Id2 and Id3 inhibit development of CD34(+) stem cells into predendritic cell (pre-DC)2 but not into pre-DC1. Evidence for a lymphoid origin of pre-DC2.

We found previously that Id3, which inhibits transcriptional activities of many basic helix-loop-helix transcription factors, blocked T and B cell development but stimulated natural killer (NK) cell development. Here we report that ectopic expression of Id3 and another Id protein, Id2, strongly inhibited the development of primitive CD34(+)CD38(-) progenitor cells into CD123(high) dendritic cell (DC)2 precursors. In contrast, development of CD34(+)CD38(-) cells into CD4(+)CD14(+) DC1 precursors and mature DC1 was not affected by ectopic Id2 or Id3 expression. These observations support the notion of a common origin of DC2 precursors, T and B cells. As Id proteins did not block development of NK cells, a model presents itself in which these proteins drive common lymphoid precursors to develop into NK cells by inhibiting their options to develop into T cells, B cells, and pre-DC2.

Galectin-1, an endogenous lectin produced by thymic epithelial cells, induces apoptosis of human thymocytes.

Galectin-1, a beta-galactoside binding protein, is produced by thymic epithelial cells and binds to human thymocytes. We have previously reported that galectin-1 induces the apoptosis of activated T lymphocytes. Because the majority of thymocytes die via apoptosis while still within the thymus, we tested whether galectin-1 could induce the apoptosis of these cells. We now report that in vitro exposure to galectin-1 induced apoptosis of two subsets of CD4(lo) CD8(lo) thymocytes. The phenotypes of susceptible thymocytes were consistent with that of both negatively selected and nonselected cells. Galectin-1-induced apoptosis was enhanced by preexposure of thymocytes to antibody to CD3, suggesting that galectin-1 may be a participant in T-cell- receptor mediated apoptosis. In contrast, pretreatment of thymocytes with dexamethasone had no effect on galectin-1 susceptibility. We noted that 71% of the cells undergoing apoptosis after galectin-1 treatment had a DNA content greater than 2N, indicating that proliferating thymocytes were most sensitive to galectin-1. We propose that galectin-1 plays a role in the apoptosis of both negatively selected and nonselected thymocytes, and that the susceptibility of thymocytes to galectin-1 is regulated, in part, by entry or exit from the cell cycle.

Human thymic epithelial cells express an endogenous lectin, galectin-1, which binds to core 2 O-glycans on thymocytes and T lymphoblastoid cells.

Thymic epithelial cells play a crucial role in the selection of developing thymocytes. Thymocyte-epithelial cell interactions involve a number of adhesion molecules, including members of the integrin and immunoglobulin superfamilies. We found that human thymic epithelial cells synthesize an endogenous lectin, galectin-1, which binds to oligosaccharide ligands on the surface of thymocytes and T lymphoblastoid cells. Binding of T lymphoblastoid cells to thymic epithelial cells was inhibited by antibody to galectin-1 on the epithelial cells, and by two antibodies, T305 and 2B11, that recognize carbohydrate epitopes on the T cell surface glycoproteins CD43 and CD45, respectively. T lymphoblastoid cells and thymocytes bound recombinant galectin-1, as demonstrated by flow cytometric analysis, and lectin binding was completely inhibited in the presence of lactose. The degree of galectin-1 binding to thymocytes correlated with the maturation stage of the cells, as immature thymocytes bound more galectin-1 than did mature thymocytes. Preferential binding of galectin-1 to immature thymocytes may result from regulated expression of preferred oligosaccharide ligands on those cells, since we found that the epitope recognized by the T305 antibody, the core 2 O-glycan structure on CD43, was expressed on cortical, but not medullary cells. The level of expression of the UDP-GlcNAc:Gal beta 1,3GalNAc-R beta 1, 6GlcNAc transferase (core 2 beta 1, 6 GlcNAc transferase, or C2GnT), which creates the core 2 O-glycan structure, correlated with the glycosylation change between cortical and medullary cells. Expression of mRNA encoding the C2GnT was high in subcapsular and cortical thymocytes and low in medullary thymocytes, as demonstrated by in situ hybridization. These results suggest that galectin-1 participates in thymocyte-thymic epithelial cell interactions, and that this interaction may be regulated by expression of relevant oligosaccharide ligands on the thymocyte cell surface.

