Spatially resolved analysis of Pseudomonas aeruginosa biofilm proteomes measured by laser ablation sample transfer

Heterogeneity in the distribution of nutrients and oxygen gradients during biofilm growth gives rise to changes in phenotype. There has been long term interest in identifying spatial differences during biofilm development including clues that identify chemical heterogeneity. Laser ablation sample transfer (LAST) allows site-specific sampling combined with label free proteomics to distinguish radially and axially resolved proteomes for Pseudomonas aeruginosa biofilms. Specifically, differential protein abundances on oxic vs. anoxic regions of a biofilm were observed by combining LAST with bottom up proteomics. This study reveals a more active metabolism in the anoxic region of the biofilm with respect to the oxic region for this clinical strain of P. aeruginosa, despite this organism being considered an aerobe by nature. Protein abundance data related to cellular acclimations to chemical gradients include identification of glucose catabolizing proteins, high abundance of proteins from arginine and polyamine metabolism, and proteins that could also support virulence and environmental stress mediation in the anoxic region. Finally, the LAST methodology requires only a few mm2 of biofilm area to identify hundreds of proteins.

Reverse diauxie phenotype in Pseudomonas aeruginosa biofilm revealed by exometabolomics and label-free proteomics

Microorganisms enhance fitness by prioritizing catabolism of available carbon sources using a process known as carbon catabolite repression (CCR). Planktonically grown Pseudomonas aeruginosa is known to prioritize the consumption of organic acids including lactic acid over catabolism of glucose using a CCR strategy termed "reverse diauxie." P. aeruginosa is an opportunistic pathogen with well-documented biofilm phenotypes that are distinct from its planktonic phenotypes. Reverse diauxie has been described in planktonic cultures, but it has not been documented explicitly in P. aeruginosa biofilms. Here a combination of exometabolomics and label-free proteomics was used to analyze planktonic and biofilm phenotypes for reverse diauxie. P. aeruginosa biofilm cultures preferentially consumed lactic acid over glucose, and in addition, the cultures catabolized the substrates completely and did not exhibit the acetate secreting "overflow" metabolism that is typical of many model microorganisms. The biofilm phenotype was enabled by changes in protein abundances, including lactate dehydrogenase, fumarate hydratase, GTP cyclohydrolase, L-ornithine N(5)-monooxygenase, and superoxide dismutase. These results are noteworthy because reverse diauxie-mediated catabolism of organic acids necessitates a terminal electron acceptor like O2, which is typically in low supply in biofilms due to diffusion limitation. Label-free proteomics identified dozens of proteins associated with biofilm formation including 16 that have not been previously reported, highlighting both the advantages of the methodology utilized here and the complexity of the proteomic adaptation for P. aeruginosa biofilms. Documenting the reverse diauxic phenotype in P. aeruginosa biofilms is foundational for understanding cellular nutrient and energy fluxes, which ultimately control growth and virulence.

Laser Desorption Combined with Laser Postionization for Mass Spectrometry

Lasers with pulse lengths from nanoseconds to femtoseconds and wavelengths from the mid-infrared to extreme ultraviolet (UV) have been used for desorption or ablation in mass spectrometry. Such laser sampling can often benefit from the addition of a second laser for postionization of neutrals. The advantages offered by laser postionization include the ability to forego matrix application, high lateral resolution, decoupling of ionization from desorption, improved analysis of electrically insulating samples, and potential for high sensitivity and depth profiling while minimizing differential detection. A description of postionization by vacuum UV radiation is followed by a consideration of multiphoton, short pulse, and other postionization strategies. The impacts of laser pulse length and wavelength are considered for laser desorption or laser ablation at low pressures. Atomic and molecular analysis via direct laser desorption/ionization using near-infrared ultrashort pulses is described. Finally, the postionization of clusters, the role of gaseous collisions, sampling at ambient pressure, atmospheric pressure photoionization, and the addition of UV postionization to MALDI are considered.

