Functional IL-2 Receptors Research Articles

Are the IL‐2 Receptors Expressed in the Murine Fetal Thymus Functional?

It is well established that the majority of murine fetal thymocytes (day 15 of gestation) express receptors for interleukin 2 (IL-2), but the functional significance of these IL-2 receptors (IL-2Rs) is not clear. In situ hybridization data show a developmentally regulated expression of IL-2 and IL-2R mRNA. IL-2 binding studies were performed on fetal thymocytes and the results show the presence of both high (kD ≅ 20 pM) and low (kD ≅ 10 nM) affinity IL-2Rs. These IL-2Rs are indeed functional: intact fetal thymic lobes (but not cell suspensions) cultured in IL-2 exhibited an in vitro proliferative response at 20 pM of IL-2, corresponding with the presence of a functional high-affinity IL-2R on fetal thymocytes. The IL-2-dependent growth was primarily observed in the IL-2R + thymic subset, which contains the CD3-/CD4-/CD8- precursor thymocytes. Furthermore, in vitro blocking of IL-2 in intact fetal thymic lobes resulted in a reduction in the cell yield, which predominantly affected the expansion of the immature CD3-/CD4-/CD8-thymocytes. Our findings strongly support the concept that the IL-2/IL-2R pathway is responsible for the proliferation of precursor cells within the fetal thymus.

IL-2 receptor expression in autoimmune MRL-lpr/lpr mice. The expanded L3T4-, Lyt-2- population does not express p75 and cannot generate functional high-affinity IL-2 receptors.

Autoimmune MRL-lpr/lpr mice develop an SLE-like disease characterized by a profound lymphadenopathy within an L3T4-, Lyt-2- (DN), B220+ T-cell population. Despite its immature phenotype this subset expresses mature alpha beta TCR belonging predominantly to the V beta 8 gene family and appears to be identical to an activated form of a minor T cell population present in both the thymus and periphery of normal mice. However, the mechanisms underlying the greatly increased cellularity in lpr/lpr-bearing mice are not understood. In this study, the IL-2R expression of lpr/lpr T cells was examined to assess the contribution of IL-2-mediated division to their expansion. The lpr/lpr DN T cells lacked high-affinity IL-2R, even after stimulation, suggesting that IL-2-dependent proliferation plays no role in the expansion of these cells and demonstrating the existence of this unusual T cell phenotype in vivo.

Adoptive immunotherapy with interleukin-2 (IL-2) results in diminished IL-2 production by stimulated peripheral blood lymphocytes

We examined the responses of peripheral blood lymphocytes (PBL) to a panel of T-cell mitogens in patients receiving adoptive transfers of tumor-infiltrating lymphocytes and continuous infusions of interleukin-2 (IL-2) for treatment of advanced cancer. All patients showed diminished proliferative responses to soluble and alloantigens, lectins, anti-CD3, and IL-2 during therapy. The non-major histocompatibility complex (MHC)-restricted cytolytic activities of PBL were increased by treatment and were further augmented by IL-2 in vitro. The expression of approximately 55-kd low-affinity IL-2 receptors (IL-2R) by PBL increased during treatment but functional IL-2R were simultaneously down-regulated. Proliferative responses were partially restored to pretreatment levels when PBL were costimulated with recombinant IL-2 and mitogens. Lectin stimulation of PBL produced little IL-2 secretion during treatment, while IFN-gamma secretion persisted. We conclude that infusions of IL-2 down-regulate the expression of functional IL-2R, decrease the secretion of IL-2, and lead to decreased mitogen responses by PBL.

