Flow cytometric evaluation of apoptosis, necrosis and recovery when culturing monocytes

Validation of an apoptosis assay for extracorporeal photopheresis

OBJECTIVES

This validation study investigated a flow cytometric apoptosis assay according to good manufacturing practice (GMP).

BACKGROUND

Extracorporeal photopheresis (ECP) is a treatment for various immunological diseases and cutaneous T-cell lymphomas. It is based on the induction of apoptosis by 8-methoxypsoralene and ultraviolet A light. The quantification of apoptosis is therefore essential for ECP improvements. However, despite numerous publications on apoptosis, validated technical details are lacking.

METHODS AND MATERIALS

Mononuclear cells were collected by apheresis and treated by ECP or camptothecin. Samples taken before and after ECP were cultured for 24, 48 and 72 h and analysed for apoptosis and viability of T cells and monocytes by flow cytometry with Annexin V and 7-AAD staining. Accuracy of the assay, intra- and inter-assay precision and the pre-analytical and analytical stability of the analytes were the investigated parameters.

RESULTS

Our data indicate that the median intra- and inter-assay precision coefficient of variation for T cells was 3.86% and 4.80%, respectively. Pre-analytical stability of T cells and monocytes was ensured during short-term storage for up to 2 h on ice. After staining, analytical stability was limited to 30 min, likely because of ongoing apoptosis and loss of monocytes due to plastic adhesion.

CONCLUSION

The results of this validation study show that the assay is GMP-compliant and that its reliability, accuracy and precision are acceptable. While pre-analytical stability of the cells was compatible with on-site procedures, our analytical stability data indicate that this assay is not suited for batch mode analysis of ECP products.

Towards biobanking technologies for natural and bioengineered multicellular placental constructs

Clinical application of a large variety of biomaterials is limited by the imperfections in storage technology. Perspective approaches utilizing low-temperature storage are especially challenging for multicellular structures, such as tissues, organs, and bioengineered constructs. Placenta, as a temporary organ, is a widely available unique biological material, being among the most promising sources of various cells and tissues for clinical and experimental use in regenerative medicine and tissue engineering. The aim of this study was to analyse the mechanisms of cryoinjuries in different placental tissues and bioengineered constructs as well as to support the viability after low temperature storage, which would contribute to development of efficient biobanking technologies. This study shows that specificity of cryodamage depends on the structure of the studied object, intercellular bonds, as well as interaction of its components with cryoprotective agents. Remarkably, it was possible to efficiently isolate cells after thawing from all of the studied tissues. While the outcome was lower in comparison to the native non-frozen samples, the phenotype and expression levels of pluripotency genes remained unaffected. Further progress in eliminating of recrystallization processes during thawing would significantly improve biobanking technologies for multicellular constructs and tissues.

Large-scale reduction of tyrosine kinase activities in human monocytes stimulated in vitro with N. meningitidis

N. meningitidis induces extensive gene expression changes in human monocytes, suggesting that complex networks of signaling pathways are activated during meningococcal sepsis. These effects are modulated by the anti-inflammatory cytokine interleukin-10 (IL-10). To further study changes in signal transduction suggested by mRNA data, we used kinase substrate arrays to identify composite kinase activities induced by lysates from a primary human monocyte model system. Cell lysates were prepared from monocytes treated with the following experimental conditions: 106 N. meningitidis/mL, 25 ng/mL IL-10, 106 N. meningitidis/mL in combination with 25 ng/mL IL-10, and vehicle. Lysates were subjected to kinase activity profiling with Tyrosine Kinase PamChip® arrays containing 144 kinase peptide substrates. In our experimental model, we were not able to detect a statistically significant large-scale change in ex vivo array peptide phosphorylation by lysates from monocytes treated for 15 minutes. Targets of the IL-10 anti-inflammatory response were not identified. A profound inhibition of array peptide phosphorylation by monocytes treated for 60 minutes was identified, suggesting low activity of a large number of kinases associated with different signaling pathways and immune cell functions, including STAT3 activity, Nf-κB and VEGF signaling, and PTEN signaling activity. The peptide representing ZBTB16, which was reduced in phosphorylation by lysates from all three experimental conditions, was in Ingenuity Pathway Analysis identified to be linked to reduced cytokine release and mRNA levels of tumor necrosis factor (TNF), IL-6, and CXCL10. Further studies should investigate changes in tyrosine kinase-mediated signal transduction in human immune cells, in order to evaluate the potential clinical application of kinome profiling in the study of systemic inflammatory responses to pathogens.

