Absence Of Mitogens Research Articles

Diploid and hyperdiploid rat Schwann cell strains displaying negative autoregulation of growth in vitro and myelin sheath-formation in vivo

Neonatal rat Schwann cells were cultured for several months with intermittent exposure to the mitogen, cholera toxin, and infrequent passaging to avoid premature transformation. A cell line SCL4.1/F7 was derived following the cloning of one of these long-term cultures by limiting dilution in liquid medium to select for cells capable of continuous proliferation in the absence of mitogen. F7 cells have been passaged 40 times (80–120 generations) over 14 months. Two substrains were identified at passage 20, one of which is diploid and the other which has trisomy 7 (t7). The cell line displays a characteristic flattened or crescent-shaped morphology, substratum adhesion which is calcium-dependent in the millimolar range, and pronounced contact-inhibition of growth. Confluent or subconfluent cultures readily cease proliferation and change to a differentiated (stellate/bipolar) morphology through the mediation of an autocrine growth-inhibitory factor. F7 cells grafted into the site of a crush injury in adult rat sciatic nerves remained viable and myelinated host axons. F7 is the first clonally derived diploid immortal Schwann cell line to have been published and should provide a suitable tool for the study of the biochemical and cellular basis of sheath cell-neuron interactions, myelin stabilization in peripheral nerve and Schwann cell growth autoregulation.

Incorporation of fatty acids by concanavalin A-stimulated lymphocytes and the effect on fatty acid composition and membrane fluidity

The fatty acid compositions of the neutral lipid and phospholipid fractions of rat lymph node lymphocytes were characterized. Stimulation of rat lymphocytes with the T-cell mitogen concanavalin A resulted in significant changes in the fatty acid composition of both neutral lipids and phospholipids (a decrease in the proportions of stearic, linoleic and arachidonic acids and an increase in the proportion of oleic acid). Membrane fluidity was measured using nitroxide spin-label e.s.r., and increased during culture with concanavalin A. Culturing the lymphocytes in the absence of mitogen did not affect fatty acid composition or membrane fluidity. The uptake and fate of palmitic, oleic, linoleic and arachidonic acids were studied in detail; there was a time-dependent incorporation of each fatty acid into all lipid classes but each fatty acid had a characteristic fate. Palmitic and arachidonic acids were incorporated principally into phospholipids whereas oleic and linoleic acids were incorporated in similar proportions into phospholipids and triacylglycerols. Oleic acid was incorporated mainly into phosphatidylcholine, palmitic and linoleic acids were incorporated equally into phosphatidylcholine and phosphatidylethanolamine, and arachidonic acid was incorporated mainly into phosphatidylethanolamine. Supplementation of the culture medium with particular fatty acids (myristic, palmitic, stearic, oleic, linoleic, alpha-linolenic, arachidonic, eicosapentaenoic or docosahexaenoic acid) led to enrichment of that fatty acid in both neutral lipids and phospholipids. This generated lymphocytes with phospholipids differing in saturated/unsaturated fatty acid ratio, degree of polyunsaturation, index of unsaturation and n - 6/n - 3 ratio. This method allowed the introduction into lymphocyte phospholipids of fatty acids not normally present (e.g. alpha-linolenic) or usually present in low proportions (eicosapentaenoic and docosahexaenoic). These three n - 3 polyunsaturated fatty acids replaced arachidonic acid in lymphocyte phospholipids. Fatty acid incorporation led to an alteration in lymphocyte membrane fluidity: palmitic and stearic acids decreased fluidity whereas the unsaturated fatty acids increased fluidity. It is proposed that the changes in lymphocyte phospholipid fatty acid composition and membrane fluidity brought about by culture in the presence of polyunsaturated fatty acids are responsible for the inhibition of lymphocyte functions caused by these fatty acids.