Autocrine growth of murine lymphoma cells.

By using an assay system in which small numbers of murine T lymphoma cells are stimulated to grow in serum-free medium, we have continued and expanded our previous studies of an autocrine growth factor that we call leukemia-derived growth factor (LDGF). We show that a T lymphoma cell line of immature phenotype, adapted to growth in serum-free medium, produces and responds to LDGF. LDGF activity is distinct from activities of 10 highly purified or recombinant hematopoietic growth factors including IL-1 and IL-2. However, growth-stimulating activity for the murine lymphoma cells is provided by a partially purified human LDGF.

Leukemia derived growth factors produced by human malignant T-lymphoid cell lines.

An autocrine (noninterleukin 2) growth factor, which we term leukemia derived growth factor (LDGF), has previously been found in the culture supernatant of the human malignant T-lymphoid cell line MOLT-4f. We now show that two other human malignant T-lymphoid cell lines, CCRF-CEM and CCRF-HSB-2 also produce such a factor. All three factors, i.e., the LDGF from MOLT-4f, CCRF-CEM, and CCRF-HSB-2 are similar to each other both in biological activity and in physicochemical characteristics. In addition to their autocrine activity, these LDGFs stimulate the growth of other malignant T-lymphoid cell lines, but they do not stimulate B-lymphoblastoid or myeloid cell lines. The results therefore suggest that these LDGFs are T-cell specific.

In vitro studies of HIV-1 expression in thymocytes from infants and children.

OBJECTIVE: To determine whether thymocytes from infants and young children can be infected with and their maturation capability altered by HIV-1, and to examine the effects of interleukin (IL)-2 and IL-4 on this process. DESIGN: Serum-free culture medium was used so that cytokine effects could be studied under defined conditions. The primary virus isolates HIV-1JR-CSF and HIV-1JR-FL were used because their effects should most closely resemble those of viruses which might be found in an infected child. METHODS: Thymocytes from infants and young children were infected with virus and cultured in serum-free medium with the cytokines IL-2 and IL-4 alone or in combination. HIV-1 expression was measured after 12 days by p24 levels in culture supernatants. Thymocyte maturation was determined by changes in surface phenotype, as measured by flow cytometry. RESULTS: HIV-1 expression by thymocytes, which increased with time of culture, occurred when thymocytes were cultured with each cytokine. p24 levels were slightly increased when cultured with IL-2, compared with IL-4. Virus expression was remarkably increased when the cytokines were combined in culture. This expression was synergistic rather than additive. The synergy, evident in mature, but not immature thymocytes, was demonstrated with both pharmacologic and physiologic concentrations of cytokines. T-cells from peripheral blood cultured under the same conditions demonstrated lower virus expression in the presence of cytokines and synergy was not shown. Cytokine-induced thymocyte maturation and thymocyte survival in vitro was unimpaired by infection with HIV-1. CONCLUSIONS: These findings indicate that the cytokines IL-2 and IL-4, which are normally present in the thymic environment, can synergize to promote HIV-1 expression by thymocytes infected in vitro. This occurs without impairing the maturation induced by these cytokines. Thus, the mature thymocyte may provide a continuous supply of virus-expressing T-cells to the peripheral blood and lymphoid tissues of the infected child.

Effect of cytokines on HIV-induced depletion of thymocytes in vivo.

