Arterial embolisation in intractable primary post-partum haemorrhage: case series.

OBJECTIVE: To evaluate the efficacy and safety of arterial embolisation in the management of intractable primary post-partum haemorrhage. DESIGN. Retrospective case series. SETTING: Regional hospital, Hong Kong. PATIENTS: Nine patients aged 28 to 39 years who were treated for severe primary post-partum haemorrhage between October 2000 and January 2003. INTERVENTION: Emergency transcatheter arterial embolisation. MAIN OUTCOME MEASURES: Clinical outcome and complications. RESULTS: All nine arterial embolisations successfully arrested the haemorrhage. The main cause of primary post-partum haemorrhage was uterine atony. No serious complication arose, although one patient experienced slight numbness of the right leg. Normal menstruation resumed in all patients, except for the one who had had a hysterectomy as initial treatment. One patient became pregnant 1 year after embolisation. Patients were followed up for 10 months. CONCLUSION: In our experience, arterial embolisation is safe and efficacious, and is the treatment of choice for patients with intractable primary post-partum haemorrhage.

Dendritic cells cross-present latency gene products from Epstein-Barr virus-transformed B cells and expand tumor-reactive CD8(+) killer T cells.

Dendritic cells (DCs) are not targets for infection by the transforming Epstein-Barr virus (EBV). To test if the adjuvant role of DCs could be harnessed against EBV latency genes by cross-presentation, DCs were allowed to process either autologous or human histocompatibility leukocyte antigen (HLA)-mismatched, transformed, B lymphocyte cell lines (LCLs) that had been subject to apoptotic or necrotic cell death. After phagocytosis of small numbers of either type of dead LCL, which lacked direct immune-stimulatory capacity, DCs could expand CD8(+) T cells capable of killing LCLs that were HLA matched to the DCs. Necrotic EBV-transformed, major histocompatibility complex (MHC) class I-negative LCLs, when presented by DCs, also could elicit responses to MHC class II-negative, EBV-transformed targets that were MHC class I matched to the DCs, confirming efficient cross-presentation of LCL antigens via MHC class I on the DC. Part of this EBV-specific CD8(+) T cell response, in both lytic and interferon gamma secretion assays, was specific for the EBV nuclear antigen (EBNA)3A and latent membrane protein (LMP)2 latency antigens that are known to be expressed at low levels in transformed cells. The induced CD8(+) T cells recognized targets at low doses, 1-10 nM, of peptide. Therefore, the capacity of DCs to cross-present antigens from dead cells extends to the expansion of high affinity T cells specific for viral latency antigens involved in cell transformation.

EBNA1-specific CD4+ T cells in healthy carriers of Epstein-Barr virus are primarily Th1 in function.

The Epstein-Barr virus (EBV) nuclear antigen-1 (EBNA1) maintains the viral episome in all host cells infected with EBV. Recently, EBNA1 was found to be the main EBV latency antigen for CD4+ T cells and could be recognized in cultures from all donors tested. We now identify a polarized Th1 phenotype and obtain evidence for its presence in vivo. When T cells were stimulated with dendritic cells infected with vaccinia vectors expressing EBNA1, 18 of 19 donors secreted IFN-gamma, whereas only two of 19 secreted IL-4. Magnetic selection was then used to isolate cells from fresh blood based on EBNA1-induced cytokine production. Specific IFN-gamma CD4+ cell lines were established from six of six donors and IL-4 lines from three of six. Only the Th1 lines specifically lysed targets expressing three different sources of EBNA1 protein. When the IgG isotype of EBNA1 plasma Ab's was tested, most specific Ab's were IgG1 and of a high titer, confirming a Th1 response to EBNA1 in vivo. Ab's to other microbial antigens generally were not skewed toward IgG1. Given emerging evidence that Th1 CD4+ T cells have several critical roles in host defense to viral infection and tumors, we propose that EBNA1-specific CD4+ Th1 cells contribute to resistance to EBV and EBV-associated malignancies.

Human CD4(+) T lymphocytes consistently respond to the latent Epstein-Barr virus nuclear antigen EBNA1.

