Inhibition by colchicine of the mitogenic stimulation of lymphocytes prior to the S phase

Hypercapnic and hypoxic responses require intact neural transmission from the pre-Bötzinger complex

The central respiratory network that includes the pre-Bötzinger complex (pre-BötC), a region believed to contain rhythmogenic neurons, is capable of responding to fluctuations in CO2 and pH. However, the role of inputs from this site in mediating ventilatory responses to hypercapnia and/or hypoxia in nonsedated animals is not well established. Therefore, in the present study we tested the hypothesis that altered transmission from the pre-BötC to its target sites would decrease chemosensory responsiveness to acute hypercapnia and modulate the ventilatory response to hypoxia. Colchicine was used to block axonal transport. At 48 h after bilateral microinjections of colchicine into the pre-BötC (100 microg/uL, 100 nL/site), but not saline, the baseline frequency of breathing decreased; however, rhythmicity was not altered. In addition, there was a significant fall in the ventilatory response to hypercapnia (5 and 12% CO2) and hypoxia (8% O2). These findings indicate that, inputs from pre-BötC neurons are of critical importance in providing the normal ventilatory response to both hypercapnia and hypoxia.

Induction by cyproterone acetate of DNA synthesis and mitosis in primary cultures of adult rat hepatocytes in serum free medium

The aim of this study was to elucidate whether serum-free conditions could be found in primary hepatocyte cultures under which the growth inducing properties of xenobiotics and hormones could be tested. Cyproterone acetate (CPA), a steroid with anti-androgenic and progestogenic activity, was chosen as a model compound because of its known strong mitogenic properties in rat liver in vivo. EGF served as a positive control. Induction of DNA synthesis was studied by [3H]-thymidine labeling and autoradiography. Mitoses were counted in hematoxylin stained specimens. The main steps which led to an efficient stimulation of DNA synthesis by CPA were (i) reduction of hormone concentrations to levels approaching (approx. 10x) physiological concentrations better than the previously used pharmacological ones (up to 2500x); (ii) supplementation with glucocorticoid (most effective at 10-100 nM dexamethasone); (iii) selection of the interval for cumulative labeling with thymidine at 44-68 h; (iv) lowering of cell density at seeding to 50,000 cells/cm2 (subconfluency); (v) treatment with concentrations of 10-100 microM CPA. With these conditions CPA labelling was 13-20% (increase 4- to 9-fold). Mitotic incidence was 0.56% (CPA) versus 0.08% in controls. From a dose response study (0.1-100 microM) a no-effect-level for induction of DNA synthesis was found in the range of 0.1-1 microM. None of the high concentrations of CPA did cause cytotoxicity as estimated by morphological observations or release of lactate dehydrogenase into the medium. This work demonstrates that CPA under appropriate, defined culture conditions induces DNA synthesis and mitosis.(ABSTRACT TRUNCATED AT 250 WORDS)

A cytoskeleton-dependent pathway for induction of IL-2 production and a cytoskeleton-independent pathway for IL-2-mediated signal transduction

We have used the synthetic microtubule inhibitor Tubulozole C in order to study the role of the microtubule system in human lymphocyte activation. Microtubule disruption prior to activation with phytohemagglutinin (PHA) resulted in a drastic reduction of IL-2 production. Similarly, using OKT3 or PHA as stimulators, a substantial decrease in proliferation was observed. Although IL-2 receptor analysis performed on the stimulated and antitubular-treated lymphocytes showed a 2-fold decrease in high-affinity and a 100-fold decrease in low-affinity IL-2 receptor expression, a proliferative response to externally added rIL-2 was noticed. This occurred provided the triggering agent was excluded or added in suboptimal concentrations. These results indicate that intact microtubules are necessary for PHA/OKT3-induced proliferation and IL-2 production, but not for IL-2-induced proliferation.

