of the p75 IL-2R was revealed in human peripheral blood CD8+ T cells and TCR delta-1+ T cells as well as in CD16+ NK cells. Anti-p75 IL-2R mAb almost completely inhibited the induction of cytolytic activity in these T cells by brief exposure to IL-2, as estimated by anti-TCR/CD3 mAb-targeted cytotoxicity. While anti-p55 IL-2R mAb alone inhibited the response only modestly, maximal inhibition was achieved by combining both anti-p55 and anti-p75 IL-2R mAbs. These results indicate that the p75 IL-2R constitutively expressed on peripheral blood CD8+ T cells and TCR delta-1+ T cells is predominantly responsible for the direct activation of these cells by IL-2.

Activation of endogenous c-fos proto-oncogene expression by human T-cell leukemia virus type I-encoded p40tax protein in the human T-cell line, Jurkat

We examined the ability of the trans-acting factor p40tax of human T-cell leukemia virus type I (HTLV-I), which is thought to be a crucial molecule in T-cell transformation by HTLV-I, to activate expression of a set of endogenous cellular genes related to T-cell proliferation. For this purpose we established a subclone (JPX-9) of Jurkat cells that was stably transfected with an expression plasmid containing the p40tax gene, whose expression is definitely dependent on heavy-metal ions. Expression of the interleukin-2 receptor alpha chain in JPX-9 cells was induced in response to the induction of p40tax expression, as has been demonstrated by others in transient transfection experiments with Jurkat cells. In addition, we found that significant enhancement of expression of the nuclear proto-oncogene c-fos was closely associated with expression of p40tax. Continous enhancement in the level of c-fos mRNA was observed in the presence of p40tax. In contrast, mRNA levels of other nuclear proto-oncogenes (c-myc, c-myb, and c-jun) were not appreciably effected by the expression of p40tax. These results suggest that (i) in addition to the interleukin-2-interleukin-2 receptor system, cellular genes such as c-fos, which regulate normal T-cell growth, are also activated directly or indirectly by p40tax and (ii) p40tax-induced modulation of gene expression plays a crucial role in T-cell transformation by HTLV-I.

Monoclonal antibody defining a molecule possibly identical to the p75 subunit of interleukin 2 receptor

A mouse hybridoma cell line, TU27, producing an mAb was established. TU27 mAb reacted with various human and Gibbon ape T cell lines bearing the IL-2R p75 (IL-2Rp75), but not with cell lines expressing only Tac antigen, IL-2Rp55, and numbers of its binding sites on cell surfaces were similar to those of high-affinity IL-2R. Radioimmunoprecipitation with TU27 mAb defined a molecule with a molecular mass of 75 kD on the surface of IL-2Rp75 bearing cells. TU27 mAb completely blocked IL-2 binding to IL-2Rp75 and to the high-affinity IL-2R but not to IL-2Rp55 composing the low-affinity IL-2R. The IL-2-dependent growth of a human T cell line, ILT-Mat, was significantly inhibited by TU27 mAb only at low concentrations of IL-2, and combination of TU27 mAb and H-31 mAb specific for IL-2Rp55 completely inhibited the cell growth even at high concentrations of IL-2. These data strongly suggest that TU27 mAb is specific for the human IL-2Rp75.

Fluorescence sandwich enzyme-linked immunosorbent assay for detecting human interleukin-2 receptors

A very sensitive fluorescence sandwich enzyme-linked immunosorbent assay (FS-ELISA) for the detection of soluble and cell-associated human interleukin-2 receptors (IL-2R) has been developed. For use in this assay system, two anti-human IL-2R monoclonal antibodies, H 48 and biotinylated HA 26, were selected from six monoclonal antibodies directed against different epitopes on the IL-2R molecule. The FS-ELISA specifically detected human IL-2R in both the culture supernatants and cell lysates of human IL-2R-bearing cells and the assay displayed a 10(3)-fold increase in sensitivity over the usual colorimetric IL-2R ELISA. The IL-2R molecules in supernatants and lysates of the PHA-stimulated mononuclear cells were of 50,000 and 60,000 molecular weight, respectively, as estimated by size exclusion high performance liquid chromatography.

Comparative effects of morphine on leukocytic antigenic markers of monkeys and humans

Knowing the in vitro effects of morphine on monkey leukocytes would be helpful in extending the utility of a monkey model for psychoneuroimmunological investigations. Morphine effects on T11, Leu2a, and Leu3a antigenic markers on leukocytes from rhesus monkeys and humans were assessed by using single- and two-color cytofluorometric analyses. Kinetics of expression of these markers was determined after modulation of the original complement of T11 markers from the surface of T11(+) cells. Percentages of leukocytes detectable by directly staining these markers before modulation were within the expected range for monkey and human cells. Also, as expected, T11 modulation reduced the percentages of cells expressing T11. This reduction was particularly obvious for T11 in the single-color analyses, with reductions being greater for monkey than human cells. Furthermore, in the single-color analyses, the effects of morphine on kinetics of T11 expression were quite similar for both human and monkey cells. In the two-color analyses, the simultaneous expression of T11 and Leu3a markers was uniform for both monkey and human cells. The effects of morphine on kinetics of expression of these markers varied only slightly between species. On the other hand, the distribution of Leu2a on T11 cells was markedly different for monkey and human T-cells. Whereas all human Leu2a(+) cells expressed similar numbers of T11 receptors, monkey cells with high-density Leu2a expressed fewer T11 markers than those with low-density Leu2a. The effects of morphine on kinetics of Leu2a and T11 expression were at obvious variance between species.(ABSTRACT TRUNCATED AT 250 WORDS)