The Epstein-Barr virus (EBV)-encoded nuclear antigen EBNA1 is critical for the persistence of the viral episome in replicating EBV-transformed human B cells. Therefore, all EBV-induced tumors express this foreign antigen. However, EBNA1 is invisible to CD8(+) cytotoxic T lymphocytes because its Gly/Ala repeat domain prevents proteasome-dependent processing for presentation on major histocompatibility complex (MHC) class I. We now describe that CD4(+) T cells from healthy adults are primed to EBNA1. In fact, among latent EBV antigens that stimulate CD4(+) T cells, EBNA1 is preferentially recognized. We present evidence that the CD4(+) response may provide a protective role, including interferon gamma secretion and direct cytolysis after encounter of transformed B lymphocyte cell lines (B-LCLs). Dendritic cells (DCs) process EBNA1 from purified protein and from MHC class II-mismatched, EBNA1-expressing cells including B-LCLs. In contrast, B-LCLs and Burkitt's lymphoma lines likely present EBNA1 after endogenous processing, as their capacity to cross-present from exogenous sources is weak or undetectable. By limiting dilution, there is a tight correlation between the capacity of CD4(+) T cell lines to recognize autologous B-LCL-expressing EBNA1 and DCs that have captured EBNA1. Therefore, CD4(+) T cells can respond to the EBNA1 protein that is crucial for EBV persistence. We suggest that this immune response is initiated in vivo by DCs that present EBV-infected B cells, and that EBNA1-specific CD4(+) T cell immunity be enhanced to prevent and treat EBV-associated malignancies.

Latent transforming growth factor beta1 activation in situ: quantitative and functional evidence after low-dose gamma-irradiation.

The biological activity of transforming growth factor beta1 (TGF-beta) is controlled by its secretion as a latent complex in which it is noncovalently associated with latency-associated peptide (LAP). Activation is the extracellular process in which TGF-beta is released from LAP, and is considered to be a primary regulatory control. We recently reported rapid and persistent changes in TGF-beta immunoreactivity in conjunction with extracellular matrix remodeling in gamma-irradiated mouse mammary gland. Our hypothesis is that these specific changes in immunoreactivity are indicative of latent TGF-beta activation. In the present study, we determined the radiation dose response and tested whether a functional relationship exists between radiation-induced TGF-beta and collagen type III remodeling. After radiation exposures as low as 0.1 Gy, we detected increased TGF-beta immunoreactivity in the mammary epithelium concomitant with decreased LAP immunostaining, which are events consistent with activation. Quantitative image analysis demonstrated a significant (P=0.0005) response at 0.1 Gy without an apparent threshold and a linear dose response to 5 Gy. However, in the adipose stroma, loss of LAP demonstrated a qualitative threshold at 0.5 Gy. Loss of LAP paralleled induction of collagen III immunoreactivity in this tissue compartment. We tested whether TGF-beta mediates collagen III expression by treating animals with TGF-beta panspecific monoclonal antibody, 1D11.16, administered i.p. shortly before irradiation. Radiation-induced collagen III staining in the adipose stroma was blocked in an antibody dose-dependent manner, which persisted through 7 days postirradiation. RNase protection assay revealed that radiation-induced elevation of total gland collagen III mRNA was also blocked by neutralizing antibody treatment. These data provide functional confirmation of the hypothesis that radiation exposure leads to latent TGF-beta activation, support our interpretation of the reciprocal shift in immunoreactivity as evidence of activation, and implicate TGF-beta as a mediator of tissue response to ionizing radiation. The sensitivity of activation to low radiation doses points to a potential role for TGF-beta in orchestrating tissue response to oxidative stress. As such, radiation may be useful as a probe to delineate the consequences of latent TGF-beta activation in situ.

Critical cytoplasmic domains of human interleukin-9 receptor alpha chain in interleukin-9-mediated cell proliferation and signal transduction.

Interleukin-9 receptor (IL-9R) complex consists of a ligand-specific alpha chain and IL-2R gamma chain. In this study, two regions in the cytoplasmic domain of human IL-9Ralpha were found to be important for IL-9-mediated cell growth. A membrane-proximal region that contains the BOX1 consensus sequence is required for IL-9-induced cell proliferation and tyrosine phosphorylation of Janus kinases (JAKs). Deletion of this region or internal deletion of the BOX1 motif abrogated IL-9-induced cell proliferation and signal transduction. However, substitution of the Pro-X-Pro in the BOX1 motif with Ala-X-Ala failed to abolish IL-9-induced cell proliferation but decreased IL-9-mediated tyrosine phosphorylation of JAK kinases, insulin receptor substrate-2, and signal transducer and activator of transcription 3 (STAT3) and expression of c-myc and junB. Another important region is downstream of the BOX1 motif and contains a STAT3 binding motif YLPQ. Deletion of this region significantly impaired IL-9-induced cell growth, activation of JAK kinases, insulin receptor substrate-2, and STAT3 and expression of early response genes. A point mutation changing YLPQ into YLPA greatly reduced IL-9-induced activation of STAT3 and expression of c-myc but did not affect cell proliferation. These results suggest that cooperation or cross-talk of signaling molecules associated with different domains of IL-9Ralpha other than STAT3 is essential for IL-9-mediated cell growth.

