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Biomedical subjects

L Levitt

Publications and source records attributed to L Levitt.

At least 19 recordsLinked to original sources
PubMed1991

Microsurgical free bone transfer in the dog.

Bone grafts have been used extensively for the reconstruction of skeletal injury in dogs. Cancellous and corticocancellous chip autografts are used for their osteoinductive and osteoconductive properties. Fresh, fresh-frozen, freeze-dried, and ethylene oxide-sterilized cortical allografts have been recommended for the reconstruction of segmental cortical defects. Donor sites for microsurgical bone transfer have been identified experimentally in the dog, but these remain to be used clinically. This paper reviews the anatomy and structural characteristics of donor sites for microsurgical bone transfer. Potential clinical indications for microsurgical bone transfer in the dog are described.

Animals↗
PubMed1991

Differential regulation of lymphokine production by distinct subunits of the T cell interleukin 2 receptor.

Most biologic responses to IL-2 have been attributed to interaction of IL-2 with a high affinity receptor which consists of a heterodimer composed of two distinct IL-2-binding proteins (IL-2R alpha/IL-2R beta). However, both low affinity IL-2R alpha (55 kD) and intermediate affinity IL-2R beta (70-75 kD) also appear to be expressed independently on the cell surface. We investigated the receptor-specific regulatory effects of IL-2 on cytokine production in unstimulated and activated T cells. T cells were activated by stimulation of the antigen receptor complex with anti-CD3 mAb. IL-2 (10(2) U/ml, 1 nM) stimulation of resting cells resulted in a fivefold increase in GM-CSF release but in only minimal IFN-gamma release. IL-2 markedly augmented mRNA expression of GM-CSF but not IFN-gamma in unstimulated T cells. IL-2R beta mAb but not IL-2R alpha mAb decreased IL-2-induced GM-CSF release and mRNA expression from unstimulated T cells. IL-2 concentrations required for GM-CSF release from resting cells suggested ligand binding to an intermediate affinity receptor. GM-CSF and IFN-gamma release from activated T cells increased four- to fivefold in response to 1 nM IL-2 and IL-2 augmented both GM-CSF and IFN-gamma mRNA. IL-2R beta mAb but not IL-2R alpha mAb reduced GM-CSF release and mRNA expression in activated T cells stimulated with 1 nM IL-2. IL-2R alpha blockade markedly decreased IL-2-induced IFN-gamma release and mRNA expression from activated cells, while IL-2R beta blockade had little effect on IFN-gamma production in activated cells. IL-2R alpha blockade altered the affinity of the receptor mediating activated cell GM-CSF release from a high affinity to an intermediate affinity state. These studies indicate an independent role for IL-2R beta in mediating GM-CSF production from T cells. They also suggest that unstimulated and activated T cells, which express distinct IL-2 receptor moieties, mediate release of separate lymphokines and that different subunits of the IL-2 receptor may play an important role in the regulation of cytokine production.

Antibodies, Monoclonal↗
PubMed1989

Primary intraosseous fibrosarcoma in a cat.

A primary intraosseous fibrosarcoma was diagnosed in a 1.5-year-old cat. Clinical signs included nonweight-bearing lameness of the right forelimb and signs of pain on palpation of the right elbow. Radiography of the right elbow revealed a well-circumscribed osteolytic lesion of the olecranon. The right fore-limb was amputated, and histologic examination revealed tumor invasion into local veins and metastasis to the axillary lymph nodes. The cat had no signs of tumor redevelopment or pulmonary metastatic disease one year after amputation.

Amputation, Surgical↗
PubMed1989

[Lymphokine-induced suppression of erythropoiesis by normal T lymphocytes and retrovirus-associated lymphoproliferative disease].