Influence of Factors of Cryopreservation and Hypothermic Storage on Survival and Functional Parameters of Multipotent Stromal Cells of Placental Origin

Human placenta is a highly perspective source of multipotent stromal cells (MSCs) both for the purposes of patient specific auto-banking and allogeneic application in regenerative medicine. Implementation of new GMP standards into clinical practice enforces the search for relevant methods of cryopreservation and short-term hypothermic storage of placental MSCs. In this paper we analyze the effect of different temperature regimes and individual components of cryoprotective media on viability, metabolic and culture properties of placental MSCs. We demonstrate (I) the possibility of short-term hypothermic storage of these cells; (II) determine DMSO and propanediol as the most appropriate cryoprotective agents; (III) show the possibility of application of volume expanders (plasma substituting solutions based on dextran or polyvinylpyrrolidone); (IV) reveal the priority of ionic composition over the serum content in cryopreservation media; (V) determine a cooling rate of 1°C/min down to -40°C followed by immersion into liquid nitrogen as the optimal cryopreservation regime for this type of cells. This study demonstrates perspectives for creation of new defined cryopreservation methods towards GMP standards.

Applications in environmental risk assessment of leucocyte apoptosis, necrosis and respiratory burst analysis on the European bullhead, Cottus sp

The use of a biochemical multi-biomarker approach proved insufficient to obtain clear information about ecosystem health. The fish immune system is considered as an attractive non-specific marker for environmental biomonitoring which has direct implications in individual fitness and population growth. Thus, the present work proposes the use of fish immunomarkers together with more common biochemical biomarkers in sampling conditions optimized to reduce biomarker variability and increase parameter robustness. European bullheads (Cottus sp.) from 11 stations in the Artois-Picardie watershed (France) were sampled. In the multiple discriminant analysis, the sites were highly correlated with apoptosis, respiratory burst, GST and EROD activities. Moreover, the use together of biochemical and immune markers increased the percentage of fish correctly classed at each site and enhanced site separation. This study argues in favor of the utilization of apoptosis, necrosis and respiratory burst for the determination of environmental risk assessment in addition to the set of biochemical biomarkers commonly used in fish.

PMA withdrawal in PMA-treated monocytic THP-1 cells and subsequent retinoic acid stimulation, modulate induction of apoptosis and appearance of dendritic cells

OBJECTIVES

To analyse proliferation, differentiation and apoptosis in THP-1 cells after stimulation with phorbol 12-myristate 13-acetate (PMA) and retinoic acid (RA).

MATERIALS AND METHODS

PMA and RA were used in a three-step-procedure: (i) treatment with 6, 30, 60 nm PMA, that induced initial, intermediate and advanced levels of monocyte-macrophage transition, respectively; (ii) recovery in PMA-free medium; (iii) incubation with 4 μm RA. Cultures were characterized cytokinetically (flow cytometry/bromodeoxyuridine uptake) and immunocytochemically (static cytometry) for expression of CD14, CD11b (monocyte-macrophage) and DC-SIGN (dendritic cell: DCs) markers.

RESULTS

Some treatments determined appearance of monocyte/macrophage, dendritic and apoptotic phenotypes, percentages of which were related to PMA dose used in step 1, and dependent on presence/absence of PMA and RA. PMA withdrawal induced dedifferentiation and partial restoration of proliferative activity, specially in 6 and 30 nm PMA-derived cells. Recovery in the presence of serum (fundamental to DC appearance) indicated that depending on differentiation level, cell proliferation and apoptosis were inversely correlated. Treatment with 30 nm PMA induced intermediate levels of monocytic-macrophagic differentiation, with expression of alternative means of differentiation and acquisition of DCs without using cytokines, after PMA withdrawal and RA stimulation.

