Phytohemagglutinin-stimulated Peripheral Blood Lymphocytes Research Articles

Klinefelter variant mosaic with a reciprocal translocation t(1;7)

To determine the constitutional karyotype in a provisional diagnosis of Klinefelter syndrome. Case report. University research facility in collaboration with a government hospital. Male patient with provisional diagnosis of Klinefelter syndrome. Chromosomal analysis of phytohemagglutinin-stimulated peripheral blood lymphocytes using conventional cytogenetic techniques. Chromosome number and structure, hormonal profile. Analysis of GTG-banded metaphases of the proband revealed the karyotype to be mos 48,XXXY,t(1;7)(q42;q32)pat[71%]/47,XXY,t(1;7)(q42;q32)pat[29%]. This is the first report of its kind, to the best of our knowledge. His father and elder brother were also found to be carriers of the same translocation with the karyotype 46,XY,t(1;7)(q42;q32). An alternate segregation of the translocation t(1;7) in spermatogenesis could have led to meiotic nondisjunction, thus supporting the hypothesis of interchromosomal effect. This case study truly emphasizes the clinical relevance of cytogenetic diagnosis in the better management of genetic disorders.

Engineering Oncolytic Measles Virus to Circumvent the Intracellular Innate Immune Response

The innate antiviral responses of tumor cells are often impaired but may still be sufficient to impede the intratumoral spread of an oncolytic virus. Here, we establish that the oncolytic measles virus (MV-eGFP) induces interferon (IFN) production in human myeloma and ovarian cancer cells. In addition, MV gene expression and virus progeny production were inhibited by IFN treatment of these tumor cells. The P gene of wild-type measles virus encodes P/V/C proteins known to antagonize IFN induction and/or response. We therefore engineered MV-eGFP for IFN evasion and more efficient intratumoral spread by arming it with the P gene from wild-type IC-B strain MV, thus generating MV-eGFP-Pwt. The chimeric virus exhibited reduced IFN sensitivity and diminished capacity to induce IFN in BJAB lymphoma, ARH-77 myeloma cells, and activated peripheral blood mononuclear cells. Interestingly, unlike the wild-type MV, MV-eGFP-Pwt was unable to shut down IFN induction completely. In immunocompromised mice bearing human myeloma xenografts, intravenously administered MV-eGFP-Pwt showed significantly enhanced oncolytic potency compared to MV-eGFP. These results indicate that oncolytic viruses are subject to control by the innate immune defenses of human tumor cells and may therefore be more effective if their natural ability to combat innate immunity is maintained.

Position Effects Due to Chromosome Breakpoints that Map ∼900 Kb Upstream and ∼1.3 Mb Downstream of SOX9 in Two Patients with Campomelic Dysplasia

Campomelic dysplasia (CD) is a semilethal skeletal malformation syndrome with or without XY sex reversal. In addition to the multiple mutations found within the sex-determining region Y-related high-mobility group box gene (SOX9) on 17q24.3, several chromosome anomalies (translocations, inversions, and deletions) with breakpoints scattered over 1 Mb upstream of SOX9 have been described. Here, we present a balanced translocation, t(4;17)(q28.3;q24.3), segregating in a family with a mild acampomelic CD with Robin sequence. Both chromosome breakpoints have been identified by fluorescence in situ hybridization and have been sequenced using a somatic cell hybrid. The 17q24.3 breakpoint maps approximately 900 kb upstream of SOX9, which is within the same bacterial artificial chromosome clone as the breakpoints of two other reported patients with mild CD. We also report a prenatal identification of acampomelic CD with male-to-female sex reversal in a fetus with a de novo balanced complex karyotype, 46,XY,t(4;7;8;17)(4qter-->4p15.1::17q25.1-->17qter;7qter-->7p15.3::4p15.1-->4pter;8pter-->8q12.1::7p15.3-->7pter;17pter-->17q25.1::8q12.1-->8qter). Surprisingly, the 17q breakpoint maps approximately 1.3 Mb downstream of SOX9, making this the longest-range position effect found in the field of human genetics and the first report of a patient with CD with the chromosome breakpoint mapping 3' of SOX9. By using the Regulatory Potential score in conjunction with analysis of the rearrangement breakpoints, we identified a candidate upstream cis-regulatory element, SOX9cre1. We provide evidence that this 1.1-kb evolutionarily conserved element and the downstream breakpoint region colocalize with SOX9 in the interphase nucleus, despite being located 1.1 Mb upstream and 1.3 Mb downstream of it, respectively. The potential molecular mechanism responsible for the position effect is discussed.