Maintenance of Alveolitis in Patients with Chronic Beryllium Disease by Beryllium-Specific Helper T Cells

Chronic beryllium disease is characterized by the accumulation of helper/inducer T cells, macrophages, and granulomas in the lungs. To evaluate the hypothesis that the proliferation of CD4+ (helper/inducer) T cells in the lungs of patients with this disorder is maintained by local activation of beryllium-specific T-cell clones, we studied T cells obtained from peripheral blood and by bronchoalveolar lavage in eight patients and five healthy controls. The proliferation of T cells in response to beryllium in vitro was confined to the CD4+ T cells from the patients and was dependent on the presentation of antigen in the presence of both major histocompatibility complex class II antigens and functional interleukin-2 receptors. T cells from the patients' lungs had a significantly greater response to beryllium than did T cells from their peripheral blood (stimulation index, 103 vs. 5; P less than 0.01). Lines and clones of cells developed from T cells from the patients' lungs showed dose-dependent proliferation in response to beryllium but did not respond to recall antigens or to other metals. Although all beryllium-specific T-cell clones were CD4+ and none were CD8+ (suppressor/cytotoxic), all beryllium-specific clones studied had different rearrangements of T-cell antigen receptors, suggesting that the response to beryllium involved T cells with diverse specificities for beryllium. We conclude that in patients with chronic beryllium disease, beryllium acts as a class II-restricted antigen, stimulating local proliferation and accumulation in the lung of beryllium-specific CD4+ (helper/inducer) T cells. Hence, chronic beryllium disease is a hypersensitivity disease in which beryllium is the specific antigen.

Structure of the functional interleukin-2 receptor: Evidence for the association of human p55 and murine p75 molecules in a mouse T cell line

The structural basis of the high affinity interleukin-2 receptor which was previously reconstituted in a cultured murine T cell line, EL4 by expressing either wild-type Tac antigen complementary DNA (cDNA) or a chimeric cDNA was characterized. The chimeric cDNA encodes a membrane portion whose extracellular portion consists of that of Tac antigen whereas transmembrane and cytoplasmic portions consists of those the human insulin beta chain. The Tac antigen/anti-Tac antibody complex was treated by chemical crosslinking reagents, purified by goat anti-mouse immunoglobulin (Ig), and was analysed by SDS-PAGE. We here demonstrated the presence in mouse EL4 transfectants of a novel membrane protein which is closely associated with the products of transfected cDNAs in the absence of interleukin-2. The protein is 75 kDa in size and is detected in cells which express high affinity interleukin-2 receptor but not in cells which only express low affinity interleukin-2 receptor. The transmembrane region and the cytoplasmic region of Tac antigen is not necessary for the formation of the complex consisting of Tac antigen and 75 kDa molecule, indicating that a murine 75 kDa molecule associates with Tac antigen extra-cellularly.

Induction of competence and progression signals in human T lymphocytes by phorbol esters and calcium ionophores

We have investigated the induction of competence (IL-2 responsiveness) and progression in human T lymphocyte proliferation triggered by phorbol ester and calcium ionophore. The degree of proliferation induced with the phorbol ester, phorbol 12,13-dibutyrate (PDB) and the calcium ionophore ionomycin was dependent on the duration of exposure to these agents, with more than 6 h required for obtaining maximum proliferation. Following brief exposure to both agents for 30 min, which did not cause significant proliferation, T cells became competent to proliferate in response to exogenous interleukin 2 (IL-2). These competent T cells also progressed to DNA synthesis following incubation with PDB in the absence of ionomycin. Induction of competence to proliferate in response to either PDB or IL-2 was blocked by EGTA, suggesting that transmembrane Ca2+ flux was obligatory at this stage. Since other phorbol esters and synthetic diacylglycerols also stimulated DNA synthesis in competent cells, it is likely that progression was triggered by activation of protein kinase C. Following a brief exposure to PDB and ionomycin, subsequent incubation with PDB induced gene expression and secretion of IL-2 and augmented the expression of IL-2 receptors in the competent cells. Thus, we have demonstrated that Ca2+ mobilization is required for rendering T cells competent to express functional IL-2 receptors, to produce IL-2 in response to subsequent incubation with PDB, and that sustained activation of protein kinase C seems necessary for IL-2 production and subsequent progression of competent T cells to DNA synthesis.

Cross-linking of T-cell receptors is insufficient to induce IL-2 responsiveness (activation) in resting Lyt-2+ T cells. IL-4 or RIF are essential as second signal.