Solid Sampling with a Diode Laser for Portable Ambient Mass Spectrometry

A hand-held diode laser is implemented for solid sampling in portable ambient mass spectrometry (MS). Specifically, a pseudocontinuous wave battery-powered surgical laser diode is employed for portable laser diode thermal desorption (LDTD) at 940 nm and compared with nanosecond pulsed laser ablation at 2940 nm. Postionization is achieved in both cases using atmospheric pressure photoionization (APPI). The laser ablation atmospheric pressure photoionization (LAAPPI) and LDTD-APPI mass spectra of sage leaves (Salvia officinalis) using a field-deployable quadrupole ion trap MS display many similar ion peaks, as do the mass spectra of membrane grown biofilms of Pseudomonas aeruginosa. These results indicate that LDTD-APPI method should be useful for in-field sampling of plant and microbial communities, for example, by portable ambient MS. The feasibility of many portable MS applications is facilitated by the availability of relatively low cost, portable, battery-powered diode lasers. LDTD could also be coupled with plasma- or electrospray-based ionization for the analysis of a variety of solid samples.

Laparoscopic radical prostatectomy: single centre experience after 5 years

OBJECTIVE

To summarise our experience of laparoscopic radical prostatectomy in a single centre in Hong Kong over 5 years.

DESIGN

Retrospective study.

SETTING

Urology Division, Department of Surgery, Tuen Mun Hospital, Hong Kong.

PATIENTS

A total of 87 patients who underwent laparoscopic radical prostatectomy from March 2002 to May 2007.

MAIN OUTCOME MEASURES

Peri-operative data and follow-up information.

RESULTS

The operative procedure used entailed Montsouris technique and its modifications, including the latest method involving the extraperitoneal descending technique. In all, 87 patients underwent the operation; in two, the procedure was converted to open surgery. Peri-operative parameters which showed improvement included: operating time, blood loss, resort to blood transfusions, and the complication rate. There was no operation-related mortality. In organ-confined disease, a clear surgical margin was achieved in 93% of the patients, but in those whose disease was not organ-confined, the positive margin rate was 87%. Among patients with organ-confined disease, 13% had evidence of biochemical recurrence. Hormonal therapy was started in five patients, none of whom died during the follow-up period (mean, 24 months). Continence recovered in 69% of the patients by 6 months and in 92% by 12 months post-surgery. Assessment of erectile function before and after the surgery was problematic and estimated to be 20% among patients having the nerve-sparing procedure performed.

CONCLUSION

Although Hong Kong has a relatively low incidence for prostate cancer, it was possible to develop laparoscopic radical prostatectomy with acceptable early results. Further follow-up is warranted before formulating definitive conclusions about this procedure.

Up-regulation of Tie gene expression by leukemia inhibitory factor and steel factor in CD34+ cells from human umbilical cord blood

Tie, a new receptor tyrosine kinase, is expressed in vascular endothelial and hematopoietic cells. To determine whether Tie might be involved in early hematopoiesis, we asked whether the Tie gene is expressed in normal human hematopoietic stem/progenitor cells and if the expression of this gene could be regulated. Using a single-cell reverse-transcriptase polymerase chain reaction (RT-PCR) assay to study expression of the Tie gene in the subset of human umbilical cord blood (UCB) CD34+++ primitive stem/ progenitor cells with extensive replating capacity, we demonstrated at the single isolated cell level that Tie was expressed in these cells. The expression of Tie gene in CD34+ cells was at a low level but was enhanced up to two- to fourfold by steel factor (SLF) or leukemia inhibitory factor (LIF), two cytokines that regulate production of stem/progenitor cells, as assessed using competitive PCR and semi-quantitative RT-PCR assays. The fold increases were observed as early as 2 h for SLF and 4 h for LIF and remained elevated for 24 h. These results demonstrate modulation of gene regulation in the rare populations of CD34+ cells and suggest the possibility that Tie may play a role in the proliferation and differentiation of immature hematopoietic cells.