Chlorphentermine suppresses the phosphatidylinositol pathway in concanavalin A-activated mouse splenic lymphocytes

We have previously demonstrated that the chlorphentermine (CP)1-induced impairment in lymphocyte blastogenesis involves drug-induced inhibition of an event which occurs very early during lymphocyte activation. An early event, which is associated with mitogen-induced lymphocyte activation, involves the hydrolysis of phosphatidylinositol by phospholipase C to yield inositol phosphates and diacylglycerol as products. Inositol phosphates and diacylglycerol then function as mediators of a trans-membrane signal for the continuation of the cellular response. It was the purpose of the present study to determine the effects of CP on this phosphatidylinositol pathway. We demonstrated that formation of inositol phosphates in lymphocytes increases progressively above control over a 2 hour period following concanavalin A (Con A)-stimulation. In contrast, lymphocytes pre-incubated with 10(-5)M CP for 60 min, then stimulated with Con A for 2 hours in the presence of 10(-5)M CP, exhibit a significantly depressed inositol phosphate formation. In addition, CP also inhibited the activity of phospholipase C (IC50 = 0.58 mM), the enzyme responsible for the formation of inositol phosphates during lymphocyte activation. Further, lymphocytes activated in a manner that bypasses the phosphatidylinositol pathway are not inhibited by 10(-7)M or 10(-9)M CP as are cells activated with Con A. These results suggest that the suppression of the phosphatidylinositol pathway may be involved in the inhibition by CP of lymphocyte blastogenesis induced by Con A.

Colchicine activates cell cycle-dependent genes in growth-arrested rat 3Y1 cells

When growth-arrested 3Y1 cells (Fischer rat fibroblasts) were exposed to 3 X 10(-5) M colchicine, they entered S phase after a 12-h lag period which is the same as that in serum-stimulated cells. The expression of genes such as c-fos, c-myc, JE, KC, ornithine decarboxylase, and histone H3, analyzed by Northern blotting, increased in a cell-cycle dependent manner after colchicine treatment. The increased level of mRNAs was much smaller in colchicine-stimulated cells than in serum-stimulated cells, corresponding to the lower frequency of the former cells entering S phase. The course of the prereplicative phase seems to be similar in terms of the expression of cell cycle-dependent genes in cells stimulated with colchicine and in those stimulated with serum.

Inhibition by cytochalasin B of DNA synthesis in a thermosensitive anchorage-independent growth mutant

After a shift from a nonpermissive to a permissive temperature, synchronized DNA synthesis and cell division were observed in a cold-sensitive anchorage-independent growth mutant (cs-17-25) of Chinese hamster lung cells in Methocel culture. Only 15 min exposure to the permissive temperature was sufficient for induction of DNA synthesis in the cells. A low dose of actinomycin D (0.02 micrograms/ml) or cytochalasin B (5 micrograms/ml) was able to inhibit the DNA synthesis when added at an early period after the temperature shift. The inhibitory effects of actinomycin D and cytochalasin B on RNA and protein synthesis were very similar at both temperatures. The degree of multinucleation caused by cytochalasin B was altered quickly depending on the incubation temperature. These results suggest that stimulation of this mutant involves an obligatory actin-mediated step closely correlated to transcription of early mRNAs.

Metabolism and possible health effects of aluminum

Literature regarding the biochemistry of aluminum and eight similar ions is reviewed. Close and hitherto unknown similarities were found. A hypothetical model is presented for the metabolism, based on documented direct observations of Al3+ and analogies from other ions. Main characteristics are low intestinal absorption, rapid urinary excretion, and slow tissue uptake, mostly in skeleton and reticuloendothelial cells. Intracellular Al3+ is probably first confined in the lysosomes but then slowly accumulates in the cell nucleus and chromatin. Large, long-lived cells, e.g., neurons, may be the most liable to this accumulation. In heterochromatin, Al3+ levels can be found comparable to those used in leather tannage. It is proposed that an accumulation may take place at a subcellular level without any significant increase in the corresponding tissue concentration. The possible effects of this accumulation are discussed. As Al3+ is neurotoxic, the brain metabolism is most interesting. The normal and the lethally toxic brain levels of Al3+ are well documented and differ only by a factor of 3-10. The normal brain uptake of Al3+ is estimated from data on intestinal uptake of Al3+ and brain uptake of radionuclides of similar ions administered intravenously. The uptake is very slow, 1 mg in 36 years, and is consistent with an assumption that Al3+ taken up by the brain cannot be eliminated and is therefore accumulated. The possibility that Al3+ may cause or contribute to some specific diseases, most of them related to aging, is discussed with the proposed metabolic picture in mind.