Constitutional t(5;7)(q11;p15) rearranged to acquire monosomy7q and trisomy 1q in a patient with myelodysplastic syndrome transforming to acute myelocytic leukemia

We report the case of a 61-year-old woman who presented with a myelodysplastic syndrome (MDS) and a t(5;7)(q11.2;p15) in her bone marrow cells. Subsequent analysis of phytohemagglutinin-stimulated peripheral blood lymphocytes and cultured skin fibroblasts showed that the translocation was constitutional. Disruption of chromosome bands 5q11.2 and 7p15 has been described recurrently in MDS and acute myelocytic leukemia (AML) and, although the age of onset was not earlier than usual, it is nonetheless possible that genes interrupted by this translocation may been a predisposing factor for her condition. With progression to AML, a further rearrangement of the constitutional der(7)t(5;7) occurred, involving chromosome arm 1q. Fluorescence in situ hybridization (FISH) with whole-chromosome paints showed that the result of the second rearrangement, a t(1;7)(q32.1;q32), was observed, leading to trisomy of the segment 1q32.1∼qter and monosomy of the segment 7q32.1∼qter. The acquired imbalances, particularly loss of 7q, are commonly associated with MDS/AML and a poor prognosis; however, this patient remained in remission after treatment for more than two years before AML relapse, perhaps because the affected regions fall outside of the critical regions of imbalance.

Overexpression of hMTH in peripheral lymphocytes and risk of prostate cancer: a case-control analysis.

Oxidative damage is an important factor in prostate carcinogenesis, and overexpression of human MutT homolog (hMTH), a repair gene that removes oxidative damage, is a molecular marker of cellular oxidative stress. Therefore, we tested the hypothesis that overexpression of hMTH in unaffected (normal) surrogate tissue is associated with risk of prostate cancer in a pilot study of 51 patients with diagnosed prostate cancer and 50 age- and ethnicity-matched controls. Total RNA was extracted from phytohemagglutinin-stimulated peripheral blood lymphocytes of these subjects. We performed the real-time reverse transcription-polymerase chain reaction assay to evaluate the relative mRNA expression of three oxidative-damage-repair genes, human MutM homolog (hMMH), hMTH, and human MutY homolog (hMYH), with beta-actin and human O(6)-methylguanine DNA methyltransferase (hMGMT) as the internal controls. The relative gene expression levels of hMMH and hMTH were borderline higher in the cases than in controls (15.3% and 28.8% higher, respectively; P = 0.046 and P = 0.035, respectively), whereas no increase was observed for hMYH and hMGMT. With the median of the controls' values as the cutoff point, we observed that a high expression level of hMTH, but not of other genes, was associated with a significantly increased risk of prostate cancer (odds ratio = 2.62; 95% confidence interval = 1.13-6.75) after adjustment for age and ethnicity. These results suggested that increased expression of hMTH in peripheral lymphocytes may be a risk factor for prostate cancer and support our priori hypothesis. Although our findings were biologically plausible and consistent with the literature, they were preliminary and need to be confirmed in larger studies. In addition, a correlation between the expression level of hMTH and the level of oxidative DNA damage in the target tissues needs to be established as well.

Human lymphocyte telomerase is genetically regulated.

Research on both cancer and aging has focused attention on the regulation of telomerase, the enzyme that synthesizes the ends of chromosomal DNA. To analyze the relative importance of genetic vs. environmental factors in determining telomerase inducibility, we have compared telomerase activity in phytohemagglutinin-stimulated peripheral blood lymphocytes from monozygotic and dizygotic twin pairs. The heritability calculated was 0.814, indicating that lymphocyte inducible telomerase activity is determined principally by genetic rather than by environmental factors.