Activation of genes for interleukin 2 (IL2) and its receptor by the tat gene product of the human retrovirus HTLV-I has been linked to the pathogenesis of adult T cell leukemia. In earlier studies we have demonstrated that IL2-induced inhibition of erythropoiesis is mediated by activated T-Lymphocytes expressing the IL2-receptor. We have now examined the role of activated T cells and interferon-gamma (IF gamma) in inhibition of normal erythropoiesis and in HTLV-I associated lymphoproliferative disease. T cells were activated by triggering of the antigen receptor complex with CD3 monoclonal antibody. Incubation with CD5 antibody recognizing a T cell epitope distinct from the antigen receptor served as a control. Supernatants derived from CD3 activated T cells generated in the presence of IL2 caused a dose-dependent suppression of erythropoiesis. Treatment of supernatant interferon-gamma neutralizing antibody caused a greater than 95% abrogation of inhibition. Next we investigated the mechanisms for acquired pure red cell aplasia in a patient with T gamma-lymphoproliferative disease (T gamma-LPD). Patient marrow erythroid progenitors were 17 +/- 9% of control and increased to 88-102% of control following marrow T cell depletion. Myeloid progenitors were normal. Patient suppressor T cells inhibited growth of autologous and allogeneic marrow erythroid but not myeloid progenitors and produced high titers of IF gamma. The inhibitory factor in patient T cell supernatant was acid labile and sensitive to trypsin, consistent with properties of IF gamma. Prior depletion of activated T cells abrogated the suppressive effect of patient T cell-derived supernatant.(ABSTRACT TRUNCATED AT 250 WORDS)

Anemia, Aplastic↗
PubMed1988

Unsuccessful surgical repair of a short soft palate in a dog.

An 8-week-old male Miniature Schnauzer had nasal discharge of milk, food, and water since birth, especially during eating. Examination of the oral cavity revealed a short soft palate. Numerous unsuccessful surgical procedures were performed to construct a shelf of tissue to prevent oronasal reflux. The dog was euthanatized.

Animals↗
PubMed1988

The T-cell CD2 determinant mediates inhibition of erythropoiesis by the lymphokine cascade.

We examined the role of the T-cell antigen CD2 in the regulation of erythropoiesis by the lymphokine cascade. T-cell interleukin-2 (IL-2) receptors (p55) were induced via triggering of the antigen receptor-associated CD3 epitope. Before CD3 triggering T cells were preincubated with a CD2-blocking (Leu-5b) or isotype control antibody. T-cell pellets were employed during incubation to facilitate interaction between T-cell LFA-3 and CD2. CD2 blockade caused a 66% to 79% inhibition of p55 expression after three to six days of culture with IL-2. Next we assessed the effect of CD2 blockade on IL-2. Next we assessed the effect of CD2 blockade on IL-2-induced inhibition of BFU-E in autologous cocultures containing CD3-triggered T cells. IL-2 caused a dose-dependent inhibition (52% to 92%) of BFU-E in the presence but not in the absence of CD3-triggered T cells. T-cell CD2 blockade prior to CD3 triggering caused a 65% to 87% abrogation of IL-2-induced inhibition of BFU-E at 10 to 10(2) U/mL IL-2. Preincubation of CD3-triggered T cells with isotype control antibody had no effect on IL-2-induced erythroid inhibition. Day 3 supernatants from CD3-triggered T cells or CD2-blocked, CD3-triggered T cells established in the presence of IL-2 were next assessed for modulation of BFU-E. CD3-triggered T-cell supernatants caused a 77% +/- 9% inhibition of BFU-E. Blockade of CD2 caused a 95% abrogation of T-cell-mediated BFU-E inhibition. In addition, CD2 blockade reduced interferon-gamma (IF gamma) release (84 to 128 U/mL) from CD3-triggered T cells by 81% at day 3 of culture. In control experiments, the addition of IF gamma-neutralizing monoclonal antibody to CD3-triggered T-cell supernatant established in the presence of IL-2 caused 75% abrogation of IL-2 inhibition of BFU-E. We conclude that blockade of the CD2 T-cell determinant induces down modulation of (a) T-cell p55 IL-2 receptor expression, (b) IL-2-induced inhibition of BFU-E, and (c) IL-2-induced marrow T-cell IF gamma release. These data suggest that the T-cell CD2 determinant can exert a regulatory effect on the control of erythropoiesis by the lymphokine cascade.

Antigens, Differentiation↗
PubMed1988

T cell regulated hematopoiesis--molecular interactions in hematopoietic control by CD2 and interleukin 2.

