Pt-tetraethynylethene molecular scaffolding: synthesis and characterization of a novel class of organometallic molecular rods.

The series of monodisperse Pt-bridged TEE oligomers 3a-f was prepared by oxidative Glaser-Hay oligomerization of monomer 7 under end-capping conditions. These novel molecular rods extend in length from 3.3 nm (monomeric 3a) to 12.1 nm (hexameric 3 f). Their isolation was achieved by high performance gel permeation chromatography (GPC), and their purification was best monitored by analytical GPC in combination with matrix-assisted laser-desorption-ionization mass spectrometry (MALDI-TOF MS). The mass spectra of each oligomer revealed the molecular ion or its sodium complex as parent ion together with a clean, highly characteristic fragmentation pattern. Delayed addition of the end-capping reagent PhC(triple bond)CH to the oligomerization mixture afforded polymer 10 with an average of approximately 32 repeat units and a remarkably narrow molecular weight distribution (Mw/Mn=1.06), which is indicative of a living polymerization process. UV/Vis spectral data as well as measurements of the second hyperpolarizability gamma by third harmonic generation (THG) revealed a nearly complete lack of pi-electron delocalization along the oligomeric backbone. The Pt atoms act as true insulating centers, and the Pt-C(sp) bonds hardly possess any pi character. The synthesis of the molecular rods 3a-f provides another demonstration of the power of oxidative acetylenic homocouplings for the preparation of unusual nanoarchitecture.

Monodisperse poly(triacetylene) oligomers extending from monomer to hexadecamer: joint experimental and theoretical investigation of physical properties

A series of monodisperse Et3-Si-end-capped poly(triacetylene) (PTA) oligomers ranging from monomer to hexadecamer was prepared by a fast and efficient statistical deprotection-oxidative Hay oligomerization protocol. The PTA oligomers exhibit an increasingly deep-yellow color with lengthening of the pi-conjugated backbone, feature excellent solubility in aprotic solvents, and exhibit melting points up to > 22 degrees C for the hexadecameric rod. This new dramatically extended oligo(enediyne) series now enables to investigate the evolution of the physico-chemical effects in PTAs beyond the linear 1/n versus property regime into the higher oligomer region where saturation becomes apparent. We report the results of joint experimental and theoretical studies, including analysis of the 13C NMR spectra, evaluation of the linear (UV/ Vis) and nonlinear [third-harmonic generation (THG) and degenerate four-wave mixing (DFWM)] optical properties, and characterization of the redox properties with cyclic and steady-state voltammetry. Up to the hexadecameric rod, an increasingly facile one-electron reduction step is observed, showing at the stage of the dodecamer, a leveling off tendency from the linear correlation between the inverse number of monomer units and the first reduction potential. The effective conjugation length (ECL) determined by means of UV/Vis spectroscopy revealed a pi-electron-delocalization length of about n = 10 monomeric units, which corroborates well with the oligomeric length for which in the 13C NMR spectrum C(sp2) and C(sp) resonances start to overlap. Third-harmonic generation (THG) and degenerate four-wave mixing (DFWM) measurements revealed for the second-order hyperpolarizability gamma a power law increase gammma-alpha-n(a) for oligomers up to the octamer with exponential factors a= 2.46+/-0.10 and a=2.64+/-0.20, respectively, followed by a smooth saturation around n = 10 repeating units. The power law coefficient a calculated with the help of the valence effective Hamiltonian (VEH) method combined to a sum-over-states (SOS) formalism corroborates well with the values found by both THG and DFWM experiments. Up to the PTA heptamer, INDO (intermediate neglect of differential overlap)-calculated gas-phase ionization potentials and electron affinities obey a linear relationship as a function of the inverse number of monomer units displaying a strong electron-hole symmetry. The onset of saturation for the electron affinity is calculated to occur around the octamer, in accordance with experimentally obtained results from electrochemical measurements.

Synthesis and physical investigation of donor-donor and acceptor-acceptor end-functionalized monodisperse poly(triacetylene) oligomers.