Uncoupling of stem cell inhibition from monocyte chemoattraction in MIP-1alpha by mutagenesis of the proteoglycan binding site.

We have studied the role of proteoglycans in the function of Macrophage Inflammatory Protein-1 alpha (MIP-1alpha), a member of the proteoglycan binding chemokine family. Sequence and peptide analysis has identified a basic region within MIP-1alpha which appears to be the major determinant of proteoglycan binding and we have now produced a mutant of MIP-1alpha lacking the basic charges on two of the amino acids within this proteoglycan binding site. This mutant (Hep Mut) appears to have lost the ability to bind to proteoglycans. Bioassay of Hep Mut indicates that it has retained stem cell inhibitory properties but has a compromised activity as a monocyte chemoattractant, thus suggesting uncoupling of these two properties of MIP-1alpha. Receptor studies have indicated that the inactivity of Hep Mut on human monocytes correlates with its inability to bind to CCR1, a cloned human MIP-1alpha receptor. In addition, studies using proteoglycan deficient cells transfected with CCR1 have indicated that the proteoglycan binding site in MIP-1alpha is a site that is also involved in the docking of MIP-1alpha to the monocyte receptor. The site for interaction with the stem cell receptor must therefore be distinct, suggesting that MIP-1alpha utilizes different receptors for these two different biological processes.

Binding affinity of transforming growth factor-beta for its type II receptor is determined by the C-terminal region of the molecule.

Transforming growth factor-beta (TGF-beta) isoforms have differential binding affinities for the TGF-beta type II receptor (TbetaRII). In most cells, TGF-beta1 and TGF-beta3 bind to TbetaRII with much higher affinity than TGF-beta2. Here, we report an analysis of the effect of TGF-beta structure on its binding to TbetaRII by using TGF-beta mutants with domain deletions, amino acid replacements, and isoform chimeras. Examination of the binding of TGF-beta mutants to the recombinant extracellular domain of TbetaRII by a solid-phase TGF-beta/TbetaRII assay demonstrated that only those TGF-beta mutants containing the C terminus of TGF-beta1 (TGF-beta1-(Delta69-73), TGF-beta1-(Trp71), and TGF-beta2/beta1-(83-112)) bind with high affinity to TbetaRII, similar to native TGF-beta1. Moreover, replacement of only 6 amino acids in the C terminus of TGF-beta1 with the corresponding sequence of TGF-beta2 (TGF-beta1/beta2-(91-96)) completely eliminated the high affinity binding of TGF-beta1. Proliferation of fetal bovine heart endothelial (FBHE) cells was inhibited to a similar degree by all of the TGF-beta mutants. However, recombinant soluble TbetaRII blocked the inhibition of FBHE cell proliferation induced by TGF-beta mutants retaining the C terminus of TGF-beta1, consistent with the high binding affinity between these TGF-beta molecules and TbetaRII. It was further confirmed that the TGF-beta2 mutant with its C terminus replaced by that of TGF-beta1 (TGF-beta2/beta1-(83-112)) competed as effectively as TGF-beta1 with 125I-TGF-beta1 for binding to membrane TbetaRI and TbetaRII on FBHE cells. These observations clearly indicate that the domain in TGF-beta1 responsible for its high affinity binding to TbetaRII, both the soluble and membrane-bound forms, is located at C terminus of the molecule.

Transforming growth factor beta 1: three-dimensional structure in solution and comparison with the X-ray structure of transforming growth factor beta 2.

