Frequency analysis of human peripheral blood B cells producing autoantibodies: differential activation requirements of precursors for B cells producing IgM-RF and anti-DNA antibody.

To investigate the mechanism of autoantibody production, the extent and nature of anti-DNA precursors within normal human B cells were examined by utilizing two different polyclonal B cell stimulators, Staphylococcus aureus Cowan I (SA) and immobilized mAb to the CD3 molecular complex (64.1). In cultures stimulated with SA and IL2, B cells produced IgM-RF, but not anti-DNA, whereas B cells produced great amounts of anti-DNA in cultures stimulated with SA and intact T4 cells. In cultures stimulated with immobilized anti-CD3, T4 cells that had been treated with mitomycin C (T4 mito) induced the production of anti-DNA as effectively as that of IgM-RF. Limiting dilution analyses revealed that the precursor frequency of anti-DNA-producing cells in SA-stimulated cultures was markedly increased in the presence of intact T4 cells (0.399 to 2.549 per 10(4) B cell) compared with that in the presence of factors generated from mitogen-activated T cells (TF) (0.022 to 0.151 per 10(4) B cells). Thus, the proportion of IgM-secreting cells that produced anti-DNA in cultures with SA + T4 cells (12 to 31%) was much greater than that noted in cultures with SA + TF (3.4 to 4.0%), whereas the proportion of IgM-secreting cells that produced IgM-RF was not significantly different in these cultures (17 to 50%). The precursor frequency of anti-DNA-producing cells (0.019-0.097 per 10(2) B cells) was almost the same as that of IgM-RF producing cells (0.025-0.104 per 10(2) B cells) in cultures stimulated with immobilized anti-CD3. Of note, addition of SA increased the precursor frequency of IgM-RF-producing cells, but not that of anti-DNA-producing cells, in anti-CD3-stimulated cultures. These results indicate that T cells, but not T cell-derived cytokines, play a central role for the production of anti-DNA antibodies. Moreover, the data support the conclusion that the precursors of anti-DNA-producing cells have activation requirement different from those of IgM-RF producing cells.     

Frequency analysis of human peripheral blood B cells producing IgM-rheumatoid factor. Differential effects of stimulation with monoclonal antibodies to CD3 and Staphylococcus aureus

The extent and nature of IgM-rheumatoid factor (RF) precursors within normal human B cells were examined by utilizing two different polyclonal B cell stimulators, Staphylococcus aureus Cowan I (SA) and immobilized mAb to the CD3 molecular complex (64.1). In cultures stimulated with SA, B cells produced IgM-RF in the presence of T4 cells, factors generated from mitogen-activated T cells (TF), or IL-2. Similarly, in cultures stimulated with immobilized anti-CD3, T4 cells that had been treated with mitomycin C (T4 mito) induced the production of large amounts of IgM-RF. Limiting dilution analyses revealed that the precursor frequencies of IgM-RF-producing cells induced by SA + TF and by immobilized anti-CD3-activated T4 mito were 0.008 +/- 0.001/100 B cells (n = 7) and 0.043 +/- 0.004/100 B cells (n = 6) (mean +/- SEM), respectively. Of note, the proportion of IgM-secreting cells that produced IgM-RF was much greater in cultures stimulated with SA + TF (30 to 61%) than that noted in cultures containing immobilized anti-CD3-stimulated T4 mito (1.0 to 3.9%). When B cells were co-stimulated with both SA and immobilized anti-CD3-activated T4 mito, the frequency of IgM-RF producing cells increased further to 0.12 to 0.27/100 B cells (4.6 to 21.2% of IgM-producing cells). These results indicate that both SA and immobilized anti-CD3 are potent stimulators of IgM-RF precursors. Moreover, the combination of SA and immobilized anti-CD3 provides a very potent in vitro signal for IgM-RF elaboration, inducing the production of this autoantibody from 1 to 3 in 1000 circulating normal B cells.     