CONCLUSIONS

Our experimental conditions favoured differentiation, dedifferentiation and transdifferentiational pathways, in monocytic THP-1 cells, the balance of which could be related to both cell proliferation and cell death.

Impairment of in vitro generation of monocyte-derived human dendritic cells by inactivated human immunodeficiency virus-1: Involvement of type I interferon produced from plasmacytoid dendritc cells

In an attempt to simplify the protocol of DC generation in vitro, studies conducted herein show that functional DCs could be generated from bulk peripheral blood mononuclear cells (PBMCs) in media containing GM-CSF and IL-4. Interestingly, when PBMCs, but not purified monocytes, were exposed to either CCR5- or CXCR4-tropic inactivated HIV-1 isolates (iHIV-1) at the initiation of the culture, DC yields were significantly reduced in a dose-dependent manner because of monocyte apoptosis. Similar impairment of DC generation was noted using type I IFNs and poly IC not only in cultures of PBMCs but also using highly enriched monocytes. This effect was reversed by antihuman type I IFN receptor, but not by anti-FasL, anti-TRAIL, anti-TNF, or a mixture of these antibodies. iHIV-1-exposed PBMCs, but not monocytes, produced high levels of IFN-alpha but not IFN-beta. PBMCs depleted of CD123(+) plasmacytoid DCs produced low levels of IFN-alpha and were resistant to iHIV-1-mediated DC impairment. Interestingly, exogenously added TNF reversed the impairment by iHIV-1 in the PBMC cultures. In conclusion, the present results indicate that iHIV-1 impairs the in vitro generation of functional DCs from PBMCs through the induction of IFN-alpha from plasmacytoid DCs in a CD4-dependent fashion in the absence of TNF.

Parathyroid hormone-related protein confers chemoresistance by blocking apoptosis signaling via death receptors and mitochondria

Parathyroid hormone (PTH) has a central role in the regulation of serum calcium and phosphate, whereas parathyroid hormone-related peptide (PTHrP) has important developmental roles. In addition, PTHrP has been discovered as a causative agent of hypercalcemia of malignancy. PTHrP is also expressed in many tumors, and expression often correlates with unfavorable prognosis. We have investigated the effects of PTHrP on apoptosis signaling pathways initiated by DNA damaging chemotherapeutic drugs. Stimulation experiments of the CD95-, the TNF-R-, and the TRAIL-R-death receptor systems in Saos human osteosarcoma cells revealed that PTHrP can block signaling via each of these death receptors. Furthermore, our findings demonstrate a link between PTHrP and the mitochondrial apoptosis pathway. PTHrP down-regulates expression of pro-apoptotic Bcl-2 family members like Bax and PUMA and up-regulates expression of antiapoptotic molecules like Bcl-2 and Bcl-xl. It is of clinical relevance that PTHrP and anticancer drugs show opposing interactions on death receptor-triggered as well as on mitochondrial apoptosis pathways. In addition, PTHrP induces chemoresistance by interference with p53 family-dependent apoptosis signaling pathways and p53-mediated transactivation of apoptosis target genes. Inhibition of CD95- and Bax gene transactivation is a mechanism by which PTHrP reduced the apoptosis response and treatment sensitivity of tumor cells. Our data indicate that PTHrP inhibits major apoptosis signaling pathways by blocking signaling via p53, death receptors and mitochondria and, consequently, confers chemoresistance of cancer cells. Thus, beyond its importance in development and differentiation, we describe an important role for PTHrP in tumorigenesis.

Cardiovascular complications of diabetes mellitus: The Tissue Factor perspective

Heightened activity of circulating Tissue Factor (TF) has been linked to a variety of macro- and microvascular cardiovascular complications commonly observed in diabetes mellitus. Systemic and localized vascular abnormalities comprise the most debilitating feature of diabetic pathophysiology. Blood monocytes are chronically activated in diabetes, and serve as the major source of bioactive intravascular TF. This review examines recent literature on this subject, with a special emphasis on the abnormal monocyte physiology in diabetes and the structural and functional diversity of circulating TF.