BACKGROUND: Cytokines play an important role in the differentiation of thymocytes into mature T cells; consequently, certain cytokines could be useful for immune reconstitution after HIV infection without increasing viral load. OBJECTIVE: To investigate whether cytokines affect immune depletion caused by HIV infection with a CXCR4-tropic strain in SCID-hu mice implanted with human fetal thymus and liver (thy/liv) tissue. METHODS: The thy/liv implants were either mock infected or infected with HIV-1 NL4-3, a CXCR4-tropic molecular clone. Interleukin (IL)-2, IL-4, IL-7, interferon-gamma (IFN-gamma) or diluent was administered to the mice during the second and third week postinfection. Viral load and immunophenotype were determined in thymocytes. RESULTS: Thymocyte subset distributions at 3 weeks postinfection were significantly influenced by treatment with certain cytokines. In particular, IL-2 caused the infected mice to retain a thymocyte profile that was more similar to that in mock-infected mice than that in diluent-treated infected mice, in that the percentages of immature CD4+CD8+ and CD5+CD1+ cells were slightly higher and much less variable than in diluent-treated infected mice. The effect of IFN-gamma treatment was similar to IL-2 but did not reach statistical significance. However, after IFN-gamma treatment, normal percentages of mature CD3+CD69+ cells were maintained whereas this population was relatively increased in diluent-treated infected mice. Although treatment with IL-4 and IL-7 delayed depletion of immature thymocytes, these cytokines increased viral load. CONCLUSIONS: Cytokines such as IL-2 and IFN-gamma maintain immature thymocytes without increasing viral load and may be useful as adjuncts to improve immune reconstitution after HIV infection.

Differential tropism of HIV-1 isolates for distinct thymocyte subsets in vitro.

OBJECTIVE: Understanding the interaction between HIV and developing thymocytes is crucial in determining how HIV infection perturbs the immune system. We determined which thymocyte subsets can harbor and express HIV. DESIGN: HIV expression in mature and immature thymocytes obtained from surgical specimens from non-infected children was determined after in vitro infection with the syncytium-inducing, cytopathic NL4-3 and the non-syncytium-inducing, relatively noncytopathic JR-CSF isolates. METHODS: Intracellular staining for the HIV p24gag antigen was combined with cell surface phenotyping to determine thymocyte subsets expressing HIV. Infection was quantitated by polymerase chain reaction on sorted subsets. RESULTS: NL4-3 replicated faster and to higher titers and caused a more severe decrease of all CD4-bearing thymocytes than did JR-CSF. In addition, both immature CD1+ and mature CD1-thymocytes expressed NL4-3, whereas only mature CD1-cells expressed JR-CSF. The tropism of NL4-3 for these immature cells suggests a mechanism for a more profound impact on T-cell maturation than that seen with JR-CSF. We also found that thymocytes lacking cell surface CD4 (CD4-CD8- and CD4-CD8+ subsets) expressed virus with either isolate late in infection, when viral levels were high. The CD4-CD8- cells expressing HIV were mature CD3bright T-cell receptor (TCR) alpha/beta bright cells. CONCLUSIONS: These results show that NL4-3 can be expressed by thymocytes at immature and mature stages of differentiation and cause severe loss of CD4+ cells. Thus, tropism of a virus for immature cells can affect the capability of the thymus to produce new T lymphocytes leading to a greater impact on development and functions of the immune system. It is proposed that this in vitro model can be used to study pathogenic mechanisms in the thymus.

Somatomedin activity and inorganic sulfate in children undergoing hemodialysis.

Bioassayable serum somatomedin activity could be estimated in uremic subjects only after appropriate correction for increased circulating inorganic sulfate. Somatomedin activity increased after hemodialysis in six of ten patients, possibly due to removal of somatomedin inhibitors.

A rapid method for measuring apoptosis and dual-color immunofluorescence by single laser flow cytometry.