The microtubular cytoskeleton and the initiation of DNA synthesis

Depending on cell type and mode of growth stimulation, an intact cytoplasmic microtubule system may either support or suppress passage through the prereplicative G1 phase (growth and maturation) and entrance into the S phase (DNA synthesis) of the cell cycle. In peripheral blood lymphocytes exposed to mitogenic lectins, colchicine and other antimicrotubular drugs inhibit blast transformation and initiation of DNA synthesis. The inhibitory effect is not due to decreased cellular binding of lectin or lack of generation of a stimulatory signal. Rather, it can be explained by an inability of the cells to pass through the G1 phase at a normal rate in the absence of cytoplasmic microtubules. The formation of new organelles and the growth in cell size that occur during this phase is markedly delayed by the drugs. For example, the Golgi complex, an organelle system that participates in membrane biogenesis and other basic cellular functions, is reduced in size and structurally disorganized. In cells with a shorter prereplicative phase, such as fibroblasts and smooth muscle cells, antimicrotubular drugs inhibit DNA synthesis in growth-arrested cultures exposed to optimal concentrations of serum, thrombin or platelet-derived growth factor (PDGF). On the other hand, antimicrotubular drugs stimulate DNA replication in serum-free cultures and enhance the stimulatory effect of insulin, epidermal growth factor (EGF), fibroblast growth factor (FGF), and prostaglandin F2 alpha on entrance into S phase. Moreover, stabilization of cytoplasmic microtubules with taxol has been found to block microtubule disassembly and initiation of DNA synthesis by colchicine and to inhibit thrombin- and EGF-stimulated DNA synthesis under serum-free conditions. These findings suggest that partial microtubule disassembly is an inherent step in the reactions that precede DNA replication and mitosis. However, the cell biological and molecular details of these reactions and the exact role of microtubules remain enigmatic.

Colchicine prevents the translation of mRNA molecules transcribed immediately after proliferative activation of hepatocytes in regenerating rat liver

A dual-labelling technique has been used to establish that partial hepatectomy has no effect on the degradation of poly (A)+mRNA and confirms that the increased incorporation of precursor into mRNA during early prereplicative development reflects an actual increase in mRNA biosynthesis. Simultaneous studies on the changes in nuclear RNA metabolism support the conclusion that an increase in gene transcription does occur. Colchicine, at concentrations known to disrupt microtubules, has no effect on this increase in gene transcription but prevents the translation of the gene products by promoting polysome disaggregation transiently during a critical stage of prereplicative development. Studies with mefenamic acid and hydrocortisone, specific inhibitors of prostaglandin metabolism, have ruled out any involvement of prostaglandins in the induction of prereplicative mRNA synthesis.

Glucocorticoid hormone modulation of both cell surface and cytoskeleton related to growth control of rat glioma cells

We have shown that glucocorticoids reversibly change the growth control of rat C6 glioma cells from a transformed to a normal pattern. Here we report that the glucocorticoid hormone hydrocortisone (Hy) modulates structure and function of cell surface and cytoskeleton. The hormone is shown to cause: (a) increased flattening and adhesion to solid substrates and to fibrin layers, (b) inhibition of the cell shape change triggered by catecholamines and cAMP, (c) extensive fibronectin deposition on normally fibronectinless cells' surface, and (d) microtubule rearrangement. Comparison of Hy-hypersensitive and Hy-resistant variants showed that microtubule rearrangements correlate with the growth control change induced by Hy, whereas fibronectin deposition does not.