Lung-Derived Growth Factors: Ontogenic Shift in Parahormone Secretion in the Perinatal Rat Lung

Primary cultures of perinatal rat fibroblasts were found to produce at least three mitogenic activities which exhibited specificity for distinct cell types. One activity, lung growth factor(LGF), was a potent mitogen for chick embryonal fibroblasts, which also stimulated fetal rat lung fibroblasts to undergo DNA synthesis, provided that these cells were first exposed to a "competence" factor such as fibroblast growth factor or platelet-derived growth factor. Although LGF was active in the somatomedin-C (SmC) radioimmunoassay and resembled buffalo rat liver multiplication-stimulating activity (brlMSA) in molecular size, it appears to consist of a component that is neither SmC nor brlMSA. The second activity produced by perinatal rat lung cultures, pneumocyte-stimulating activity (PSA), stimulated mitosis in type II pneumocytes of postnatal rats, and was found to have physical attributes that are distinct from those of the other known pneumocyte-influencing factors. The third activity is a non-dialyzable substance which complements the mitogenic action of LGF on fetal lung fibroblasts, and appears to be a "competence" activity. An examination of the production of LGF and PSA by rat lung fibroblasts taken at various intervals of development revealed that fetal lung fibroblasts produce maximal levels of LGF but low levels of PSA, whereas, in neonatal lung fibroblasts, the situation is reversed. This ontogenic shift in the type of parahormone produced by the developing perinatal rat lung may be an important regulatory event in postnatal lung morphogenesis in this species.     

Ia-positive nonlymphoid cells and T cell development in murine fetal thymus organ cultures: monoclonal anti-Ia antibodies inhibit the development of T cells

A fetal thymus organ culture system has been developed to study the differentiation of murine thymus-derived immunocompetent cells (T cells) such that cell yields can be easily monitored. This system has been used to study the effects of monoclonal anti-I-A antibodies on the growth of T cells. The addition of anti-I-A antibodies, but not anti-H2K monoclonal antibodies, to fetal thymus organ cultures resulted in a decreased yield of lymphoid cells. Anti-I-A-treated cultures did not produce cells that gave an immune response in MLC assays. Anti-I-A antibodies stained a small subpopulation of nonlymphoid cells in untreated cultures by indirect immunofluorescence that were no longer detectable in cultures that had been pretreated with anti-I-A antibody. Culture of fetal thymus lobes at low temperature (20 degrees C) for 1 wk resulted in a decrease in lymphocyte production, as well as a concomitant increase in the frequency of Ia-positive nonlymphoid cells. Co-culture of fetal liver or anti-thy-1 plus complement-treated adult bone marrow with such Ia-positive cell-enriched fetal thymus lobes at 37 degrees C resulted in the production of T cells. Anti-Thy-1.1 or -1.2 staining by indirect immunofluorescence of cells obtained from co-cultures that differed at the Thy-1 locus showed that the T cells produced were derived from the bone marrow or fetal liver. T cell production occurred in both syngeneic and allogeneic cocultures. However, if co-cultures were made by using 14-day gestation fetal thymus instead of fetal liver or bone marrow as donors of T cell precursors, T cell growth was observed only in syngeneic combinations. These results suggest that Ia-positive nonlymphoid cells play a role in the development of T cells in the fetal thymus, and that "thymus processed" T cell progenitors (but not the more immature progenitors in the fetal liver or bone marrow) are self-Ia restricted in their differentiation.     

Production of progestin-stimulatory factor(s) by enriched populations of rat T and B lymphocytes

We have previously demonstrated that a progestin-stimulatory factor(s) (PSF) is present in the supernate of concanavalin A-activated rat splenocytes. In the absence of FSH, PSF evokes dose-dependent increases in both progesterone and 20 alpha-hydroxypregn-4-en-3-one (20 alpha-OH-P) production by undifferentiated rat granulosa cells while basal estrogen production is unaffected. Because splenocytes are composed predominantly of T and B lymphocytes, we sought to determine if PSF production is restricted to one of these specific cell types. To accomplish this, dispersed splenocytes were prepared from the spleens of adult female rats. Macrophages were removed by standard adherence procedures, and highly enriched populations of T and B lymphocytes were obtained by negative selection panning utilizing monoclonal antibodies to T and B lymphocytes. Purity of the T- and B-cell populations (typically greater than 85-95%) was assessed by single-color flow cytometry. Enriched populations of T cells, B cells, or unseparated lymphocytes were then seeded into tissue culture flasks and stimulated with 2.5 micrograms/ml concanavalin A. Following a 48-h incubation at 37 degrees C, cytokine-rich fractions were prepared from the conditioned medium of these cultures by ammonium sulfate fractionation. The presence of PSF was assessed by the ability of the resulting fractions to specifically stimulate progestin production by undifferentiated rat granulosa cells in vitro. Granulosa cells were treated with increasing doses (ranging from 0-30% v/v) of supernatants from cultures of T cells, B cells, or unseparated splenocytes for 48 h. Media were removed and progesterone, 20 alpha-OH-P, and estrogen levels were quantified by RIA.(ABSTRACT TRUNCATED AT 250 WORDS)     