A sensitive method for quantification of cells undergoing apoptosis that permits the simultaneous measurement of dual-color cell surface immunofluorescence is presented. Unfixed cells are stained with 7-amino-actinomycin D (7-AAD) for discrimination of live from early apoptotic cells and from cells which have lost membrane integrity (late apoptotic or necrotic, dead cells). Owing to its spectral characteristics 7-AAD can be combined with fluorescein-isothiocyanate (FITC) and phycoerythrin (PE) cell surface staining. After staining, the samples can be treated with paraformaldehyde (PF) solution to eliminate the risk for exposure of laboratory personnel to biohazardous agents and to preserve the cells through fixation for later analysis on the flow cytometer. The value of the method is shown on the measurement of apoptosis in human thymocytes and in human peripheral blood mononuclear cells (PBMC) exposed to various inducers of active cell death. The method is validated by fluorescent activated cell sorting in combination with morphologic examination of the sorted cells. The technique we are presenting is particularly valuable in a clinical setting because it allows rapid multiparameter analysis of apoptosis in combination with cell surface phenotype on biohazardous samples with single laser instrumentation.

A simple and rapid method for preparation of HIV-expressing targets for functional assays.

Standardized samples of target cells expressing viral antigen are necessary to perform reproducible and comparable functional assays for immune responses to human immunodeficiency virus (HIV-1). HIV-infected cultured cell lines show wide variability in the number of HIV-expressing cells and in the amount of viral antigen per cell. They, as well as cells coated with the infectious virus, are a biohazard. 0.015% v/v beta-propiolactone (BPL) in buffered solution at pH 7.5 inactivates the infectivity of HIV but retains its antigenicity. BPL-inactivated HIV easily binds to T4 receptor bearing T-lymphocytes in a 30 min incubation at 22 degrees C. The process of adsorption is dose-dependent and results in a standardized and reproducible sample of target cells. Applications for the method are demonstrated and include: (1) preparation of target cells for assay of antibody-dependent cellular cytotoxicity (ADCC), and (2) characterization of antisera to HIV for their capacity to block HIV binding to cells.

Simultaneous flow cytometric measurement of viability and lymphocyte subset proliferation.

Combined analysis of DNA content and immunofluorescence on single cells by flow cytometry provides information on the proliferative response of cellular sub-populations in mixed cell preparations. However, the presence of considerable numbers of dead (nonviable) cells impairs accurate flow cytometric data analysis, mainly, because dead cells can bind antibodies non-specifically and show alterations in their DNA staining profiles. We developed a rapid method for identification of dead cells by fluorescence in cell preparations that are stained simultaneously for two-color immunofluorescence and DNA content. Cells are stained with 7-aminoactinomycin D (7-AAD) for dead cell discrimination and with fluorescein-isothiocyanate (FITC) and phycoerythrin (PE)-labeled monoclonal antibodies (mAb) for cell surface immunofluorescence. Diffusion of 7-AAD from stained, dead cells into unstained, live cells after cell permeabilization is blocked by the addition of its non-fluorescent analogue actinomycin D (AD). DNA is stained with red-excitable TO-PRO-3 iodide (TP3) which has an emission spectrum that can be effectively separated from the emissions of FITC, PE, and 7-AAD. TP3 staining is performed in the presence of ribonuclease A (RNAse) in phosphate-citrate buffer containing saponin (PCBS) at low pH. FITC fluorescence is sensitive to acid pH; therefore, PCBS is replaced after DNA staining with 1x PBS at pH 7.2 containing saponin to permit accurate detection of FITC immunofluorescence on the flow cytometer. We apply this method to the analysis of differential proliferation of lymphocyte subsets in cultures of human peripheral blood mononuclear cells (PBMC) with low viability.

Cadaver renal transplantation in children with cystinosis.

