Activation by IL-2, but not IL-4, up-regulates the expression of the p55 subunit of the IL-2 receptor on IL-2- and IL-4-dependent T cell lines

We have investigated the effects of IL-2 and IL-4 on different parameters of T cell activation using three T cell lines. The Th cell line L14 and the cytotoxic T cell line C30.1, both grown in IL-2-containing medium, and a line derived from C30.1 cells (line 1) cultured in IL-4 for a prolonged period were studied. All three cell lines could be activated with IL-2 or IL-4. T cell stimulation by either IL-2- or IL-4-induced identical patterns of cell size enlargement and transferrin receptor expression. However, only IL-2 up-regulated cell-surface expression of the p55 subunit of the IL-2R (p55 IL-2R) as measured by flow cytometry and RIA. This difference was also reflected by the accumulation of soluble p55 IL-2R in the culture medium. No significant increase in expression of membrane or soluble forms of p55 IL-2R was detected after IL-4 stimulation. mAb specific for p55 IL-2R which block IL-2-induced T cell growth did not affect IL-4-mediated T cell proliferation indicating that p55 IL-2R is not involved in IL-4-mediated T cell growth. Analysis of IL-4R expression performed on line 1 using biotinylated IL-4 revealed that IL-4, but not IL-2, is capable of increasing IL-4R expression. Together these results suggest that during IL-2- or IL-4-induced T cell proliferation, each lymphokine specifically up-regulates its own receptor.     

Synergistic action of monoclonal antibodies directed at p55 and p75 chains of the human IL-2-receptor

TU27, a mouse IgG1 mAb directed at the p75 chain of the human IL-2R, was analyzed for its ability to interact with IL-2 binding on isolated p75 chains (YT-2C2 cells) and high affinity p55/p75 receptors (human alloreactive T cell clone 4AS), to inhibit IL-2-induced proliferation (4AS cells) and to cooperate with an anti-p55 chain mAb (33B3.1) for inhibiting IL-2 binding and proliferation. TU27 and IL-2 bound to the isolated p75 chain expressed by YT-2C2 cells with respective dissociation constants (Kd) of 1.3 and 1 nM. They cross-inhibited each other for binding with inhibition constants (Ki) in agreement with their respective Kd values. The nature of the interaction was, however, not purely competitive and suggested nonidentical epitopes for the two ligands on the p75 chain. On 4AS cells, IL-2 bound with high affinity (Kd = 50 pM) and TU27 with an affinity similar to that found on YT-2C2 cells. The binding of TU27 and IL-2 were also mutually exclusive on 4AS cells. However, the mechanism of interaction of TU27 with IL-2 was complex since the inhibitory potency of the antibody depended on temperature, antibody preincubation and time of assay. Data obtained at 4 degrees C in the presence of suboptimal, tracer-like concentrations of IL-2 indicated that the intrinsic affinity of TU27 for the high affinity configuration was 15-fold lower than for the isolated p75 chain and argued in favor of the affinity-conversion model (as opposed to the preformed complex model) in which p55 and p75 are dissociated in the absence of IL-2. At 37 degrees C, TU27 inhibited IL-2 binding only on short time assays (6 min). Longer time (30 min) of IL-2 binding resulted in an almost complete disappearance of the effect of TU27, suggesting that internalization of the high affinity p55/p75/IL2 complex enables the cells to escape from the inhibitory effect of TU27. In the presence of the 33B3.1 mAb, the interaction of TU27 with IL-2 resembled the one observed on YT-2C2 cells, suggesting that 33B3.1 is able to inhibit the IL-2-induced association of p55 and p75. Both antibody were found to synergize on 4AS cells, as a result of a cooperative mechanism in which 33B3.1 blocks the formation of the high affinity complex hence allowing TU27 to bind with higher affinity, and TU27 blocks IL-2 binding to the p75 chain. Proliferation studies corroborated the binding experiments.(ABSTRACT TRUNCATED AT 400 WORDS)     