Specificity of the T cell immune response to acetylcholine receptor in experimental autoimmune myasthenia gravis. Response to subunits and synthetic peptides

Myasthenia gravis (MG) and its animal model, experimental autoimmune MG (EAMG), are T cell-dependent diseases mediated by antibodies against acetylcholine receptor (AChR) on skeletal muscle. Most of the antibodies are directed toward conformation-dependent epitopes on the AChR, whereas T cells recognize denatured AChR. In search of T cell epitopes in EAMG, we tested 24 synthetic peptides covering 62% of the alpha-subunit sequence of Torpedo californica electric organ AChR in the T cell proliferation assay with lymph node cells from rats immunized with AChR. In Lewis rats, 2 of these peptides, [Tyr 100]alpha 100-116 and [Gly 89, Tyr 90]alpha 73-90, strongly stimulated T cells and, of these, [Tyr 100]alpha 100-116 was much more potent; 4 other peptides were weakly mitogenic and 18 were ineffective. None of the 24 synthetic peptides alone stimulated anti-AChR production and, when added to cultures along with AChR, [Tyr 100]alpha 100-116 and [Gly 89, Tyr 90]alpha 73-90 suppressed antibody production. Of twelve cloned T cell lines specific to AChR, 4 responded to [Tyr 100]alpha 100-116, indicating the importance of the epitope in alpha 101-116 in Lewis rats. In three other strains of rats whose responses to AChR and its subunits were similar to those in the Lewis rat, neither [Tyr 100]alpha 100-116 nor [Gly 89, Tyr 90]alpha 73-90 was stimulatory. Instead, completely different sets of peptides stimulated their T cells. When peptides were used as immunogens, each strain (except Lewis rats) responded only to the peptides that stimulated AChR-immune T cells from the same strain. Genetically restricted T cell recognition of AChR peptides in rats suggests that T cells from MG patients with different major histocompatibility haplotypes may recognize different AChR peptides.     

Enhancement of human B cell proliferation and differentiation by tumor necrosis factor-alpha and interleukin 1

The role of tumor necrosis factor-alpha (TNF-alpha) in human B cell responses was examined and compared with that of interleukin (IL) 1 by assessing the ability of each cytokine to support proliferation and differentiation. Recombinant TNF-alpha (rTNF-alpha) and recombinant IL-1 (rIL-1) each enhanced the generation of immunoglobulin-secreting cells (ISC) in cultures of pokeweed mitogen-stimulated B cells incubated with T cells. To examine the direct effect of rTNF-alpha and rIL-1 on the responding B cell, highly purified peripheral blood B cells were stimulated with Cowan I Staphylococcus aureus (SA). In the absence of T cell factors, proliferation was minimal and there was no generation of ISC. Recombinant IL-2 (rIL-2) supported both responses. Although rTNF-alpha alone did not support SA-stimulated generation of ISC, it did increase SA-stimulated B cell DNA synthesis by two- to eightfold. In addition, rTNF-alpha augmented B cell proliferation in rIL-2 supported SA-stimulated cultures. Moreover, rTNF-alpha enhanced the generation of ISC stimulated by rIL-2 alone or rIL-2 and SA. rIL-1 also augmented DNA synthesis and generation of ISC by B cells stimulated with SA and rIL-2. However, rTNF-alpha enhanced proliferation and ISC generation in SA + rIL-2-stimulated cultures even when they were supplemented with saturating concentrations of rIL-1. Utilizing a two-stage culture system, it was found that the major effect of rTNF-alpha was to enhance responsiveness of SA-activated B cells to rIL-2, whereas it exerted only a minimal effect during initial stimulation. These results indicate that TNF-alpha as well as IL-1 augment B cell responsiveness. Moreover, the ability of rTNF-alpha to enhance B cell responsiveness was not an indirect effect resulting from the induction of Il-1 production by contaminating monocytes, but rather resulted from the delivery of a signal by rTNF-alpha directly to the responding B cell that promoted both proliferation and differentiation after initial activation. The data therefore indicate that human B cell responsiveness can be independently regulated by the action of two separate monocyte-derived cytokines.     

