An evaluation of an assay for DNA synthesis in lymphocytes with [3H]thymidine and harvesting on to glass fibre filter discs

Detection of Antigen-specific T cells in Spleens of Vaccinated Mice Applying 3[H]-Thymidine Incorporation Assay and Luminex Multiple Cytokine Analysis Technology

For many infectious diseases T cells are an important part of naturally acquired protective immune responses, and inducing these by vaccination has been the aim of much research. Here, we describe a protocol for the analysis of vaccine-induced antigen-specific immune responses. For this purpose, cells of whole spleens obtained from vaccinated BALB/c mice were ex vivo stimulated with the antigen incorporated in the vaccine. Evaluation and characterization of vaccine-induced adaptive T cell responses was performed by assaying spleen cell proliferation through radioactive ³[H]-thymidine incorporation and multiplex cytokine analysis of IL-2, IFN-γ and TNFα in supernatants from spleen cell suspensions. This protocol can be very useful as a starting point for assessing vaccine-induced memory T cell populations in pre-clinical studies.

Assays for in vitro monitoring of proliferation of human airway smooth muscle (ASM) and human pulmonary arterial vascular smooth muscle (VSM) cells

Vascular and airway remodeling, which are characterized by airway smooth muscle (ASM) and pulmonary arterial vascular smooth muscle (VSM) proliferation, contribute to the pathology of asthma, pulmonary hypertension, restenosis and atherosclerosis. To evaluate the proliferation of VSM and ASM cells in response to mitogens, we perform a [3H]thymidine incorporation assay. The proliferation protocol takes approximately 48 h and includes stimulating cells synchronized in G0/G1 phase of the cell cycle with agonists, labeling cells with [3H]thymidine and examining levels of [3H]thymidine incorporation by scintillation counting. Although using radiolabeled [3H]thymidine incorporation is a limitation, the greatest benefit of the assay is providing reliable and statistically significant data.

Extracellular matrix alters the relationship between tritiated thymidine incorporation and proliferation of MC3T3-E1 cells during osteogenesis in vitro

Bone cells in vivo exist in direct contact with extracellular matrix, which regulates their basic biological processes including metabolism, development, growth and differentiation. Thus, the in vitro activity of cells cultured on tissue culture treated plastic could be different from the activity of cells cultured on their natural substrate. We selected MC3T3-E1 pre-osteoblastic cells to study the effect of extracellular matrix on cell proliferation because these cells undergo a progressive developmental sequence of proliferation and differentiation. MC3T3-E1 cells were cultured on plastic or plastic coated with ECM, fibronectin, collagen type I, BSA or poly l-lysine and their ability to proliferate was assessed by incorporation of [3H]dT or by enumeration of cells. Our results show that (1) ECM inhibits incorporation of [3H]dT by MC3T3-E1 cells; (2) collagen type I, but not BSA, poly l-lysine or fibronectin also inhibits incorporation of [3H]dT; (3) the level of ECM inhibition of [3H]dT incorporation is directly related to the number of cells cultured, but unrelated to the cell cycle distribution or endogenous thymidine content; (4) the kinetic profile of [3H]dT uptake suggest that ECM inhibits transport of [3H]dT from the extracellular medium, and (5) cell counts are similar in cultures whether cells are grown on plastic or ECM. These results suggest that decreased incorporation of [3H]dT by cells cultured on ECM is not reflective of bone cell proliferation.