Studies are reviewed, which establish a novel regulatory role for the T cell surface molecule CD2 and the T cell lymphokine IL-2: Immunoregulation of hematopoiesis. IL-2 induces a receptor-specific inhibition of early erythroid progenitors. IL-2-induced inhibition of erythropoiesis is mediated by interferon-gamma protein release and is associated with interferon-gamma mRNA accumulation. CD3-triggered p55 IL-2 receptor expression is a prerequisite for IL-2-induced erythropoietic inhibition and is associated with p55 mRNA synthesis. Hematopoietic effects of IL-2 are mediated by CD2/LFA-3 receptor ligand interactions. The studies demonstrate that the regulatory roles of IL-2 and CD2 extend beyond governance of the immune system itself and can subserve to control red cell production in vitro.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1987

Receptor-specific modulation of myelopoiesis by recombinant DNA-derived interleukin 2.

T cells and T cell-derived lymphokines have been implicated in the regulation of myelopoiesis. This study examines the regulatory effects of recombinant DNA-derived human IL 2 on the phagocyte progenitor cell (CFU-GM), utilizing a receptor-specific model for T cell regulation of myelopoiesis. IL 2 receptors were induced on immunopurified marrow T cells by triggering the T cell antigen receptor complex with CD3 monoclonal antibody. IL 2 receptor expression was assessed by cytofluorography with IL 2 receptor monoclonal antibody. IL 2 receptor-positive and IL 2 receptor-negative marrow T cells were cocultured with autologous adherent and T cell-depleted marrow mononuclear cells in the absence and presence of various concentrations of IL 2. In the presence of IL 2 receptor-positive T cells, IL 2 caused a dose-dependent inhibition of CFU-GM (86% at 10(2) U/ml). IL 2 did not inhibit CFU-GM in the absence of T cells or in the presence of IL 2 receptor-negative T cells. The addition of IL 2 receptor blocking monoclonal antibody completely abrogated IL 2-induced inhibition of CFU-GM. Conditioned media prepared from IL 2 receptor-positive marrow T cells in the presence of IL 2 also inhibited CFU-GM expression from marrow NAB-T cells (50% +/- 16). In contrast, conditioned media from IL 2 receptor-positive T cells prepared in the absence of IL 2 or from IL 2 receptor-negative T cells prepared in the presence or absence of IL 2 did not significantly affect CFU-GM growth. IL 2 receptor-positive, but not IL 2 receptor-negative, T cells released large amounts (190 +/- 60 U/10(6) cells X ml-1) of IFN-gamma but only low amounts of tumor necrosis factor beta (less than 10 U/ml) in response to IL 2. In control experiments, recombinant DNA-derived IFN-gamma caused a 37% +/- 19 inhibition of CFU-GM in the presence of resting T cells and adherent cells. However, IFN-gamma failed to inhibit CFU-GM in the presence of activated (IL 2 receptor-positive) T cells, indicating that release of IFN-gamma cannot solely explain IL 2-induced inhibition of CFU-GM. The addition of neutralizing IFN-gamma monoclonal antibody partially abrogated IL 2-induced inhibition of CFU-GM (41 to 60%) in the presence of CD3-triggered T cells, suggesting that although IFN-gamma participates in IL 2-induced inhibition of myelopoiesis, it is not the sole mediator of that inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

Antigen-Presenting Cells↗
PubMed1987

Norfloxacin for prevention of bacterial infections in granulocytopenic patients.

The efficacy and safety of norfloxacin were compared with those of placebo, vancomycin-polymyxin, and trimethoprim-sulfamethoxazole (TMP/SMX) for prophylaxis of bacterial infections in granulocytopenic patients. The study results showed that norfloxacin treatment, which was well tolerated and not associated with any serious systemic adverse effects, prevented acquisition of gram-negative bacillary organisms. Fewer norfloxacin-treated patients (38 of 108 patients, or 35 percent) experienced microbiologically documented infections compared with patients receiving placebo (27 of 40 patients, or 68 percent), vancomycin-polymyxin (16 of 30 patients, or 53 percent), or TMP/SMX (14 of 28 patients, or 50 percent). Gram-negative bacteremia developed in five of 108 norfloxacin-treated patients (5 percent), compared with 17 of 40 placebo-treated patients (43 percent), five of 30 treated with vancomycin-polymyxin (17 percent), and one of 28 patients treated with TMP/SMX (4 percent). The incidence of gram-positive bacteremia was similar in all study groups and was not affected by norfloxacin or any other oral prophylactic antibiotics. These results suggest that norfloxacin is both safe and effective for the prevention of serious gram-negative bacillary infections in granulocytopenic patients. More effective prophylaxis of gram-positive bacterial infections, however, is needed.