Microtubules and lymphocyte responses: effect of colchicine and taxol on mitogen-induced human lymphocyte activation and proliferation

The role of microtubules in mitogen-induced human lymphocyte activation and proliferation was examined. The effect of colchicine, a microtubule-disrupting agent, was compared with taxol, a microtubule-stabilizing drug, and with isaxonine (N-isopropyl-amino-2-pyrimidine orthophosphate), a proposed microtubular-active drug. Lymphocyte proliferation, assessed by measuring the increase in the number of cells in mitogen-stimulated cultures, was completely suppressed by both colchicine and taxol (100 nM) whereas significant inhibition by isaxonine required much higher concentrations (5 mM). In order to characterize the inhibition, initial lymphocyte blast transformation and subsequent DNA synthesis were investigated. Neither colchicine nor taxol inhibited lymphocyte blast transformation assessed by quantitating the change in volume of the stimulated cells after a 24-hour incubation. In contrast, isaxonine (2-5 mM) suppressed blast transformation. Initial DNA synthesis, evaluated by measuring the cumulative incorporation of [3H]thymidine between 30 and 48 hours of culture, was inhibited in a concentration-dependent manner by both isaxonine and colchicine but not by taxol. Electron microscopic studies confirmed that both taxol and colchicine (10 nM) arrested the responding lymphocytes in mitosis, and that isaxonine inhibited initial activation. These results suggest that normal microtubule function is only necessary for cell division and that drug effects on blast transformation and initial DNA synthesis are unrelated to microtubules.

Inhibition by colchicine of human lymphocytotoxic function: dependence on cell-bound drug level, spontaneous reversibility and antagonism by desacetylcolchicine (DAC)

Colchicine elicits inhibition of spontaneous, PHA-dependent and antibody-dependent forms of lymphocytotoxicity of peripheral blood lymphocytes (PBL) against allogeneic target cells. The findings are that it does so in cell-bound form and to near-maximum effect in the amount of this produced in PBL exposed to it at 10(-6)M concentration for 2 h at 37 degrees C. This represents only a small fraction of the cells' binding capacity, which suggests that it involves sites special in kind (localisation) rather than number (occupied at random). Desacetylcolchicine (DAC) (a known inhibitor of the colchicine-tubulin binding reaction) afforded the PBL protection at concentrations that antagonised the binding of colchicine to them. That DAC itself hardly inhibited PBL function is attributed by inference to a weaker binding affinity making for readier loss of it upon removal of the free drug. It did, however, exhibit a tight form of binding to other, functionally-insensitive cell sites not competed for by colchicine at 100-fold higher concentration. Contrary to the impression lent by other workers' studies (on mouse lymphocytes), colchicine-induced suppression of cytotoxic function is not necessarily irreversible. PBL cultured in drug-free medium gradually lost bound colchicine and they recovered in capacity to express spontaneous and PHA-dependent activity, but not in antibody-dependent activity. The residual cytolytic activity shown by colchicine pre-treated PBL appears in the case of antibody-dependent activity to be truly colchicine resistant; it survived unchanged a 10-fold increase in cell-bound drug level and it cannot be explained as a possible product of recovery. This colchicine-independence may reflect the existence of tubulin/microtubule-independent mechanisms contributing to antibody-dependent activity. Examination of colchicine-treated PBL for membrane fluidity changes, using the probe molecule DPH and the technique of fluorescence polarisation, has yielded negative results, even for cells treated at excessively high colchicine concentration (10(-4)M). All three forms of lymphocytotoxic activity were retained in PBL reconstituted after cryopreservation in liquid nitrogen.

Alteration of lymphocyte function by quinones through a sulfhydryl-dependent disruption of microtubule assembly