Two series of monodisperse, terminally donor-donor [D-D, D=4-(dimethylamino)phenyl] and acceptor-acceptor [A-A, A=4-nitrophenyl] functionalized poly(triacetylene) (PTA) oligomers ranging from monomer to hexamer were synthesized by oxidative Hay oligomerization under end-capping conditions. The corresponding D-D and A-A end-substituted polymers with an average degree of polymerization (DP) of n approximately 18 and n approximately 12, respectively, were also prepared and served as reference points for the corresponding infinitely long polymers. These terminally functionalized PTA oligomers and polymers are yellow- to orange-colored compounds, displaying excellent solubility in aprotic solvents with melting points above 200 degrees C for the hexamers. For the 4-(dimethylamino)phenyl substituted compounds, a consistent first oxidation potential around +0.42 V versus Fc/Fc+ (ferrocene/ferricinium) was observed, whereas the 4-nitrophenyl functionalized systems underwent a reversible reductive two-electron transfer around -1.40V versus Fc/Fc+. The nature of the end-groups has a dramatic influence on the electronic absorption spectra. Saturation of the linear optical properties in the D-D series occurs at significantly shorter chain-length [effective conjugation length (ECL) of n approximately 4 monomer units] than in the A-A substituted or the previously reported Me3Si- and Et3Si-end-capped PTA oligomer series (ECL: n approximately 10 monomer units). Similar observations with respect to the ECL were made by measurement of the Raman-active v(C triple bound C) stretches. Third-harmonic generation (THG) and degenerate four-wave mixing (DFWM) experiments showed that shorter oligomers of terminally D-D or A-A functionalized PTAs display higher second hyperpolarizabilities gamma than the corresponding R3Si-end-capped series (R=alkyl). Moreover, they disclose a distinct peak of the nonlinearity per monomer unit at intermediate backbone lengths. In THG experiments, the second hyperpolarizabilities for long D/A-functionalized PTA oligomers attained the same saturation values as observed for the corresponding R3Si-end-capped rods. The nonlinearities measured by DFWM of the D-D and A-A substituted PTAs were found to be larger than for the silylated ones, which can be explained by the closeness of the two-photon resonance.

T helper differentiation proceeds through Stat1-dependent, Stat4-dependent and Stat4-independent phases.

Much of our focus in understanding Th1/Th2 development has been on the signals delivered by IL-12 and IL-4 as final determinants of terminal T cell differentiation. Because extinction of IL-12 signaling in early Th2 development could potentially be important in imprinting a more permanent Th2 phenotype on a population of T cells, we have also examined various parameters regulating the IL-12 signaling pathway. Whereas IL-4 appears to repress functional IL-12 signaling through inhibition of IL-12R beta 2 expression, IFN-gamma in the mouse, and IFN-alpha in the human appear to induce IL-12R beta 2 expression and promote IL-12 responsiveness. We propose that Th1 development can be considered in two stages, capacitance and development. Capacitance would simply involve expression of IL-12R beta 1 and beta 2 subunits, regulated by TCR, IL-4 and IFNs. The second stage, development, we propose is the true IL-12 induced developmental stage, involving expression of Stat4 inducible proteins. In the human, this may also occur via IFN-alpha, which is able to activate Stat4. It is perhaps possible that all of Stat4 actions on Th1 development may be exert directly by Stat4 at the IFN-gamma gene, however we suggest that, more likely, Stat4 may act to induce Th1 development through the induction of other non-cytokine genes, whose stable expression maintains the transcriptional state of a Th1 cell.

Scaling law for second-order hyperpolarizability in poly(triacetylene) molecular wires.

Poly(triacetylenes) are rodlike molecules with electrons delocalized over a one-dimensional path. We show that they exhibit a power-law dependence of the second-order hyperpolarizability gamma on the monomer unit n for short molecules and a smooth saturation toward a linear increase in longer molecules. The power law of gamma?n(a) with a approximately 2.5 from dengenerate four-wave mixing and third-harmonic generation measurements is in good agreement with quantum-chemical calculations. The critical conjugation length for saturation in the three cases is shown to be approximately 60 carbon-carbon bonds, which indicates the upper boundary for the electron delocalization in such a one-dimensional molecular wire.

Low dose TGF-beta attenuates IL-12 responsiveness in murine Th cells.