Expression of low-, intermediate-, and high-affinity IL-2 receptors on B cell lines derived from patients with undifferentiated lymphoma of Burkitt's and non-Burkitt's types

IL-2 receptors on T cells exist in at least three forms which differ in their ligand-binding affinity. The low-affinity IL-2 receptor (IL-2R) consists of the 55-kDa Tac protein (p55 alpha), the intermediate-affinity site corresponds to the 70-kDa molecule (p70 beta), and the high-affinity IL-2R consists of a noncovalent heterodimeric structure involving both p55 alpha and p70 beta. We studied 24 B cell lines (8 EBV-negative and 16 EBV-positive) for IL-2R expression in the presence or absence of the tumor promoter, teleocidin. 125I-IL-2 radioreceptor binding assays and crosslinking studies demonstrated the sole expression of p55 alpha in EBV-negative cell lines only, whereas p55 alpha present in EBV-positive cell lines was always associated with p70 beta to construct high-affinity IL-2R. p70 beta was not detected in any of the EBV-negative cell lines, but was expressed on most of the EBV-positive cell lines (13 of 16). Our data also indicate that the expression of p55 alpha and p70 beta by radiolabeling correlates with their expression in flow cytometry, and that a large excess of p55 alpha is required to construct high-affinity IL-2R. Coexpression of p55 alpha and p70 beta on human B cells contributed to constructing high-affinity IL-2R hybrid complex as shown by (i) rapid association rate contributed by p55 alpha and slow dissociation rate by p70 beta; (ii) teleocidin's ability to induce p55 alpha on cell lines which express p70 beta only, resulting in appearance of high-affinity IL-2R; (iii) blocking p55 alpha by anti-Tac mAb in cell lines which constitutively express high-affinity IL-2R eliminated both high- and low-affinity components. The existence of low, intermediate, and high IL-2R on human B cells bears important future implications for understanding the mechanism of IL-2 signaling and the role of IL-2 in B cell activation, proliferation, and differentiation.     

Structure-function study of the p55 subunit of murine IL-2 receptor by epitope mapping.

Using a cell-free translation system we have expressed the Mr 55,000 subunit of the murine IL-2R (p55 IL-2R), which binds IL-2 with low affinity (Kd = 10 nM). Mutants and truncated forms of p55 IL-2R have been used to map the epitopes recognized by three anti-p55 IL-2R mAb: 135D5, 7D4, and 2E4. The mAb 135D5 inhibits IL-2 binding to p55 IL-2R and recognizes an epitope located between amino acids 64 to 125. This epitope can be mimicked by a synthetic peptide corresponding to the region defined by residues 72 to 88. However, the mAb 7D4 and 2E4 do not affect the IL-2 binding to p55 IL-2R. These mAb recognize an epitope of p55 IL-2R lying between residues 125 to 212 that can be mimicked with a peptide corresponding to amino acids 188 to 208. A strong correlation emerged between the experimental results on epitope mapping and predictions of potential antigenicity of murine p55 IL-2R. In addition, we described two internal initiation sites of p55 IL-2R mRNA under the in vitro conditions used leading to the production of significant amounts of N-terminal truncated p55 IL-2R proteins.     

Presence of a p70 IL-2-binding peptide on leukemic cells from various hemopoietic lineages