Loss of T cell responses following long-term cryopreservation

Although cryopreservation of peripheral blood mononuclear cells (PBMC) is a commonly used technique, the degree to which it affects subsequent functional studies has not been well defined. Here we demonstrate that long-term cryopreservation has detrimental effects on T cell IFN-gamma responses in human immunodeficiency virus (HIV) infected individuals. Long-term cryopreservation caused marked decreases in CD4(+) T cell responses to whole proteins (HIV p55 and cytomegalovirus (CMV) lysate) and HIV peptides, and more limited decreases in CD8(+) T cell responses to whole proteins. These losses were more apparent in cells stored for greater than one year compared to less than six months. CD8(+) T cell responses to peptides and peptide pools were well preserved. Loss of both CD4(+) and CD8(+) T cell responses to CMV peptide pools were minimal in HIV-negative individuals. Addition of exogenous antigen presenting cells (APC) did not restore CD4(+) T cell responses to peptide stimulation and partially restored T cell IFN-gamma responses to p55 protein. Overnight resting of thawed cells did not restore T cell IFN-gamma responses to peptide or whole protein stimulation. A selective loss of phenotypically defined effector cells did not explain the decrement of responses, although cryopreservation did increase CD4(+) T cell apoptosis, possibly contributing to the loss of responses. These data suggest that the impact of cryopreservation should be carefully considered in future vaccine and pathogenesis studies. In HIV-infected individuals short-term cryopreservation may be acceptable for measuring CD4(+) and CD8(+) T cell responses. Long-term cryopreservation, however, may lead to the loss of CD4(+) T cell responses and mild skewing of T cell phenotypic marker expression.

Electrokinetic measurements of dielectric properties of membrane for apoptotic HL-60 cells on chip-based device

The specific membrane capacitance and conductance of mammalian cells reflect the surface morphological complexities and barrier functions of cell membrane, respectively, and could potentially respond to cell physiological and pathological changes in a measurable manner. In this study, an electrokinetic system was developed by using negative dielectrophoretic force (nDEP force) assisted positioning and electroroation (ROT) measurement. Numerical simulations regarding the geometric model of the electrode were performed primarily for the electric field analysis. The dielectric responses of membrane for apoptotic HL-60 cells induced by bufalin were detected. The membrane capacitance of the cells was found to fall from an initial value of 15.6 +/- 0.9 mF/cm(2) to 6.4 +/- 0.6 mF/cm(2) after a 48 h treatment with 10 nM bufalin. However, the membrane conductance remained almost constant at (2.25 +/- 1.1) x 10(3) S/m(2) during the first 12 h of bufalin treatment and then increased distinctly to (4.2 +/- 1.3) x 10(3) S/m(2) thereafter. Scan electron microscopy (SEM) studies of the cells revealed a decreased complexity in cell membrane morphology following bufalin treatments, suggesting that the observed changes in the membrane capacitance was dominated by the alterations of cell surface structures. The results demonstrate that the ROT technique gives a quantitative analysis of the toxic damage by chemicals to cells and can be exploited in the testing and development of new pharmaceuticals and active cell agents.

Human CD4+CD25+ regulatory T lymphocytes inhibit lipopolysaccharide-induced monocyte survival through a Fas/Fas ligand-dependent mechanism

Although it is known that septic shock induces immunosuppression, the mechanism for this phenomenon is not well understood. Monocytes play a central role in septic shock pathophysiology, which is also characterized by an increased proportion of natural regulatory T (Treg) cells. We therefore investigated whether Treg could be involved in the decreased monocyte expression of CD14 and HLA-DR observed during septic shock. We demonstrated that human Treg inhibit LPS-induced retention of monocyte CD14. Because loss of CD14 is a hallmark of monocyte apoptosis, this suggests that Treg inhibit monocyte survival. This effect was largely mediated through the release of a soluble mediator that was not identical with either IL-10 or IL-4. The Fas/FasL pathway participated in the effect as it was blocked by anti-FasL Abs and reproduced by Fas agonist and recombinant soluble FasL. Furthermore, expression of FasL was much higher on Treg than on their CD25(-) counterparts. Collectively, these results indicate that Treg act on monocytes by inhibiting their LPS-induced survival through a proapoptotic mechanism involving the Fas/FasL pathway. This may be an important mechanism for septic shock-induced immunosuppression and may offer new perspectives for the treatment of this deadly disease.