Macrophage-derived Chemokine Is a Functional Ligand for the CC Chemokine Receptor 4

Macrophage-derived chemokine (MDC) is a recently identified member of the CC chemokine family. MDC is not closely related to other chemokines, sharing most similarity with thymus- and activation-regulated chemokine (TARC), which contains 37% identical amino acids. Both chemokines are highly expressed in the thymus, with little expression seen in other tissues. In addition, the genes for MDC and TARC are encoded by human chromosome 16. To explore this relationship in greater detail, we have more precisely localized the MDC gene to chromosome 16q13, the same position reported for the TARC gene. We have also examined the interaction of MDC with CC chemokine receptor 4 (CCR4), recently shown to be a receptor for TARC. Using a fusion protein of MDC with secreted alkaline phosphatase, we observed high affinity binding of MDC-secreted alkaline phosphatase to CCR4-transfected L1.2 cells (Kd = 0.18 nM). MDC and TARC competed for binding to CCR4, while no binding competition was observed for six other chemokines (MCP-1, MCP-3, MCP-4, RANTES (regulated on activation normal T cell expressed and secreted), macrophage inflammatory protein-1 alpha, macrophage inflammatory protein-1 beta). MDC was tested for calcium mobilization in L1.2 cells tranfected with seven different CC chemokine receptors. MDC induced a calcium flux in CCR4-transfected cells, but other receptors did not respond to MDC. TARC, which also induced calcium mobilization in CCR4 transfectants, was unable to desensitize the response to MDC. In contrast, MDC fully desensitized a subsequent response to TARC. Both MDC and TARC functioned as chemoattractants for CCR4 transfectants, confirming that MDC is also a functional ligand for CCR4. Since MDC and TARC are both expressed in the thymus, one role for these chemokines may be to attract CCR4-bearing thymocytes in the process of T cell education and differentiation.

S-adenosylhomocysteine hydrolase inhibitors interfere with the replication of human immunodeficiency virus type 1 through inhibition of the LTR transactivation.

Various analogues of adenosine have been described as inhibitors of S-adenosylhomocysteine (AdoHcy) hydrolase, and some of these AdoHcy hydrolase inhibitors (e.g., 3-deazaadenosine, 3-deazaaristeromycin, and 3-deazaneplanocin A) have also been reported to inhibit the replication of human immunodeficiency virus type 1 (HIV-1). When evaluated against HIV-1 replication in MT-4 cells, macrophages, or phytohemagglutinin-stimulated peripheral blood lymphocytes infected acutely or chronically with HIV-1IIIB or HIVBaL strains, a wide range of adenosine analogues did not inhibit HIV-1IIIB replication for 50% at subtoxic concentrations. However, they inhibited HIV-1 replication in HeLa CD4+ LTR-LacZ cells at concentrations well below cytotoxicity threshold. A close correlation was found among the inhibitory effect of the compounds on AdoHcy hydrolase activity, their inhibition of HIV-1 replication in Hela CD4+ LTR-LacZ cells, and their inhibition of the HIV-1 Tat-dependent and -independent transactivation of the long terminal repeat, whereas no inhibitory effect was seen on HIV-1 reverse transcription or a Tat-independent cytomegalovirus promoter. Our results suggest that AdoHcy hydrolase and the associated S-adenosylmethionine-dependent methylation mechanism play a role in the process of long terminal repeat transactivation and, hence, HIV replication.

Suppressive factor or factors derived from head and neck squamous cell carcinoma induce apoptosis in activated lymphocytes.

Our laboratory has previously identified a soluble factor derived from head and neck squamous cell carcinoma that impairs lymphocyte proliferative responses in vitro. This study further investigates the nature of the interaction between these factors and T lymphocytes. The proliferative activity of phytohemagglutinin-stimulated peripheral blood lymphocytes and the Jurkat T-cell line was significantly suppressed (>50%) by the supernatants of 13 (41.9%) of 31 recently explanted head and neck squamous cell carcinoma samples. A characteristic morphologic appearance of these suppressed cells and ladderlike pattern of DNA fragmentation on gel electrophoresis indicated that the suppressive supernatants were inducing or predisposing T cells to apoptotic death. This apoptosis-inducing activity may be similar to that previously described in a suppressive supernatant obtained from an esophageal carcinoma cell line. These results shed further light on the mechanism behind a soluble immunosuppressive factor or factors produced by head and neck squamous cell carcinoma.