Recent studies have shown that IL-2R are composed of at least two polypeptide chains of 55 kDa (Tac or alpha-chain) and 70 to 75 kDa (p70 or beta-chain). The association of both chains forms high affinity IL-2R, whereas each chain alone binds IL-2 with a low (alpha-chain) or intermediate (beta-chain) affinity. So far, the p70 peptide has been found, in the absence of the Tac peptide, on the surface of lymphoid cells of T, B, or NK lineage. In this study, we investigated whether leukemic cells of various hemopoietic lineages expressed the p70 IL-2-binding protein. We found that both fresh leukemic cells obtained from patients, and cells from established leukemic lines of T cells, B cell, and myeloid origin constitutively expressed a p70 IL-2-binding protein on their surface, as detected by affinity cross-linking of radioiodinated IL-2. IL-2 binding and cross-linking to these cells was completely inhibited in the presence of an excess unlabeled rIL-2, but not with an anti-Tac mAb. Binding experiments on pre-B and myeloid cell lines revealed intermediate affinity IL-2R, whereas both high and intermediate affinity IL-2R were detected in T leukemic cells. The intermediate affinity binding of 125I-rIL-2 to the leukemic cell lines MOLT4 and Reh6 was inhibited by the TU27 mAb, which recognized the p75 chain of IL-2R. Moreover, the TU27 mAb could stain the K562, KM3, and MOLT4 (weakly) cell lines by indirect immunofluorescence. A high dose of rIL-2 (400 U/ml) enhanced the proliferation of cells from one out of three patients with acute myeloblastic leukemia, but it did not induce differentiation of the cells in any of three cases. Thus the finding of p70 IL-2-binding molecules on immature lymphoid and nonlymphoid hemopoietic cells should disclose new biologic functions for IL-2.     

The IL-2 receptor alpha-chain alters the binding of IL-2 to the beta-chain

The binding of IL-2 to its high affinity receptor results in the formation of the ternary complex consisting of IL-2, alpha-chain (p55, Tac) and beta-chain (p75). We studied the role of alpha-chain in IL-2 binding to the high affinity receptor using IL-2 analog Lys20 which was made by the substitution of Lys for Asp20 of wild-type rIL-2. Lys20 bound to MT-1 cells solely expressing alpha-chain at low affinity, but did not bind to YT-2C2 cells which solely expressed beta-chain. However, direct binding of radiolabeled Lys20 to ED515-D cells, an HTLV-I-infected and IL-2-dependent T cell line, revealed both high affinity and low affinity binding although the Kd value of high affinity binding was 50 to 100 times higher than that of the high affinity binding of wild-type rIL-2. High affinity binding of Lys20 was completely blocked by 2R-B mAb recognizing IL-2R beta-chain. Anti-Tac mAb recognizing IL-2R alpha-chain abolished all of the specific Lys20 bindings. In contrast to the replacement of cell bound 2R-B mAb with wild-type rIL-2 at 37 degrees C, the addition of an excess of Lys20 did not cause the detachment of cell-bound radiolabeled or FITC-labeled 2R-B mAb. Consistent with the results of binding studies, Lys20 induced the proliferation of ED515-D cells, but not large granular lymphocyte leukemic cells. The growth of ED-515D cells was completely suppressed by either anti-Tac mAb or 2R-B mAb. These results strongly suggest that coexpression of the IL-2R alpha- and beta-chains alters the binding affinity of Lys20 and that the interaction between IL-2 and the alpha-chain is a key event in the formation of the IL-2/IL-2R ternary complex.     

Characterization of the soluble murine IL-2R and estimation of its affinity for IL-2

IL-2 induces cells of the cytotoxic T cell line C30.1 to express large numbers of membrane IL-2R (mIL-2R). At the height of activation, these cells also release a soluble form of IL-2R (sIL-2R). Using either crude supernatant or a semi-purified preparation of sIL-2R obtained by affinity chromatography, studies were performed to characterize murine sIL-2R. Its m.w. was determined by both gel filtration and SDS-PAGE. The affinity of sIL-2R for a panel of mAb known to recognize different epitopes of mIL-2R (p55 subunit) was assessed by saturation and competition experiments. The relationship between the various epitopes was studied by cross-inhibition experiments. The data suggest that sIL-2R and mIL-2R (p55 subunit) are structurally similar. The ability of sIL-2R to bind IL-2 was assessed by measuring the dissociation and the inhibition constant of the molecule for IL-2. Both values coincide and indicate that the affinity of sIL-2R for IL-2 is at least 10-fold lower than the that of low affinity mIL-2R. The biologic implications of these findings are discussed.     