High-density (resting) murine Lyt-2+ T cells exposed in vitro to the ligand concanavalin A (Con A), or immobilized F23.1 monoclonal antibody (mAb) recognizing an allotypic determinant on the T-cell receptor (TCR), or high-density (resting) allogeneic B stimulator cells remain IL-2-unresponsive; such cells do not express functional IL-2 receptors unless reconstituted with accessory cells. We conclude that cross-linking of TCR is insufficient as signal to induce IL-2 responsiveness, that is, activation. Both the macrophage product RIF and the T-cell product interleukin-4 efficiently induce the IL-2 responsiveness in resting Lyt-2+ T cells exposed in vitro either to the ligand Con A, or to immobilized F23 mAb, or to nonimmunogenic allogeneic stimulator cells. We conclude that two restricting points control the induction of IL-2 responsiveness (activation) in antigen-driven Lyt-2+ T-cell responses, that is, cross-linking of TCR by way of presented antigen and "costimulator" activity expressed by accessory cells. Both RIF and IL-4 express costimulator activity, therefore replacing the requirement for accessory cells.

T cell-replacing factor (TRF)/interleukin 5 (IL-5): molecular and functional properties.

TRF has originally been defined as a T-cell-derived lymphokine that triggers activated B cells for a terminal differentiation into Ig-secreting cells. HPLC-purified TRF from Sup of a murine TRF-producing B151 cell is an acidic glycoprotein, exerts BCGF II activity and induces expression of IL-2 receptors. It does not show IL-1, IL-2, IL-3, BSF-1/IL-4, or IFN gamma activity. We prepared monoclonal TB13 and NC17 antibodies against HPLC-purified B151-TRF which are specific for and can inhibit TRF as well as BCFG II activity of B151-TRF. Moreover, TB13 as well as NC17 antibody can immunoprecipitate the 46 Kd molecule from B151 Sup which exerts TRF as well as BCGF II activity. Complementary DNA (pSP6K-mTRF23) encoding for murine TRF/IL-5 was cloned and its entire nucleotide sequences were determined. The murine TRF/IL-5 cDNA encodes 133 amino acids including N-terminal strongly hydrophobic regions. Secreted recombinant TRF/IL-5 (apparent m.w. of 46 Kd) has 113 amino acid residues and also comprises homodimers of a molecule with an apparent m.w. of 25 to 30 Kd. TRF/IL-5 mRNA is constitutively expressed in constitutively TRF-producing B151 and is inducible in some T cell lines upon stimulation with PMA or Con A. TRF/IL-5 mRNA is also expressed in Tbc-primed T cells upon the stimulation with PPD, whereas its expression is not effectively induced in non-primed spleen cells by stimulation with Con A or PMA plus calcium ionophore. The translation product of murine TRF/IL-5 cDNA triggers resting as well as activated (DNP-primed or LPS-stimulated) murine B cells for terminal differentiation into Ig-secreting cells (IgM, IgG1, or IgA) accompanied by increased mRNA expression for secreted forms of relevant Ig heavy chain (mu, gamma, or alpha). Among these, increases in the level of mu, and alpha-specific mRNA for the secreted form of IgM and IgA, respectively, are prominent. Moreover, TRF/IL-5 induces maturation of resting B cells into IgM-secreting cells. TRF/IL-5 promotes growth of activated B cells as well as BCL1 cells. TRF/IL-5 is, therefore, a growth as well as a differentiation inducing factor for B cells. Moreover, it induces functional IL-2 receptors on resting as well as activated B cells, besides TRF and BCGF II activities.(ABSTRACT TRUNCATED AT 400 WORDS)

Primary activation of murine CD8 T cells via cross-linking of T3 cell surface structures: two signals regulate induction of interleukin 2 responsiveness.