Hematologic effects of stem cell factor in vivo and in vitro in rodents

Recombinant rat stem cell factor (rrSCF) administered to rats as a single intravenous injection causes a dose-dependent neutrophilia and lymphocytosis as well as the appearance of immature myeloid cells and occasional blast cells in the circulation. Neutrophilia begins at 2 hours, peaks at 4 to 6 hours, and subsides between 12 and 24 hours. Lymphocytosis occurs at 0.5 hours and has subsided by 2 hours. rrSCF-induced neutrophilia and lymphocytosis are abrogated by boiling, demonstrating that endotoxin-contamination of the rrSCF preparation is not responsible for the observed hematologic effects. The bone marrow at 6 hours after injection of rrSCF shows a left-shifted myeloid and erythroid hyperplasia as evidenced by significant increases in the absolute numbers of morphologically recognizable early myeloid and erythroid precursors. A concurrent decrease in the absolute numbers of mature marrow neutrophils is noted, suggesting that the release of marrow neutrophils contributes to the peripheral neutrophilia. After 2 weeks of daily injections of rrSCF, bone marrow smears demonstrate a remarkable mast cell hyperplasia accompanied by a decrease in total marrow cellularity and by a striking erythroid and lymphoid hypoplasia. rrSCF also causes mast cells to appear in the circulation and causes a systemic increase in embryonic connective tissue-type, but not mucosal-type, mast cells. In vitro long-term culture of lineage-depleted mouse bone marrow cells with rrSCF results in an almost pure outgrowth of mast cells.

Presence of tumour necrosis factor or a related factor in human basophil/mast cells

The observation that mast cell products and cachectin/tumour necrosis factor (TNF) mediate similar responses suggested an investigation of cultured human basophil/mast cells for production of TNF. Using in situ hybridization and the avidin biotin-complex (ABC) immunoperoxidase method, we have demonstrated the presence of TNF mRNA in the cytoplasm and TNF protein in the granules of individual human basophil/mast cells. The production of TNF by these cells could explain many of their reported functions.

Relationship of cytotoxic activity of natural killer cells to growth rates and serum zinc levels of female RIII mice fed zinc

This study examined a) the dietary zinc (Zn) requirement of RIII female weanling mice and b) the cytotoxicity of murine natural killer (NK) cells obtained from spleens of these mice fed varying levels of Zn. Zn was fed in a biotin-enriched egg albumen diet in amounts ranging from 0.9 to 40.4 micrograms/g diet. During a 28-day growth assay, maximum carcass growth was obtained with a diet containing 5.4 micrograms Zn/g diet. Maximal serum levels of Zn, however, were observed in mice fed diets containing 3.4 micrograms Zn/g diet. The cytotoxic activity of NK cells obtained from spleens of selected treatment groups was maximal at 40.4 micrograms Zn/g diet and was significantly higher (p less than or equal to 0.05) than that observed in spleens from mice fed diets that maximized carcass growth rates and serum Zn concentrations. It is concluded that female RIII mice have a dietary Zn requirement for growth similar to that observed for other murine strains but considerably lower than that reported for the rat. Our findings also suggest that RIII NK cells are particularly sensitive to dietary Zn intake: the optimal functional activity of these cells may result from intake of Zn higher than that necessary to maximize carcass growth and serum Zn concentrations.

Generation of natural killer cell lines from murine long-term bone marrow cultures

Functionally active natural killer (NK) cells with the ability to lyse 51Cr-labeled YAC-1 lymphoma target cells are no longer detectable by 1 wk of culture in cultured marrow cells harvested from Dexter-type long-term marrow cultures (LMC). Interferon, which enhances NK cell-mediated target cell lysis, fails to induce NK activity from LMC cells even at high effector to target cell ratios. However, such LMC cells, when placed in secondary cultures in the presence of Con A-splenic leukocyte-conditioned medium (spleen-CM) generated a population of cells with NK activity within 1 wk. Kinetic studies showed that the generation of NK activity was not due simply to proliferation of a few surviving NK cells, but suggested derivation from NK precursors through clonal expansion and functional maturation. This NK activity was further shown to be associated with a subpopulation of cells bearing surface Thy-1, Ly-5, and NK-1 as well as asialo-GM1 antigens but lacking Ly-1 antigen. The expression of Ly-2 antigen, however, was variable. Electron microscopy studies of isolated asialo-GM1-positive cells showed a uniform lymphoblastoid morphology with large cytoplasmic to nuclear ratios and prominent electron dense cytoplasmic granules characteristic of large granular lymphocytes. In support of the NK nature of such cultured cells was the ability of anti-asialo-GM1 and complement to abrogate, and of interferon to augment, target cell lysis. Isolated cell lines also showed target selectivity similar to NK cells. The implications of the studies on further analysis of the nature of NK precursors is discussed.