IL-6 is an accessory signal in the alternative CD2-mediated pathway of T cell activation

Recent studies have demonstrated that IL-1 and IL-6 are synergistic accessory signals for activation of T cells. In this study, highly purified human T cells were cultured with either a stimulating pair of anti-CD2 mAb or with immobilized anti-CD3 mAb. Monocytes, a cellfree monocyte culture supernatant or IL-1 were required for anti-CD2-stimulated T cell proliferation, and they each strongly enhanced anti-CD3-induced T cell growth. IL-6 was synergistic with IL-1 as a helper factor for T cell growth after activation via CD2, but we could not demonstrate any effect of IL-6 in the CD3 pathway. The mechanism of the synergistic helper activity of IL-1 and IL-6 on T cell activation in the CD2 pathway was further examined. IL-1 (but not IL-6) was required for induction of IL-2 production. Both IL-1 and IL-6 enhanced IL-2R (p55) expression and the proliferative response to IL-2. T cell proliferation after stimulation with anti-CD2 and IL-1 or IL-1/IL-6 proceeded through an autocrine IL-2-dependent pathway. Moreover we found that, in the absence of IL-1, IL-6 still supported a transient and limited proliferation of anti-CD2- (but not of anti-CD3-) stimulated T cells, which apparently was independent of the autocrine growth factors IL-2 or IL-4. Our data suggest that IL-6 is important as an accessory signal for T cell growth in the CD2 pathway of T cell activation.     

IL-2 regulation of tyrosine kinase activity is mediated through the p70-75 beta-subunit of the IL-2 receptor

The stimulation of activated human T lymphocytes with IL-2 results in increased tyrosine kinase activity. IL-2 treatment of Tac+ T cells stimulates the rapid phosphorylation of multiple protein substrates at M of 116, 100, 92, 70 to 75, 60, 56, 55, 33, and 32 kDa. Phosphorylation on tyrosine residues was detected by immunoaffinity purification of protein substrates with Sepharose linked antiphosphotyrosine mAb, 1G2. Although phorbol ester stimulated serine phosphorylation of the IL-2R alpha (p55) subunit recognized by alpha TAC mAb, IL-2 did not stimulate any detectable phosphorylation of IL-2R alpha or associated coimmune precipitated proteins. In fact, the tyrosine phosphorylated proteins did not coprecipitate with alpha Tac antibody and similar phosphoproteins were stimulated by IL-2 in IL-2R alpha- human large granular lymphocytes which express only the 70 to 75 kDa IL-2R beta subunit of the high affinity IL-2R. Anti-Tac mAb could inhibit IL-2-stimulated tyrosine phosphorylation in activated T cells, which express both IL-2R subunits that together form the high affinity receptor complex, but not in large granular lymphocytes expressing only the IL-2R beta subunit. The data suggest that IL-2 stimulation of tyrosine kinase activities requires only the IL-2R beta subunit.     

p55 IL-2 receptor mRNA precursors in murine T lymphocyte nuclei

An unusual family of cDNA clones homologous to human p55 IL-2R sequences was isolated from the murine HT-2 Th cell line. These clones were mapped, partially sequenced, and compared with previously published human and mouse IL-2R sequences. They appear to consist of various combinations of exons and introns, suggesting that they are derived from p55 IL-2R mRNA precursors. The configuration of exons in the splicing intermediates indicates that the murine and human gene organizations are similar and that the 3' end of intron 3 is well conserved between the two species. RNA mapping experiments using nuclear, cytoplasmic, and total RNA and probes derived from various parts of the p55 IL-2R gene support and extend the sequence data. They indicate that detectable amounts of immature p55 IL-2R mRNA are found specifically in the cell nucleus of the HT-2 cell line. Similar data were obtained for the Th cell clone 52.3 and the cytotoxic T cell line CTLL. All these results indicate that the T cell nucleus contains significant amounts of immature p55 IL-2R mRNA.     

Monoclonal antibodies block murine IL-4 receptor function.