Expression of IL-12Rs is one important checkpoint for Th1 development. BALB/c DO11.10 CD4+ T cells stimulated by Ag in neutral conditions lose expression of the IL-12R beta 2 subunit and become unresponsive to IL-12. In contrast, B10.D2 or F1 (BALB/c x B10.D2) DO11.10 CD4+ T cells maintain IL-12R beta 2 expression when stimulated similarly. Here we show that the loss of IL-12 responsiveness by BALB/c T cells involves the action of endogenous TGF-beta. BALB/c T cells stimulated in the presence of anti-TGF-beta specifically maintain IL-12 responsiveness, express IL-12R beta 2 mRNA, and can stimulate nitric oxide production in peritoneal exudate cells. Low concentrations of TGF-beta added exogenously during primary activation of B10.D2 or F1 T cells significantly inhibit their development of IL-12 responsiveness. These effects of anti-TGF-beta are dependent on endogenous IFN-gamma and are inhibited by exogenously added IL-4. Thus, at least one effect of TGF-beta on Th1/Th2 development may be the attenuation of IL-12R beta 2 expression.

The interleukin-12/interleukin-12-receptor system: role in normal and pathologic immune responses.

Interleukin-12 (IL-12) is a heterodimeric cytokine that plays a central role in promoting type 1 T helper cell (Th1) responses and, hence, cell-mediated immunity. Its activities are mediated through a high-affinity receptor composed of two subunits, designated beta 1 and beta 2. Of these two subunits, beta 2 is more restricted in its distribution, and regulation of its expression is likely a central mechanism by which IL-12 responsiveness is controlled. Studies with neutralizing anti-IL-12 antibodies and IL-12-deficient mice have suggested that endogenous IL-12 plays an important role in the normal host defense against infection by a variety of intracellular pathogens. However, IL-12 appears also to play a central role in the genesis of some forms of immunopathology. Inhibition of IL-12 synthesis or activity may be beneficial in diseases associated with pathologic Th1 responses, such as multiple sclerosis or Crohn's disease. On the other hand, administration of recombinant IL-12 may have utility in the treatment of diseases associated with pathologic Th2 responses such as allergic disorders and asthma.

Analysis of the multiple interactions between IL-12 and the high affinity IL-12 receptor complex.

IL-12 is a heterodimeric cytokine, composed of a p40 and a p35 subunit, that exerts its biological effects by binding to specific cell surface receptors. Two IL-12R proteins, designated human IL-12 (huIL-12) receptor beta1 (huIL-12Rbeta1) and huIL-12Rbeta2, have been previously identified. These IL-12R individually bind huIL-12 with low affinity and in combination bind huIL-12 with high affinity and confer IL-12 responsiveness. In this study the interactions of hulL-12 with these two identified human IL-12R protein subunits are examined. The heterodimer-specific anti-huIL-12 mAb 20C2, which neutralizes huIL-12 bioactivity but does not block 125I-huIL-12 binding to huIL-12Rbeta1, blocked binding of huIL-12 to huIL-12Rbeta2. In contrast, anti-huIL-12Rbeta1 mAb 2B10 and mouse IL-12 p40 subunit homodimer (mo(p40)2) blocked 125I-huIL-12 binding to huIL-12Rbeta1, but not to huIL-12Rbeta2. Therefore, two classes of IL-12 inhibitors can be identified that differ in their ability to block huIL-12 interaction with either huIL-12Rbeta1 or huIL-12Rbeta2. Both mo(p40)2 and 20C2 blocked high affinity binding to huIL-12Rbeta1/beta2-cotransfected COS-7 cells, although, as previously reported, mo(p40)2 does not block high affinity binding to IL-12R on PHA-activated human lymphoblasts. Furthermore, these two classes of IL-12 inhibitors synergistically decreased hulL-12-stimulated proliferation and IFN-gamma production. Therefore, IL-12, in binding to the high affinity IL-12R, interacts with IL-12Rbeta1 primarily via regions on the IL-12 p40 subunit and with IL-12Rbeta2 via 20C2-reactive, heterodimer-specific regions of IL-12 to which the p35 and p40 subunits both contribute.

T cell genetic background determines maintenance of IL-12 signaling: effects on BALB/c and B10.D2 T helper cell type 1 phenotype development.