A novel role for thyroid hormone, glucocorticoids and retinoic acid in timing oligodendrocyte development

The timing of oligodendrocyte differentiation is thought to depend on an intrinsic clock in oligodendrocyte precursor cells that counts time or cell divisions and limits precursor cell proliferation. We show here that this clock mechanism can be separated into a counting component and an effector component that stops cell proliferation: whereas the counting mechanism is driven by mitogens that activate cell-surface receptors, the effector mechanism depends on hydrophobic signals that activate intracellular receptors, such as thyroid hormones, glucocorticoids and retinoic acid. When purified oligodendrocyte precursor cells are cultured at clonal density in serum-free medium in the presence of mitogens but in the absence of these hydrophobic signals, the cells divide indefinitely and do not differentiate into postmitotic oligodendrocytes. In the absence of mitogens, the precursor cells stop dividing and differentiate prematurely into oligodendrocytes even in the absence of these hydrophobic signals, indicating that these signals are not required for differentiation. The levels of these signals in vivo may normally regulate the timing of oligodendrocyte differentiation, as the maximum number of precursor cell divisions in culture depends on the concentration of such signals and injections of thyroid hormone into newborn rats accelerates oligodendrocyte development. As thyroid hormone, glucocorticoids and retinoic acid have been shown to promote the differentiation of many types of vertebrate cells, it is possible that they help coordinate the timing of differentiation by signalling clocks in precursor cells throughout a developing animal.

Experimental evidence for 60 Hz magnetic fields operating through the signal transduction cascade: Effects on calcium influx and c-MYC mRNA induction

We tested the hypothesis that early alterations in calcium influx induced by an imposed 60 Hz magnetic field are propagated down the signal transduction (ST) cascade to alter c-MYC mRNA induction. To test this we measured both ST parameters in the same cells following 60 Hz magnetic field exposures in a specialized annular ring device (220 G (22 mT), 1.7 mV cm maximal E induced, 37°C, 60 min). Ca 2+ influx is a very early ST marker that precedes the specific induction of mRNA transcripts for the proto-oncogene c-MYC, an immediate early response gene. In three experiments influx of 45Ca 2+ in the absence of mitogen was similar to that in cells treated with suboptimal levels of Con-A (1 μg ml ). However, calcium influx was elevated 1.5-fold when lymphocytes were exposed to Con-A plus magnetic fields; this co-stimulatory effect is consistent with previous reports from our laboratory [FEBS Lett. 301 (1992) 53-59; FEBS Lett. 271 (1990) 157-160; Ann. N.Y. Acad. Sci. 649 (1992) 74-95]. The level of c-MYC mRNA transcript copies in non-activated cells and in suboptimally-activated cells was also similar, which is consistent with the above calcium influx findings. Significantly, lymphocytes exposed to the combination of magnetic fields plus suboptimal Con-A responded with an approximate 3.0-fold increase in band intensity of c-MYC mRNA transcripts. Importantly, transcripts for the housekeeping gene GAPDH were not influenced by mitogen or magnetic fields. We also observed that lymphocytes that failed to exhibit increased calcium influx in response to magnetic fields plus Con-A, also failed to exhibit an increase in total copies of c-MYC mRNA. Thus, calcium influx and c-MYC mRNA expression, which are sequentially linked via the signal transduction cascade in contrast to GAPDH, were both increased by magnetic fields. These findings support the above ST hypothesis and provide experimental evidence for a general biological framework for understanding magnetic field interactions with the cell through signal transduction. In addition, these findings indicate that magnetic fields can act as a co-stimulus at suboptimal levels of mitogen; pronounced physiological changes in lymphocytes such as calcium influx and c-MYC mRNA induction were not triggered by a weak mitogenic signal unless accompanied by a magnetic field. Magnetic fields, thus, have the ability to potentiate or amplify cell signaling.

Growth and differentiation of normal human melanocytes in a TPA-free, cholera toxin-free, low-serum medium and influence of keratinocytes.