Suppressive factor or factors derived from head and neck squamous cell carcinoma induce apoptosis in activated lymphocytes

Our laboratory has previously identified a soluble factor derived from head and neck squamous cell carcinoma that impairs lymphocyte proliferative responses in vitro. This study further investigates the nature of the interaction between these factors and T lymphocytes. The proliferative activity of phytohemagglutinin-stimulated peripheral blood lymphocytes and the Jurkat T-cell line was significantly suppressed (>50%) by the supernatants of 13 (41.9%) of 31 recently explanted head and neck squamous cell carcinoma samples. A characteristic morphologic appearance of these suppressed cells and ladderlike pattern of DNA fragmentation on gel electrophoresis indicated that the suppressive supernatants were inducing or predisposing T cells to apoptotic death. This apoptosis-inducing activity may be similar to that previously described in a suppressive supernatant obtained from an esophageal carcinoma cell line. These results shed further light on the mechanism behind a soluble immunosuppressive factor or factors produced by head and neck squamous cell carcinoma. (Otolaryngol Head Neck Surg 1997; 116:458-65.)

Localization of the Kappa Opioid Receptor Gene to Human Chromosome Band 8q11.2

Using the cloned mouse kappa opioid receptor cDNA clone as a probe, screened a human genomic library and isolated a clone containing part of the human kappa opioid receptor gene (OPRK1), designated [lambda]hSR4-1. To determine the chromosomal localization of OPRK1, [lambda]hSR4-1 DNA was labeled with biotin by nick-translation in the presence of bio-11-dUTP and hybridized to human metaphase cells prepared from phytohemagglutinin-stimulated peripheral blood lymphocytes as described previously. Hybridization of the OPRK1-specific probe [lambda]hSR4-1 DNA to normal human metaphase chromosomes resulted in specific labeling only of chromosome 8. Specific labeling of 8q11 was observed on all 4 (6 cells), 3 (9 cells), 2 (9 cells), or 1 (1 cell) chromatid of the chromosome 8 homologs in 25 cells examined. Of 72 signals observed, 70 were located at 8q11. 1 signal was located at 7q11 and at 12p11. In most cells, the signal on 8q was located at 8q11.2. 7 refs., 1 fig.

Sensitivity of lymphocytes from vulcanizers to the in vitro induction of sister chromatid exchanges.

Spontaneous frequencies of sister chromatid exchanges (SCEs) and SCEs induced in vitro by chemicals with different mechanisms of action such as mitomycin C, 4-nitroquinoline oxide, and 3-aminobenzamide were examined in phytohemagglutinin-stimulated peripheral blood lymphocytes from a group of workers in a rubber plant and a control group, both of which had been analyzed for levels of spontaneous SCEs 2 years earlier. An interindividual variability in the induction of SCEs was found after in vitro treatments with the different mutagens, which did not correlate with occupational exposure. This variability in the sensitivity to the induction of SCEs might be correlated to genetic differences among individuals, which have to be taken into account in environmental monitoring programs.

X-ray-induced chromatid damage in relation to DNA repair and cancer incidence in family members.

The cytogenetic response to G2-phase X-irradiation was examined in phytohemagglutinin-stimulated peripheral-blood lymphocytes from 69 individuals, a few of whom were cancer patients. The cancer patients had not received radiation or chemotherapy. The responses of cells arrested by Colcemid 30 to 90 min after X-irradiation (58R) could be divided into 2 distinct categories: 51 individuals had aberration frequencies typical of normal individuals in previous studies, while 18 others had a 2- to 3-fold higher frequency of chromatid breaks and gaps. Because chromatid breaks and gaps result from unrepaired DNA strand breaks, the first category may represent an efficient DNA repair phenotype, while the second may represent a deficient repair phenotype. The individuals with the deficient G2 response reported having first- and second-degree relatives with a 3.6- and 2.2-fold higher mean frequency of cancer, respectively. The present results, together with those from earlier studies of families with a genetic disorder predisposing to cancer, suggest that this deficient cytogenetic response to G2 phase X-irradiation is associated with a high risk of cancer.

Age‐associated chromosome 21 loss in Down syndrome: Possible relevance to mosaicism and Alzheimer disease

We previously observed low level mosaicism (2-4% normal cells) in phytohemagglutinin-stimulated peripheral blood lymphocytes (PBL) in 29% of a small group of elderly persons with Down syndrome (DS). An analysis of cytogenetic data on 154 trisomy 21 cases (age 1 day to 68 years) showed that the proportion of diploid cells in such cultures significantly increased (P < 0.005) with advancing age. Thus, the "occult" mosaicism in PBL of the elderly persons with DS is likely due to the accumulation of cells that have lost a chromosome 21. A consequence of chromosome 21 loss could be uniparental disomy of the 2n cells, a factor that might have significant biological consequences if some chromosome 21 genes are imprinted. Loss of a chromosome 21 from trisomic cells might result in tissue-specific mosaicism and "classical" mosaicism in different age groups. Chromosome 21 loss might also be relevant to the development of Alzheimer-type dementia in DS and in the general population.