Cyclooxygenase-2 Inhibition Induces Apoptosis Signaling via Death Receptors and Mitochondria in Hepatocellular Carcinoma

Inhibition of cyclooxygenase (COX)-2 elicits chemopreventive and therapeutic effects in solid tumors that are coupled with the induction of apoptosis in tumor cells. We investigated the mechanisms by which COX-2 inhibition induces apoptosis in hepatocellular carcinoma (HCC) cells. COX-2 inhibition triggered expression of the CD95, tumor necrosis factor (TNF)-R, and TNF-related apoptosis-inducing ligand (TRAIL)-R1 and TRAIL-R2 death receptors. Addition of the respective specific ligands further increased apoptosis, indicating that COX-2 inhibition induced the expression of functional death receptors. Overexpression of a dominant-negative Fas-associated death domain mutant reduced COX-2 inhibitor-mediated apoptosis. Furthermore, our findings showed a link between COX-2 inhibition and the mitochondrial apoptosis pathway. COX-2 inhibition led to a rapid down-regulation of myeloid cell leukemia-1 (Mcl-1), an antiapoptotic member of the Bcl-2 family, followed by translocation of Bax to mitochondria and cytochrome c release from mitochondria. Consequently, overexpression of Mcl-1 led to inhibition of COX-2 inhibitor-mediated apoptosis. Furthermore, blocking endogenous Mcl-1 function using a small-interfering RNA approach enhanced COX-2 inhibitor-mediated apoptosis. It is of clinical importance that celecoxib acted synergistically with chemotherapeutic drugs in the induction of apoptosis in HCC cells. The clinical relevance of these results is further substantiated by the finding that COX-2 inhibitors did not sensitize primary human hepatocytes toward chemotherapy-induced apoptosis. In conclusion, COX-2 inhibition engages different apoptosis pathways in HCC cells stimulating death receptor signaling, activation of caspases, and apoptosis originating from mitochondria.

Calcium ionophore-induced de-encryption of tissue factor in monocytes is associated with extensive cell death

INTRODUCTION

Cell surface tissue factor (TF) is normally encrypted, but can be activated by various cellular perturbations. Exposure of TF bearing cells to calcium ionophore has been reported to increase TF activity, de-encrypt TF, by phosphatidylserine (PS)-dependent and -independent mechanisms. Our aim has been to examine at the single cell level, if increased cell surface PS coincided with increased cell surface TF antigen, and cell death (necrosis, 7-AAD-intercalation), and relate this to monocyte- and microparticle (MP)-associated procoagulant activity.

MATERIALS AND METHODS

We exposed lipopolysaccharide-stimulated, human, elutriation-purified, cryopreserved TF bearing monocytes to increasing concentrations of calcium ionophore (A23187) and measured procoagulant activity in cells and supernatants. These measurements were compared with quantification of cell surface TF and PS (Annexin V) and of cell necrosis (7-AAD) by flow cytometry, and complemented by confocal microscopy.

RESULTS

We observed that calcium ionophore increased cellular and MP-associated TF activity, but not cell surface TF antigen. The discrepancy between TF activity and TF antigen coincided with a dose-dependent increase in the number of cells expressing PS. These cells were to a large extent necrotic and many of them also expressed TF.

CONCLUSIONS

We suggest such TF positive dying cells to contribute to the discordance between TF activity and TF expression. Calcium ionophore also increased MP-associated TF activity and release of MPs may be a way to disseminate procoagulant activity. Our findings emphasize the importance of adequately assessing cell death and taking into consideration its possible role in experiments with calcium ionophore.