IL-4 is a cytokine which can induce B-lymphocyte proliferation, increase cell-surface Ia expression, and induce some activated B cells to differentiate and begin to secrete IgE. IL-4 binds specifically to a cell-surface receptor (IL-4R) on cells from a variety of lineages including T and B cells. In general both primary cells and in vitro cell lines express less than 5000 receptors per cell. Utilizing a subclone of the cytotoxic T cell line CTLL-2 expressing a high level of IL-4R, mAb against the murine IL-4R were prepared. Two mAb have been identified which have different properties. These antibodies, designated M1 and M2, recognize sequences specific to the murine IL-4R. Immunoprecipitation studies with M1 and M2 on CTLL-2 cells have identified the receptor as a Mr = 145,000 cell-surface protein. Similar results have been obtained with the recently isolated full length murine IL-4R cDNA expressed in COS-7 cells. In addition the antibodies are capable of inhibiting IL-4 binding. One antibody, M1, is also a potent inhibitor of IL-4-induced proliferation. These antibodies will be useful in dissecting a wide array of activities attributed to IL-4.     

Synergistic and antagonistic effects of IL-1 alpha and IL-4, respectively, on the IL-2-dependent growth of a T cell receptor-gamma delta+ human T leukemia cell line

The TALL-103/2 cell line was derived from an immature acute T lymphocytic leukemia with T-myeloid differentiating capacity. The leukemic cells were first expanded in recombinant human IL-3 in which they acquired a myeloid phenotype, and subsequently were adapted to grow in human rIL-2 in which they became lymphoid committed. The TALL-103/2 cell line expresses only T cell-specific differentiation Ag (CD2, CD3, CD7, and CD8) but has retained the CD33 myeloid Ag originally present on the IL-3 expanded population. By using mAb directed at the TCR-alpha beta or specific for framework determinants on human TCR-gamma and -delta chains, the TALL-103/2 cells were shown to be WT31-, TCR delta 1+, TCS-1+, and Ti gamma A-, thus representing a T cell subset expressing the nondisulfide-linked form of the TCR-gamma delta. The TALL-103/2 cells have been maintained for more than 1 y in the presence of human rIL-2 on which they are strictly dependent. Chemical cross-linking and immunofluorescence studies indicate the presence of both high and intermediate affinity IL-2R on the TALL-103/2 cells. Whereas mAb antiTac and H-31 with reactivity to the IL-2R alpha-chain (p55) compete only partially for the IL-2-induced proliferation of these cells, mAb TU27, specific to the IL-2R beta-subunit (p75), inhibits such growth completely even at high concentrations of IL-2. The interactions of the two T cell-stimulating factors IL-1 and IL-4 on the IL-2-dependent growth of TALL-103/2 cells were investigated. IL-1 alpha synergizes with IL-2 in supporting the short and long term growth of this cell line, whereas IL-4 abrogates its growth. These effects are, at least in part, due to the modulation of IL-2R expression induced by the two lymphokines. Functionally, the TALL-103/2 cells display MHC-nonrestricted cytotoxic activity that is significantly enhanced by addition of either IL-4, IL-6, or IFN-gamma. Because of its properties and its stable requirement for IL-2 for continuous growth, this T lymphocytic leukemia-derived cell line represents an interesting model to analyze ontogeny and function of leukemic T cells.     

Identification of a novel protein capable of interacting with the IL-3 receptor

IL-3 has numerous functions in hematopoiesis yet its receptor has not been fully characterized. We have developed two mAb, 4G8 and 2F2, that markedly inhibited IL-3-dependent proliferation whereas only marginally affecting IL-2 or IL-4-induced proliferation. On Western blots, both antibodies identified the same protein, which varied in size from 115 to 145 kDa in six cell lines tested. The 4G8/2F2 Ag was detected at moderate density, on a wide variety of cells including IL-3-dependent cell lines and T lymphocytes. Radioligand binding studies revealed that 4G8, but not 2F2, could inhibit the binding of 125I-IL-3 to the high affinity IL-3R. These data suggest that the mAb 4G8 and 2F2 recognize different epitopes on the same Ag, and suggest furthermore that the inhibition of IL-3-dependent proliferation mediated by 2F2, in particular, does not occur via inhibition of ligand binding. Neither antibody showed an enhanced level of fluorescent staining of Cos 7 cells transfected with the low affinity IL-3R cDNA. In addition, 4G8 did not inhibit IL-3 binding to L cells transfected with the cloned IL-3R or IL-4R despite the fact that 4G8 was expressed on these cells. These data suggest that the 4G8/2F2 Ag is a unique cell surface protein that can interact with the endogenous functional IL-3R.     

