Human lymphocytic metabolism. Effects of cyclic and noncyclic nucleotides on stimulation by phytohemagglutinin

Function of macrophage prostaglandins in the process of phagocytosis

The role of prostaglandins (PGs) in phagocytosis of sheep erythrocytes (SRC) by mouse spleen adherent cells was examined. A decrease of about 50% in the phagocytosis was observed when macrophages were treated with 5 microgram/ml indomethacin. Concomitant addition of PGs (10(-6) mg/ml), however, prevented the inhibitory effect of indomethacin. It is thus suggested that PGs play an important role in phagocytosis.

Suppressor cells in vitro: differential effects of indomethacin and related compounds

In vitro immune response systems known to involve suppressor cell regulation were examined for effects produced by the drug indomethacin and other compounds known to inhibit the cyclooxygenase pathway of arachidonic acid metabolism. In all cases tested where suppressor T cell activity is known to be the dominant inhibitory mechanism, suppression was not blocked by drug addition and was sometimes more pronounced. In the cases tested where suppression could be attributed to a non-T cell, most likely a macrophage-like cell (M0), suppression could be abolished by drug treatment. Indomethacin and related compounds may be useful analytical tools for separation of T cell vs. non-T cell mediated suppression.

Isolation and purification of human large bowel mucosal lymphoid cells: effect of separation technique on functional characteristics

Human large bowel lamina propria lymphoid cells have been isolated using both mechanical and enzymatic techniques. Their separation from other cell types after isolation was effected with greater efficiency by sedimentation on isokinetic gradients than by filtration through glass bead columns. After being purified, the capacity of the lamina propria lymphocytes to function in vitro as effector cells in antibody-dependent cellular cytotoxicity was determined. Mechanical distruption of the mucosa gave low yields of lymphoid cells, which lacked the capacity for cytotoxicity. Enzymatic digestion of mucosal tissue, by comparison, yielded large numbers of viable lymphoid cells which retained a significant level of cytotoxic activity. Investigation revealed that mechanical homogenisation stimulated the synthesis of prostaglandin E2, and inhibitor studies showed that this mediator was responsible for the lack of cytotoxic activity in mechanically-liberated lymphocytes.

PGI2 and PGD2 effects on cyclic AMP and human T-cell mitogenesis

The effects of PGI2, PGD2, and PGF2 alpha on human peripheral blood lymphocytes (HPBL) cyclic AMP levels and their response to a T cell mitogen (PHA) were investigated. It was determined that although PGI2, PGD2, and PGE2 all elevate intracellular levels of cyclic AMP in HPBL, only PGD2 and PGE2 exert potent suppression of PHA-induced lymphocyte proliferation. It is suggested that the instability of PGI2 in aqueous solution is at least partially responsible for its relative inability to maintain elevated levels of cyclic AMP and concomitant suppression of mitogenesis. PGD2 was found to exert an effect very similar to PGE2, both in terms of cyclic AMP elevation and suppression of T cell mitogenesis.

Prostaglandin regulation of colony-stimulating factor production by lipopolysaccharide-stimulated murine leukocytes

The production of colony-stimulating factor by lipopolysaccharide-stimulated murine peritoneal leukocytes and their adherent subpopulations (greater than 80% macrophages) was markedly enhanced by indomethacin at concentrations sufficient to block prostaglandin E synthesis. Addition of physiological concentrations of E-series prostaglandins reversed this enhancing effect of indomethacin in a dose-dependent manner. These results indicate that colony-stimulating factor production by stimulated leukocytes is regulated by E-series prostaglandins and suggest that prostaglandins function to limit myelopoiesis by inhibiting colony-stimulating factor production and concomitantly the induction of cell proliferation.

Conversion of a stable T-cell lesion to a progressive B-cell lesion in the pathogenesis of chronic inflammatory periodontal disease: an hypothesis

Changes in the host's immunological response or, alternatively, changes in the oral microflora have been implicated as possible mechanisms by which a stable lesion of chronic inflammatory periodontal disease may become a progressive lesion leading to tissue destruction and tooth loss. It has recently been established that the progressive lesion in humans can be unequivocally considered as a B-cell response. Circumstantial evidence exists which suggests that the stable lesion is in fact a T-cell-mediated mechanism. An hypothesis is presented to explain the change from a stable to a progressive state in terms of a shift from a predominantly T-cell lesion to one involving large numbers of B-cells. Mechanisms of this shift in cell populations are considered together with a discussion of possible means of preventing such a shift.