Serological survey and virus isolation of simian T-cell leukemia/T-lymphotropic virus type I (STLV-I) in non-human primates in their native countries

Infection with a simian retrovirus (STLV-I) closely related to human T-lymphotropic virus type I (HTLV-I) was investigated in non-human primates living in their native countries in Africa and Asia. Serum antibodies cross-reacting with HTLV-I antigens were detected in 85 of 567 non-human primates of 30 species. Seropositive animals were found among African green monkeys, olive baboons, Sykes' monkeys, mandrills and patas monkeys in several countries in Africa, and cynomolgus monkeys, Celebes macaques and siamangs in Indonesia. The frequency of seropositivity was much higher in adult than in young African green monkeys, cynomolgus monkeys and Celebes macaques. STLV-Is were isolated by establishing II lines of virus-producing lymphoid cells in the presence of interleukin-2 from 5 species of seropositive non-human primates, i.e. the African green monkey, Sykes' monkey, Celebes macaque, cynomolgus monkey and siamang. All these cell lines had T-cell markers and Tac antigen, and the cell lines from the African green monkey and Sykes' monkeys were Leu2a+ while those from other species were Leu3a+. These cell lines expressed viral antigens reacting with human sera from adult T-cell leukemia (ATL) patients and monoclonal antibodies (MAbs) against p19 and p24 of HTLV-I core proteins, and produced virus particles having RNA-dependent DNA polymerase activity. Cellular DNAs from these cell lines contained provirus sequences homologous to HTLV-I, shown by Southern blot hybridization. The restriction patterns of these provirus genomes were different from those of HTLV-I and were also dissimilar in the different species.

Tyrosine phosphorylation of interleukin 2 receptor-related proteins in phytohemagglutinin-activated human lymphocytes

Three classes of proteins (mol wts 70k, 64k and 45k) having the characteristics of interleukin 2 receptor were detected in phytohemagglutinin-activated human lymphocytes using two monoclonal antibodies which recognize distinct epitopes on the receptor. It was shown that at least portions of these proteins were phosphorylated on tyrosine by analyses for phosphotyrosine by immunoblotting and by immunoaffinity chromatography with antibodies to phosphotyrosine. In addition an iodinated phosphotyrosine derivative was identified in partial hydrolysates of these proteins iodinated in vitro.

Tyrosine phosphorylation of an interleukin 2 receptor-like protein in cells transformed by human T cell leukemia virus type I

Three interleukin 2 (IL-2)-independent human T cell lines transformed with human T cell leukemia virus type I were analyzed for o-phosphotyrosine-containing proteins (Ptyr proteins). Membrane and intracellular immunofluorescence was positive with antibody to Ptyr (Ptyr antibody). 10 size classes of Ptyr proteins with molecular masses of 81-28 kD were isolated with Ptyr antibodies. Among these, proteins of 64 kD (pI 4.5 and 4.8-5.3) and 45 kD (pI 4.3) were found on the outer cell surface. The Ptyr protein of 64 kD (pI 4.5) had the characteristics of the IL-2 receptor (IL-2-R) in that it was recognized by two monoclonal antibodies directed against different epitopes on the IL-2-R.

Characterization of interleukin 2-stimulated phosphorylation of 67 and 63 kDa proteins in human T-cells

We have investigated rapid and marked phosphorylation of cellular proteins induced by interleukin 2 (IL-2) in both phytohaemagglutinin-stimulated normal peripheral blood leucocytes, and IL-2-dependent or -independent human T-cell lines bearing human T-cell leukaemia (lymphotropic) virus type I. Two-dimensional electrophoretic analysis showed that the IL-2-induced phosphoprotein was of Mr 67,000 with a pI of 5.8 (pp67) and was distinct from the IL-2 receptor. IL-2 also stimulated phosphorylation of four other proteins, with an Mr of 63,000 and pI values 5.3-6.1 (pp63s). The stimulation of pp67 phosphorylation was observed within 5 min after addition of IL-2 and was maximal after 15 min. The maximal phosphorylation was more than 10-fold that observed initially. In IL-2-dependent cells, IL-2 dose responses of pp67 phosphorylation and cell proliferation were exactly correlated. Phosphoamino acid analysis showed that the phosphorylation site of pp67 and pp63s was a serine residue. Subcellular-fractionation studies indicated that pp67 was localized in cytosol, whereas pp63s phosphorylation was induced by IL-2 in nuclear and cytosol fractions. Similar phosphorylation of pp67 and pp63s was observed when the cells were treated with phorbol 12-myristate 13-acetate instead of IL-2. These results suggest that IL-2-IL-2-receptor interaction leads to activation of protein kinase(s), resulting in phosphorylation of certain cellular proteins such as pp67 and pp63s, and that this phosphorylation could be an early event in the transmission of intracellular growth signalling from the IL-2 receptors.