Adolescent↗
PubMed1987

Augmentation of in vitro human marrow erythropoiesis under physiological oxygen tensions is mediated by monocytes and T lymphocytes.

Tissue and marrow (BM) in vivo O2 tensions have been estimated at 23 to 40 mm Hg (3% to 5% O2). We have investigated cellular regulation of burst-forming units-erythroid (BFU-E) under 5% O2. BFU-E from BM mononuclear cells (MNC) were cultured in methylcellulose medium and erythropoietin (Ep) +/- monocyte-conditioned medium (MoCM, a source of burst-promoting activity, BPA) in the presence or absence of autologous T cells (T) and/or monocytes (M phi) under either 5% or 21% O2 after depletion of T (MNC-T), M phi (nonadherent buoyant cells, NAB) or both T and M phi depletion (NAB-T). MNC BFU-E growth under 5% O2 was augmented over 0.1 to 1.5 U/mL of Ep. BFU-E augmentation under 5% O2 was abolished by depletion of BM M phi, T, or both from MNC. The addition of MoCM affected neither a BFU-E increase under 5% O2 nor the abrogation of that increase upon T or M phi depletion. The addition of 5% to 20% M phi or 10% to 20% T to NAB-T failed to restore the BFU-E increase under 5% O2. However, BFU-E augmentation under 5% O2 was reestablished when 10% autologous M phi, 10% T, or 10% T plus 10% M phi were added back to marrow NAB, MNC-T, or NAB-T. BM BFU-E was not augmented in the presence of varying concentrations of catalase, superoxide dismutase, or reduced glutathione at 21% O2; moreover, BFU-E augmentation was maintained at 5% O2 relative to 21% O2 in the presence of each of these antioxidants. CM prepared under 5% or 21% O2 from BM M phi, T, or M phi plus T were assessed for BPA against BM NAB-T using a sensitive BPA assay incorporating delayed Ep addition to cultures. Only CM from mixtures of M phi and T cells at 5% O2 demonstrated potent BPA; little or no BPA was detected with T or M phi CM at 5% O2 and at 21% O2 or T and M phi CM at 21% O2. The sensitivity of NAB-T BFU-E to exogenous BPA was virtually identical at 21% and 5% O2. These results indicate that human BM BFU-E are augmented under 5% O2 and that T cells and M phi together mediate that augmentation by collaborating to produce BPA-like activity in response to physiological O2 tensions.

Antioxidants↗
PubMed1985

Human bone marrow and peripheral blood T lymphocyte depletion: efficacy and effects of both T cells and monocytes on growth of hematopoietic progenitors.

The efficacy of four separate methods of human bone marrow T lymphocyte depletion was assessed, and the effect of T cells and monocytes on in vitro growth of marrow (CFU-GEMM, BFU-E, and CFU-GM) and peripheral blood (BFU-E) hematopoietic progenitors was determined. Extent of T cell depletion was assessed by multiparameter fluorescent cell sorter (FACS) analysis and by functional studies. Cells staining positively by FACS analysis for one or more of three separate fluorescent pan-T cell monoclonal antibodies (MCAbs) comprised 8.4% to 9.5% of control marrow mononuclear cells (MNCs). T cells constituted 3.2% to 5.1% of marrow following single, sequential, or combination treatment with two different pan-T cell MCAbs (Leu 1 and TM1) plus complement, 1.5% to 2.2% of marrow following solid-phase immunoabsorption ("panning"), 0.2% of marrow after sheep cell rosetting, and only 0.05% of marrow after FACS selective cell sorting and gated separation. T cells made up 59% to 73% of control peripheral blood MNCs and 0.8% to 2.8% of peripheral MNCs following sheep cell rosetting plus treatment with Leu 1 MCAb and complement. Mitogen (PHA, Con A) and allogeneic MLC-induced blastogenic responses (stimulation indices, experimental/control or E/C) revealed a concordant decrement in marrow T cell function after MCAb plus complement (E/C of 3.9 to 9.0), after panning (E/C of 1.6 to 3.5) and after sheep cell rosetting (E/C of 0.7 to 1.3), compared with control marrow (E/C of 5.3 to 15.7). After T cell depletion, marrow BFU-E growth was 95% to 120% of control, CFU-GM growth was 90% to 108% of control, and CFU-GEMM growth was 89% to 111% of control. Marrow T cell and/or monocyte depletion did not alter erythropoietin-dependent BFU-E growth in the absence of Mo-conditioned medium (81% to 95% of control), and the addition of as many as 50 to 100 X 10(3) purified marrow monocytes or T cells to 10(5) autologous nonadherent T cell-depleted marrow target cells had a negligible (P greater than .1) effect on marrow BFU-E growth in vitro. Peripheral blood (PB) BFU-E/10(5) T-depleted target cells were 106% +/- 19% of expected; PB BFU-E growth was significantly diminished after monocyte depletion alone (7% +/- 6% of expected) or after monocyte plus T cell depletion (8% +/- 4% of expected).(ABSTRACT TRUNCATED AT 400 WORDS)