Effects of prostaglandins E2 and I2 on human lymphocyte transformation in the presence and absence of inhibitors of prostaglandin biosynthesis

1 The reactivity of human peripheral blood mononuclear cells to phytohaemagglutinin ([3H]-thymidine incorporation) was enhanced in indomethacin- and eicosatetraynoic acid-treated cells compared with untreated cells, from normal volunteers. This suggests that endogenously synthesized prostaglandins have an inhibitory effect during cell preparation and/or culture. 2 Prostaglandin E2 inhibited [3H]-thymidine incorporation induced by suboptimal phytohaemagglutinin concentrations and had a more potent effect on indomethacin-treated cells than on untreated cells. 3 Prostaglandin I2 also exhibited an inhibitory effect and, under defined conditions, was more potent than prostaglandin E2 or than prostacyclin which had been allowed to decay at pH 7.4 and 37 degrees C. 4 These results indicate that, in attempting to define altered lymphocyte reactivity in disease states, the involvement of prostaglandins should be considered both during cell preparation and culture.

In vitro of adenosine on lymphocytes and erythrocytes from horses with combined immunodeficiency

The effect of adenosine on the mitogenic response of peripheral blood lymphocytes (PBL) and on the nucleotide pools of erythrocytes from normal horses, horses heterozygous for the combined immunodeficiency (CID) trait (carriers), and foals with CID was studied. When PBL from normal, carrier, and CID horses were stimulated by phytohemagglutinin (PHA), concanavalin A, or pokeweed mitogen, [3H]thymidine uptake was inhibited by adenosine (0.1 microM) to 1.0 mM) in a dose-dependent manner. Adenosine (100 microM) mediated inhibition of [3H]thymidine uptake was prevented in both normal and carrier horse PBL by incubation with uridine. Uridine had no sparing effect on PBL from horses with CID. Differences were detected between human and horse PBL in response to adenosine and erythro-9(2-hydroxy-3-nonyl) adenine (EHNA), a competitive inhibitor of adenosine deaminase. In the first assay, mitogen-stimulated PBL from horses were more sensitive to adenosine. In the second assay, adenosine was added to PBL cultures at various times after PHA addition. Adenosine inhibited mitogenesis in horse PBL if added within the first 24 h. In human PBL cultures, adenosine inhibited mitogenesis only if added within the first 4 h. The third assay measured capacity of PHA-stimulated human and horse lymphocytes to escape inhibition by adenosine or EHNA. At the end of a 72-h culture period, horse PBL were still inhibited of mitogenesis in both human and horse PBL. With prolonged incubation (72 h), synergistic inhibition was detected only in horse PB. With high-pressure liquid chromatography, nucleotide levels in erythrocytes of normal, carrier, and CID horses were found to be similar. Incubation with adenosine produced a 1.5- to 2-fold increase in total adenine nucleotide pools in erythrocytes from all horses. However, these increases were accompanied by alterations in the relative amounts of the nucleotide components. This was seen as a significant decrease in the ATP:(AMP plus ADP plus ATP) ratio and energy charge in erythrocytes from normal horses. In contrast, the ATP:(AMP plus ADP plus ATP) ratio decreased only slightly in erythrocytes from CID horses, whereas no change in the energy charge was detected. The data from these studies indicate a difference in adenosine metabolism exists between human and horse lymphoyctes, and an abnormality may exist in purine metabolism or in an interconnecting pathway in horses with CID.

Inhibition of guinea-pig lymphocyte activation by histamine and histamine analogues

1 The incorporation of [3H]-thymidine into guinea-pig lymphocytes stimulated by a plant lectin (concanavalin A), soluble antigen (tuberculin (P.P.D.)) and syngeneic hepatoma cells, was partially inhibited (50%) by histamine in vitro. 2 The effect of histamine on both mitogen and antigen dose-response curves suggests a non-competitive, probably physiological antagonism. 3 The inhibitory dose range of histamine lay between 10 nM and 30 microM with an ID50 of approximately 400 nM. 4 The potency order for histamine analogues for the inhibition of lymphocyte activation was histamine greater than or equal to 4-methylhistamine greater than 2-methylhistamine greater than 3-methylhistamine. This is in accord with the mediation of the response through an H2-receptor. 5 H2-receptor antagonists reversed the inhibitory effect of histamine in a dose-related manner, but both metiamide and burimamide, in high concentrations, augmented lymphocyte activation in their own right. This precluded the determination of affinity constants and made it impossible to state with certainty that the inhibition of lymphocyte activation by histamine was mediated by an H2-receptor.