Generation of natural killer cell lines from murine long-term bone marrow cultures

Functionally active natural killer (NK) cells with the ability to lyse 51Cr-labeled YAC-1 lymphoma target cells are no longer detectable by 1 wk of culture in cultured marrow cells harvested from Dexter-type long-term marrow cultures (LMC). Interferon, which enhances NK cell-mediated target cell lysis, fails to induce NK activity from LMC cells even at high effector to target cell ratios. However, such LMC cells, when placed in secondary cultures in the presence of Con A-splenic leukocyte-conditioned medium (spleen-CM) generated a population of cells with NK activity within 1 wk. Kinetic studies showed that the generation of NK activity was not due simply to proliferation of a few surviving NK cells, but suggested derivation from NK precursors through clonal expansion and functional maturation. This NK activity was further shown to be associated with a subpopulation of cells bearing surface Thy-1, Ly-5, and NK-1 as well as asialo-GM1 antigens but lacking Ly-1 antigen. The expression of Ly-2 antigen, however, was variable. Electron microscopy studies of isolated asialo-GM1-positive cells showed a uniform lymphoblastoid morphology with large cytoplasmic to nuclear ratios and prominent electron dense cytoplasmic granules characteristic of large granular lymphocytes. In support of the NK nature of such cultured cells was the ability of anti-asialo-GM1 and complement to abrogate, and of interferon to augment, target cell lysis. Isolated cell lines also showed target selectivity similar to NK cells. The implications of the studies on further analysis of the nature of NK precursors is discussed.

Characterization of mast cell precursors by physical means: dissociation from T cells and T cell precursors

Murine bone marrow precursors (MCP) differentiate into mast cells and proliferate in response to mast cell growth factor (MCGF). An assay system based on the incorporation of [3']thymidine by proliferating mast cells in response to substantially purified MCGF was used to titrate MCP. Murine bone marrow was separated into fractions by Percoll density gradient centrifugation or velocity sedimentation at unit gravity. Individual fractions were analyzed to determine the relative concentrations of MCP. To determine if mast cells were derived from precursors different from those for T lymphocytes and granulocytes and macrophages, separated cells were also analyzed for responsiveness to interleukin 2 (IL 2) in standard [3H] thymidine incorporation assays and to granulocyte-macrophage colony stimulating factors (CSF) in agar cloning (CFU-GM) assays. Cultured marrow cells from Dexter type long-term marrow cultures (LMC) were included as a source of marrow cells devoid of mature T cells, so as to dissociate MCP from pre-T cells. MCP were readily dissociable from T cells and/or pre-T cells present in fresh, as well as cultured, marrow cells by either density or velocity of sedimentation separation techniques. MCP were, however, not readily separable from CFU-GM. Nevertheless, MCP appeared not to share a common precursor with pure macrophage type colony-forming cells (CFU-M phi). The implications of the findings on the lineage origin of mast cells were discussed.

Characterization of mast cell precursors by physical means: dissociation from T cells and T cell precursors

Murine bone marrow precursors (MCP) differentiate into mast cells and proliferate in response to mast cell growth factor (MCGF). An assay system based on the incorporation of [3']thymidine by proliferating mast cells in response to substantially purified MCGF was used to titrate MCP. Murine bone marrow was separated into fractions by Percoll density gradient centrifugation or velocity sedimentation at unit gravity. Individual fractions were analyzed to determine the relative concentrations of MCP. To determine if mast cells were derived from precursors different from those for T lymphocytes and granulocytes and macrophages, separated cells were also analyzed for responsiveness to interleukin 2 (IL 2) in standard [3H] thymidine incorporation assays and to granulocyte-macrophage colony stimulating factors (CSF) in agar cloning (CFU-GM) assays. Cultured marrow cells from Dexter type long-term marrow cultures (LMC) were included as a source of marrow cells devoid of mature T cells, so as to dissociate MCP from pre-T cells. MCP were readily dissociable from T cells and/or pre-T cells present in fresh, as well as cultured, marrow cells by either density or velocity of sedimentation separation techniques. MCP were, however, not readily separable from CFU-GM. Nevertheless, MCP appeared not to share a common precursor with pure macrophage type colony-forming cells (CFU-M phi). The implications of the findings on the lineage origin of mast cells were discussed.