The cytoskeleton plays a pivotal role in lectin-induced lymphocyte blastogenesis. Microtubule disrupting agents, many of which are sulfhydryl (SH) reagents, interfere with cytoskeletal-dependent cell functions including lymphocyte blastogenesis and agglutination. For example, hydroquinone (HQ) and N-ethylmaleimide (NEM) inhibit lectin-stimulated lymphocyte blastogenesis and agglutination at concentrations (10(-5)M) that do not reduce cell viability or ATP production. Indicative of the SH-specificity of these effects, only L-cysteine protects against HQ or NEM inhibition of blastogenesis and agglutination. Other compounds, including L-serine, DL-lysine and imidazole, have no protective effect. These and other findings previously reported suggest a selective interaction of HQ, or its oxidation product, p-benzoquinone (p-BQ) with SH groups critical to early G1 events associated with lymphocyte activation. These compounds show similar SH specificity in inhibiting microtubule assembly in vitro. The subcellular target specificity (cytoskeleton) exhibited by these compounds was compared to that of Adriamycin (ADR), a complex polycyclic quinone with known immunotoxic activity. ADR inhibited microtubule assembly in vitro and inhibited lymphocyte blastogenesis, however, these effects were not correlated with a loss of agglutination nor was toxicity protected against by the addition of SH compounds. The combination of cell culture methods together with application of techniques to measure microtubule assembly in vitro provides an effective means to discriminate between agents that selectively interfere with cytoskeletal-dependent function and those producing non-specific effects associated with cell death, such as decreased energy production or increased membrane permeability.

Enhancement of altered-cell foci in baby mouse skin cultures by antitubulin treatment: nuclear mechanisms

When primary baby mouse skin (BMS) cultures were subcultured for 48 hours into media containing 10(-6) to 10(-7) M colchicine or demecolcine, the number of altered cell foci appearing after 3-4 weeks' maintenance at 36 degrees C was substantially enhanced over drug-free controls. This applied whether or not the primary cultures had been irradiated with white fluorescent light. The additional presence of cytochalasin D and 12-O-tetradecanoyl-phorbol-13-acetate (TPA) sometimes improved and sometimes partly suppressed the enhancing effect of the antitubulin drugs, and these drugs were omitted for reproducible focus enhancement. The enhancement depended on passage through DNA synthesis in presence of colchicine, which did not prevent concurrent or subsequent DNA synthesis but induced a substantial proportion (greater than 33%) to replicate in the tetraploid (4n to 8n) chromosome configuration. Another effect was to induce widespread asymmetric nuclear division, allowing the potential for chromosome loss. All these effects occurred within the first one or few cell cycles after removal of the antitubulin drugs. The results suggest that the generation of tetraploidy perhaps followed by chromosome loss may be an important factor in the rapid induction of altered cell foci. Pre-existing DNA damage is another important factor.

Commitment and proliferation kinetics of human lymphocytes stimulated in vitro: effects of colchicine on mitogen response

We have examined the effects of colchicine on concanavalin A (Con A)-and phytohemagglutinin (PHA)-stimulated human peripheral blood lymphocytes and from the time course of proliferation have extracted the relative size of the responding cell population, the rate of entry of this population into S-phase, and the length of the lag period. Additions of colchicine at any time did not appear to influence the size of the responding population nor did it greatly affect the duration of the lag period. Only the rate at which the cell population enters initial S-phase is a function of the time of previous exposure to colchicine. Colchicine does not appear to inhibit the commitment of stimulated lymphocytes to enter the cell cycle. Rather, it merely serves to decrease the biochemical processes responsible for fixing a maximal rate of entry into S-phase.

Inhibition of human lymphocyte transformation by two aryloxyalkylamidines

The incorporation of [3H]thymidine into human lymphocytes stimulated by phytohaemagglutinin (PHA) was inhibited by anilino-N-2-m-chlorophenoxypropylacetamidine (501C) and xylamidine. These amidines antagonize 5-HT, but 5-HT did not alter [3H]thymidine incorporation. 501C inhibited PHA-induced lymphocyte transformation as observed by [3H]thymidine incorporation, [3H]uridine incorporation, [3H]leucine incorporation, DNA content, potassium content, and histological examination. 501C also inhibited increased [3H]thymidine incorporation in human mixed lymphocyte cultures. The IC50 of 501C for inhibition of these processes lay between 4 and 8 microM. When added late in culture (after 6-8 h) 501C was less effective. Possible mechanisms by which 501C inhibits transformation are discussed.