Melanocyte cultures were obtained from a modification of the keratinocyte culture system MCDB153. Either promelanocytes or mature melanocytes were selected from epidermal cell primary cultures. Pure subcultures of actively dividing melanocytes of both types were grown in a low-serum medium totally deprived of TPA and cholera toxin called melanocyte growth medium (MGM). Early passaged cells from MGM primary cocultures were similar to normal adult human melanocytes in vivo, exhibiting numerous melanosomes, strong dopa positivity and a high dendricity. The ability of MGM to support melanocyte growth was mainly a consequence of its basic composition, combined with a low serum concentration. Bovine pituitary extract significantly enhanced melanocyte growth. Using complete MGM, in the absence of mitogens and keratinocytes, cell growth was maintained, but the differentiation of melanocytes decreased. The presence of keratinocytes was found to promote melanocyte growth. The coculture system used strongly suggests the action of soluble keratinocyte-derived factors. Keratinocyte contact was necessary to sustain melanocyte dendricity and melanization. Melanization and dendricity behaved mostly as independent features when keratinocyte influence was withheld. Our results underline the essential role of keratinocytes in the regulation of melanocyte growth and differentiation in a physiological culture system.

Phenotypically diverse mouse thymic stromal cell lines which induce proliferation and differentiation of hematopoietic cells.

The heterogeneity of the thymic stroma has made careful characterization of particular thymic stromal cell types difficult. To this end, we have derived a panel of cloned thymic stromal cell lines from simian virus 40 T antigen (SV40-T antigen) transgenic mice. Based on their analysis with monoclonal antibodies that distinguish among subsets of thymic stroma cells, and on the morphology and ultrastructural features of the different clones, we suggest that our panel includes representatives of the thymic subcapsular cortex or thymic nurse cells (427.1), the deep cortex or cortical reticular cells (1308.1) and the medulla including medullary interdigitating (IDC)-like cells (6.1.1) and medullary epithelial cells (6.1.7). A fifth cell type of undesignated but apparent medullary origin (6.1.11) was also isolated. All of the cell lines constitutively express the SV40 T antigen transgene and the class I antigens of the major histocompatibility complex (MHC), and they can be induced to express MHC class II antigens upon stimulation with recombinant interferon-gamma (IFN-gamma). These cell lines elaborate a factor(s) that induces the proliferation of cells from the fetal liver and bone marrow, but not from the neonatal thymus. A factor(s) elaborated by the 1308.1 cell line also induces the proliferation of fetal thymocytes in the absence of mitogens, phorbol esters or calcium ionophore which is augmented with the addition of recombinant interleukin-2 (IL-2). Analysis by reverse transcription polymerase chain reaction with primers for some mouse cytokines reveals that each of these cell lines contain granulocyte-macrophage colony-stimulating factor (GM-CSF) transcripts and that 1308.1, 6.1.1 and 6.1.7 produce IL-6 mRNA. Cell lines 1308.1 and 6.1.1 also produce IL-7; 6.1.1 produces IL-1 beta and tumor necrosis factor (TNF)-alpha while the 427.1 cell line produces IL-5 and IFN-gamma mRNA. None of the cell lines tested express the IL-2 receptor, IL-2, IL-3, IL-4, TNF-beta or macrophage inflammatory proteins mRNA. Conditioned medium (CM) from 1308.1 and 6.1.11 induced differentiation of cells purified from the mouse fetal liver into granulocytes; 1308.1 CM also induced differentiation of the mouse hematopoietic stem cell line 32DCl3(G) suggesting that the CM contains granulocyte (G)-CSF activity. Each cell line produces GM-CSF but the greatest activity is associated with 1308.1 and 6.1.11 CM. The availability of these well-characterized, functional, cloned thymic stromal cells will allow a more detailed analysis of the role of each cell type in both myeloid and T cell development.