The three-dimensional solution structure of human transforming growth factor beta 1 (TGF-beta 1) has been determined using multinuclear magnetic resonance spectroscopy and a hybrid distance geometry/ simulated annealing algorithm. It represents one of the first examples of a mammalian protein structure that has been solved by isotopic labeling of the protein in a eukaryotic cell line and multinuclear NMR spectroscopy. The solution structure of the 25 kDa disulfide-linked TGF-beta 1 homodimer was calculated from over 3200 distance and dihedral angle restraints. The final ensemble of 33 accepted structures had no NOE or dihedral angle violations greater than 0.30 A and 5.0 degrees, respectively. The RMSD of backbone atoms for the ensemble of 33 structures relative to their mean structure was 1.1 A when all residues were used in the alignment and 0.7 A when loop regions were omitted. The solution structure of TGF-beta 1 follows two independently determined crystal structures of TGF-beta 2 (Daopin et al., 1992, 1993; Schlunegger & Grütter, 1992, 1993), providing the first opportunity to examine structural differences between the two isoforms at the molecular level. Although the structures are very similar, with an RMSD in backbone atom positions of 1.4 A when loop regions are omitted in the alignment and 1.9 A when all residues are considered, there are several notable differences in structure and flexibility which may be related to function. The clearest example of these is in the beta-turn from residues 69-72: the turn type found in the solution structure of TGF-beta 1 falls into the category of type II, whereas that present in the X-ray crystal structure of TGF-beta 2 is more consistent with a type I turn conformation. This may be of functional significance as studies using TGF-beta chimeras and deletion mutants indicate that this portion of the molecule may be important in receptor binding.

The recombinant proregion of transforming growth factor beta1 (latency-associated peptide) inhibits active transforming growth factor beta1 in transgenic mice.

All three isoforms of transforming growth factors beta (TGF-betal, TGF-beta2, and TGF-beta3) are secreted as latent complexes and activated extracellularly, leading to the release of the mature cytokines from their noncovalently associated proregions, also known as latency-associated peptides (LAPs). The LAP region of TGF-beta1 was expressed in a baculovirus expression system and purified to homogeneity. In vitro assays of growth inhibition and gene induction mediated by TGF-beta3 demonstrate that recombinant TGF-beta1 LAP is a potent inhibitor of the activities of TGF-betal, -beta2, and -beta3. Effective dosages of LAP for 50% neutralization of TGF-beta activities range from 4.7- to 80-fold molar excess depending on the TGF-beta isoform and activity examined. Using 125I-labeled LAP, we show that the intraperitoneal application route is effective for systemic administration of LAP. Comparison of concentrations of LAP in tissues shows a homogenous pattern in most organs with the exception of heart and muscle, in which levels of LAP are 4- to 8-fold lower. In transgenic mice with elevated hepatic levels of bioactive TGF-betal, treatment with recombinant LAP completely reverses suppression of the early proliferative response induced by TGF-beta1 in remnant livers after partial hepatectomy. The results suggest that recombinant LAP is a potent inhibitor of bioactive TGF-beta both in vitro and in vivo, after intraperitoneal administration. Recombinant LAP should be a useful tool for novel approaches to study and therapeutically modulate pathophysiological processes mediated by TGF-beta3.

Heterodimers of placenta growth factor/vascular endothelial growth factor. Endothelial activity, tumor cell expression, and high affinity binding to Flk-1/KDR.

Here we show that the Escherichia coli expressed monomers of placenta growth factor (PLGF)129 and vascular endothelial growth factor (VEGF)165 can be re-folded in vitro to form PLGF/VEGF heterodimers. The purified recombinant PLGF/VEGF heterodimers and VEGF homodimers have potent mitogenic and chemotactic effects on endothelial cells. However, PLGF/VEGF heterodimers display 20-50-fold less mitogenic activity than VEGF165 homodimers. In contrast, PLGF129 homodimers have little or no effect in these in vitro assays. We also demonstrate the presence of natural PLGF/VEGF heterodimers in the conditioned media of various human tumor cell lines. While PLGF/VEGF heterodimers bind with high affinity to a soluble Flk-1/KDR receptor, PLGF129 homodimers fail to bind to this receptor. Cross-linking of 125I-ligands to human umbilical vein endothelial cells reveals that PLGF/VEGF heterodimers and VEGF165 homodimers, but not PLGF129 homodimers, form complexes with membrane receptors. VEGF165 homodimers and PLGF/VEGF heterodimers stimulate tyrosine phosphorylation of a 220-kDa protein, the expected size for the KDR receptor in human umbilical vein endothelial cells, whereas PLGF129 homodimers are unable to induce tyrosine phosphorylation of this protein. These data indicate that PLGF may modulate VEGF-induced angiogenesis by the formation of PLGF/VEGF heterodimers in cells producing both factors.