Expression of protease-activated receptor-2 by osteoblasts

Osteoblasts express protease-activated receptor-1 (PAR-1), which is activated by thrombin or by synthetic peptides corresponding to the new "tethered ligand" N-terminus of PAR-1 created by receptor cleavage. Both thrombin and human PAR-1-activating peptide stimulate an elevation of [Ca2+]i in the human SaOS-2 osteoblast-like cell line, but the peptide stimulates receptor-mediated Ca+ entry, whereas thrombin does not. Stimulation of proliferation in rat primary osteoblast-like cells is greater in response to rat PAR-1-activating peptide than to thrombin. Because the PAR-1-activating peptides are now known to activate PAR-2, the current study was undertaken to investigate whether osteoblasts express this receptor and, if so, whether this could account for the observed discrepancies between responses of osteoblasts to thrombin and to PAR-1-activating peptides. Reverse transcriptase-polymerase chain reaction (RT-PCR) and immunocytochemical studies demonstrated expression of PAR-2 by primary cultures of rat calvarial osteoblast-like cells. In immunohistochemical studies of embryonic mouse bones, osteoblasts showed positive staining for the presence of PAR-2. Activators of PAR-2 include trypsin, mast cell tryptase, gingipain-R, and synthetic peptides corresponding to the PAR-2 tethered ligand sequence. Treatment of primary rat osteoblast-like cells with rat PAR-2-activating peptide (SLIGRL), or SaOS-2 cells with human PAR-2-activating peptide (SLIGKV), caused a dose-dependent increase in [Ca2+]i. Trypsin or gingipain-R also induced an increase in intracellular calcium concentration, and caused reciprocal cross desensitization. Activators of PAR-2 caused a sharp peak in [Ca2+]i followed by a sustained plateau; [Ca2+]i returned to baseline levels upon treatment with ethylene-glycol tetraacetic acid (EGTA). Treatment of rat osteoblast-like cells in vitro with SLIGRL did not affect thymidine incorporation or endogenous alkaline phosphatase activity. The results presented here demonstrate that osteoblasts express PAR-2, and that such expression is able to account for the observed discrepancies between thrombin and PAR-1-activating peptides in their ability to evoke calcium entry, but not proliferative responses.

Modulation of osteoblast-like cell behavior by activation of protease-activated receptor-1

In addition to playing a central role in thrombosis and hemostasis, the serine protease thrombin is a specific agonist for a variety of functional responses in cells including osteoblast-like cells. Many of the cellular responses to thrombin are mediated by protease-activated receptor-1 (PAR-1). Since osteoblasts express PAR-1 in vivo during development, the effect of PAR-1 activation on proliferation and differentiation in primary rat osteoblast-like cells was investigated. Thrombin or the rat PAR-1-activating peptide SFFLRNPSENTFELVPL (SFFL) stimulated cell proliferation (as assessed by 3H- thymidine incorporation) of primary osteoblast-like cells derived from long bone or calvaria, and treatment with antibodies to PAR-1 abolished the proliferative response to thrombin. Activation of PAR-1 by thrombin or SFFL inhibited endogenous alkaline phosphatase (ALP) activity and caused a transient elevation of intracellular calcium in the osteoblast-like cells. Calcium mobilization was not, however, required for thrombin's effect on proliferation or ALP activity. The ability of a number of growth factors and hormones to regulate expression of PAR-1 in osteoblast-like cells was investigated. Expression of PAR-1 transcript and protein by osteoblast-like cells in vitro was markedly increased by treatment with transforming growth factor-beta (TGF-beta), and the proliferative response to thrombin was enhanced by TGF-beta pretreatment. Platelet-derived growth factor-BB caused a slight but significant down-regulation of PAR-1 mRNA expression. Thrombin caused a transient increase in PAR-1 expression, whereas neither parathyroid hormone-related peptide nor 1, 25-dihydroxyvitamin D3 had any effect. The observations described here suggest that PAR-1 mediates thrombin-induced osteoblast proliferation, which in turn may contribute to responses of osteoblasts to osteogenic growth factors.

Quantitative binding of covalently closed circular DNA to nitrocellulose in NaI

A procedure for quantitatively binding covalently closed circular DNA to nitrocellulose is detailed. The procedure involves making DNA saturated with respect to Nat at 25 degrees C, denaturing the DNA by heating to 80-100 degrees C, then passing the DNA-NaI solution through a nitrocellulose membrane at 50-60 degrees C. Form I DNA remains denatured throughout the loading procedure and is quantitatively deposited on the membrane as denatured DNA. The mechanism of binding DNA to nitrocellulose in NaI appears to be different from the binding promoted by NaCl.