Modulation of the adherence of human lymphocytes to measles-infected cells by prostaglandin E1: a differential effect on lymphocyte subpopulations

Prostaglandins of the E series (PGE) may serve as important regulators of human immune responsiveness. The present study was designed to examine the possibility that PGE may effect human lymphocyte function by the modulation of surface receptors. The presence of surface binding sites on human lymphocytes for measles virus antigens was studied using a rosette adherence assay. We observed that the addition of PGE1 increased the proportion of measles-infected cells (Hela-Kll) with adherent lymphocytes (75% increase at 3 x 10(-6) M PGE1). PGE was observed to enhance the adherence of purified normal peripheral T cells (87%) and T lymphoid cells (Molt 3) (27%). In contrast, no significant change in normal peripheral B cell or B lymphoid cell (Raji) adherence was observed with the addition of PGE. These results are consistent with a selective modulation of surface measles virus binding sites by PGE1 on T and not B lymphoid cells.

Adenylate cyclase in thymus-derived and bone marrow-derived lymphocytes from normal donors and patients with chronic lymphocytic leukemia

Lymphocytes were purified from peripheral blood of normal donors and patients with chronic lymphocytic leukemia (CLL) by Ficoll-Hypaque centrifugation. Adenylate cyclase activity, expressed as picomoles [(32)P]cyclic AMP generated per milligram protein per minute, was 57+/-4 in normals and 26+/-4 in CLL patients. Enzyme activity, expressed as picomoles [(32)P]cyclic AMP generated per 10(6) lymphocytes per minute, was 2.09+/-0.19 for normal lymphocytes and 1.10+/-0.16 for CLL lymphocytes. The differences between normal and CLL peripheral lymphocytes are highly significant (P < 0.001) with either method of calculating activity. Cyclic AMP levels (picomoles per 10(6) lymphocytes) also differed significantly: 1.38+/-0.29 for normals and 0.45+/-0.08 for CLL lymphocytes. Adenylate cyclase was assayed in lymphocytes enriched for bone marrow-derived (B) cells by removing E-rosetted thymus-derived (T) cells, and enriched for T cells by harvesting E-rosetted lymphocytes or by removing B cells with nylon wool absorption. Solutions to simultaneous equations gave the following calculated enzyme activities for pure B- and T-cell subpopulations (in picomoles [(32)P]cyclic AMP generated per milligram mg protein per minute): normal B, 196+/-22; normal T, 30+/-10; CLL B, 34+/-6; CLL T, 19+/-4. Thus. normal B-lymphocyte adenylate cyclase exceeds normal T-lymphocyte activity by more than sixfold, whereas in the case of CLL the enzyme activity in B lymphocytes is markedly reduced to levels comparable to T lymphocytes. The responses of lymphocytes to stimulation with the hormones prostaglandin E(1) and isoproterenol, and with NaF, were assessed. Compared with normal lymphocytes, enzyme activities were reduced in CLL lymphocytes incubated with these agents, but to a degree paralleling the reduced basal activities. Thus, the ratios between stimulated and basal adenylate cyclase levels in Ficoll-Hypaque-purified, normal lymphocytes were 2.3+/-0.1 after incubation with 10 muM isoproterenol, and 3.9+/-0.2 with 10 mM NaF, values which did not differ significantly from those obtained with CLL lymphocytes. When the enzyme activities calculated for purified T- and B-lymphocyte subpopulations were used to derive the stimulation ratios, the responses of normal and CLL T and B cells to these agents were also indistinguishable. The simplest explanation for these findings is a reduced number of normally responsive enzyme sites on the surface membranes of CLL lymphocytes, although alternative explanations are possible.

Inhibitory effect of cytokinins on PHA-induced human lymphocyte stimulation

The inhibitory effect of various purine derivatives on PHA-induced human lymphocyte blast formation was studied. Two nucleoside cytokinins, N6-benzyladenosine and N6-isopentenyladenosine, inhibited blast formation at concentrations as low as 10(-6) M. However, the other cytokinins, which lacked the ribosyl residue at N9 position, had to be at the higher molar concentration of 10(-4) before they could induce the same inhibitory effect.