In this report, we examined the molecular basis underlying the genetic difference between BALB/c and B10.D2 T cells for T helper phenotype development in vitro. We found a strain-dependent difference in early maintenance of IL-12 responsiveness by T cells developing in vitro in unmanipulated (neutral) conditions. Thus, when activated without addition of exogenous cytokines or neutralization of endogenous cytokines, B10.D2, but not BALB/c, T cells remain responsive to IL-12 when activated for 7 days. The pattern of IL-12 responsiveness correlated with expression of the IL-12R signaling subunit, IL-12R beta2, and with IL-12-induced STAT4 phosphorylation. When activated under neutral conditions, BALB/c T cells rapidly lose IL-12R beta2 expression, STAT4 phosphorylation, and functional IL-12 responsiveness. More efficient maintenance of IL-12R beta2 expression by B10.D2 T cells activated under neutral conditions may explain the previously observed increase in IFN-gamma production relative to that of BALB/c. This difference could potentially provide greater protection from certain pathogens that do not immediately elicit strong Th1-inducing conditions via activation of the innate immune system.

Selective expression of an interleukin-12 receptor component by human T helper 1 cells.

Interleukin-12 (IL-12), a heterodimeric cytokine produced by activated monocytes and dendritic cells, plays a crucial role in regulating interferon (IFN)-gamma production and in the generation of IFN-gamma-producing T helper 1 (Th1) cells. Here we show that the IL-12 receptor (IL-12R) beta 2 subunit, a recently cloned binding and signal transducing component of the IL-12R, is expressed on human Th1 but not Th2 clones and is induced during differentiation of human naive cells along the Th1 but not the Th2 pathway. IL-12 and type I but not type II interferons induce expression of the IL-12R beta 2 chain during in vitro T cell differentiation after antigen receptor triggering. The selective expression and regulation of the IL-12R beta 2 subunit may help to understand the basis of Th1/Th2 differentiation and may provide therapeutic options for altering the Th1/Th2 balance in several immuno-pathological conditions such as autoimmune diseases and allergies.

Regulation of the interleukin (IL)-12R beta 2 subunit expression in developing T helper 1 (Th1) and Th2 cells.

The developmental commitment to a T helper 1 (Th1)- or Th2-type response can significantly influence host immunity to pathogens. Extinction of the IL-12 signaling pathway during early Th2 development provides a mechanism that allows stable phenotype commitment. In this report we demonstrate that extinction of IL-12 signaling in early Th2 cells results from a selective loss of IL-12 receptor (IL-12R) beta 2 subunit expression. To determine the basis for this selective loss, we examined IL-12R beta 2 subunit expression during Th cell development in response to T cell treatment with different cytokines. IL-12R beta 2 is not expressed by naive resting CD4+ T cells, but is induced upon antigen activation through the T cell receptor. Importantly, IL-4 and IFN-gamma were found to significantly modify IL-12 receptor beta 2 expression after T cell activation. IL-4 inhibited IL-12R beta 2 expression leading to the loss of IL-12 signaling, providing an important point of regulation to promote commitment to the Th2 pathway. IFN-gamma treatment of early developing Th2 cells maintained IL-12R beta 2 expression and restored the ability of these cells to functionally respond to IL-12, but did not directly inhibit IL-4 or induce IFN-gamma production. Thus, IFN-gamma may prevent early Th cells from premature commitment to the Th2 pathway. Controlling the expression of the IL-12R beta 2 subunit could be an important therapeutic target for the redirection of ongoing Th cell responses.

Differential associations between the cytoplasmic regions of the interleukin-12 receptor subunits beta1 and beta2 and JAK kinases.

The role of the cytoplasmic regions of interleukin-12 receptors (IL-12R) beta1 and beta2 in stimulating proliferation was examined. The transmembrane and cytoplasmic regions of IL-12Rbeta1 or IL-12Rbeta2 were fused to the extracellular domain of the epidermal growth factor (EGF) receptor, yielding chimeric receptors E12R1 and E12R2, respectively. These chimeras were stably transfected into BaF3 cells, a factor-dependent murine pro-B cell line. Only E12R2 or E12R1+E12R2 transfectants were capable of EGF-dependent proliferation. EGF-dependent phosphorylation of E12R2, JAK2, Tyk2, and STAT3 was observed. JAK2 was phosphorylated in E12R1-, E12R2-, and E12R1+E12R2-expressing cells. However, direct associations were detectable only between E12R2 and JAK2. Tyk2 phosphorylation was observed only in cells expressing E12R1 or E12R1+E12R2. In parallel with this activation pattern, direct interactions only between Tyk2 and E12R1 were demonstrable. Phosphorylation of STAT3 was observed in cells expressing E12R1, E12R2, and E12R1+E12R2. The expression levels of STAT4 protein in BaF3 cells are undetectable by the methods employed here; therefore, STAT4 phosphorylation was not observed. Taken together, the data indicate that differential interactions take place between the cytoplasmic regions of the two IL-12R subunits and JAK2/Tyk2 and that the cytoplasmic region of IL-12Rbeta2 alone is capable of delivering a proliferative signal.