Five children with end-stage renal disease resulting from cystinosis received seven cadaver renal allografts. Four recipients have functioning grafts eight to 55 months after receiving the transplant and one recipient lost two grafts at 17 and 26 months after the transplant. There was no florid recurrence of the Fanconi syndrome although proximal renal tubular dysfunction developed in two patients, in one in association with chronic rejection and in one without apparent etiology. Free cystine content of white blood cells, cultured skin fibroblasts and allograft tissue was significantly increased. Cystine crystals were observed in the mesangium of two grafts and in the interstitial tissue of all grafts; however, no cystine crystals were found in the tubules. The location of the cystine crystals, as well as the fact that the highest free level of cystine of allograft tissue was observed in the graft undergoing chronic rejection. led to the hypothesis that recipient cells infiltrating the graft were the source of cystine deposition. The data indicate that successful cadaveric transplantation does not correct the primary metabolic defect in cystinosis, thereby explaining the persistence of the extrarenal clinical manifestations, such as photophobia and hypothyroidism, after renal transplantation in cystinosis.

Long-term cadaver allograft survival in the recipient with a positive B lymphocyte crossmatch.

Over a 2 1/2-year period, prospective standard, T, and B lymphocyte crossmatches were performed in 45 cadaver renal transplants using the microlymphocytotoxicity technique. Twenty-three of the 45 recipients had a positive B lymphocyte crossmatch. Cumulative graft survival rates did not differ between recipients with a positive and negative B lymphocyte crossmatch. High levels of presensitization in routine lymphocytotoxic antibody screening or transplant number did not adversely affect graft survival in recipients with a positive B lymphocyte crossmatch. Five recipients had moderately positive standard crossmatches which were attributable to anti-B lymphocytotoxicity. Four of these five grafts are presently functioning with normal serum creatinine levels 9 to 14 months post-transplant. A positive B lymphocyte crossmatch is compatible with good long-term cadaveric renal allograft survival. In addition, a weakly positive standard crossmatch is not a contraindication to transplantation when the positive crossmatch is attributable to anti-B lymphocyte antibody.

Circulating immune complexes in pediatric renal allograft rejection.

Previous reports on the generation and nephritogenic capacity of post-transplant circulating immune complexes (CICs) are conflicting. To assess the pathogenicity of CICs in acute rejection (AR), 784 CIC determinations were performed on 392 serum samples from 27 pediatric renal allograft recipients using the C1q-solid phase assay (C1q-SPA) and the Raji cell radioimmunoassay (Raji-RIA). Serum samples from transplant recipients not undergoing rejection episodes and from normal subjects served as controls. Of the 784 CIC determinations, 723 (92.3%) were negative in both assays. CICs were present at some point post-transplant in eight (19.6%) recipients. Correlation of CIC levels with allograft rejection was found in only two patients with CIC levels responding to antirejection therapy; however, statistical analysis of data by chi 2 analysis failed to reveal a significant correlation of CICs with AR episodes. Allograft histology in three recipients demonstrated characteristic signs of AR. Immunofluorescent studies did not reveal significant deposition of immunoglobulin or complement. Sucrose density gradient ultracentrifugation studies confirmed the immune complex nature of materials reactive with the CIC assays. There was no immunological evidence supporting antithymocyte globulin (ATG) as an immunogen in patients demonstrating CICs post-transplant. CICs do not appear to be an important mediator of AR. Statistical analysis of data using the chi 2 test failed to reveal a positive correlation of CIC levels with AR or ultimate allograft outcome.

Use of antithymocyte globulin (dose by rosette protocol) in pediatric renal allograft recipients.

Total rosette-forming cells (TRFCs) and percentage of rosette-forming cell (RFC) levels were measured in patients undergoing dialysis and in recipients following renal transplantation. The percentage of RFCs of the dialysis patients was not different from the percentage of RFCs of normal subjects, whereas the TRFCs were significantly lower in the dialysis patients. After transplantation, the percentage of RFCs and TRFCs was significantly lower in recipients treated with antithymocyte globulin (ATG) than in those of the control group; however, there was no difference in allograft survival between the ATG-treated and control recipients when using ATG in the dose by rosette protocol.