Thymosin-induced suppression of proliferative response of human lymphocytes to mitogens

The proliferative response of human peripheral blood lymphocytes to phytohemagglutinin, concanavalin A, and pokeweed mitogen were suppressed by thymosin. Greatest decreases were observed when cells were preincubated with thymosin for 18 h before a 3-d culture with mitogen in the presence of thymosin. However, significant suppression also occurred when lymphocytes were preincubated for 2 h and cultured with thymosin or preincubated for either 2 or 18 h and washed free of thymosin before culture. These effects were related to the concentration of thymosin and time of exposure to thymosin but not merely to a delay in the response to mitogen or to toxicity. The suppression of mitogen-induced proliferation by thymosin appeared to result from effects of thymosin on a suppressor cell because lymphocytes incubated with thymosin did not acquire increased responsiveness to mitogens as did cells incubated for 18 h in its absence and because mixing thymosin-pretreated lymphocytes with cells not preincubated with thymosin resulted in decreased responsiveness to photohemagglutinin.

Adenosine-adenosine deaminase modulation of histamine release from human basophils in vitro

Since extracellular adenosine is a physiologically important regulator of adenylate cyclase and cell function in various mammalian tissues, we have examined the effect of adenosine on histamine release from human basophils. Adenosine inhibited IgE-mediated histamine release by its ability to increase leukocyte cyclic AMP levels; the same concentrations of adenosine which inhibited histamine release increased the cyclic AMP level of mixed leukocytes. Inhibition of histamine release was also observed with an adenosine deaminase (ADA) inhibitor [erythro-9-(2-hydroxy-3-nonyl)-adenine: EHNA] in the presence of autologous serum. We suggest that the adenosine-ADA system normally modulates histamine release and that this contributes to the severe combined immune deficiency (SCID) associated with a lack of ADA.

Initiation-promotion skin carcinogenesis: inhibition by cyclic and non-cyclic nucleotides

The effect of nucleotides on initiation-promotion skin carcinogenesis in Swiss mice was investigated. Cyclic AMP was given before initiation with DMBA, between initiation and promotion, and at the same time as promotion with croton oil. Cyclic AMP was more effective in inhibiting tumor development when injected at the same as promotion with croton oil. 5'-adenosine-monophosphate (5'-AMP) and cyclic GMP were as effective as cyclic AMP in inhibiting tumor development under these conditions. However, adenosine, dibutyryl-cyclic AMP and 5'-guanosine-monophosphate (5'-GMP) were ineffective.

Prostaglandin effect on lymphokine production in multiple sclerosis

Production of the lymphokine LIF (leukocyte migration inhibitory factor) by normal lymphocytes on stimulation with mitogens in inhibited by E type prostaglandins (PGE). It has been reported that the leukocytes of patients with multiple sclerosis (MS) are resistant to this inhibitory effect. We have studied 10 MS patients using an indirect technique for measuring LIF activity. This allows separation of the effects of PGE on lymphocyte LIF production from the effects on the action of LIF on the target granulocytes. There was no difference between normal subjects and MS patients in the effects of prostaglandins E1 and E2 in concentrations of 2.5 and 0.25 microgram per milliliter, on LIF production, or on granulocyte response to LIF. These results do not support the hypothesis that the chronic inflammatory process in MS is the result of resistance to the normal inhibitory effects of PGE on the cellular immune response.

Augmentation of the in vitro humoral immune response by pharmacologic agents. II: comparison of the effects of antiproliferative agents with DBcAMP

We have compared the stimulatory activity of DBcAMP with various antiproliferative agents on the induction of the humoral immune response. When they are present only during an early stage of immune induction, DBcAMP, colcemid, cytosine-arabinoside, hydroxy urea, and high specific activity 3H-thymidine can all enhance the primary 19s antibody response to SRBC. In contrast, each of these agents inhibits the PFC response, when they are incubated with the cells during late stages of induction of humoral immunity. Because all of these agents can inhibit proliferation of cultured cells, the results suggested that DBcAMP and other agents that elevate cAMP could augment humoral immunity via their effects on cellular proliferation. However, we also found that although each agent could modulate induction of the immune response to SRBC, only DBcAMP produced a dose- and time-dependent augmentation of the response to DLF. We conclude that although antiproliferative effects of drugs may contribute to augmentation of some humoral antibody responses, this effect alone is insufficient to account for the mechanism by which agents that elevate intracellular levels of cAMP produce enhancement of humoral immunity.