Long-term in vitro culture of murine mast cells. III. Discrimination of mast cells growth factor and granulocyte-CSF

Long-term in vitro growth of murine mast cells was dependent on the presence of a mast cell growth factor (MCGF) present in media conditioned by mitogen-activated splenic leukocytes or by various murine leukemic cell lines. MCGF shared a number of properties with granulocyte colony-stimulating factor (G-CSF). Both factors were present in media conditioned by the myelomonocytic leukemic WEHI-3 and the T cell lymphoma, LBRM-33 cell lines. They were relatively sensitive to trypsin treatment, and were resistant to boiling temperature. NZB mice that failed to respond to WEHI-3-derived G-CSF also failed to respond to MCGF. MCGF differed from G-CSF, however, in sensitivity to neuraminidase and lactoferrin, an inhibitor of macrophage CSF production, suppressed G-CSF production by WEHI-3 cells without affecting MCGF production. Furthermore, peritoneal cells produced G-CSF but not MCGF when stimulated with lipopolysaccharide. In vitro production of MCGF by normal spleen cells required the presence of T lymphocytes and is relatively macrophage-independent. The role of T cells in the maturation and growth of mast cells and the physiologic function of MCGF are discussed.

Long-term in vitro culture of murine mast cells. III. Discrimination of mast cells growth factor and granulocyte-CSF

Long-term in vitro growth of murine mast cells was dependent on the presence of a mast cell growth factor (MCGF) present in media conditioned by mitogen-activated splenic leukocytes or by various murine leukemic cell lines. MCGF shared a number of properties with granulocyte colony-stimulating factor (G-CSF). Both factors were present in media conditioned by the myelomonocytic leukemic WEHI-3 and the T cell lymphoma, LBRM-33 cell lines. They were relatively sensitive to trypsin treatment, and were resistant to boiling temperature. NZB mice that failed to respond to WEHI-3-derived G-CSF also failed to respond to MCGF. MCGF differed from G-CSF, however, in sensitivity to neuraminidase and lactoferrin, an inhibitor of macrophage CSF production, suppressed G-CSF production by WEHI-3 cells without affecting MCGF production. Furthermore, peritoneal cells produced G-CSF but not MCGF when stimulated with lipopolysaccharide. In vitro production of MCGF by normal spleen cells required the presence of T lymphocytes and is relatively macrophage-independent. The role of T cells in the maturation and growth of mast cells and the physiologic function of MCGF are discussed.

Long-term in vitro culture of murine mast cells. II. Purification of a mast cell growth factor and its dissociation from TCGF

Procedures are described for the isolation of a mast cell growth factor (MCGF) from medium conditioned by mitogen-activated splenic leukocytes (CM). Although optimal conditions for the production of MCGF in CM are identical to those for the production of T cell growth factor (TCGF), MCGF can be dissociated from TCGF after the first stage of purification on a DEAE-cellulose column. MCGF elutes from the column in the breakthrough fraction, whereas TCGF binds avidly to DEAE and is eluted only at high salt concentration. MCGF also differs from TCGF with respect to m.w. (as estimated by Sephadex G-150 chromatography) and sensitivity to trypsin. In addition, MCGF is produced by the murine myelomonocytic leukemia WEHI-3 and the radiation induced thymic lymphoma LBRM-33 cells, whereas TCGF is produced only by the latter in the presence of a mitogen. Another hemopoietically active factor, granulocyte colony-stimulating factor (G-CSF) present in media conditioned by WEHI-3 and LBRM-33 cells, however, shares a number of properties with MCGF. Although studies with purified or partially purified MCGF have thus far failed to reveal a correlation between MCGF and G-CSF, further biochemical analyses are necessary to dissociate MCGF from G-CSF.

Long-term in vitro culture of murine mast cells. II. Purification of a mast cell growth factor and its dissociation from TCGF

Procedures are described for the isolation of a mast cell growth factor (MCGF) from medium conditioned by mitogen-activated splenic leukocytes (CM). Although optimal conditions for the production of MCGF in CM are identical to those for the production of T cell growth factor (TCGF), MCGF can be dissociated from TCGF after the first stage of purification on a DEAE-cellulose column. MCGF elutes from the column in the breakthrough fraction, whereas TCGF binds avidly to DEAE and is eluted only at high salt concentration. MCGF also differs from TCGF with respect to m.w. (as estimated by Sephadex G-150 chromatography) and sensitivity to trypsin. In addition, MCGF is produced by the murine myelomonocytic leukemia WEHI-3 and the radiation induced thymic lymphoma LBRM-33 cells, whereas TCGF is produced only by the latter in the presence of a mitogen. Another hemopoietically active factor, granulocyte colony-stimulating factor (G-CSF) present in media conditioned by WEHI-3 and LBRM-33 cells, however, shares a number of properties with MCGF. Although studies with purified or partially purified MCGF have thus far failed to reveal a correlation between MCGF and G-CSF, further biochemical analyses are necessary to dissociate MCGF from G-CSF.