Effects of alveolar surfactant aggregates on T-lymphocyte proliferation

The effects of alveolar large aggregate (LA) and small aggregate (SA) surfactant subfractions isolated from healthy adult rats on mitogen-stimulated proliferative responses of human peripheral blood mononuclear cells (PBMC) was examined. Various concentrations of total surfactant suppressed proliferation of stimulated lymphocytes by up to 95% of mitogen-stimulated cells alone. LA subfractions of total surfactant had no effect on proliferation, whereas SA significantly enhanced the lymphocyte proliferation at lower concentrations (7.8 microg/ml) compared to mitogen-stimulated cells alone. Higher concentrations of SA (62.5 microg/ml) inhibited lymphocyte proliferation. This concentration-dependent effect of SA on proliferation of PBMC was also present when cells were stimulated with various lectins including anti-CD3, concanavalin A and phytohemagglutinin. Analysis of the supernatant of mitogen-stimulated cell cultures treated with inhibitory concentrations of SA showed decreased amounts of interleukin (IL)-2, compared to cells alone, which could be reversed by adding exogenous IL-2 to the cell cultures with the SA. These results suggest that alveolar surfactant subfractions have distinct functions within the alveoli, both biophysically and with respect to their effects on the host's immunomodulatory responses.     

Characterization of a somatomedin (insulin-like growth factor) synthesized by fetal rat liver organ cultures.

Explants of 19- to 20-day fetal rat liver synthesize polypeptides biochemically and immunologically related to the well characterized somatomedin (insulin-like growth factor) BRL-MSA, multiplication-stimulating activity. Fetal MSA was purified from media conditioned by fetal liver explants by chromatography on Sephadex G-75 under acid conditions. Partially purified fetal MSA: 1) inhibited the binding of BRL-MSA to the MSA receptor of rat liver plasma membranes, to somatomedin-binding proteins from rat serum, and to rabbit anti-BRL-MSA serum; 2) had a molecular weight of 4,500 to 12,500 determined by polyacrylamide gel electrophoresis in sodium dodecyl sulfate; 3) stimulated the incorporation of [3H]thymidine into the DNA of chick embryo fibroblasts and induced cell multiplication; 4) stimulated glucose oxidation in rat adipocytes and weakly inhibited the binding of insulin to the insulin receptors of IM-9 lymphocytes; and 5) stimulated sulfate uptake in costal cartilage from hypophysectomized rats. These activities were associated with the same molecular species in fetal MSA preparations following disc acrylamide electrophoresis and co-migrated with active BRL-MSA peptides.     

Soluble insulin-like growth factor II/mannose 6-phosphate receptor inhibits DNA synthesis in insulin-like growth factor II sensitive cells