In vivo and in vitro effects of thymosin and adenosine deaminase on adenosine-deaminase-deficient lymphocytes

Two siblings with adenosine deaminase deficiency were studied before and during "enzyme replacement" therapy (partial exchange transfusions with normal red cells containing the missing enzyme). The younger sib showed improvement of immunologic function during red-cell therapy alone, whereas in the older sib this improvement occurred only when the transfusions were supplemented by thymosin injections. Their clinical courses correlated with in vitro findings: lymphocytes from the younger sib differentiated to T-cell-rosette-forming cells upon addition of adenosine deaminase alone; lymphocytes from the older sibling required supplemental thymosin to form these cells. Thymic factors appear to influence the response to transfusion therapy in some patients deficient in adenosine deaminase, and supplementation of red-cell transfusion with thymic factors may be required.

Cyclic nucleotides in joint fluid in rheumatoid arthritis and in Reiter's syndrome

Levels of cyclic adenosine 3',5'-monophosphate (cAMP) and cyclic guanosine 3',5'-monophosphate (cGMP) have been investigated in joint fluid in inflammatory arthropathies. A disturbed balance between cAMP and cGMP due to a depressed level of cAMP was found in rheumatoid arthritis (RA) and Reiter's syndrome, in comparison with patients with osteoarthritis. No correlation could be demonstrated between the absolute levels of cAMP or cGMP and the degree of local inflammatory activity, white cell count, or lysosomal enzyme activity in the joint fluid. Intra-articular injection of epinephrine showed just as good an effect on local pain as betamethasone (Cellestona), but the steriod reduced the swelling more effectively. An increase in intracellular levels of cAMP at 20 min was observed following injection of epinephrine with a slight change in cGMP. Intra-articular injection of dibutyryl-cAMP (db-cAMP) produced a marked easing of local pain and swelling in each of the 4 patients so treated. It is concluded that stimulation of the beta-adrenergic system or injection with db-cAMP may be beneficial in rheumatoid inflammation.

Effect of frentizole on mitogen-induced blastogenesis in human lymphocytes

Frentizole is a new immunoregulatory agent developed as an alternative to cytotoxic agents. In human lymphocytes, Frentizole inhibits the response to various phytomitogens without decreasing cell viability. Frentizole (500 ng/ml) inhibited thymidine incorporation into DNA most effectively when added to lymphocyte cultures at the same time as the addition of the mitogen. Frentizole (500 ng/ml) markedly inhibited the response to Con A (% inhibition, corporation was dose dependent with 125 ng/ml of Frentizole sufficient to inhibit significantly the response of all three mitogens. Frentizole (62.5 ng/ml) maximally inhibited uridine incorporation, and inhibition of uridine incorporation was independent of the phytomitogen employed. Increasing concentrations of Frentizole were found to have no effect on thymidine or uridine incorporation into unstimulated normal lymphocytes.

The effect of prostaglandin E1 or E2 on the in vitro blastogenic response of lymphocytes from normal and tumor-bearing mice

The in vitro effect of exogenously added prostaglandin (PG) E1 or E2 over concentrations ranges of from 1 X 10(-4) to 1 X 10(-9) M were studied in order to determine their effect on the in vitro lymphocyte proliferation of thymic and splenic T and B cells from normal and tumor-bearing CD2F1 mice. It was found that PGE1 generally caused greater inhibition of blastogenesis than did PGE2 when reacted with splenic lymphocytes from normal mice. Indeed, PGE2 was found to be stimulatory for both Con A- and LPS-sensitive normal splenic lymphocytes. Both PGE1 and PGE2 caused potent inhibition of Con A- and PHA-sensitive splenic lymphocytes from the tumor-bearing mice. Additionally, PGE2 was found to stimulate the LPS-reactive lymphocytes from the tumored mice. PGE1 and PGE2 both inhibited the Con A- and PHA-reactive thymic lymphocytes from normal mice at the lower concentrations studied, i.e., 10(-4) to 10(-6) M. Thereafter, at concentration ranges of from 10(-7) to 10(-9) M both PGE1 and PGE2 were both found to be stimulatory. Finally, both PGE1 and PGE2 at all concentrations studied, strongly inhibited the thymic lymphocytes from tumored mice.