Long-term in vitro culture of murine mast cells. I. Description of a growth factor-dependent culture technique

A feeder layer independent long-term in vitro culture system for murine mast cells is described. Concanavalin A-activated murine splenic leukocyte-conditioned medium, prepared under conditions optimal for T cell growth factor production, has been found also to contain a growth-promotion activity for murine mast cells identified by their morphology, characteristic ultrastructure of the granules, positive reactions with toluidine blue and alcian blue, presence of receptors for IgG and IgE, as well as presence of histamine, serotonin, L-Dopa, 5-hydroxytryptophan, and sulfated products within the cytoplasm. After 2 to 3 wk of culture in the presence of the conditioned medium, mast cell lines were established from various sources initially devoid of matured mast cells. Such sources included spleen and bone marrow of athymic nude mice, long-term cultured marrow cells as well as T cell-depleted normal marrow. Cultured mast cells are absolutely dependent upon the conditioned medium-derived growth factor(s) for growth and viability. Death ensues within 24 hr in the absence of the factor(s). Established mast cell lines have been maintained in exponential growth for over 1 yr by passaging in the conditioned medium every 3 to 7 days.

Long-term in vitro culture of murine mast cells. I. Description of a growth factor-dependent culture technique

A feeder layer independent long-term in vitro culture system for murine mast cells is described. Concanavalin A-activated murine splenic leukocyte-conditioned medium, prepared under conditions optimal for T cell growth factor production, has been found also to contain a growth-promotion activity for murine mast cells identified by their morphology, characteristic ultrastructure of the granules, positive reactions with toluidine blue and alcian blue, presence of receptors for IgG and IgE, as well as presence of histamine, serotonin, L-Dopa, 5-hydroxytryptophan, and sulfated products within the cytoplasm. After 2 to 3 wk of culture in the presence of the conditioned medium, mast cell lines were established from various sources initially devoid of matured mast cells. Such sources included spleen and bone marrow of athymic nude mice, long-term cultured marrow cells as well as T cell-depleted normal marrow. Cultured mast cells are absolutely dependent upon the conditioned medium-derived growth factor(s) for growth and viability. Death ensues within 24 hr in the absence of the factor(s). Established mast cell lines have been maintained in exponential growth for over 1 yr by passaging in the conditioned medium every 3 to 7 days.

[Production of a mastocyte growth factor in lymphocyte cultures stimulated by a mitogen or by allogenic cells]

Supernatants from mouse spleen leukocytes stimulated by concanavalin A or from a secondary MLC between donor and recipient of a skin allograft can induce in bone marrow cells an exponential growth of mononuclear cells with cytoplasmic basophilic granules. These cells can be maintained in liquid suspension culture for up to 6 months. They lack the properties of T or b lymphocytes, monocytes or macrophages. They have the morphological features of mast cells or basophils; the cytoplasmic granules are metachromatic for toluidine blue, alcian blue-positive at pH 0.3 and contain histamine. In addition, these cells bind monoclonal mouse IgE. They may be considered as cells of the basophil-mast cell lineage.

Induction and long-term maintenance of Thy-1 positive T lymphocytes: derivation from continuous bone marrow cultures

In the present study we investigated the presence of T-lymphocyte progenitors in the long-term murine bone marrow culture system described by Dexter: mature Thy-1 antigen-bearing T lymphocytes are lost in these cultures after a few days. By culturing nonadherent cells from such cultures in the presence of a supernatant of concanavalin A-stimulated spleen cells, a source of T-cell growth factor, we found that Thy-1 positive blast cells proliferated together with a second population of Thy-1 negative cells. These two populations of cells have been maintained in long-term in vitro cultures by passaging the cells in fresh conditioned medium at regular intervals. Moreover, we have been able to establish pure cultures of the Thy-1 bearing blast cells after separating them from the non-T cells using their adherence property to plastic surfaces. Long-term cultures of T lymphocytes can thus be established from long-term marrow cultures as well as from the spleen, thymus or fresh bone marrow.