Glucocorticoid-Prolactin Interactions in Nb2 Lymphoma Cells: Antiproliferative versus Anticytolytic Effects

The interaction between the immunosuppressive effects of glucocorticoids and the mitogenic effects of prolactin (PRL) were examined in Nb2 lymphoma cells, a pre-T cell line. The synthetic glucocorticoid, dexamethasone (Dex), caused a concentration-dependent (6.25-200 nM) inhibition of basal and ovine PRL (oPRL)-stimulated Nb2 cell proliferation. Although Dex was antiproliferative, the steroid had no effect on cell viability in the presence of PRL. However, when PRL was omitted from the medium, Dex increased the proportion of dead Nb2 cells by 24 hr in a concentration (25-200 nM)-dependent fashion without affecting total cell number. The antiproliferative and cytolytic effects of Dex were mimicked by other corticosteroids (cortisol, corticosterone, aldosterone, and deoxycorticosterone) in the expected order of glucocorticoid potency, but not by other steroids (17-beta-estradiol, progesterone, testosterone, 5-alpha-dihydrotestosterone, and dehydroepiandrosterone) or triiodothyronine. In addition, the antiproliferative and cytolytic effects of glucocorticoids were antagonized by the glucocorticoid receptor antagonist RU 486. Since corticosteroid-induced cytolysis was apparent only in the absence of mitogen, the anticytolytic effects of oPRL were tested. In the presence of Dex (100 nM), oPRL (25-1600 pg/ml) caused a concentration-dependent inhibition of cytolysis without changing cell number. Other lactogenic hormones (human growth hormone, human placental lactogen, rat PRL), but not trophic nonlactogenic hormones (rat growth hormone, human chorionic gonadotropin, ACTH), also inhibited Dex (100 nM)-induced cytolysis. Agarose gel electrophoresis of DNA extracted from Nb2 cells revealed that within 12 hr, 100 nM Dex induced DNA fragmentation, indicative of programmed cell death or apoptosis. Coincubation of cells with Dex and oPRL (1 ng/ml) inhibited Dex-induced fragmentation of Nb2 cell genomic DNA. These studies reveal a complex interaction between glucocorticoids and PRL in Nb2 cells. Although a glucocorticoid receptor-mediated antiproliferative effect is evident, PRL (at concentrations that usually stimulate cell proliferation) has the capacity to protect the cell against glucocorticoid-receptor-mediated induction of apoptosis.

Standardization of in vitro synthesis and detection of HIV-1-specific antibodies

Optical conditions for in vitro anti-human immunodeficiency virus type 1 (HIV-1) antibody (Ab) synthesis and detection were re-appraised. Western blot (WB) and radioimmunoassay (RIA) could detect about 1 and 10 ng, respectively, of HIV-1-specific Ab (HIV-Ab), while the sensitivity of an enzyme-linked immunosorbent assay (ELISA) was much lower. Optimal HIV-Ab recovery was obtained by culturing 2.5 × 10 6 peripheral blood mononuclear cells (PBMC)/ml from seropositive subjects for 16 days in the absence of mitogens; at higher cell concentrations, background levels were unacceptably high. The background of non-de novo synthesized HIV-Ab was due to insufficient PBMC washing and/or cytophilic immunoglobulin (Ig); a particular washing procedure, as well as 24 h peripheral blood mononuclear cells (PBMC) pre-culture, might help in limiting this phenomenon. However, results should be compared with those obtained in cultures containing puromycin especially in infants, where a higher CD16 antigen expression in lymphocytes is likely responsible for increased amounts of cytophilic Ig released in culture supernatants, compared to adults.

Inhibition of proliferative responses of mouse spleen lymphocytes by bovine milk κ‐casein digests

The inhibitory effects of bovine milk κ‐casein and its enzymatic digests on the proliferative responses of mouse spleen lymphocytes induced or not induced by mitogens were studied with a colorimetric assay using 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl tetrazolium bromide (MTT). κ‐Casein and its glyco‐macropeptide (residues 106–169) inhibited the lipopolysaccharide (LPS)‐induced proliferative response, but the inhibitory effect was lost significantly after neuraminidase and chymotrypsin digestions. In contrast, trypsin and pronase digestions of K‐casein increased inhibitory effects. The pronase digest inhibited the proliferative responses not only induced by LPS but also in the absence of mitogen or when induced by concanavalin A and phytohemagglutinin. The pronase digest seemed to possess weak cytotoxity for lymphocytes. The inhibitory peptide was a glycopeptide(s) having specific size, and the inhibitory effects were reduced significantly by neuraminidase and chymotrypsin digestions. Moreover, similar ...