Effects of anchorage-modulating doses of concanavalin A, microtubule-disrupting drugs and microfilament perturbants, cytochalasins, on the phosphatidylinositol response of rat lymph-node cells

In lymphocytes isolated from rat lymph nodes, concanavalin A stimulated the 32PO4 incorporation into phosphatidylinositol and phosphatidic acid in a dose-dependent manner up to 200 micrograms of the lectin per ml of the lymphocyte culture. [3H]Thymidine incorporation was found to be optimal at 2 micrograms concanavalin A per ml of the culture when the incorporation was examined at the same cell density as was used in the determination of the 32PO4 incorporation. As previously described (Wang, J.L. and Edelman, G.M. (1978) J. Biol. Chem. 253, 3000-3007), the [3H]thymidine incorporation was inhibited at doses higher than 5 micrograms/ml in a dose-dependent manner. These results indicate that concanavalin A produced the phosphatidylinositol PI response of rat lymph-node cells in the dose range in which the mobility and distribution of lymphocyte surface receptors were modulated by the lectin (Yahara, I. and Edelman, G.M. (1972) Proc. Natl. Acad. Sci. U.S.A. 69, 608--612). Colchicine and vinblastine at a concentration of 10(-4) M did not inhibit the concanavalin A-induced PI response of rat lymph-node cells. Cytochalasins B and D at a concentration of 10(-5) M enhanced the concanavalin A-induced PI response to some degree. All the results obtained suggest that submembranous assemblies of microtubules and microfilaments do not play an indispensable role in the sequence of events involved in the PI response of rat lymph-node cells.

Microtubule stabilization by taxol inhibits initiation of DNA synthesis by thrombin and by epidermal growth factor

Several observations have suggested that microtubule depolymerization might act as a regulator of cell proliferation. To determine whether microtubule depolymerization is required for growth-factor-induced initiation of DNA synthesis, we treated serum-free cultures of mouse embryo cells with taxol to stabilize their microtubules and measured the initiation of DNA synthesis by thrombin and epidermal growth factor (EGF). Pretreatment of quiescent cultures of mouse embryo cells with 10 microgram/ml taxol inhibited up to 60% of the thrombin-stimulated and 47% of the EGF-stimulated DNA synthesis. This inhibition was dose-dependent for taxol concentrations from 0.3 to 20 microgram/ml. Control experiments showed that taxol did not simply affect uptake of nucleotides, glucose or amino acids, nor did it nonspecifically affect protein synthesis, cell morphology or cell viability. Taxol did not affect binding and internalization of 125I-thrombin or 125I-EGF indicating that the drug does not alter receptor number, affinity or distribution after growth factor binding. Taxol also did not affect the proteolytic activity of thrombin. Thus it appears that the inhibitory effects of taxol are mediated by a direct effect of taxol on microtubules. To determine at what point microtubule stabilization was interrupting the initiation signal, we added taxol at various times after addition of thrombin or EGF. Taxol addition during the first 8 hr after growth factor addition inhibited initiation, but after 8 hr had little if any effect. These results confirm that taxol was not nonspecifically affecting transport or metabolism required for DNA synthesis and indicate that thrombin and EGF may initiate cell proliferation through a gradual microtubule depolymerization or rearrangement that is necessary to commit cells to a replicative cycle.

Inhibition of lymphocyte transformation by mepacrine and chloroquine

Mepacrine inhibited uptake and the incorporation of leucine, thymidine and uridine into acid-insoluble material in human lymphocytes stimulated by phytohaemagglutinin (PHA) in vitro. The IC50 for each uptake was of the order of 2 microM. Mepacrine was inhibitory if applied at any time up to 48 h after PHA. The inhibition differed from that produced by colchicine and prostaglandin E1. The dose-response curve was steep, nearly all incorporation being inhibited by 2 x IC50. Chloroquine also had a steep dose-response curve, was about one-fifth as potent as mepacrine and was maximally effective in the first 6 h after PHA.

Microtubules: are they involved in the initiation of lymphocyte activation?