Interphase Cytogenetics of Gastric and Esophageal Adenocarcinomas

Numerical changes affecting chromosomes 1, 2, 3, 4, 6, 7, 8, 10, 11, 12, 16, 17, 18, and the X and Y chromosomes have been analyzed using chromosome-specific centromeric alpha-satellite repeat DNA probes in a panel of biopsies of six gastric and three esophageal adenocarcinoma and one epidermoid carcinoma of esophagus obtained at surgery. For each case, with each probe, the number of hybridization signals were determined in 200 nuclei. Hybridization of each probe to phytohemagglutinin-stimulated normal peripheral blood lymphocytes served as controls. Monosomy was defined by loss of one signal in 15% or more cells and trisomy or tetrasomy was defined by the presence of 3 or 4 signals in 7% or more cells, respectively. The Y chromosome was lost in 6 of 8 cases and monosomy 10 was seen in 5 of 10 cases. Trisomy for chromosomes 17, 8, 7, 12, 11, and 1 was seen in 4 of 10, 4 of 10, 4 of 10, 2 of 10, 2 of 8, and 2 of 10 cases, respectively, and tetrasomy for chromosome 7 was seen in 1 of 10 cases. These data show that the Y chromosome and chromosomes 10, 8, 7, 17, and 12 are most frequently involved in nondisjunctional changes in these tumors. They also document the feasibility and utility of interphase cytogenetics of gastric adenocarcinomas.

Cell type-specific anti-human immunodeficiency virus type 1 activity of the transactivation inhibitor Ro5-3335.

The drug Ro5-3335 [7-chloro-5-(2-pyrryl)-3H-1,4-benzodiazepin-2(H)-one] inhibits human immunodeficiency virus type 1 (HIV-1) gene expression at the transcriptional level through interference with Tat-mediated transactivation (M.-C. Hsu, A. D. Schutt, M. Holly, L. W. Slice, M. I. Sherman, D. D. Richman, M. J. Potash, and D. J. Volsky, Science 254:1799-1802, 1991). We confirmed this specific inhibitory effect in a quantitative bioassay based on transactivation of a chimeric gene comprising the HIV-1 long terminal repeat promoter fused to the lacZ gene of Escherichia coli and transfected in a HeLa cell line expressing Tat. Ro5-3335 was found to inhibit HIV-1 long terminal repeat-driven lacZ gene expression at a 50% inhibitory concentration of 0.5 microM. The in vitro anti-HIV-1 activity of Ro5-3335 was highly dependent on the nature of the host cells. The highest selectivity index, 50, was found in phytohemagglutinin-stimulated peripheral blood lymphocytes. The selectivity index was between 1 and 10 in the CD4+ T-cell lines CEM, MOLT-4 (clone 8), and HUT-78. In MT-4 and MT-2 cells, Ro5-3335 had no inhibitory effect on HIV-1 replication. The absence of anti-HIV-1 activity of Ro5-3335 in MT-4 cells was confirmed by using different parameters of virus replication and different multiplicities of infection. In persistently HIV-1-infected HUT-78/IIIB/LAI cells, Ro5-3335 failed to demonstrate any activity at subtoxic concentrations. The cytotoxicity of Ro5-3335 was significantly lower in peripheral blood lymphocytes than in the CD4+ T-cell lines.

Dehydroepiandrosterone (DHEA) and synthetic DHEA analogs are modest inhibitors of HIV-1 IIIB replication.

Down-regulation of Epstein-Barr virus (EBV) induced transformation of human lymphocytes in vitro by dehydroepiandrosterone (DHEA), a naturally occurring human steroid secreted by the adrenal gland has been demonstrated. This article reports on the effects of DHEA and its novel synthetic analogs 16 alpha-fluoro-5-androsten-17-one (8354) and 3 beta-hydroxy-16 alpha-fluoro-5 alpha-androstan-17-one (OH8356) on human immunodeficiency virus (HIV-1) replication. Treatment with DHEA, 8354, or OH8356 resulted in a modest down-regulation of HIV-1 replication in phytohemagglutinin-stimulated peripheral blood lymphocytes as measured by syncytia formation, release of p24 antigen, and accumulation of reverse transcriptase activity. DHEA and 8354 also reduced syncytia formation in HIV-1-infected SupT1 lymphoblasts. DHEA and synthetic analogs of DHEA, which have been shown previously to have antiproliferative effects, now are shown to reduce HIV-1 replication. DHEA or synthetic analogs of DHEA could provide an alternative and/or adjuvant for HIV-1 infection.