In the model system used here to study the minimal signal requirements for the activation of murine resting CD8 T cells, cross-linking of T cell receptor structures by antigen-presenting cells is substituted for by the use of anti-CD3 monoclonal antibodies immobilized in Sepharose beads. We show that cross-linking of CD3 structures, even in combination with CD8 structures, is necessary but insufficient to induce responsiveness to the growth-promoting effect of interleukin 2 (IL2), i.e. fails to induce expression of functional IL2 receptors. A macrophage cell line product termed IL2 receptor-inducing factor (RIF), but not IL1, IL3, IL4 or tumor necrosis factor, efficiently functions as costimulator. Once activated, growth of CD8 T cells is entirely driven by IL2. We conclude that two restriction points control the activation of resting CD8 T cells. While cross-linking of CD3 structures is essential as a first step, RIF is required as competence factor to induce IL2 responsiveness. We consider the possibility that the ability of antigen-presenting cells to produce RIF determines the immunogenicity of presented antigen towards antigen-reactive resting CD8 T cells.

Abnormalities of T cell activation in the rheumatoid synovium detected with monoclonal antibodies to CD3.

The chronic inflammation of rheumatoid arthritis (RA) is associated with hypofunction of synovial fluid (SF) T cells. We studied the mechanisms leading to this abnormality using a mitogenic monoclonal antibody specific for the T cell receptor-associated CD3 complex. We found that SF cells are defective in their response to anti-CD3 antibodies as measured by proliferation, generation of natural cytotoxicity, and induction of the Tac (p55) component of the IL2 receptor. Nevertheless, these cells do bear functional IL2 receptors and are more responsive to IL2 than are resting peripheral blood T cells. In searching for a mechanism to explain the reduced IL2 production, we found that polyamines (whose oxidation products can down-regulate proliferation and IL2 production) are elevated in RA cells from both blood and SF. We postulate that the chronic activation of RA T cells triggers this feedback loop which constitutes a defensive mechanism aimed at reducing the T cell driven autoimmune and inflammatory process.

Expression of functional interleukin-2 receptors in human light chain/Tac transgenic mice.

The growth of mature T lymphocytes is regulated by interaction between interleukin-2 (IL-2) and its receptor. Three distinct binding sites for IL-2, namely low- (Kd 10 nM), intermediate- (Kd 100 pM) and high- (Kd 10 pM) affinity sites, have been found on human and primate T lymphocytes. Chemical crosslinking of labelled IL-2 to human T cells shows that two polypeptide chains, p55 (L chain) and p75 (H chain), bind IL-2 with low and intermediate affinities respectively. The high-affinity binding was shown to arise from ternary complex formation of IL-2, L and H chains. Construction of mutants of the L-chain complementary DNA indicated that the L chain is not directly involved in growth signal transduction. Nevertheless, expression of the IL-2 receptor L chain is tightly regulated by antigen or mitogen stimulation. To investigate the L chain function, we have produced transgenic mice using human L-chain cDNA of the IL-2 receptor under the control of a constitutive promoter. Studies on the L-chain transgenic mice showed that functionally active IL-2 receptors with high affinity were expressed on unstimulated spleen and thymus cells. The results indicate that the H chain of the IL-2 receptor is constitutively expressed in T cells.

The IL-2 Receptor β Chain (p70): Role in Mediating Signals for LAK, NK, and Proliferative Activities

Interleukin-2 (IL-2) induces cytolytic activity and proliferation of human blood lymphocytes. Yet, prior to activation, these cells do not express IL-2 receptors recognized by monoclonal antibodies to the Tac antigen. A novel glycoprotein (IL-2R beta), identified on several lymphocytoid cell lines, has the ability to bind IL-2 alone and to associate with Tac antigen (IL-2R alpha) to form high-affinity IL-2 receptors. It is now reported that IL-2R beta is expressed on both circulating T lymphocytes and large granular lymphocytes in quantities approximately proportional to their responsiveness to IL-2. Studies of the responses of these cells to IL-2 suggest that IL-2R beta mediates the initial phase of induction of lymphokine activated killer (LAK), natural killer (NK), and proliferative activities. Subsequently, IL-2R alpha is induced and functional high-affinity IL-2 receptors are expressed.