Antibodies to donor B lymphocytes and mixed lymphocyte culture blocking in cadaveric renal transplantation.

In 33 renal allograft recipient-donor pairs, B and T lymphocyte complement-dependent cytotoxicity crossmatches and mixed lymphocyte culture (MLC) blocking experiments were performed and the results were correlated with graft outcome. MLC blocking particularly in the unidirectional culture against donor-stimulating cells, was highly correlated with the presence of complement-dependent cytotoxicity antibodies against donor B lymphocytes. Grafts in both MLC blocking and B lymphocyte crossmatch-positive groups fared equally as well as those without positive tests. No difference in graft outcome was noted when the presence or absence of MLC blocking was examined in relationship to positive or negative B lymphocyte complement-dependent cytotoxicity crossmatching.

Nitric oxide induces necrotic but not apoptotic cell death in oligodendrocytes.

We have investigated the mechanism of nitric oxide-induced damage in glial cells. Genomic DNA isolated from astrocytes and microglia, treated for 18 h with varying concentrations of a nitric oxide donor, was analysed by electrophoresis. No DNA damage was evident. Oligodendrocytes, treated with 2 mM nitric oxide for 3-48 h, showed single stranded breaks at 48 h but no laddering of nucleosomic fragments of DNA. When analysed by electron microscopy, ultrastructural changes in oligodendrocytes treated with 1 mM nitric oxide for 24 h showed intact nuclei but alterations in membranes and organelles characteristic of necrosis, including disrupted mitochondria with dissolution of their christae. Astrocytes, a glial cell type that we have previously shown to be much less sensitive to nitric oxide-induced damage, did not show ultrastructural changes. DNA analysis by flow cytometry of glial cells treated with nitric oxide supported the apparent necrotic-type death in oligodendrocytes. Double staining of oligodendrocytes, using Hoechst 33342 and propidium iodide for the simultaneous assessment of both apoptotic and necrotic cells, demonstrated that, while the proportion of dead cells increased with time and increasing concentrations of nitric oxide, the death was due to necrosis and not apoptosis. In this study, we demonstrate that direct exposure to soluble nitric oxide, produced in vitro from a nitric oxide donor chemical, ultimately kills oligodendrocytes by necrosis. Microglia and astrocytes maintain DNA and organelle integrity when exposed to exogenous nitric oxide.

Human thymocyte responsiveness to stem cell factor: synergy with interleukin-2 for the generation of NK/LAK cytotoxicity.

Human recombinant stem cell factor (SCF) increases the viability and cell size of a subset of thymocytes in vitro, but does not independently induce phenotypic changes on thymocytes indicative of T cell differentiation. The SCF-responsive thymocytes have characteristics of large granular cells, that do not express T, B or NK cell-related antigens, and are primarily found in immature thymocyte subsets. These large granular thymocytes do not display cytotoxic activity. However, SCF acts synergistically with IL-2 in the generation of cytotoxic effector cells from thymocyte precursors. Synergy in cytotoxicity is observed to both NK-sensitive and NK-resistant targets. Studies of the SCF receptors on thymocytes show that receptors are expressed on mature 'bright' CD3+ cells, immature 'dim' CD3+ cells as well as CD3- cells. IL-2 increases the frequency of SCF receptor-positive cells in cultured thymocytes, which may explain its synergy with SCF in the generation of NK/LAK cytotoxicity. These data show that SCF enhances the functional development of thymic NK/LAK cells in vitro.

Pretransplant T cell levels and renal allograft survival rates.

Total rosette forming cell (TRFC) levels were measured in 50 patients awaiting cadaveric renal transplantation. Preliminary data show a statistically significant difference in allograft survival in patients with low TRFC levels before transplant as compared with patients with medium or high TRFC levels. Pretransplant TRFC levels may be predictive of a nonresponder status and portend a favorable renal allograft outcome.