Apoptosis of monocytes and the influence on yield of monocyte-derived dendritic cells

Monocyte-derived dendritic cells (DC) are currently under extensive evaluation as cell vaccines for cancer treatment. The requirement for large-scale cell products demands optimized and standardized protocols. However, the yield of DCs from inoculated monocytes is reported to be always lower than 50%. In this present study we investigated whether this cell loss was caused by the properties of the starting population of inoculated monocytes. CD14 cells were enriched by immunomagnetic-bead selection and analyzed for apoptosis by an annexin V/propidium iodide assay. We found that 37.8+/-11.1% (n=8) of freshly isolated monocytes from buffy coats of healthy donors underwent programmed cell death. Further analysis of the fate of apoptotic cells during differentiation suggested phagocytosis. Monocytes were differentiated with GM-CSF and interleukin-4 into a viable, non-apoptotic population of immature dendritic cells. Addition of tumor necrosis factor-alpha and prostaglandin E2 resulted in fully matured dendritic cells, which were evaluated by phenotypic analysis and by allogeneic and MHC class-I-restricted T-cell responses. About 90.2+/-16.7% of the non-apoptotic monocyte population differentiated to viable matured dendritic cells. These results indicate that the yield of dendritic cells is mainly influenced by the percentage of apoptotic cells in the inoculum, and this has implications for DC generation in clinical applications.

Evaluation of elutriation and magnetic microbead purification of canine monocytes

An elutriation technique was developed to obtain large quantities of pure canine monocytes. Firstly, peripheral blood mononuclear cells (PBMC) were isolated from whole blood by Ficoll gradient. Then, the PBMC were separated by an elutriation procedure. We demonstrated that these techniques allow the isolation of canine peripheral blood monocytes with a purity of 64% +/- 7.9 when labelled with anti-CD14 antibody. This purity increased to 83% +/- 2.2 after separation by magnetic anti-CD14 microbeads. The cell viability was more than 95% and apoptotic cells were less than 10%. The monocytes purified by these methods were functionally active in a mixed leukocyte reaction (MLR). A lymphocyte fraction was obtained directly only by elutriation with an average of 79.9% +/- 10.7 of CD5+, 7.9% +/- 3.5 of CD21+ and 1.78% +/- 2.53 of CD14+. Our results indicate that this elutriation procedure is a safe method to purify monocytes as well as lymphocytes, useful in MLR.

Method for large scale isolation, culture and cryopreservation of human monocytes suitable for chemotaxis, cellular adhesion assays, macrophage and dendritic cell differentiation

This paper presents an improved method of isolating, culturing and cryopreserving human monocytes in large quantity with high purity using standard laboratory centrifuges. Monocytes were isolated from 300 to 360 ml of heparinized human blood using a Double Density technique employing Ficoll Isopaque and 46% iso-osmotic Percoll. Yields of monocytes ranged from 75 to 205 million (from 300 to 360 ml of blood) with an average purity of 90.6%. The ability of fresh or frozen monocytes to adhere to endothelial cells in the presence of oxidized L-alpha-1-palmitoyl-2-arachidonosyl-sn-glycero-3-phosphocholine (oxPAPC) or lipopolysaccharide (LPS) did not differ and no significant difference in response to the chemotactic stimulant N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) was observed. We define a useful method for the culture and differentiation of fresh or frozen monocytes isolated by this method, into macrophages as judged by morphology, expression of the macrophage marker SRA-1 and induction of inflammatory genes TNF-alpha, IL-6 and COX-2. Also, fresh or frozen Double Density isolated cells can be successfully differentiated into dendritic cells in the presence of GM-CSF and IL-4 as judged by the expression of the hallmark surface proteins CD1a and DC-sign and the absence of CD14. This method also yields a pure population of lymphocytes.

CC Chemokine Receptor 2 Expression in Donor Cells Serves an Essential Role in Graft-versus-Host-Disease

The complete repertoire of cellular and molecular determinants that influence graft-vs-host disease (GVHD) is not known. Using a well-established murine model of GVHD (B6-->bm12 mice), we sought to elucidate the role of the donor non-T cell compartment and molecular determinants therein in the pathogenesis of GVHD. In this model the acute GVHD-inducing effects of purified B6 wild-type (wt) CD4(+) T cells was inhibited by wt non-T cells in a dose-dependent manner. Paradoxically, unlike the chronic GVHD phenotype observed in bm12 mice transplanted with B6wt unfractionated splenocytes, bm12 recipients of B6ccr2-null unfractionated splenocytes developed acute GVHD and died of IFN-gamma-mediated bone marrow aplasia. This switch from chronic to acute GVHD was associated with increased target organ infiltration of activated CD4(+) T cells as well as enhanced expression of Th1/Th2 cytokines, chemokines, and the antiapoptotic factor bfl1. In vitro, ccr2(-/-) CD4(+) T cells in unfractionated splenocytes underwent significantly less activation-induced cell death than B6wt CD4(+) T cells, providing another potential mechanistic basis along with enhanced expression of bfl1 for the increased numbers of activated T cells in target organs of B6ccr2(-/-) splenocyte-->bm12 mice. Collectively, these findings have important clinical implications, as they implicate the donor non-T cell compartment as a critical regulator of GVHD and suggest that ccr2 expression in this cellular compartment may be an important molecular determinant of activation-induced cell death and GVHD pathogenesis.