[Cryopreservation of lymphocytes using polyethylene glycols of high polymerization grade (author's transl)]

Human peripheral lymphocytes and mouse spleen cells were frozen under controlled rates in the presence of polyethylene glycols (PEG) of high polymerization grade, stored in liquid nitrogen and tested, following thawing and mitogen-stimulation, for their capacity to incorporate 3H-thymidine and to form colonies in soft agar. We found that human lymphocytes, frozen with 10% PEG 20,000 and PHA-stimulated afterwards, showed an 8 fold higher incorporation rate versus 7.5% dimethylsulfoxide, whilst colony growth was unaffected. The potentiating effect by PEG was also seen with mouse spleen cells. PHA-prestimulated human lymphocytes also revealed an increased incorporation rate. Due to their lower toxicity the PEG offer, as cryoprotecting agents, a useful alternative to dimethylsulfoxide.

On the mode of action of the immunosuppressive sesquiterpene ovalicin

When the potent immunosuppressive sesquiterpene ovalicin is added to lymphocyte cultures one first observes a preferential inhibition of uridine incorporation into rRNA. The uptake of the nucleoside, its conversion into the triphosphate or the polymerizing activity itself are not affected. A longer period of incubation with the drug results in a marked decrease in the number of ribosomes, with a concomitant reduction of the rate of leucine incorporation into all cellular proteins. After extended periods of time, the incorporation of thymidine into DNA in stimulated lymphocytes as well as in SV49.1 lymphoma cells is inhibited by 1 nM ovalicin or less, although part of the incorporation seems to be resistant to the drug even at much higher concentrations. A similar affect is observed with 3T6 mouse fibroblasts or HeLa cells. Here, however, a much longer incubation with the drug is required. This observation explains the selective effect of ovalicin on lymphocytes observed in vivo.

Cytosine arabinoside triphosphate production in human leukaemic myeloblasts: interactions with deoxycytidine

The effect of 1 mu M deoxycytidine (dC) on Ara-C conversion to Ara-CTP and on inhibition of DNA synthesis by Ara-C was measured in intact leukaemic myeloblasts. dC decreased Ara-CTP production in blasts with high Ara-C phosphorylation, but not those with low activity. The Ki for dC was similar to values found with partially purified deoxycytidine kinase. The change in Ara-CTP concentration was associated with a proportional reduction in inhibition of DNA synthesis. dC decreased the effects of Ara-C by inhibition of Ara-CTP production, rather than by production of dCTP and competition with Ara-CTP. Since low Ara-CTP production in patients' blasts is a predictor of poor therapeutic response to Ara-C, the use of dC with Ara-C may improve the therapeutic index in this group of patients.

Light transmission analysis of lymphocyte activation by mitogens: a new technique

In vitro lymphocyte transformation was evaluated by laser light transmission cytometry. Criteria are given for optimal application of this system to assessment of total cells and proportion of lymphoblasts in cultures. The light transmission studies revealed that cell numbers in mitogen stimulated cultures increase steadily, reaching a plateau. The percentage of lymphoblasts reached a peak after 4 days culture. The kinetics of [3H]-thymidine incorporation are similar. The increase in total cell number concomitant with decrease in [3H]thymidine incorporation at the fifth and sixth days indicates discordance between the cell proliferation and utilization of exogenous thymidine. The kinetics of total cell numbers and percentage of lymphoblasts suggest that in vitro reversion of lymphoblasts to small lymphocytes occurred. In addition to examining directly the cellular events during blastogenesis with ease, the current method appeared to be more reproducible than the [3H]thymidine incorporation assay.