Promotion of human T lymphocyte proliferation by IL-4

The capacity of human rIL-4 to support the proliferation of mitogen-stimulated T cells directly as well as by increasing IL-2 production or enhancing IL-2 responsiveness was investigated. IL-4 augmented proliferation of T cells stimulated with PHA, Con A, immobilized mAb to the CD3 molecular complex (OKT3), or PMA. IL-4 increased the number of mitogen-stimulated cells entering the cell cycle as well as enhancing ongoing proliferation of mitogen-activated lymphoblasts. Facilitation of initial activation by IL-4 was not inhibited by mAb to the p55 component of the IL-2R, anti-Tac, and, therefore, was not dependent on endogenous IL-2 activity. However, IL-4-mediated enhancement of ongoing T cell proliferation stimulated by PHA or OKT3 was partially but not completely blocked by anti-Tac. Analysis of the supernatants from PHA-stimulated T cell cultures indicated that IL-4 increased the production of IL-2 by mitogen-activated cells. Moreover, IL-4 increased the amount of IL-2 mRNA that accumulated in mitogen-stimulated T cells. In addition, IL-4 markedly augmented IL-2R expression by PHA-stimulated T cells. Although IL-4 promoted ongoing DNA synthesis of mitogen-stimulated T cells in an IL-2-dependent manner, it was also able to sustain their proliferation directly. Thus, IL-4 supported proliferation of PMA-activated T cells in a manner that was not inhibited by anti-Tac. Furthermore, IL-4 could augment proliferation and IL-2R expression of T cells stimulated with PHA in the presence of cyclosporin A, which blocks endogenous cytokine production or anti-Tac. Finally, IL-4 was noted to enhance proliferation of both CD4+ and CD8+ T cell subsets. The results indicate that IL-4 enhances proliferation of mitogen-activated human T cells by a number of mechanisms, including the direct promotion of cell cycle entry and subsequent DNA synthesis, enhanced production of IL-2, and increased responsiveness to IL-2 in part by up-regulation of IL-2R expression.     

Stimulation of human T cells via anti-T cell receptor monoclonal antibody BMA031: distinct cellular events involving interleukin-2 receptor and lymphocyte function antigen 1

We have analyzed activation of resting human T cells by anti-T cell receptor (TCR) monoclonal antibody (mAb) BMA031, a murine mAb of the G2b isotype. Human peripheral blood lymphocytes (PBL) respond to anti-TCR mAb by short-term proliferation in vitro and by acquisition of responsiveness to interleukin 2 (rIL-2) in the absence of detectable IL-2 production. Cell depletion and limiting dilution experiments indicate that anti-TCR mAb +/- rIL-2 stimulation covers a substantial portion of human T cells, including CD4+ and CD8+ cells. Enhancement by rIL-2 of anti-TCR mAb-induced proliferation is blocked by anti-IL-2 receptor (IL-2R, p55) mAb, while anti-TCR mAb-induced proliferation is not. In contrast, anti-TCR mAb-induced proliferation is blocked by anti-lymphocyte function antigen 1 (LFA-1, CD11a) mAb and is not demonstrable in PBL from two patients with severe congenital LFA-1 deficiency, not even in the presence of irradiated LFA-1+ PBL. We conclude that stimulation of resting human T cells by anti-TCR mAb BMA031 enables dissociation of distinct steps in T cell activation that specifically require participation of IL-2R (p55) and LFA-1 cell surface molecules in a mutually exclusive way.     

Highly concentrated urine-purified Tac peptide fails to inhibit IL-2-dependent cell proliferation in vitro.

