Regulatory substances produced by lymphocytes--VII. IDS (inhibitor of DNA synthesis) inhibits stimulated lymphocyte proliferation by activation of membrane adenylate cyclase at a restriction point in late G1

Cyclic adenosine monophosphate regulates the expression of the intercellular adhesion molecule and the inducible nitric oxide synthase in brain endothelial cells

The authors studied whether cyclic AMP (cAMP), a widespread regulator of inflammation, modulates the cytokine-mediated expression of the intercellular adhesion molecule, intercellular adhesion molecule-1 (ICAM-1), and the inflammatory nitric oxide synthase 2 (NOS-2), in primary and immortalized brain endothelial cell cultures (GP8.3 cell line). When measured by enzyme-linked immunosorbent assay (ELISA), ICAM-1 was constitutively expressed and was up-regulated twofold by interleukin-1beta, with no effect of interferon-gamma. The NOS-2 activity, assessed by nitrite accumulation, was absent from untreated cultures but was induced by interleukin-1beta and interferon-gamma acting synergistically. Stimulation of cAMP-dependent pathways with forskolin or dibutyryl cAMP decreased ICAM-1 protein expression, whereas it increased NOS-2 protein expression. For both ICAM-1 and NOS-2, mRNA expression correlated with protein expression. Blockade of NOS activity with L-N-monomethylargiuine (L-NMMA) did not alter ICAM-1 expression, indicating that the nitric oxide released by NOS-2 did not cause the down-regulation of ICAM-1. Analysis of NFKB activation indicated that cAMP acted through a mechanism other than inhibition of nuclear translocation of NFKB. The authors conclude that cAMP modulates the expression of proinflammatory molecules in brain endothelium. This suggests that inflammatory processes at the blood-brain barrier in vivo may be regulated by perivascular neurotransmitters via cAMP.

In vitro and in vivo anti-leukemic efficacy of cyclic AMP modulating agents against human leukemic B-cell precursors

We show that the adenylate cyclase activating diterpine, forskolin, the phosphodiesterase inhibitor, aminophylline, and the permeant cAMP analog dibutyryl cAMP inhibit the in vitro clonogenic growth of leukemic B-cell precursors. We also used a SCID mouse xenograft model of refractory human B-cell precursor leukemia to evaluate the anti-leukemic effect of aminophylline in vivo. Treatment with aminophylline (6 mg/kg bolus followed by 0.1-0.5 mg/kg/hour x 7 days) significantly prolonged the event-free survival of SCID mice (median survival of control mice, 39 days, N = 79; median survival of aminophylline-treated mice, 60 days, N = 10; P < 0.0001 by log-rank test) and it was more effective than treatment with vincristine (median survival = 51 days, N = 5) or L asparaginase (median survival = 44 days, N = 5). However, aminophylline was not as effective as methylprednisolone (median survival: 103 days, N = 5). These results indicate that cAMP modulating agents may be useful in treatment of refractory human B-cell precursor leukemia.

Human nonspecific suppressive lymphokines

Since the term "lymphokine" first appeared in print over 20 years ago, a tremendous number of these soluble mediators of the immune system have been described. Within the past few years, many human nonspecific suppressive lymphokines have been identified. This review discusses the historical basis of immunologic suppression and suppressor factors. Later reports describing suppressive human lymphokines are then grouped into four categories: primarily stimulatory lymphokines that also mediate certain suppressive activities, suppressive lymphokines produced during altered states of immunity, suppressive lymphokines produced by exogenously stimulated lymphocytes, and suppressive lymphokines produced by unstimulated lymphocytes. Recent work I have been involved in focusing on the human suppressive lymphokine soluble suppressor factor (SSF) is also discussed.

Purinergic modulation of T-lymphocyte activation: differential susceptibility of distinct activation steps and correlation with intracellular 3',5'-cyclic adenosine monophosphate accumulation

The mechanism by which purinergic agonists modulate murine T-lymphocyte activation and proliferation was investigated. Adenosine and other compounds such as ATP and 2-chloroadenosine (ClAdo) were found to block T-cell mitogenesis induced by concanavalin A (Con A) in a dose-dependent fashion. The nonmetabolizable adenosine analog ClAdo was the most potent agent capable of inhibiting T-cell mitogenesis. Extracellular addition of the permeable cAMP analog dibutyryl cyclic AMP (dbcAMP) also led to a dose-dependent blockade of T-cell mitogenesis, although with less efficiency when compared to ClAdo. Addition of IL-2-enriched fluids failed to reverse blockade of T-cell mitogenesis by ClAdo or dbcAMP. ClAdo blocked T-cell enlargement induced after 20 hr of culture with Con A. We analyzed the effect of micromolar concentrations of ClAdo on interleukin-2 (IL-2) production, expression of IL-2 receptors (7D4 and 3C7 surface antigens), and induction of IL-2 responsiveness after in vitro cultivation with Con A. ClAdo inhibited both IL-2 secretion and induction of IL-2 responsiveness up to control levels in the same dose range it inhibited T-cell mitogenesis. However, cell surface expression of IL-2 receptors was not affected. Short incubations of resting splenic T cells with ClAdo led to a dose-dependent accumulation of cyclic AMP in responding cells. This effect was markedly reduced by the purinergic antagonist 3-isobutyl-1-methylxanthine (IBMX) but was not prevented by the adenosine uptake blocker dipyridamole. ClAdo elicited cAMP accumulation in the same dose range it inhibited T-cell activation events. Extracellular administration of dbcAMP to splenic T cells stimulated by Con A mimicked the effects of ClAdo on T-cell activation parameters, as revealed by a dose-dependent blockade of both IL-2 secretion and IL-2 responsiveness induction, without affecting IL-2 receptor expression. Short incubations of Con A-activated T-cell blasts with ClAdo also led to a dose-dependent accumulation of cAMP. We then analyzed the effect of purines and dbcAMP on IL-2-mediated activated T-cell growth. Purines caused a dose-dependent inhibition of IL-2-mediated T-cell proliferation and ClAdo was the most potent purinergic agonist tested. The effect of ClAdo on Con A-induced T blasts was shifted to the right, if compared to earlier T-cell activation steps.(ABSTRACT TRUNCATED AT 400 WORDS)