A functional interleukin 12 receptor complex is composed of two beta-type cytokine receptor subunits.

We have identified a cDNA from a human phytohemagglutinin-activated lymphoblast library encoding a protein that binds 125I-labeled human interleukin 12 (125I-huIL-12) with a Kd of about 5 nM when expressed in COS-7 cells. When coexpressed in COS-7 cells with the previously identified IL-12 beta receptor (IL-12R beta) protein, two classes of 125I-huIL-12 binding sites were measured with Kds of about 55 pM and 8 nM, corresponding to the high- and low-affinity binding sites seen on phytohemagglutinin-activated lymphoblasts. This newly identified huIL-12R subunit is a member of the cytokine receptor superfamily, with closest resemblance to the beta-type cytokine receptor gp130 and the receptors for leukemia inhibitory factor and granulocyte colony-stimulating factor. Consequently, we have reclassified the previously identified IL-12R beta subunit as huIL-12R beta 1 and designated the newly identified subunit as huIL-12R beta 2. huIL-12R beta 2 is an 862-amino acid type I transmembrane protein with a 595-amino-acid-long extracellular domain and a cytoplasmic tail of 216 amino acids that contains three tyrosine residues. A cDNA encoding the mouse homolog of the huIL12R beta 2 protein has also been isolated. Human and mouse IL-12R beta 2 proteins show a 68% amino acid sequence identity. When expressed in COS-7 cells, huIL-12R beta 2 exists as a disulfide-linked oligomer with an apparent monomeric molecular weight of 130 kDa. Coexpression of the two identified IL-12R subunits in Ba/F3 cells conferred IL-12 responsiveness, and clones of these cotransfected Ba/F3 cells that grew continuously in the presence of IL-12 were isolated and designated LJM-1 cells. LJM-1 cells exhibited dose-dependent proliferation in response to huIL-12, with an ED50 of about 1 pM huIL-12. Interestingly, Ba/F3 cells transfected with IL-12R beta 2 alone proliferated in response to huIL-12 with an ED50 of about 50 pM, although a role for endogenous mouse IL-12R beta 1 in IL-12 signal transduction in these transfectants cannot be ruled out. These results demonstrate that the functional high-affinity IL-12R is composed of at least two beta-type cytokine receptor subunits, each independently exhibiting a low affinity for IL-12.

Molecular biology of interleukin-12 receptors.

IL-12 receptors are expressed primarily on activated T and NK cells. Using labeled IL-12, three classes of IL-12-binding sites have been identified on human PHA-activated lymphoblasts. Their Kd values are 5-20 pM (high affinity), 50-200 pM (intermediate affinity), and 2-6 nM (low affinity). Using a monoclonal antibody, a cDNA encoding a human IL-12 receptor was isolated by expression cloning. The homologous mouse cDNA was isolated by cross hybridization. These proteins are gp130-like members of the cytokine receptor superfamily. Individually, however they bind IL-12 with low affinity. An expression cloning approach was undertaken to isolate an additional human IL-12 receptor component that would act as a high-affinity converter. A cDNA encoding another IL-12 receptor was isolated. The mouse homologue was obtained by cross hybridization. These IL-12 receptors are also gp130-like cytokine receptor superfamily members. Because these two types of IL-12 receptors have the general makeup of beta-type cytokine receptor subunits, they are designated as IL-12R beta 1 and IL-12R beta 2. Coexpression of IL-12R beta 1 and IL-12R beta 2 leads to the formation of high-affinity IL-12-binding sites and reconstitution of IL-12-dependent signaling.

Evidence for multiple sites of interaction between IL-12 and its receptor.