The soluble form of the insulin-like growth factor II (IGF-II)/mannose 6-P (IGF-II/M6P) receptor is released by cells in culture and circulates in the serum. It retains its ability to bind IGF-II and blocks IGF-II-stimulated DNA synthesis in isolated rat hepatocytes. Because these cells are not normally stimulated to divide by IGF-II in vivo, the effect of soluble IGF-II/M6P receptor on DNA synthesis has been further investigated in two cell lines sensitive to IGF-II; mouse 3T3(A31) fibroblasts, stimulated by low levels of IGF-II following priming by epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) and Buffalo rat liver (BRL) cells, which secrete IGF-II and proliferate in the absence of exogenous growth factors. Soluble IGF-II/M6P receptor (0.2-2.0 microgram/ml) purified from a rat hepatoma cell line inhibited DNA synthesis (determined by dThd incorporation) in both cell lines. Basal DNA synthesis was very low in serum-free 3T3 cells, but high in serum-free BRL cells, possibly as a result of autocrine IGF-II production. The inhibitory effect was reversible in cells preincubated with soluble receptor prior to incubation with growth factors and could also be overcome by excess IGF-II. Soluble receptor was more potent in IGF-II-stimulated 3T3 cells and serum-free BRL cells than in BRL cells incubated with serum. Mean inhibition by four preparations of soluble receptor (1 microgram/ml) was 34.7% +/- 4.4% in BRL cells stimulated with fetal calf serum (FCS) (5%) compared to 54.8% +/- 4.2% in serum-free BRL cells (P = 0.05) and 60.6% +/- 6.5% (P = 0.02) in 3T3 cells stimulated by PDGF, EGF, and IGF-II. Soluble receptor had no effect on DNA synthesis in 3T3 cells stimulated with IGF-I. These results demonstrate that soluble receptor, at physiological concentrations, can block proliferation of cells by IGF-II and could therefore play a role in blocking tumor growth mediated by IGF-II.     

IL-2 dependence of the promotion of human B cell differentiation by IL-6 (BSF-2)

The effect of rIL-6 on the growth and differentiation of highly purified human peripheral blood B cells was examined. IL-6 alone induced minimal incorporation of [3H]thymidine by unstimulated or Staphylococcus aureus (SA)-stimulated B cells and did not augment proliferation induced by SA and IL-2. Similarly, IL-6 alone did not support the generation of Ig-secreting cells (ISC) or induce the secretion of Ig by unstimulated or SA-stimulated B cells. However, IL-6 did augment the generation of ISC and the secretion of all isotypes of Ig induced by SA and IL-2. Maximal enhancement of B cell responsiveness by IL-6 required its presence from the initiation of culture. Delaying the addition of IL-6 to B cells stimulated with SA and IL-2 beyond 24 h diminished its effect on ISC generation. However, increased Ig production but not ISC generation was observed when IL-6 was added to B cells that had been preactivated for 48 h with SA and IL-2. This effect was most marked when the activated B cells were also stimulated with IL-2. IL-6 in combination with other cytokines such as IL-1 and IL-4 did not induce the secretion of Ig or generation of ISC in the absence of IL-2. Moreover, antibody to IL-6 did not inhibit the effect of IL-2 on the growth and differentiation of B cells stimulated with SA, but did inhibit the IL-6-induced augmentation of Ig secretion by B cells stimulated with SA and IL-2. IL-6 alone enhanced T cell dependent induction of B cell differentiation stimulated by PWM. Part of this enhancement was related to its capacity to increase the production of IL-2 in these cultures. These results indicate that IL-6 has several direct enhancing effects on the differentiation of B cells, all of which are at least in part dependent on the presence of IL-2. In addition, IL-6 can indirectly increase B cell differentiation by increasing IL-2 production by T cells.     

Effects of thyroid and luteinizing hormones on the onset of precursor cell differentiation into leydig progenitor cells in the prepubertal rat testis