Purified human blood lymphocytes were stimulated with concanavalin A or phytohemagglutinin. DNA synthesis was measured with 2-h pulses of [3H]thymidine between 48 h and 73 h after stimulation. Colchicine, at concentrations between 0.1 muM and 10 muM, suppressed consequent DNA synthesis without affecting viability of the cells when added at any time up to 18 h before incorporation of [3H]thymidine was assessed. In concanavalin-A-stimulated lymphocytes, removal of the mitogen by methyl alpha-mannoside only prevented proliferation when added initially, but was without any effect when added after 20 h of stimulation, regardless of when DNA synthesis was measured. Thus, there was a period after 20 h of concanavalin A stimulation, when DNA synthesis was still sensitive to colchicine, but no longer required the presence of the mitogen. Colchicine also suppressed incorporation of [3H]leucine into protein, in resting as well as mitogen-stimulated lymphocytes. Similarly, colchicine decreased amino acid transport, as determined by uptake of alpha-amino-isobutyrate, which appeared to be the rate-limiting step in the incorporation of amino acids into protein in colchicine-treated cells. When the rate of protein synthesis was followed by the relative distribution of ribosomal particles, especially the increase of polysomes in activated lymphocytes, colchicine was without any detectable effect. The early increase in the incorporation of [14C]oleate into phospholipids was identical in the presence or absence of the microtubule-active drug. The data strongly suggest that microtubules are not involved in the initiation of lymphocyte growth or mitogenesis.

Effects of colchicine, vinblastine, griseofulvin and deuterium oxide upon phospholipid metabolism in concanavalin A-stimulated lymphocytes

Colchicine has previously been shown to inhibit the incorporation of [3H]-inositol into phosphatidylinositol in lymphocytes stimulated with concanavalin A. In the present study other agents known to interact with tubulin or affect microtubule assembly/disassembly were examined for effects on 32PO4 incorporation into phospholipids and [3H]inositol incorporation into phosphatidylinositol. Vinblastine inhibited the enhanced incorporation caused by concanavalin A of either [3H]inositol or 32PO4 into phosphatidylinositol and phosphatidic acid. It had no effect on basal incorporation of 32PO4 and enhanced basal incorporation of [3H]inositol into nonstimulated lymphocytes. Griseofulvin at concentrations up to 10(-3) M had no effect on uptake of either label. Deuterium oxide had effects similar to vinblastine in that basal incorporation of both labels was enhanced while inhibition of the concanavalin A stimulated incorporation was observed. These results suggest an action of these various compounds other than or in addition to their known effects on cytoplasmic microtubules.

Cell cycle-specific effects of glucocorticoids on phytohaemagglutinin-stimulated lymphocytes

Effects of steroid hormones and colchicine on the response of pig lymphocytes to phytohaemagglutinin (PHA) were assessed by measurement of [6-3H]thymidine incorporation. At steroid concentrations of 1 microM and below, only glucocorticoids and progesterone inhibited PHA-stimulated [6-3H]thymidine incorporation but at 100 microM inhibition was also produced by oestrogens, androgens and physiologically inactive steroids. Measurement of [6-3H]thymidine incorporation 18-24 hr, 6-12 hr or 0-6 hr after the delayed addition of the synthetic glucocorticoid, dexamethasone, to PHA-stimulated lymphocytes revealed a succession of alternating phases of sensitivity and insensitivity to the effects of the steroid which suggested that it was acting, perhaps indirectly, in a cell cycle stage-specific manner to arrest the progression of activated lymphocytes from G1 to S. Similar effects were observed with colchicine, but 100 microM 11-epicortisol inhibited [6-3H]thymidine incorporation in a non-cycle-specific manner. Glucocorticoid receptor levels in pig lymphocytes were increased 2-5-fold within 24 hr of PHA stimulation.