Tac peptide, i.e., the p55 chain of the human interleukin-2 receptor (IL-2R) complex, is detectable as a soluble from (sIL-2R) in normal sera and, at increased levels, in patients with different diseases. Since several immunological abnormalities are observed in most conditions associated with an increase in sIL-2R levels, a down-regulatory effect on IL-2-dependent functions has been postulated as a consequence of binding and functional block of IL-2 by the excess of sIL-2R. To test this hypothesis, we purified sIL-2R from the urine of a patient with hairy cell leukemia and investigated the possible inhibitory effect of this peptide on the in vitro IL-2-induced cell proliferation. The urine-purified molecule was detectable by the specific immunoassay utilized to measure the serum Tac peptide and was constructed by a single polypeptide of about 50 kDa which was able to bind IL-2. Experiments performed with the IL-2-dependent murine CTLL-2 cell line and with PHA-stimulated human peripheral blood mononuclear cells showed that the purified sIL-2R at concentrations up to about 300 nM was unable to block IL-2-dependent cell proliferation. According to these data, which can be explained by the low affinity for IL-2 of the p55 IL-2R chain, it seems unlikely that in vivo the soluble Tac peptide can exert a down regulatory effect on IL-2-induced phenomena through a functional block of IL-2.     

Differential expression of the IL-2 receptor subunits, p55 and p75 on various populations of primary peripheral blood mononuclear cells

Unstimulated PBL were examined for expression of IL-2R subunits, IL-2Rp55 and IL-2Rp75, by two-color flow cytometric analyses using mAb. NKH-1+ non-T non-B cells expressed IL-2Rp75 but not IL-2Rp55, and the IL-2Rp75 sites on purified NKH-1+ cells were determined to be 1630 sites/cell by binding of 125I-labeled TU27 mAb specific for IL-2Rp75. In the CD4+ T cell population, IL-2Rp55+ cells were significantly detected, but little or marginally of the IL-2Rp75+ cells. However, IL-2Rp75+ cells were significantly detected, but little of the IL-2Rp55+ cells in the CD8+ T cell population. The IL-2Rp75 sites on CD8+ T cells were estimated at approximate 180-410 sites/cell. In the CD4+ T cells, expression of IL-2Rp75 as well as IL-2Rp55 was induced by stimulation with PHA. IL-2Rp75+ cells, but not IL-2Rp55+ cells, were also detected in the CD14+ monocyte population. In the CD20+ B cell population, a small number of IL-2Rp55+ cells was detected, but little of the IL-2Rp75+ cells.     

IL-2-R beta expression and function within resting CD8+ T cells preferentially segregate with the CD45R0+ subset.

Human peripheral blood CD8+ T cells constitutively express a low level of IL-2-R beta chains which were shown in this study to be preferentially carried by the CD45R0+ subset. Such receptors can transduce signals for in vitro IL-2-induced cytolytic function and for the initiation of soluble anti-CD3 and IL-2-induced cell proliferation. Using these stimulation models, a comparison was made between the responsiveness of resting, small CD45R0+ and CD45RA+ subpopulations of CD8+ T cells, both of them being isolated by negative selection and rigorously depleted of monocytes and of IL-2-inducible non-MHC-restricted CTL. Strong proliferation was induced in CD8+/CD45R0+ cells in response to IL-2 and soluble anti-CD3 (each of these stimuli being by itself ineffective), while in contrast, CD8+/CD45RA+ cells manifested, in this system, little reactivity. Accordingly, no conversion to the CD45R0 phenotype occurred in single stained CD45RA+ T cells following their incubation with the stimuli. A similar restriction of reactivity to CD8+/CD45R0+ T cells was observed with respect to IL-2-induced targetable T cell cytotoxicity. The CTL activity induced by IL-2 alone occurred without cell division. In contrast, the additional increase in CTL activity occurring upon the synergistic actions of anti-CD3 mAb and IL-2 coincided with intense cell proliferation, with no generation of LAK activity. The inhibition exerted by anti-IL-2-R beta mAb in the cytolytic and the proliferative activities induced by these stimuli in resting CD8+/CD45R0+ T cells emphasizes the importance of constitutive IL-2-R beta chains in the biology of these cells.