Leydig cells in the adult rat testis differentiate during the neonatal-prepubertal period. However, the stimulus for the initiation of their differentiation is still not clear. In the present study our objectives were to test the effects of thyroid hormone and LH on the initiation of precursor cell differentiation into Leydig cells in the prepubertal rat testis. Four groups of Sprague-Dawley rats were used. All treatments began at postnatal Day 1. Rats in groups I, II, and III received daily s.c. injections of saline (200 microl, controls), triiodothyronine (T(3), 50 microg/kg body weight, hyperthyroid), and LH (ovine LH 10 microg/rat/day), respectively. Rats in group IV were made hypothyroid from postnatal Day 1 by adding 0.1% propylthiouracil (PTU) to their mother's drinking water. Testes of rats were collected at 7, 8, 9, 10, 11, 12, 16, and 21 days of age, fixed in Bouin's solution, and embedded in paraffin for immunocytochemical studies. Immunoexpression of 3beta-hydroxysteroid dehydrogenase (3beta-HSD) and LH receptors (LHR) in testicular interstitial cells (other than the fetal Leydig cells) was observed using the avidin-biotin method. In control rats, out of all spindle-shaped cell types in the testis interstitium, only the peritubular mesenchymal cells showed positive immunolabeling for 3beta-HSD, beginning from the postnatal Day 11. However, positive immunolabeling for LHR was first detected in these cells at Day 12, i.e., after acquiring the steroidogenic enzyme activity. In T(3)-treated rats 3beta-HSD positive spindle-shaped cells were first observed at Day 9 (i.e., 2 days earlier than controls), and LHR-positive cells were first observed on Day 11 (2 days later than obtaining 3beta-HSD immunoactivity); they were exclusively the peritubular mesenchymal cells. The 3beta-HSD- and LHR-positive spindle-shaped cells were absent in the testis interstitium of LH-injected rats from Days 7 through 12 but were present at postnatal Day 16. In addition, more fetal Leydig cell clusters and fetal Leydig cells in mitosis were present in LH-treated rats compared to rats in all other treatment groups. Following their first detection, the number of positive cells for each protein continued to increase at each subsequent age in controls, T(3)-, and LH-injected groups. In PTU rats, 3beta-HSD and LHR-positive spindle-shaped cells were absent throughout the experimental period. From these observations, it is possible to suggest the following regarding the developing rat testis interstitium. 1) The precursor cells for the adult generation of Leydig cells in the postnatal rat testis are the peritubular mesenchymal cells. 2) Luteinizing hormone does not initiate the onset of mesenchymal cell differentiation into Leydig cells, instead it delays this process. However, daily LH treatment causes mitosis in fetal Leydig cells and increase in fetal Leydig cell clusters. 3) Thyroid hormone is critical to initiate the onset of mesenchymal cell differentiation into adult Leydig cells.     

Stimulation by glucocorticoids of myoblast growth at low cell densities

Proliferation of rat myoblasts was stimulated by addition of 10(-7) M dexamethasone to cells plated at 25 cells/cm(2). In the presence of fetal calf serum and chick embryo extract, physiological levels of glucocorticoids caused a 3- to 7-fold increase in colony formation. In mass cultures, proliferation of myoblasts was also stimulated by dexamethasone, but fibroblast growth was inhibited. These opposite effects of glucocorticoids on myoblast and fibroblast growth suggest their use in cloning muscle cells from mixed cell populations.     

Glucose uptake in human and animal muscle cells in culture

Human muscle cells were grown in culture from satellite cells present in muscle biopsies and fusion-competent clones were identified. Hexose uptake was studied in fused myotubes of human muscle cells in culture and compared with hexose uptake in myotubes of the rat L6 and mouse C2C12 muscle cell lines. Uptake of 2-deoxyglucose was saturable and showed an apparent Km of about 1.5 mM in myotubes of all three cell types. The Vmax of uptake was about 6000 pmol/(min.mg protein) in human cells, 4000 pmol/(min.mg protein) in mouse C2C12 muscle cells, and 500 pmol/(min.mg protein) in L6 cells. Hexose uptake was inhibited approximately 90% by cytochalasin B in human, rat, and mouse muscle cell cultures. Insulin stimulated 2-deoxyglucose uptake in all three cultures. The hormone also stimulated transport of 3-O-methylglucose. The sensitivity to insulin was higher in human and C2C12 mouse myotubes (half-maximal stimulation observed at 3.5 X 10(-9) M) than in rat L6 myotubes (half-maximal stimulation observed at 2.5 X 10(-8) M). However, insulin (10(-6) M) stimulated hexose uptake to a larger extent (2.37-fold) in L6 than in either human (1.58-fold) or mouse (1.39-fold) myotubes. It is concluded that human muscle cells grown in culture display carrier-mediated glucose uptake, with qualitatively similar characteristics to those of other muscle cells, and that insulin stimulates hexose uptake in human cells. These cultures will be instrumental in the study of human insulin resistance and in investigations on the mechanism of action of antidiabetic drugs.     

Growth control in primary fetal rat liver cells in culture.