Antibodies, Monoclonal↗
PubMed1985

Human spleen cell generation of factors stimulating human pluripotent stem cell, erythroid, and myeloid progenitor cell growth.

Mitogen-stimulated murine spleen cells produce humoral substances capable of supporting murine hematopoiesis and pluripotent stem cell proliferation in vitro. Thus, we evaluated conditioned media generated by human spleen cells (SCM) in the presence or absence of mitogens for factors stimulatory for human pluripotent (CFU-GEMM), erythroid (BFU-E), and myeloid (CFU-GM) precursors. Two and one half percent to 10% SCM stimulated proliferation of all three types of precursor cells from nonadherent buoyant human marrow target cells. Mitogen-stimulated SCM augmented CFU-GM (175% to 225%), whereas CFU-GEMM and BFU-E growth was essentially unchanged. Cell separation procedures used to determine which cells provided these microenvironmental stimuli indicated that nonadherent mononuclear spleen cells provided the bulk of the CSF-GM, whereas adherent cells (95% nonspecific esterase + monocyte-macrophages) and nonadherent cells provided similar proportions of CSF-mix and erythroid burst-promoting activity (BPA). The nonadherent cells generating high levels of CSF-mix, BPA, and CSF-GM were predominantly Leu-1-negative, ie, non-T, cells. In the presence or absence of mitogens, SCM was a more potent source (1.3- to 3.8-fold) than peripheral leukocyte CM of the growth factors for the three progenitor cell types. Specific in situ cytochemical stains for analyzing morphology of myeloid colonies demonstrated that SCM stimulated the proliferation of the same types and proportions of colonies as human placental CM, suggesting that these CMs may contain similar CSF-GMs. These data show the contribution of spleen cell subsets to the generation of hematopoietic growth factors and the responsiveness of these cells to various mitogenic stimuli.

Bone Marrow Cells↗
PubMed1979

The use of stem cell assays to monitor the proliferative potential of bone marrow cells.

A number of assays exist for hematopoietic stem cells in both humans and mice, but the appropriate stem cell assay for the repopulating potential of human marrow is not clear. Two murine models suggest that these assays may not always predict marrow proliferative potential. In vivo diffusion chamber culture growth of CD1 marrow depleted of pluripotent stem cells (CFU-S) by exposure to mouse-brain antisera plus complement was equivalent to or greater than that of normal serum treated control marrow. Furthermore, CF1 mice repeatedly injected with endotoxin had markedly stimulated granulopoiesis with increases in the number of marrow CFU-S and the % in S phase but no changes in the number or proliferative status of marrow CFU-C. However, inbred BDF1 mice chronically injected with endotoxin although also showing striking increases in granulopoiesis had no significant alteration in their marrow CFU-S or CFU-C number or cell cycle status relative to saline injected controls. Both models present examples where conventional stem cell assays do not provide insight into marrow cell production and suggest that in vitro clonal assays of human marrow cells may not always predict for the potential of marrow to repopulate a human transplant recipient.

Animals↗