The fate of monocytes during 24 h of culture as revealed by flow cytometry and electron microscopy

Culturing elutriation-purified and cryopreserved human monocytes gives a cell loss of about 60% after a week. The main loss is during the first 24 h when one cell population dies by apoptosis and secondary necrosis, while another survives with minimal signs of apoptosis and necrosis. We have studied this initial cell loss using flow cytometry (FCM) and electron microscopy (EM) in parallel. Thawed cells were cultured in ultra low attachment wells and studied by FCM using Annexin V, Propidium iodide (PI), JC-1, APO2.7 and APO-BrDU. The EM studies comprised both transmission EM (TEM) and scanning EM (SEM), the latter employing cells labelled with antiCD14/gold and Annexin V/gold. Cells were counted by light microscopy to provide cell recoveries. DNA ladder patterns were investigated by electrophoresis. Camptothecin (CAM) was used as an apoptosis inducer. In the first 6 h of culture, there was an apoptotic phase with Annexin V(+)/PI(-) positive cells in FCM, chromatin condensation in TEM, a rapid and short phase with Annexin V/gold positively labelled cells in SEM and the cells disappeared by 6 h. All of these effects were enhanced by CAM. The necrotic phase (6-24 h) was associated with Annexin V(+)/PI(+) in FCM, and the data at 24 h was in agreement with the semiquantitatvive results from TEM. Discrepancies in the results for CD14 and Annexin V between FCM and SEM indicated phagocytosis. APO2.7 and APO-BrDU increases also indicated an accumulation of ingested material in vital cells. Centrifugation of supernatants, labelling pellets with Annexin V/FITC and examination by flow cytometry revealed no Annexin V positive cell fragments. We found evidence of rapid and efficient phagocytosis. CAM not only induced apoptosis, but also appeared to stabilise the cell membrane and increase both cell recovery and phagocytosis.

Enhanced ELISPOT detection of antigen-specific T cell responses from cryopreserved specimens with addition of both IL-7 and IL-15--the Amplispot assay

The importance of the enzyme-linked immunosorbent spot (ELISPOT) assay as a tool for studying immune responses in vitro is becoming increasingly apparent. However, there remains a need for enhanced sensitivity for the detection of low frequency antigen-specific T cell responses. We reasoned that the addition of a combination of the cytokines interleukin (IL)-7 and IL-15 would selectively increase interferon-gamma (IFN-gamma) production from antigen-stimulated CD4+ and CD8+ effector memory T cells. Freshly isolated or cryopreserved peripheral blood mononuclear cells (PBMC) from four healthy donors were analysed by ELISPOT for the frequency of purified protein derivative (PPD)-specific CD4+ T cells or cytomegalovirus (CMV) peptide-specific CD8+ T cells. Addition of IL-7 and IL-15 increased the number of PPD-specific CD4+ T cells up to 2.4-fold in fresh PBMC and up to 18-fold in cryopreserved PBMC. The cytokines also increased the number of CMV peptide-specific CD8+ T cells in fresh PBMC up to 7.5-fold. No additional increases were seen when antibodies to co-stimulatory molecules CD28 and CD49d were applied together with the cytokine combination. These data demonstrate that the sensitivity of the ELISPOT assay may be significantly augmented by addition of the cytokines IL-7 and IL-15 to antigen-stimulated cells. This method will be particularly useful for the assessment of antigen-stimulated cytokine production by T cells in cryopreserved biological specimens.