Characterization of Interleukin-2 Receptors Expressed on Acute Leukemic B Cells

AbstractMore than 90% of both unfractionated and blast-enriched T cell-depleted mononuclear cells (MNC) from a patient with a morphologically and phenotypically unclassified acute leukemia expressed interleukin 2 receptors (IL2-R), whereas 50% unfractionated MNC displayed monocyte/myeloid- (My7, My9, and OKM1) and B cell-restricted (B4) antigens. Two-color fluorescence studies showed that 80% of the My9+ cells expressed the B4 antigen and 63% of the B4 + cells were IL2-R+. Cell incubation with phorbol myristate acetate (PMA) increased the expression of B4 antigen and significantly decreased the proportion of My9+ and IL2-R-bearing cells. Southern analysis of DNA from leukemic cells revealed monoclonal rearranged heavy- and k light-chain immunoglobulin genes. Immunoprecipitation of leukemic cell membrane proteins with a monoclonal antibody recognizing the IL2-R (anti-Tac) revealed a protein with the same molecular weight (55 kilodaltons) as that of the IL2-R present on PHA-stimulated normal T cells. Fresh leukemic cells did not express high-affinity IL2-R and did not proliferate in liquid culture or in a colony assay in the presence of recombinant IL2 (rlL2). PMA-treated blast cells, however, generated B cell colonies in the presence of rlL2, thus suggesting that PMA could induce functional IL2-R on immature leukemic B cells.

Characterization of interleukin-2 receptors expressed on acute leukemic B cells

More than 90% of both unfractionated and blast-enriched T cell-depleted mononuclear cells (MNC) from a patient with a morphologically and phenotypically unclassified acute leukemia expressed interleukin 2 receptors (IL2-R), whereas 50% unfractionated MNC displayed monocyte/myeloid- (My7, My9, and OKM1) and B cell-restricted (B4) antigens. Two-color fluorescence studies showed that 80% of the My9+ cells expressed the B4 antigen and 63% of the B4+ cells were IL2-R+. Cell incubation with phorbol myristate acetate (PMA) increased the expression of B4 antigen and significantly decreased the proportion of My9+ and IL2-R-bearing cells. Southern analysis of DNA from leukemic cells revealed monoclonal rearranged heavy and k light-chain immunoglobulin genes. Immunoprecipitation of leukemic cell membrane proteins with a monoclonal antibody recognizing the IL2-R (anti-Tac) revealed a protein with the same molecular weight (55 kilodaltons) as that of the IL2-R present on PHA-stimulated normal T cells. Fresh leukemic cells did not express high-affinity IL2-R and did not proliferate in liquid culture or in a colony assay in the presence of recombinant IL2 (rIL2). PMA-treated blast cells, however, generated B cell colonies in the presence of rIL2, thus suggesting that PMA could induce functional IL2-R on immature leukemic B cells.

Analysis of prostaglandin E2 effect on T lymphocyte activation. Abrogation of prostaglandin E2 inhibitory effect by the tumor promotor 12.0 tetradecanoyl phorbol-13 acetate.

We have investigated the inhibitory potential of prostaglandin E2 (PGE2) with respect to intracellular messengers implicated in the signaling system of T-lymphocyte activation pathway. Using the fluorescent indicator Quin 2, it is demonstrated that PGE2 inhibits the increase in cytosolic-free calcium concentration [Ca2+]i. Reconstitution of calcium mobilization in the presence of PGE2 by the calcium ionophore A23187 results in a partial restoration of both interleukin 2 (IL2) production and cell proliferation and has no effect on the inhibition of transferrin receptor expression. In contrast, the treatment of cell cultures with the tumor promotor 12.0 tetra decanoyl phorbol-13-acetate (TPA) abrogates the suppressor activity of PGE2. When T lymphocyte stimulation is provided by the combination of A23187 and TPA, the PGE2 inhibitory effect does not occur. These data also indicate that the down regulation of transferrin receptor by PGE2 is proximal to protein kinase C activation and is not associated with decreased expression of the functional IL2 receptor.