An improved salmonid lymphocyte culture medium incorporating plasma for in vitro antibody production and mitogenesis

This study describes an improved culture medium utilising salmonid plasma sources as an alternative serum supplement to foetal bovine serum (FBS). Salmonid leucocyte antibody and mitogen responses were examined in cultures supplemented with either salmonid plasma or FBS. Salmonid plasma sources repeatedly enhanced the mitogen specific proliferation of the leucocyte cultures above that seen with FBS. Additionally, antibody responses of these cultures were enhanced when plasma was employed, demonstrating factor(s) present in plasma were necessary for differentiation as well as proliferation. This phenomenon was observed for both peripheral blood and anterior kidney leucocytes. A comparison of non-specific stimulation of cultures in the absence of mitogen revealed FBS, alone, frequently elicited significant proliferation, while plasma-supplemented cultures did not. Utilisation of plasma as an alternative serum supplement has broad applications as enhancement of the mitogenic response was observed for three distinct salmonid species. In addition, plasma sources were effective across species, suggesting plasma supplementation may be adapted to many fish systems.

A role for tumor necrosis factor-alpha and interferon-gamma in the regulation of interleukin-4-induced human thymocyte proliferation in vitro. Heightened sensitivity in the Down syndrome (trisomy 21) thymus.

The influence of recombinant interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF) on IL-4-induced proliferation of postnatal human thymocytes from eight children with Down syndrome (DS, trisomy 21) and 18 control children was evaluated. DS thymuses were studied because they are characterized by cortical depletion and abnormal thymocyte differentiation. IL-4, without mitogen, induced a dose-dependent proliferation of both DS and control thymocytes. The proliferation was comparable to that induced by IL-2 and far greater than the proliferation mediated by IL-1 beta in the absence of mitogen. The level of IL-4 responsiveness correlated with the proportion of cells expressing the gamma, delta chains of the T cell receptor. Furthermore, thymocyte preparations greatly enriched for T cell receptor gamma, delta-bearing cells were found to vigorously proliferate when treated with IL-4. Both IFN-gamma and TNF inhibited IL-4-driven proliferation in a dose-dependent manner, but DS thymocytes were found to be significantly more sensitive to inhibition by both cytokines. Our studies suggest an important role for IL-4 in the proliferation of T cell receptor gamma, delta+ thymocytes and demonstrate regulatory functions for IFN-gamma and TNF in human thymocyte proliferation. The increased sensitivity of DS thymocytes to IFN-gamma and TNF may explain anatomical abnormalities in DS thymuses and suggests the involvement of genes encoded on human chromosome 21 in the responses to both IFN-gamma and TNF.

Characterization of HTLV-I in vivo infected T cell clones. IL-2-independent growth of nontransformed T cells.

Mononuclear cells from subjects infected with human T lymphotrophic virus type I (HTLV-I) display a unique ability to proliferate in vitro in the absence of mitogens or exogenous growth factors. Subjects who have developed an HTLV-I-associated myelopathy (HAM) show an even higher degree of spontaneous proliferation concomitant with transcription of the HTLV-I provirus. The mechanism underlying HTLV-I-induced T cell activation was investigated by characterizing a series of HTLV-I-infected T cell clones generated from the blood of subjects with HAM. Approximately 15% of the T cell clones generated were HTLV-I infected as determined by polymerase chain reaction and Southern blotting. Infected T cell clones displayed altered growth kinetics as they continued to incorporate tritiated thymidine 7 to 14 days after stimulation, a time when noninfected T cell clones had returned to a resting state. This was not due to transformation as all the T cell clones required periodic restimulation with mitogens and feeder cells for continued growth. Although HTLV-I-infected T cell clones showed increased expression of the IL-2 receptor p55 chain, the spontaneous clonal proliferation was not inhibited by anti-IL-2 receptor mAb. Moreover, the spontaneous clonal proliferation was insensitive to cyclosporin A and FK 506 while being highly sensitive to rapamycin, which is known to inhibit IL-2-mediated signaling. Together these results demonstrate that IL-2 is not required for the HTLV-I-induced spontaneous clonal proliferation and further suggest that HTLV-I may induce signaling pathways replacing an IL-2 receptor signal proximal to the site of action of rapamycin.