Primary fetal rat liver cells cultured in medium deficient in, but not free of, arginine in the presence of dialyzed fetal calf serum grow until the final cell density is attained and cells become quiescent in the Go phase of the cell cycle. When growing cells are transferred into arginine free medium, cells become reversibly arrested in Go. Fetal rat liver cells can be induced to synthesize DNA by addition of high levels of arginine to serum free medium. Low arginine levels in the culture medium do not induce cell growth unless serum is present. Serum stimulates arginine uptake in fetal rat liver cells suggesting that serum growth factor(s) act by increasing intracellular arginine levels high enough to initiate the growth cycle. Fractionation of fetal calf serum by gel filtration on G-200 Sephadex yields a partially purified arginine uptake stimulating activity which is eluted from the column in the same fractions that contain fetal rat liver cell growth promoting activity. Insulin induces DNA synthesis in quiescent fetal rat liver cells. Glucagon reverses the stimulatory effects of insulin. N-6,O-2-Dibutyryl adenosine 3:5-cyclic monophosphoric acid (But2c-AMP) (10-minus4 M) and theophilline (10-minus3 M) inhibit arginine uptake and the initiation of DNA synthesis by serum. The role of arginine in the control of DNA synthesis in fetal rat liver cells and the mechanism of action of serum growth factors are discussed.     

Regulation of human B cell responsiveness by CD8+ T cells: differential effects of stimulation with monoclonal antibodies to CD3 and pokeweed mitogen

Previous studies have shown that human CD8-positive T cells activated by immobilized mAb to the CD3 complex have the capacity to support the generation of Ig secreting cells (ISC). The experiments reported here were undertaken to examine the nature of CD8+ T cell helper function in greater detail. CD8+ T cells that had been treated with mitomycin C (CD8+ mito) and stimulated by immobilized mAb to CD3 (64.1) provided help for the generation of ISC from resting B cells. By contrast, CD8+ mito did not support the generation of ISC in cultures stimulated by pokeweed mitogen (PWM). This could not be explained by differences in the production of IL2, since PWM and anti-CD3 induced comparable amounts of IL2 from CD8+ mito. In anti-CD3-stimulated cultures, CD8+ mito supported the generation of larger numbers of ISC when B cells were also activated with Staphylococcus aureus (SA). By contrast, in PWM-stimulated cultures, CD8+ mito did not provide help for SA-activated B cells. Rather, PWM-stimulated CD8+ mito appeared to suppress the generation of ISC induced by PWM-activated CD4+ mito or by SA + IL2, whereas anti-CD3-stimulated CD8+ mito did not. Only control CD8+ T cells, which were able to proliferate, exerted suppressive effects in anti-CD3-stimulated cultures. Examination of the functional capacities of a battery of CD8+ T cell clones indicated that the same clonal population of CD8+ cells could provide help or suppress responses when stimulated with anti-CD3 or PWM, respectively. The functional activities of CD8+ clones differed from those of fresh CD8+ cells. Thus, anti-CD3-stimulated CD8+ clones provided help for B cells regardless of whether they were treated with mitomycin C. Moreover, PWM stimulated suppression by CD8+ clones was abrogated by treating the clones with radiation or mitomycin C. These results indicate that helper T cell function is not limited to the CD4+ T cell population, but that help can also be provided by appropriately stimulated CD8+ T cells. Taken together, these results indicate that CD8+ T cells are not limited in their capacity to regulate B cell responses, but rather can provide positive or negative influences depending on the nature of the activating stimulus.     

Biosynthesis of hepatic corticosteroid-binding globulin: ontogeny and effect of thyroid hormone.

The present study reports on the ontogeny and the effect of thyroid hormones on liver corticosteroid-binding globulin (CBG) biosynthesis, in relation to plasma CBG binding capacity in the rat. We show that mRNACBG contents were high in liver of 18-day-old fetuses and decreased with age to reach almost undetectable levels by postnatal day 1. Interestingly, at the latter time point plasma CBG concentration remained elevated and disappeared thereafter from the circulation with a half-life of about 3 days. The messenger was localized in parenchymatous cells and not in hematopoietic ones, although the latter constitute the major cell population in fetal liver. It is not until after 10 days of age that mRNACBG and plasma CBG levels increased in concert, with a sex-difference being noticed by postnatal day 30. Treatment of rats with 3,3',5-triiodo-L-thyronine (T3), but not reverse T3 (rT3) (the predominant form present in fetal serum), enhanced CBG biosynthesis. These findings show that liver mRNACBG contents undergo dramatic changes during ontogeny and suggest the existence of a differential regulation of the messenger in fetal and neonatal rats.     