Cytokine assays and their limitations.

With the increasing popularity of the use of cytokine immunoassays in basic and clinical research, there is an urgent need for cytokine immunoassay reference preparations and standards in order that results published by various investigators can be directly compared. Until such standards are available, it is recommended that results obtained using immunoassays from different sources be compared with caution. Additionally, users of immunoassays should clearly understand the biology of the systems they are studying and the characteristics of their immunoassays with respect to cross-reactivities with cytokine isoforms, interferences by soluble receptors, and matrix effects on samples of interest. It is also recommended that immunoassay developers take special precautions in the selection of antibodies and only use antibodies that are not biased against one or the other of the recombinant forms.

Primary structure of the V3 region of gp120 from sequential human immunodeficiency virus type 1 isolates obtained from patients from the time of seroconversion.

V3 loop sequences were compared from 5 human immunodeficiency virus type 1 (HIV-1)-infected patients over time. Three patients remained asymptomatic and 2 became symptomatic with large decrease in CD4 cell counts. The patient isolates were previously evaluated for phenotypic and antigenic properties and had different sensitivities to serum neutralization and changes in phenotype. This study showed a number of amino acid changes for the 2 symptomatic patients, each of whom progressed to AIDS during the study. The only amino acid substitution consistently associated with reduced CD4 cell counts, cytopathic effect, and progression to AIDS was Arg at position 11. Specific amino acid changes could not be correlated with increasing serum neutralization resistance or cytotropism changes. Increased loop charge was associated with a switch from macrophage to T cell tropism and a decrease in the number of CD4 cells. The study shows the importance of naturally occurring mutations in the V3 loop in controlling the biologic properties of HIV-1.

Immunohistochemical detection of active transforming growth factor-beta in situ using engineered tissue.

The biological activity of transforming growth factor-beta 1 (TGF-beta) is governed by dissociation from its latent complex. Immunohistochemical discrimination of active and latent TGF-beta could provide insight into TGF-beta activation in physiological and pathological processes. However, evaluation of immunoreactivity specificity in situ has been hindered by the lack of tissue in which TGF-beta status is known. To provide in situ analysis of antibodies to differentiate between these functional forms, we used xenografts of human tumor cells modified by transfection to overexpress latent TGF-beta or constitutively active TGF-beta. This comparison revealed that, whereas most antibodies did not differentiate between TGF-beta activation status, the immunoreactivity of some antibodies was activation dependent. Two widely used peptide antibodies to the amino-terminus of TGF-beta, LC(1-30) and CC(1-30) showed marked preferential immunoreactivity with active TGF-beta versus latent TGF-beta in cryosections. However, in formalin-fixed, paraffin-embedded tissue, discrimination of active TGF-beta by CC(1-30) was lost and immunoreactivity was distinctly extracellular, as previously reported for this antibody. Similar processing-dependent extracellular localization was found with a neutralizing antibody raised to recombinant TGF-beta. Antigen retrieval recovered cell-associated immunoreactivity of both antibodies. Two antibodies to peptides 78-109 showed mild to moderate preferential immunoreactivity with active TGF-beta only in paraffin sections. LC(1-30) was the only antibody tested that discriminated active from latent TGF-beta in both frozen and paraffin-embedded tissue. Thus, in situ discrimination of active versus latent TGF-beta depends on both the antibody and tissue preparation. We propose that tissues engineered to express a specific form of a given protein provide a physiological setting in which to evaluate antibody reactivity with specific functional forms of a protein.

Interleukin-9 induces tyrosine phosphorylation of insulin receptor substrate-1 via JAK tyrosine kinases.

Interleukin (IL)-9 stimulates the proliferation of a variety of hematopoietic lineages through its interaction with a receptor of the cytokine receptor superfamily. In the studies presented here, we have begun to characterize the downstream signaling pathways activated by IL-9. In addition to the activation of JAK1 and JAK3 tyrosine kinases, IL-9, unlike most hematopoietic cytokines but similar to IL-4, induces the tyrosine phosphorylation of a 170-kDa protein that is related to the insulin receptor substrate-1 (IRS-1). We further demonstrate for the first time that IRS-1 is not only associated with JAK1 but also tyrosine phosphorylated and functionally involved in IL-9 signaling in TS1 lymphocytes transfected with the murine IRS-1 cDNA. Cotransfection studies and in vitro experiments directly demonstrate that JAK1, JAK2, or JAK3 is capable of tyrosine phosphorylating IRS-1, suggesting a functional role for these kinases in vivo. Lastly, we demonstrate that IL-9 induces the tyrosine phosphorylation of Stat3 and in this regard differs from IL-4, which triggers tyrosine phosphorylation of Stat6. Taken together, these results strongly suggest that IL-9 and IL-4 utilize common and unique signaling pathways via inducing the similar and distinct tyrosine-phosphorylated proteins.