Experimental inoculation of monkeys with autologous lymphoid cell lines immortalized by and producing human T-cell leukemia virus type-I

Cynomolgus monkeys and squirrel monkeys were inoculated with autologous lymphoid cell lines immortalized by and producing human T-cell leukemia virus type-I (HTLV-I) in order to serve as an animal model of adult T-cell leukemia (ATL). The autologous cell lines were established from peripheral blood mononuclear cells (PBMC) from each monkey by co-cultivation with lethally irradiated MT-2 cells producing HTLV-I. All of these cell lines, which had monkey karyotypes, grew continuously without addition of interleukin-2 (IL-2) and expressed virus-specific proteins of HTLV-I and IL-2 receptor. After inoculation with the autologous cell lines, specific antibodies against HTLV-I proteins could be detected in their plasma, and transformed HTLV-I-infected cells could be recovered from their peripheral blood for at least 6 months. However, no signs of ATL have been observed to data, i.e. 2 years after inoculation.

Molecular basis for two different affinity states of the interleukin 2 receptor: affinity conversion model

Two affinity species of the interleukin 2 (IL-2) receptor are different states of a single receptor molecule. We assumed that a binary complex between the IL-2 receptor and another lymphocyte-specific protein would constitute the high-affinity receptor. To test this assumption, we counted the numbers of IL-2 receptors with high and low affinity in a murine T-cell line CT/hR-1 that expresses not only murine but also human receptors by cDNA transfection. We found that human high-affinity receptors disappeared when the murine high-affinity receptors were already occupied by the ligand. The results were incompatible with a fixed number of human and murine receptors with high affinity in CT/hR-1 cells. We suggest that the high-affinity state of the IL-2 receptor is a ternary complex of IL-2, the IL-2 receptor, and a postulated "converter" protein, which is fewer in number than the receptors. The converter would be unable to form a complex with the IL-2 receptor unless IL-2 was already bound to it. The ligand binding to the receptor would cause a conformational change in the receptor, increasing its affinity to the converter. Ternary complex formation would, in turn, change the apparent affinity of the receptor to the ligand from low to high by reduction of the dissociation constant.

Structure and function of the interleukin 2 receptor: affinity conversion model

We cloned cDNAs of the human and mouse IL-2 receptors. Comparison of their structures allowed us to identify several conserved regions localized to exons 2 and 4, the cytoplasmic portion and the transmembrane portion. These regions might be important for the functions of the IL-2 receptor. The human IL-2 receptor, which was expressed on an IL-2-dependent murine T-cell line, CTLL-2, by cDNA transfection, was shown to be functionally active by blocking the endogenous mouse IL-2 receptor with monoclonal antibodies. On the other hand, the human IL-2 receptors expressed on non-lymphoid cells were functionally inactive. They were unable to mediate the growth signal, were of low affinity species and aberrant in internalization. We postulated that the dysfunction of the IL-2 receptors in non-lymphoid cells would be due to the absence of the putative converter protein which is expressed specifically in lymphoid cells. Since the human IL-2 receptor is active in the murine T cell, the converter may interact with the receptor at the portions conserved between man and mouse. We proposed the affinity conversion model that explained the high affinity state of the receptor by the ternary complex formation between IL-2, the IL-2 receptor and the converter.

New monoclonal antibodies that define multiple epitopes and a human-specific marker on the interleukin 2 receptor molecules of primates

Twelve hybridoma cell lines producing monoclonal antibodies to the human interleukin 2 (IL-2) receptor (IL-2R) molecule were prepared. These antibodies were characterized by competitive antibody-binding assay and sequential immunoprecipitation assay with four known monoclonal antibodies to the human IL-2R molecule. The twelve new monoclonal antibodies were divided among the four known antibody types, the HIEI-, H-A26-, H-31-, and anti-Tac-type, and an additional new type, the H-48-type. The H-48 antibody did not compete with any other antibodies in the competitive binding assay. The binding of 125I-IL-2 to MT-2 cells and the IL-2-dependent growth of normal activated T-cells were both strongly inhibited by all the H-31- and anti-Tac-type antibodies, and partially or slightly inhibited by HIEI- and H-A26-type antibodies, but were not inhibited by the H-48 antibody. Thus, the same type of monoclonal antibodies had a similar effect on the function of IL-2R. These results suggest that epitopes for the same type of antibodies could be single identical epitopes or epitopes closely associated with each other. On the other hand, these antibodies also reacted variously with a panel of various human and simian lymphoid cell lines immortalized with human T-cell leukemia virus type-I (HTLV-I): the H-45 antibody reacted only with the human cell lines, the H-C1 and H-44 and H-47 antibodies reacted with human and ape cell lines, and the other antibodies reacted with cell lines of humans, apes and Old and New World monkeys. These differences in the reactivity of the antibodies with the primate cell lines suggest that the antigenic structure of the IL-2R molecule changed during evolutionary divergence of the primates.