Selectivity of hemoregulatory peptide (HP5b) action in culture

A synthetic analog of a hemoregulatory peptide associated with mature human granulocytes (HP5b) has been investigated for inhibitory effects on various cell types in culture as compared to inhibitory action on mouse and human myelopoietic colonies (CFU-gm), which occurs from 1 X 10(-13) to 1 X 10(-6) M in vitro. This includes colony formation by lymphoid T and B cells in capillary cultures, as well as mitogen activation of T, B and NK cells. At higher concentrations, i.e., above 1 X 10(-7) M, an inhibitory effect was found on colony formation. Neither the production of interleukin (IL) 3 by mitogen-activated T cells, nor the proliferation of the IL-3-dependent L/B cell line were affected by the peptide up to 1 X 10(-5) M. A slight inhibitory effect was found above 1 X 10(-9) M on mouse 3T3 fibroblasts. A series of malignant cell lines was also tested. No effect was seen between 1 X 10(-11) and 1 X 10(-7) M on human mammary carcinoma cells in culture. On Ehrlich ascites mouse mammary carcinoma cells a 30% inhibition was seen at 10(-6) M. On a human glioblastoma cell line (GaMg) no effect was seen, and on a rat glioma cell line (BT5C) an inhibitory effect was seen at 1 X 10(-7) M and above. No significant inhibition of cell growth was seen on SC1 mouse lymphoma cells from 1 X 10(-9) to 1 X 10(-5) M during 7 days of culture. The investigated normal and malignant cell types in culture were thus not inhibited in very low concentrations which act on CFU-gm. However, a variable inhibitory effect was found at higher concentrations where the inhibition of myelopoiesis was maximal and at concentrations where the inhibition is released. The hemoregulatory peptide thus seems to be a concentration-dependent selective inhibitor of myelopoiesis. The finding that various malignant cells do not respond at lower concentrations supports the possibility of using the peptide as a protector of normal cells during cancer chemotherapy.     

Maintenance of cell proliferation and steroidogenesis in cultured human fetal adrenal cells chronically exposed to adrenocorticotropic hormone: rationalization of in vitro and in vivo findings

Previous studies indicated that acute exposure of adrenal cells to adrenocorticotropic hormone (ACTH) markedly stimulates steroidogenic capacity in vitro but also inhibits cell proliferation. However, in vivo, ACTH is known to stimulate adrenal cell growth. To address this discrepancy, we determined the effect of long-term (9-11 days) continuous or intermittent exposure to ACTH on human fetal adrenal cell proliferation and steroidogenesis. Adrenal glands from fetuses 18-22 wk gestation were studied. Fetal zone cells were plated either on plastic or on an extracellular matrix (ECM) in the presence and absence of basic fibroblast growth factor (bFGF) (0.5 ng/ml) and 1 or 10 nM ACTH. As determined by cell counting, bFGF stimulated cell proliferation during 9 days in culture. In the presence of bFGF, the average doubling time decreased from 44 to 30 h on plastic and from 37 to 26 h on ECM. Under these conditions, ACTH did not inhibit cell proliferation. Proliferation of fetal adrenal corticosteroid-producing cells in the ACTH-treated cultures also was assessed by histochemical staining for 3 beta-hydroxysteroid dehydrogenase (3 beta HSD). The number of positive cells increased more than 4-fold between Days 5 and 9 in culture. Continuous treatment with 1 nM ACTH increased dehydroepiandrosterone sulfate (DHAS) production 5- to 10-fold during the first 5 days in culture. Thereafter, the stimulated hormone production decreased over time, although there was still a difference of almost 100-fold between the control and ACTH-treated cultures at the end of 9 days.(ABSTRACT TRUNCATED AT 250 WORDS)