Proliferative response of bovine mononuclear cells to recombinant bovine somatotropin (sometribove)

Bovine mammary gland mononuclear cells (MGMC) and peripheral blood mononuclear cells (PBMC) were isolated during the non‐lactating period to determine if recombinant bovine somatotropin (rbST) enhanced mitogen‐stimulated mononuclear cell proliferation and/or overcame suppressive effects of mammary secretions on mononuclear cell proliferation in vitro. MGMC were hyporesponsive to mitogenic stimulation compared with PBMC. Mammary secretions markedly suppressed the MGMC and PBMC response to mitogens. rbST had no effect on mononuclear cell proliferation in the presence or absence of mitogens. Similarly, rbST did not reverse the suppression of mononuclear cell proliferation by mammary secretions. Under the conditions of this study, rbST had no direct effect on the proliferation of mature bovine mononuclear cells.

Endorphin-like immunoreactivities in uncultured and cultured human peripheral blood mononuclear cells

It has been reported that cells of the immune system produce and release considerable amounts of pro-opiomelanocortin (POMC) -derived peptides in response to coculture with a variety of stimulatory agents. The present study investigated whether extracts of human peripheral blood mononuclear cells (PBMC) contain immunoreactivity for β-endorphin (βE) and related peptides. Using four endorphin RIA systems with different specificities, extracts of freshly isolated PBMC and PBMC cultured in the presence or absence of mitogens or of corticotropin releasing factor (CRF) and vasopressin (VP), were analyzed. With a radioimmunoassay (RIA) system directed to the midportion of βE, immunoreactivity (MPβE-IR) was readily detectable, although the concentration was extremely low (ca. 200 pg/10 7 cells). βE immunoreactivity (βE-IR) and α-endorphin immunoreactivity (αE-IR), as determined in C-terminally directed RIA systems, were present in even lower concetrations. γ-Endorphin immunoreactivity (γE-IR) was hardly detectable. Of subsets enriched in T-cells, B-cells or monocytes, the highest concentration of MPβE-IR was detected in extracts of monocytes. Coculture of PBMC with the mitogen Concanavalin A (Con A) or Phytohaemagglutinin (PHA) increased the amount of MPβE-IR in extracts of the cells. No increase in αE-IR, however, was detected, whereas βE-IR was only increased in extracts of cells cultured in the presence of Con A. No increase, in any of the immunoreactivities, was observed in extracts of PBMC cultured with bacterial lipopolysaccharide (LPS) or with the combination of CRF and VP, both stimuli that have been reported to induce POMC peptides in cultured PBMC. The present data show that human PBMC contain endorphin-like immunoreactivity, but in very small amounts. The extremely low concentrations and the ineffectiveness of LPS and the combination of CRF and VP to increase the endorphin-like immunoreactivity raise questions about the reported capacity of PBMC to synthesize POMC-derived peptides.

Antimitogenic Effects of Dexamethasone in Chemically Transformed Mouse Fibroblasts