Tac antigen forms disulfide-linked homodimers.

Interleukin 2 (IL-2) is responsible for stimulating T-cell proliferation via interaction with specific, high-affinity membrane receptors. Although an IL-2-binding protein has been identified by virtue of its reactivity with a monoclonal antibody that competes with IL-2 for binding (anti-Tac), the complete and precise structure of functional IL-2 receptors is still unknown. To define further the composition of IL-2 receptors, both IL-2 itself and anti-Tac were used as ligands to adsorb membrane proteins for analysis by sodium dodecyl sulfate/polyacrylamide gel electrophoresis (NaDodSO4/PAGE). A variety of experimental approaches yield results indicating that the Tac antigen, which migrates as a single protein on NaDod-SO4/PAGE under reducing conditions, is also expressed as disulfide-linked homodimers and oligomers. Examined under nonreducing conditions, both activated normal human T cells and cell lines from patients with adult T cell leukemia (HUT-102; MT-1) express Tac antigen homodimers (Mr 105,000) in addition to monomers (Mr 54,000). Formation of the disulfide bond is not a consequence of the experimental procedures used to isolate the proteins for analysis, inasmuch as identical results are obtained when the receptor proteins are iodinated and extracted in the presence of N-ethylmaleimide or prepared for electrophoresis in the absence of heat denaturation. Accordingly, these findings point to Tac antigen associating with itself preferentially. The physiologic significance of homodimer and oligomer formation, especially as it relates to the formation of high-affinity IL-2 receptors, is presently unknown.

T cell replacing factor/interleukin 5 induces not only B-cell growth and differentiation, but also increased expression of interleukin 2 receptor on activated B-cells

A T-cell replacing factor (TRF)/interleukin-5 (IL-5) is a B-cell growth and differentiation factor. In the present study, we examined the role of TRF/IL-5 in the increase in the levels of interleukin-2 (IL-2) receptor expression on activated B-cells. High pressure liquid chromatography (HPLC)-purified TRF/IL-5 (B151-TRF) from TRF-producing T-cell hybridoma, B151K12, as well as recombinant TRF/IL-5 (rec-TRF) were used for the analysis. Maximum anti-2,4-dinitrophenyl (DNP) IgG antibody response of DNP-primed B-cells or polyclonal IgM secretion of B-cell tumor line BCL 1 was seen when HPLC-purified B151-TRF was added or when suboptimal doses of B151-TRF were added to the culture in the presence of IL-2. Normal resting B-cells gave maximum anti-SRBC IgM PFC responses when HPLC-purified B151-TRF and IL-2 were present. The purified B151-TRF as well as rec-TRF also induced on B-cells increased expression of IL-2 receptors that react with monoclonal anti-murine IL-2 receptor antibody, PC61, and 125I-labelled IL-2. The numbers of functional high affinity IL-2 receptors on activated B cells increased at least 20-fold by culturing them with purified B151-TRF. Moreover, B151-TRF induced increase in the levels of steady-state mRNA for IL-2 receptor by approximately 8-fold. These results suggest that activated B-cells as well as BCL 1-cells may express functional IL-2 receptors or closely related molecules when stimulated with HPLC-purified B151-TRF as well as rec-TRF.

Induction of responsiveness to interleukin 2 in mouse lymphocytes by synergistic action of ionophore A 23187 and diacylglycerol.

We investigated whether the protein kinase C-binding agents 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and 1-oleoyl-2-acetyl-rac-glycerol (OAG) induced reactivity to interleukin 2 (IL-2) in mouse lymphocytes. 10(-8) M TPA was a strong inducer of reactivity to IL-2 measured by [3H]thymidine incorporation. In contrast OAG alone (6-25 micrograms/ml) did not induce a significant IL-2 mediated proliferative response. Cells stimulated with the ionophore A 23187 + OAG neither proliferated nor produced IL-2. In contrast, cells stimulated with A 23187 + OAG + IL-2 showed a significant proliferative response, indicating the expression of functional high affinity IL-2 receptors. The expression of reactivity to IL-2 induced by A 23187 + OAG was inhibited by 0.04 mM Mn2+; in contrast the TPA-mediated induction of IL-2 responsiveness was not affected by Mn2+. The data suggest differences in the mechanism of induction of IL-2 responsiveness by the two protein kinase C-binding agents, TPA and OAG.