Prostaglandin suppression of mitogen-stimulated lymphocytes in vitro. Changes with mitogen dose and preincubation

In this study we further characterize the properties of the prostaglandin-producing suppressor cell. Overnight preincubation of peripheral blood mononuclear cells results in an increased response of the cells to phytohemagglutinin or Concanavalin A compared to the response of fresh cells. This increase in mitogen response with preincubation was similar in magnitude to the increase in mitogen response of fresh cells after the addition of indomethacin. The two manipulations were not additive; that is, after preincubation, indomethacin caused much less enhancement of mitogen stimulation of peripheral blood mononuclear cells (100 +/- 12% increase before preincubation vs. 12 +/- 6% after preincubation; mean+/-SEM, P < 0.001). Preincubated cells also lose sensitivity to inhibition by exogenous prostaglandin E(2). It requires the addition of 100- to > 1,000-fold more exogenous PGE(2) to produce comparable inhibition of phytohemagglutinin-stimulated preincubated cells than is required for inhibition of phytohemagglutinin-stimulated fresh cells. The enhancing effect of indomethacin increases with decreasing doses of phytohemagglutinin. Indomethacin causes a 1,059+/-134% increase in [(3)H]thymidine incorporation at the lowest dose of phytohemagglutinin (0.2 mug/ml), and a 4+/-3% increase at the highest dose (20 mug/ml). This increase in response to indomethacin with a lower dose of phytohemagglutinin is due to increased sensitivity to inhibition by PGE(2) at lower mitogen doses. The prostaglandin-producing suppressor cell assay and the short-lived suppressor cell assay measure over-lapping phenomena. The increased suppressive effect of the prostaglandin-producing suppressor at suboptimal mitogen dose must be taken into account in the interpretation of any study where the response to a range of mitogen doses is studied.

Prostaglandins as regulators in cellular immunity

Guinea-pig peritoneal macrophages have been shown to generate substantial concentrations of E-type prostaglandins during culture in vitro. Partially purified lymphokine preparations stimulate PGE production by macrophages. Exogenous PGE1 and PGE2 are potent inhibitors of lymphocyte activation and secretion of lymphokines causing lymphocyte mitogenesis and macrophage migration inhibition. Also indomethacin augments the secretion of these lymphokines in vitro. It is therefore suggested that production of PGE by macrophages provides a physiological mechanism for the regulation of lymphocyte activation in reactions of delayed hypersensitivity.

Effect of cyclic nucleotides, isoproterenol and cholera toxin on DNA synthesis triggered by mitogens

The effect of cyclic nucleotides, isoproterenol and cholera toxin on phytohaemagglutinin (PHA), concanavalin A (Con A) and anti-allotype-induced rabbit lymphoid cell proliferation was examined. Cholera toxin in concentrations ranging from 10(-8) microgram to 1 microgram per culture inhibited DNA synthesis, triggered by PHA, Con A and nocardia water-soluble mitogen (NWSM). It had the opposite effect on stimulation with antibodies directed against allotypic specificities of the immunoglobulin light chains: over the entire range of tested concentrations, cholera toxin stimulated DNA synthesis triggered by antibodies to Ab4, Ab5, Ab9 and to Aa1 allotypic specificities. Relatively high concentrations of dibutyryl adenosine 3':5'-cyclic monophosphate (cAMP) and isoproterenol (10(-3) M) inhibited mitogen-stimulated thymidine incorporation; lower concentrations (10(-9) M) had an enhancing effect. A similar enhancing effect was observed when high (10(-3) M) concentrations of dibutyryl guanosine 3':5'-cyclic monophosphate (cGMP) were used.

Rise and fall of cyclic AMP required for onset of lymphocyte DNA synthesis

The adenosine 3',5'-monophosphate (cyclic AMP) levels of mouse lymphocytes rose and fell sharply 10 hours after stimulation with concanavalin A. Treatment of the cells with indomethacin reversibly prevented the increase in cyclic AMP and the subsequent onset of DNA synthesis. When the heightened cyclic AMP before S phase was maintained by either inhibiting phosphodiesterase or by adding the 8-bromo derivative of cyclic AMP, DNA synthesis was also blocked. Both the increase and decrease in cyclic AMP appear to be required for progression of lymphocytes into the S phase of growth.