Dexamethasone (a synthetic glucocorticoid) inhibited the entry into the S-phase of quiescent chemically transformed mouse fibroblasts (BP-A31) stimulated with 12-O-tetradecanoyl 13-acetate (TPA; a protein kinase-C activator) or with basic fibroblast growth factor. The basal rate of DNA synthesis was also strongly reduced by dexamethasone. In contrast, the mitogenic activity of insulin (acting via the insulin-like growth factor-I receptor) was little or not at all affected by dexamethasone. The antimitogenic activity of dexamethasone was enhanced when the steroid was included in the culture medium 24 h before the addition of mitogens. The effects of dexamethasone were glucocorticoid specific, partially reversed by the antiglucocorticoid RU 486, and prevented by cycloheximide (suggesting the involvement of glucocorticoid-induced protein synthesis in the antimitogenic activity of dexamethasone). Under the conditions of exponential growth in serum-free medium as well as in the presence of TPA, dexamethasone arrested the proliferation of sparsely seeded cells after a delay of 24-48 h. The BP-A31 cells are known to be constitutively competent and express at quiescence certain genes related to the G0/G1 transition in the original nontransformed A31 cell line. Of the transcripts corresponding to these genes, dexamethasone caused a rapid elimination of the JE mRNA, coding for a protein of the family of cytokines. The cell content of c-jun mRNA was also strongly reduced in the cells incubated at quiescence with dexamethasone (in the absence of mitogen). The presence of TPA along with dexamethasone prevented the elimination of c-jun, but not of JE mRNA. Short (30-min; together with the inducers) or long (24-h) treatment of the cells with dexamethasone did not prevent the induction of the c-fos gene expression by either TPA or basic fibroblast growth factor, indicating that dexamethasone does not interfere with mitogenic signal transduction. We conclude that in TPA-stimulated cells, the antiproliferative effect of dexamethasone is not due to interference with the expression of the c-jun gene, but may be related to the decreased level of the JE cytokine mRNA as well as to the synthesis of growth inhibitory protein(s).

Regulation of thymocyte proliferation by α β TcR + CD3 + CD4 − CD8 − cloned natural suppressor (NS) cells

Cloned α β TcR + CD3 + CD4 − CD8 − T cells, with natural suppressor (NS) activity, were cocultured with thymocytes in the presence or absence of mitogen or cytokines. Whereas thymocytes show a minimal response to phytohemagglutinin (PHA), IL-2, or IL-4 alone, they proliferate vigorously when cocultured with irradiated cloned NS cells in the presence of PHA or IL-2 or IL-4, but not with IL-1, IL-3, IL-6, IL-7, IFN-γ, or GM-CSF. Among a total of 11 NS cell clones, derived from the spleen or thymus, only one clone (NR-1) did not induce thymocyte activation in synergy with PHA. This costimulation is most likely mediated by soluble factor(s), since supernatants, obtained from NS cells activated with phorbol ester (PMA) and calcymicin (A23187) or with solid phase anti-CD3 mAb, enhance thymocyte DNA synthesis in the presence of a mixture of PHA, IL-2, and IL-4. The latter factor does not appear to be a previously described lymphokine, since PMA- and A23187-activated NS cells secrete IL-3, TGF-β, IFN-γ, GM-CSF, and TNF-α, but not IL-1, IL-2, IL-4, IL-5, IL-6, IL-7, nor IL-10. None of the factors, identified in the NS cell supernatants, was able to stimulate thymocyte DNA synthesis.This study shows that, in addition to their previously reported suppressor function, cloned NS cells can exert immunostimulatory activities by virtue of a soluble mediator.

Interleukin-1-like activity in synovial fluids and sera of horses with arthritis

Synovial fluid samples of horses with osteoarthritis were investigated to detect interleukin-1 ( IL-1) activity which could contribute to the disease pathogenesis. Of the 32 samples tested, 12 (37·5 per cent) showed an augmented phytohaemagglutinin induced proliferation of C 3H/HeJ mouse thymocytes. Positive results were also seen in horses with infected arthritis, osteochondritis, traumatic arthritis and undefined synovial effusions. Normal synovial fluid and sera from all groups failed to show any detectable IL-1 activity. Fractionation of synovial fluid showed that the IL-1 activity was in the 15 to 20 Kd fractions. In the absence of mitogen, synovial fluid failed to stimulate thymocytes and did not stimulate the growth of an interleukin-2 ( IL-2) dependent CTLL cell line, but synovial fluid stimulated IL-2 release by mouse spleen cells incubated with suboptimal doses of lectin. Evidence of an IL-1 inhibitor in synovial fluid from osteoarthritic horses was provided by ultrafiltration experiments and by the inhibitory activity of synovial fluid at particular dilutions in the thymocyte assay. The presence of IL-1-like activity could be relevant in the pathogenesis of arthritis in horses.