Interleukin-2 effects on human B cells activated in vivo.

While activated B cells, as well as T cells, can express functional interleukin-2 receptors (IL-2R), the physiologic role of IL-2 in B-cell responses is still in doubt. Accordingly, we have examined the role of recombinant IL-2 (rIL-2) in the proliferative response, IL-2R expression, and the terminal differentiation of tonsillar B cells in comparative studies with T cells from the same source. For these analyses of physiologically activated lymphocytes, the B and T cells were first separated, then divided into subpopulations enriched for either resting or preactivated cells on the basis of relative cell density or activation antigen expression. As expected, the relatively low-density fraction of T cells was enriched for IL-2R-positive (Tac+) cells and displayed vigorous proliferative responses to IL-2 along with heightened Tac antigen expression. Moreover, limiting dilution analysis revealed that growth of these activated T cells could be perpetuated with the addition of IL-2. By comparison, relatively few tonsillar B cells expressed the Tac antigen. The addition of rIL-2 to cultured B cells of relatively low density resulted in an increase in Tac+ cells but only a minimal proliferative response. The subpopulation of tonsillar B cells expressing the Bac-1 activation antigen contained most of the IL-2 inducible Tac+ B cells, and rIL-2 induced an efficient but transient proliferative response by these activated B cells. The rIL-2-induced Tac+ B cells were noted to be relatively large. A fraction of these Tac+ cells, but not the Tac- cells, produced and secreted immunoglobulins. Incubation with rIL-2 enhanced the Ig secretion, and the anti-Tac antibody blocked this enhancement. Time-course analysis revealed that rIL-2 induced transient Tac expression, whereas mature plasma cells in 6-day cultures no longer expressed detectable Tac antigen. In conclusion, these observations suggest that IL-2 transiently upregulates expression of IL-2R, via which it induces the terminal growth and differentiation of activated B cells into plasma cells.

The proliferative response of B cell chronic lymphocytic leukemia to interleukin 2: functional characterization of the interleukin 2 membrane receptors

To determine the growth properties of B cell chronic lymphocytic leukemia (B CLL) and to identify possible abnormalities thereof, we examined the in vitro action of interleukin 2 (IL2) in four patients. Using radiolabeled IL2 and monoclonal antibodies reactive with IL2 membrane receptors we show that CLL cells, after their activation in vitro, express IL2 receptors of a high- as well as a low-affinity type, exactly as has been reported for normal T and B blasts. In three of the four reported cases, CLL proliferation (measured with 3H-thymidine incorporation) depended on the addition of phytohemagglutinin (PHA) to activate the cells and IL2 (optimal concentration, 10 to 100 U IL2/mL). In contrast, the cells of the fourth case of CLL (CLL-4) proliferated in an autonomous fashion, ie, without a need for PHA and IL2 in culture. Specific blocking of the IL2-binding sites with anti-IL2 receptor monoclonal antibodies almost completely inhibited the proliferation of these cells, which indicated that functional IL2 receptors were required for the autonomous proliferation. The demonstration of low concentrations of IL2 activity in the culture medium conditioned by the cells suggests that endogenous IL2 had been responsible for the spontaneous 3H-thymidine uptake by the CLL cells of patient 4. However, we were unable to extract IL2 mRNA from the cells (neither fresh nor after various in vitro incubations) in quantities detectable by Northern blot analysis that would prove that the CLL cells of patient 4 were actively synthesizing IL2 during culture. Thus, individual cases of B CLL are subject to variable growth regulation involving functional IL2 receptors on the cell surface: after activation with PHA the cells respond to exogenous IL2 in a fashion similar to normal B lymphocytes, or the cells are stimulated by endogenous IL2 (or an IL2-like activity) and do not require activation with PHA.