External malformations in chick embryos following concomitant administration of methylxanthines and beta-adrenomimetic agents: 1. Gross pathologic features

The objectives of this report are to document external malformations observed in chick embryos following concomitant administration of methylxanthines (caffeine, theophylline) and beta-adrenomimetic agents (isoproterenol, epinephrine) and to suggest reasonable explanations for the anomalies. Administration of caffeine or theophylline alone (2.5-5.0 mg/egg) retarded growth in a dose-dependent fashion. Doses of 5.0 mg caffeine and theophylline produced beak malformations in 4.9% and 57.1% of embryos, respectively. Limb malformations, seen in low frequency (3.6% in 56 embryos) after administration of 1 microgram isoproterenol, were not seen in 224 methylxanthine-treated embryos. Structural defects following coadministration of methylxanthines and beta-adrenomimetics were frequently observed in limbs (primarily lower limbs with predilection for left-sided oligodactyly) and beak. Other findings included limb hematomas, hygromas in the nuchal region, and prominent generalized edema. The most dramatic effects observed in this study were those induced by concomitant administration of 2.5 mg caffeine and 1 microgram isoproterenol. This combination produced at least one of the embryopathies listed above in 87.9% of treated embryos and frequently induced beak (24.2%) and lower limb defects (75.8%) in addition to nuchal hygromas (9.1%). Similar severe malformations were observed following administration of 3.8 mg theophylline with 1 microgram epinephrine. Embryos that died within 12-48 hours following drug insult demonstrated marked cardiac dilation, apparently due to congestive heart failure. The results of this study suggest that methylxanthines and beta-adrenomimetic agents are synergistic in their action in the developing chick. Doses of alpha-adrenomimetic agents that were used in this study were not synergistic with methylxanthines. Increased intracellular cyclic adenosine monophosphate (AMP) is offered as an explanation for digital anomalies due to inhibition of proximodistal development of limbs. Increased intracellular cyclic AMP may also explain limb hypoplasia and loss of intermediate limb structures as a result of inhibited mitosis and/or necrosis of embryonic tissue.

Effects of beta-adrenergic agents on the murine lymphocyte response to mitogen stimulation

The presence of beta-adrenergic receptors on murine lymphocytes has recently been demonstrated (8). beta-adrenergic agonists and antagonists have been found to alter the murine lymphocyte's response to either Concanavalin A or Lipopolysaccharide B. The regulation of the response to Concanavalin A or Lipopolysaccharide B by these beta-adrenergic ligands is most effective if the beta-adrenergic ligand is added within one hour of the addition of mitogen and at concentrations greater than 1 x 10(-7) M. The possibility that adrenergic modulation of the lymphocyte response may be beta-receptor mediated is supported by the observation of competition between adrenergic agonists and antagonists.

Immunosuppressive lymphocyte factors: characterization of the IDS-producing cell in the experimental model of antigenic competition

Inhibitor of DNA synthesis, is a soluble, protein lymphocyte factor which nonspecifically suppresses in vitro lymphocyte responses to antigens or mitogens. It is secreted in large amounts in vivo in some experimentally induced immunological paralysis. Here, we have defined the cell secreting IDS in one experimental model of non-specific immune-suppression, ie., that of antigenic competition. Lymphocytes of rats injected with a large dose of ovalbumin intravenously, show no immunologic response to the same or other antigens or mitogens 24 hr later. At this time, spleen cells of these rats secrete large amounts of the inhibitor into culture supernatants. However spleen cell supernatants of T-depleted rats do not contain the activity. Further, maximal inhibitor concentrations are obtained in the first 2 days of culture when more than 65% of cultured cells are large blasts actively synthesizing protein. As the number of actively metabolizing blast cells decrease in subsequent days of culture inhibitor concentration falls. Finally thymocytes of rats pretreated with hydrocortisone acetate, to deplete thymus cortex cells are unable to secrete inhibitor in culture. These findings reveal that the cells producing inhibitory DNA synthesis in an animal made tolerant with a supra-optimal dose of antigen is an active blast transformed T cell (present in the spleen and thymus). In the thymus the cell making inhibitor appears to reside in the thymus cortex. Previous experiments have confirmed that an identical cell causes nonspecific immune-suppression in vitro. We suggest that this cell produces in vivo tolerance in antigenic competition through the release of inhibitor to DNA synthesis.