Methyl inosine monophosphate (MIMP), a new purine immunomodulator for HIV infection

Prior work has documented the thymomimetic and immunotherapeutic activity of purine molecules related in structure to inosine. Synthesis of a series of new structures has yielded a stable methylated form of IMP resistant to hydrolysis by 5′ nucleotidase. With both human peripheral blood lymphocytes and murines splenocytes, Methyl Inosine Monophosphate (MIMP) augments proliferative responses to T-cell mitogens like phytohemagglutinin (PHA), but less so, or not at all, to B-cell mitogens like pokeweed or endotoxin (LPS). MIMP does not directly stimulate lymphocytes alone in the absence of mitogen. The optimal effects of MIMP parallel the optimal effects of PHA. The magnitude of the effect is greater and more consistent than with other purine immunomodulators. MIMP is non-toxic in vitro and in vivo and is orally active in mice. Significant effects are observed as low as 0.1 and 1 μg/ml in vitro and 0.1 or 1 mg/kg in vivo. MIMP is a candidate third generation purine under development for immunotherapeutic purposes.

Modification of Mitogen-Induced Proliferation of Murine Splenic Lymphocytes by in Vitro Tocopherol

The effect of alpha-tocopherol on in vitro proliferation of murine splenic lymphocyte cultures supplemented with various concentrations of the vitamin has been measured at sub-optimal, optimal and supra-optimal levels of the T-cell mitogen Concanavalin A (Con A). In the concentration range (1-25 micrograms/ml), tocopherol enhanced proliferation when administered up to 24 hours after exposure to sub-optimal and optimal concentrations of Con A; however, at supra-optimal levels of the mitogen, it appeared to inhibit proliferation. In the concentration range 50-100 micrograms/ml, tocopherol supplementation only enhanced proliferation in response to sub-optimal concentration of Con A. The spontaneous proliferation of lymphocytes in the absence of mitogens was increased by tocopherol supplementation at all concentrations tested. In contrast, there appeared to be only slight stimulation of B-cell proliferation in response to optimal concentration of bacterial lipopolysaccharide (LPS) by lower levels of vitamin E. Tocopherol supplementation of cultures over a broad range of concentrations (0.5-100 micrograms/ml) had no significant effect on cell viability before onset of proliferation at 18 hours after exposure to Con A, nor was there evidence of earlier onset of DNA synthesis in response to mitogen in the presence of 5 micrograms/ml of the vitamin. Although macrophage depletion of cultures impaired proliferation induced by Con A, tocopherol supplementation continued to stimulate proliferation at optimal and sub-optimal levels of mitogen.

カテプシンＧのリンパ球活性化作用

Cathepsin G is one of serine proteases with chymotrypsin-like proteolytic activity and known to exist in neutrophils and spleens. We purified the protease from human bone marrow cells by extraction with 1 M potassium phosphate buffer (pH 7.0) and ap-plying to column chromatography of DEAF-cellulose, Sephadex G-100, CM-cellulose, and Mono-S. We further separated it into three isozymes by employing hydrophobic chromatography, and named them cathepsin.Purified cathepsin G potentiated the effect of mitogens such as Con A and PHA on human lymphocytes. The protease further stimulated synthesis of both DNA and RNA of lymphocytes in the absence of mitogens. Effect of cathepsin G on the lymphocyte activity was prevented by inhibitors of cathepsin G. Therefore, the effect of it on lymphocyte activity is considered to be due to its proteolytic activity. The effect of cathepsin G on the function of lymphocytes differed among isozymes of the protease. From these results, we suppose that cathepsin G plays an important role in biophylaxis by regulating functions of lymphocytes.