Characterization of recombinant soluble human transforming growth factor-beta receptor type II (rhTGF-beta sRII).

Recombinant human transforming growth factor soluble receptor Type II (rhTGF-beta sRII) corresponding to the 159 amino acid extracellular domain of hTGF-beta RII has been expressed in insect cells using the baculovirus expression system or in a mouse myeloma cell line. N-terminal sequence analysis of the purified protein revealed the removal of the 23 amino acid signal peptide. In SDS-PAGE, the rhTGF-beta sRII resolves into multiple bands due to N-linked glycosylation. Recombinant hTGF-beta sRII is a TGF-beta antagonist and will inhibit the biological activities of TGF-beta 1, TGF-beta 3, and TGF-beta 5 on TGF-beta-responsive cell lines, such as murine HT-2 or human TF-1 with an ED50 of approximately 0.3 micrograms/mL. However, hTGF-beta sRII does not inhibit TGF-beta 2 bioactivities in these cell lines, suggesting that hTGF-beta RII has low affinity for TGF-beta 2. Polyclonal antibodies to hTGF-beta sRII have been produced in goats and purified on Protein-G affinity columns. This antibody can inhibit TGF-beta 1,2,3,5-dependent bioactivities on human cell lines such as TF-1. Additionally, this antibody has species cross-reactivity and will also inhibit TGF-beta-dependent bioactivities on murine cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Neutralizing antibodies against sequential autologous human immunodeficiency virus type 1 isolates after seroconversion.

The emergence of human immunodeficiency virus type 1 (HIV-1) variants with different sensitivities to serum neutralization and biologic phenotype was studied for 2-5 years after primary HIV-1 infection in 5 subjects. In 3 subjects, the initial virus isolate from seroconversion could be neutralized by autologous serum, but isolates obtained at two subsequent times exhibited reduced sensitivity to serum neutralization, decreased replication in primary macrophages, and increased ability to induce syncytia. Two of these 3 subjects progressed to AIDS and died. Sequential virus isolates from the other 2 subjects showed variability in sensitivity to serum neutralization or biologic features. These patients remained relatively stable in clinical status. Thus, viruses isolated at seroconversion appear to be either non-syncytium-inducing, strong macrophage-tropic, serum neutralization-sensitive phenotypes with stable clinical status or to have escaped neutralization by autologous sera over time, have reduced macrophage tropism and increased syncytia formation, and be associated with disease progression.

JAK1 kinase forms complexes with interleukin-4 receptor and 4PS/insulin receptor substrate-1-like protein and is activated by interleukin-4 and interleukin-9 in T lymphocytes.

Interleukin (IL)-4 and IL-9 regulate the proliferation of T lymphocytes through interactions with their receptors. Previous studies have shown that unknown tyrosine kinases are involved in the proliferative signaling triggered by IL-4 and IL-9. Here we show that IL-4 and IL-9 induce overlapping (170, 130, and 125 kilodalton (kDa)) and distinct (45 and 88/90 kDa, respectively) protein tyrosine phosphorylation in T lymphocytes. We further identify the 170-kDa tyrosine-phosphorylated protein as 4PS/insulin receptor substrate-1-like (IRS-1L) protein and 130-kDa protein as JAK1 kinase. Furthermore, we demonstrate for the first time that JAK1 forms complexes with the IL-4 receptor and 4PS/IRS-1L protein following ligand-receptor interaction. In addition, we demonstrate that IL-9, but not IL-4, induced tyrosine phosphorylation of Stat 91 transcriptional factor. The overlapping and distinct protein tyrosine phosphorylation and activation of the same JAK1 kinase in T lymphocytes strongly suggests that IL-4 and IL-9 share the common signal transduction pathways and that the specificity for each cytokine could be achieved through the unique tyrosine-phosphorylated proteins triggered by individual cytokines.