Effect of cyclic nucleotides on mitogen. Responsiveness of lymphocytes from patients undergoing dialysis

Lymphocytes from 10 asymptomatic patients undergoing hemodialysis and from eight control subjects were repeatedly cultured with exposure to various concentrations of cyclic nucleotides and theophylline in addition to mitogen. The blastogenic response of the patients' lymphocytes was inhibited by molar concentrations of dibutyryl cyclic AMP which had much less or no inhibitory effected on the response of the control subjects' lymphocytes. This suppressive effect was not potentiated by theophylline. Cyclic GMP enhanced the proliferative response of the patients' lymphocytes as well as that of the controls. In contrast to absolute counts per minute per culture, the suppression by dibutyryl cyclic AMP of mitogen-induced blastogenesis noted in this study clearly separated the in vitro behavior of the patients' lymphocytes from that of the controls' lymphocytes and may serve as a useful marker of cellular dysfunction in such patients.

The effects of dibutyryl cyclic adenosine 3':5'-monophosphate on concanavalin A-stimulated sterol and fatty acid synthesis in mouse spleen lymphocytes

Substantial increases in both 3beta-OH sterol and fatty acid synthesis were observed after concanavalin A addition to mouse spleen lymphocytes cultured in serum-free media. The rate of sterol synthesis increased linearly up to 60 h. The rate of fatty acid synthesis increased up to 20 h, reaching a plateau in synthetic activity which was the maintained. CO2 production from acetate was slightly stimulated by concanavalin A. In contrast to sterol and fatty acid synthesis, the rate of CO2 production in both mitogen-stimulated and resting cultures declined with time. Dibutyryl cyclic AMP had a strong inhibitory effect on concanavalin A-stimulated sterol and fatty acid synthesis from acetate, but only a slight effect on CO2 production. Delayed addition of dibutyryl cyclic AMP resulted in reduced inhibition. The data suggest a sequence of initiation for fatty acid and sterol synthesis prior to DNA synthesis and a possible regulatory role of cyclic AMP in this initiation. The results support the hypothesis that lymphocyte activation is sequential within the spleen cell population and is accompanied by fatty acid and sterol synthesis.

Prostaglandin E and mitogenic stimulation of human lymphocytes in serum-free medium

Sera used in cell cultures contain significant ammounts of prostaglandins (PGs). In order to avoid any effects of contaminating PGs, the present study employed a serum-free culture medium and confirmed the inhibitory effect of prostaglandin E (PGE) on the human lymphocyte activation which had been observed previously employing a serum-containing medium. PGE1 displayed a significantly stronger inhibitory effect on the cells than previously shown. Furthermore, reported enhancement of PGE synthesis by mitogen-activated lymphocytes could not be reproduced.

Prostaglandin E production by human blood monocytes and mouse peritoneal macrophages

Purified populations of both human peripheral blood monocytes and murine peritoneal macrophages synthesize and release Prostaglandin E in vitro. In contrast, prostaglandin E was detected in neither the supernate fluids from cultures of highly enriched human lymphocytes and granulocytes, nor in nonadherent murine peritoneal cells. Macrophage prostaglandin E production was markedly enhanced by endotoxin, and completely suppressed by indomethacin. All neoplastic monocyte-macrophage cell lines examined elaborated prostaglandin E in vitro, either constitutively or after induction with endotoxin. In contrast, prostaglandin E production could not be detected from either a T- or B-cell lymphoma, whether or not they were treated with endotoxin. These findings thus indicate that the blood monocyte and tissue macrophage represent an important source of prostaglandin E, a function shared by both normal and neoplastic mononuclear phagocytes.

Prostaglandin E inhibition of mitogen stimulation in patients with multiple sclerosis

Kirbey et al have reported that leukocyte function from patients with multiple sclerosis is not suppressed by PGE2, as are normal leukocytes. We examined the ability of PGE2 (0.01-0.5 microgram/ml) to suppress Phytohemagglutinin induced 3H-thymidine incorporation in peripheral blood lymphocytes from multiple sclerosis patients and normals. There was no difference in sensitivity between the two groups. There was also no difference in activity of the prostaglandin producing suppressor cell between the multiple sclerosis patients and controls.