Kinetics of human lymphocyte responses in vitro: determination of clone size and initial rate of entry into DNA synthesis

In this third paper on the kinetics of lymphocyte stimulation we present a simple stochastic model for the entry of mitogen stimulated human lymphocytes into the proliferative cycle. The model is based on the assumption that responder 'recruitment' is a process of simple exponential decay. The model can be applied to the initial rapid rise in thymidine uptake after stimulation and successfully predicts the behavior of colchicine inhibited mitogen responses. Application of the model allows the estimation of the following constants; the size of the responding clone, the rate of entry of committed cells into the initial cell cycle, the duration of the lag period before uptake of thymidine increases above background and the average duration of thymidine uptake in responding lymphocytes (Ts). If we analyze the experimental results of mitogen stimulation experiments in these terms we can show that the first three constants are sensitive functions of both the dose of mitogen and the source of the responding lymphocytes. The most interesting finding may be the fact that low doses of mitogen seem to decrease the rate of entry of committed lymphocytes into cell cycle. This would imply that the rate determining step in this process is not of an all or none type.

Concanavalin A is mitogenic for resident peritoneal macrophages

Con A, a known T-cell mitogen, is also mitogenic for resident peritoneal macrophages. The stimulated cells morphologically resemble macrophages and are actively phagocytic. The concentration of con A (30 micrograms/ml) required to stimulate 3H-TdR incorporation is ten times that required for T-cell activation. Con A must be present throughout the entire culture period to produce the maximum effect, and con A-depleted supernatant fluids from con A-stimulated cells cannot replace the con A requirement. Stimulation of 3H-TdR incorporation occurs after a 48-hour lag period and is maximal on the fifth to seventh day of culture. At the peak of the response, 20-30% of the macrophages can be stimulated to incorporate 3H-TdR, but little or no increase in the total number of cells present in the culture occurs. This and pulse-chase experiments indicate that only a single cycle of replication occurs in the stimulated cells. Con A-responsive peritoneal macrophages appear to be a distinct subpopulation and might play a different role in the interaction with T cells and B cells in the immune response than the con A-non-responsive cells.

Quantification of non-specific immunosuppressive factors

A simple, reproducible and quantitative method for evaluating certain non-specific immunological inhibitors in a variety of biological fluids is described. Human lymphocytes were stimulated with PHA in the presence of colchicine. Phytohaemagglutinin stimulated a large percentage of cells and colchicine's selective blockage of mitosis limited the stimulated cells to one S phase. These conditions effectively established a maximum amount of DNA synthesis within each culture. Quantification of suppression was then achieved by measuring a decrease from this maximum. The PHA-colchicine assay was successfully used to quantify inhibition by normal plasma, normal mouse sera, mouse neonate sera, murine Ehrlich's and sarcoma I ascitic fluids and an immunoregulatory alpha-globulin peptide preparation. Because of the ability to obtain a specific inhibitory activity for the suppressive factors, this assay was particularly suited for following the isolation of inhibitors during the fractionation of suppressive substances from complex fluids.

Initiation of the blastogenic response of lymphocytes by hyperoptimal concentrations of concanavalin A

The blastogenic response of human lymphocytes in vitro to hyperoptimal concentrations of concanavalin A (Con A) has been studied by means of volume spectroscopy (measuring cellular and nuclear volume), flow cytofluorometry (measuring cellular DNA content) and incorporation of [3H]thymidine ([3H]dThd). The optimal Con A dose with respect to [3H]dThd incorporation was about 30 micrograms/ml. In cultures given hyperoptimal doses, e.g. 100 micrograms/ml, [3H]dThd incorporation was strongly inhibited, whereas the number of cells entering S-phase and significantly increasing their cellular and nuclear volume was considerably larger than with 30 micrograms/ml. With 200 micrograms/ml Con A, which induced negligible [3H]dThd incorporation, the percentage of responding cells was even larger. Hence, doses of Con A, which were hyperoptimal with regard to [3H]dThd incorporation, induced blastogenic response, including DNA synthesis, in a larger percentage of the cells than did the optimal dose. However, in cultures with hyperoptimal Con A doses, the progression of the cell cycle stagnated mainly during S- and G2-phase and few cells completed mitosis. Thus, the blocking effect of hyperoptimal doses was not confined to any particular point of the cell cycle. The reduced [3H]dTd incorporation, seen with hyperoptimal doses, is attributed partly to a failure of this assay under such conditions.