Mutation in the primer binding site of the type 1 human immunodeficiency virus genome affects virus production and infectivity.

In an effort to understand the contribution of the primer-binding site (PBS) region to human immunodeficiency virus (HIV) replication, we have constructed a mutant HIV proviral DNA with an alteration in the 5' end of the PBS. The PBS mutant proviral DNA was characterized by transfection of the viral DNA into CD4+ and non-CD4+ target cells. The results indicate that mutation in the PBS reduced the level of viral particles released into the medium of transfected cells in comparison to wild-type proviral DNA. The viral particles were noninfectious upon transmission to established CD4+ cell lines and phytohemagglutinin-stimulated peripheral blood lymphocytes. Electron microscopic analysis of the transfected cells revealed no abnormalities in the structure of the virion directed by the mutant proviral DNA. Also, the protein and RNA contents of the mutant virions were similar to the wild type. The quantitation of intracellular viral structural protein in the transfected cells, however, indicated that the PBS mutation may have an effect on the assembly of viral particles in addition to completely abolishing reverse transcription of viral RNA into DNA. These results provide evidence that the PBS region of the viral genome has multiple functions in HIV-1 replication.

Generation of hybrid human immunodeficiency virus utilizing the cotransfection method and analysis of cellular tropism

Human immunodeficiency viruses (HIV) isolated from infected individuals show tremendous genetic and biologic diversity. To delineate the genetic determinants underlying specific biologic characteristics, such as rate of replication, cytopathic effects, and ability to infect macrophages and T4 lymphoid cells, generation of hybrid HIV using viruses which exhibit distinct biologic features is essential. To develop methods for generating hybrid HIV, we constructed truncated HIV proviral DNA plasmids. Upon digestion with restriction enzymes, these plasmid DNAs were cotransfected into human rhabdomyosarcoma cells to generate hybrid HIV. The hybrid HIVs derived by this method were infectious upon transmission to both phytohemagglutinin-stimulated peripheral blood lymphocytes and established human leukemic T-cell lines. The virus derived from molecular clone pHXB2 (HIVHTLV-III) productively infected CEMx174 cells. On the other hand, molecular clone pARV (HIVSF2)-derived virus did not show productive infection of CEMx174 cells when used as a cell-free virus. The hybrid HIV containing the 3' end of the genome from pARV and the 5' end of the genome from pHXB2 was effective in infecting CEMx174 cells, but the converse hybrid containing 5' pARV and 3' pHXB2 was not effective in infecting CEMx174 cells. These results suggest that differences in the genes outside of env and nef play a role in the ability of the virus to infect a certain cell type. The intracellular ligation method should be useful in the analysis of related and unrelated HIV-1 isolates with common restriction enzyme cleavage sites.

Interleukin-2 receptor regulates activation of phosphatidylinositol 3-kinase

Interleukin-2 (IL-2) stimulates proliferation of T lymphocytes and is involved in the activation of both natural killer and lymphokine-activated killer precursor cells. The intracellular messengers which mediate IL-2-dependent events have not yet been identified. IL-2 receptor is not a protein-tyrosine kinase. Activation of a cellular protein-tyrosine kinase and direct association of a protein-tyrosine kinase activity with the IL-2 receptor occurs within minutes of IL-2 stimulation. We investigated the activation of phosphatidylinositol 3-kinase (PI 3-kinase) in IL-2-mediated signal transduction using the IL-2-dependent murine T-cell line, CTLL-2, and human phytohemagglutinin-stimulated peripheral blood lymphocytes (phytohemagglutinin blasts). Within a minute following stimulation of these cells with IL-2, PI 3-kinase activity could be detected in antiphosphotyrosine (anti-P-Tyr) antibody immunoprecipitates. IL-2 triggered a direct association of PI 3-kinase with the IL-2 receptor as detected in immunoprecipitates using anti-IL-2 receptor beta chain antibody. In vivo labeled CTLL-2 cells have a time-dependent increase in D-3-phosphorylated polyphosphoinositides following stimulation with IL-2. This is the first group of second messengers identified in IL-2-mediated signal transduction.