We have previously described the identification of a protein, now designated IL-12R beta 1, that binds 125I-huIL-12 with a Kd of about 10 nM, corresponding to the low affinity 125I-huIL-12 binding sites seen on PHA-activated human lymphoblasts. Using expression cloning techniques, we have recently identified an additional IL-12-binding protein subunit, IL-12R beta 2, which binds 125I-huIL-12 with a Kd of about 5 nM when expressed alone in COS-7 cells. Coexpression of IL-12R beta 1 and IL-12R beta 2 in COS-7 cells results in formation of two classes of 125 I-huIL-12-binding sites with Kds of about 50 pM and 5 nM. Mouse IL-12 p40 subunit homodimer (mo(p40)2) blocked 125I-huIL-12 binding to human IL-12R beta 1, but did not inhibit binding to human IL-12R beta 2. In contrast, anti-huIL-12 monoclonal antibody 20C2, which does not block 125I-huIL-12 binding to human IL-12R beta 1, completely blocked binding to human IL-12R beta 2. These results demonstrate that two classes of IL-12 inhibitors, one that primarily blocks IL-12/IL-12R beta 1 interaction (e.g., mo(p40)2), and one that primarily blocks IL-12/IL-12R beta 2 interaction (e.g., 20C2), can be identified.

Biological function and distribution of human interleukin-12 receptor beta chain.

We previously described the cloning of a cDNA encoding an interleukin-12 receptor (IL-12R) subunit, designated beta, that bound IL-12 with low affinity when expressed in COS cells. We now report that a pair of monoclonal antibodies (mAb), 2B10 and 2.4E6, directed against different epitopes on the IL-12R beta chain, when used in combination, strongly inhibited IL-12-induced proliferation of activated T cells, IL-12-induced secretion of interferon-gamma by resting peripheral blood mononuclear cells (PBMC), and IL-12-mediated lymphokine-activated killer cell activation. The mAb had no effect on lymphoblast proliferation induced by IL-2, -4, or -7. Thus, the IL-12R beta chain appears to be an essential component of the functional IL-12R on both T and natural killer (NK) cells. We previously observed that high affinity IL-12R were expressed on activated T and NK cells, but not B cells. Studies using flow cytometry and reverse transcription-polymerase chain reaction analysis showed that IL-12R beta chain was expressed on several human T, NK, and (surprisingly) B cell lines, but not on non-lymphohematopoietic cell lines. The Kit225/K6 (T cell) and SKW6.4 (B cell) lines were found to express the greatest amounts of IL-12R beta chain (800-2500 sites/cell); however, Kit225/K6 but not SKW6.4 cells bound IL-12. Similar to SKW6.4 B cells, activated tonsillar B lymphocytes expressed IL-12R beta chain but, consistent with previous results, did not display detectable IL-12 binding. Likewise, up to 72% of resting PBMC from normal volunteer donors expressed IL-12R beta, but did not bind measurable amounts of IL-12. These results indicate that expression of IL-12R beta is essential, but not sufficient, for expression of functional IL-12R. We speculate that expression of functional, high-affinity IL-12R may require the presence of a second subunit that is more restricted in its expression than IL-12R beta.

Cloning and characterization of a mouse IL-12 receptor-beta component.

Using DNA cross-hybridization, we have isolated and characterized cDNA clones encoding a mouse (mo) IL-12R beta component. Two forms of cDNA were found. The first form encodes a receptor protein that has an overall structure very similar to that of the known human (hu) IL-12R beta with 54% amino acid identity, whereas in the second type of mouse cDNA, the equivalent of the transmembrane region has been deleted. This presumed alternative splicing event also gives rise to a frame shift that results in a receptor with an identical extracellular domain but a different C-terminal sequence. Whether this alternative C terminus is capable of signaling is not yet known. Both types of receptors when expressed in COS-7 cells are membrane associated and bind moIL-12 with an affinity of 1 nM, similar to the affinity of huIL-12R beta for huIL-12. The monomeric size of both moIL-12R beta proteins is about 100 kDa. Similar to huIL-12R beta, moIL-12R beta is expressed at the surface of COS-7 and Ba/F3 cells as a dimer/oligomer whose formation is independent of IL-12 binding. When expressed in Ba/F3 cells, moIL-12R beta binds moIL-12 with two affinities of 50 and 470 pM, corresponding to the medium and high affinity IL-12 binding sites previously identified on mouse Con A lymphoblasts. Despite the higher affinity displayed by the moIL-12R beta in Ba/F3 cells, this receptor alone is not sufficient to transduce a signal, suggesting that another subunit is probably required to generate a functional moIL-12R complex.