Prostaglandins as regulators in cellular immunity

Recent research and developmental strategy of anti-asthma drugs

Extensive research over the past decade has provided information about the pharmacotherapy of bronchial asthma (BA). Anti-asthma drugs are classified into two categories: relievers (for the relief of asthma attack symptoms) and controllers (for the prevention of asthma symptoms). This paper aims to review the recent advancements of anti-asthma drugs that are controller medicines. The controllers mainly act on immune and inflammatory responses in BA development. 1) Immunomodulators. Drugs that act on the immune response are classified into two categories: immunosuppressors and immunomodulators, including immunopotentiators. The immunomodulation of the Th1 and Th2 imbalance is the first strategy of the controller because allergic BA is thought to be caused by Th2-polarized immunity. Suplatast is a novel immunomodulator that can adjust the imbalance in the Th1/Th2 immune response and shows clear clinical efficacy against BA. The immunomodulator approach has shifted from a more theoretical and conceptual model to one supported by evidence of clinical efficacy.2) Anti-inflammatory agents. Corticosteroids,mast cell stabilizers and autacoid inhibitors are anti-inflammatory agents for BA. The clinical superiority of the combined therapy of inhaled corticosteroids and long-acting beta2 agonists is evident. This combined therapy shows a potent synergic anti-inflammatory effect compared to the effect by corticosteroids alone. Currently, the anti-inflammatory agents for BA under development are drugs affecting lipid mediators. The prostaglandin (PG) D2 antagonist, PGE2, EP3 agonist and PGI2 agonist are being considered in addition to well-established leukotriene and thromboxane A2 inhibitors. New development strategies and therapeutics for controllers are described in this review.

Vitamin E and immunity

Vitamin E is a potent antioxidant and has an ability to modulate host immune functions. This chapter consists of five parts: (1) vitamin E deficiency and immunity, (2) vitamin E supplementation and immunity, (3) vitamin E and the decreased cellular immunity with aging, (4) vitamin E and T-cell differentiation in the thymus, and (5) vitamin E and acquired immune deficiency syndrome (AIDS). In vitamin E deficiency most of the immune parameters show a downward trend, which is associated with increased infectious diseases and the incidence of tumors. In contrast, vitamin E supplementation has various beneficial effects on the host immune system. The decreased cellular immunity with aging or during the development of AIDS is markedly improved by the intake of a high vitamin E diet. In addition, vitamin E plays an important role in the differentiation of immature T cells in thymus. Vitamin E deficiency induces the decreased differentiation of immature T cells, which results in the early decrease of cellular immunity with aging in spontaneously hypertensive rats. Conversely, vitamin E supplementation induces a higher differentiation of immature T cells via increased positive selection by thymic epithelial cells, which results in the improvement of decreased cellular immunity in the aged. Furthermore, vitamin E supplementation induces the early recovery of thymic atrophy following X-ray irradiation. Taken together, these results suggest that vitamin E is an important nutrient for maintaining the immune system, especially in the aged.

Augmentation of antigen-specific lymphoproliferative responses in vitro by biological response modifiers

The detection of antigen-specific T cell responsiveness, particularly of resting memory lymphocytes, in cultures of peripheral blood mononuclear cells (PBMC) may be hampered by a less than optimal antigen presentation in vitro. Augmented sensitivity of the test system may be achieved by the addition of reagents with a beneficial effect on lymphocyte and antigen-presenting cell (APC) functions. In this study the effect of several biological response modifiers on antigen-specific T cell proliferation was determined, using nickel sulphate and tetanus toxoid as test antigens. IL-1 alpha (100 U/ml), interferon-gamma (IFN-gamma) (10 U/ml), and indomethacin (2 microM) were found to significantly enhance nickel-induced proliferation in PBMC cultures from nickel-hypersensitive donors (n = 6). Tetanus-induced proliferation (n = 5) was similarly enhanced, both by the above supplements and by the addition of polyethylene glycol (PEG) or a neuraminidase treatment of the PBMC before culture. The addition to PBMC cultures of a combination of IL-1 alpha (30 U/ml), IFN-gamma (10 U/ml), and indomethacin (2 microM) is recommended to specifically enhance antigen-induced lymphoproliferative signals.

Immune response developing in tumorous organism as a result of immunotherapy. Chance of recovery?

S-allylgutimine has immunostimulant and tumor cell inhibitory activities. This complex action may be a result of the stimulation of IL-2 production. The effectiveness of immunotherapy depends on the uncoupling of IL-2 downregulation. This principle can be widely used with those immunological diseases where IL-2 level is decreased through downregulation. The Kokonov reaction, which was used originally to indicate tumors, is presumably a marker of immunoreactivity. According to one hypothesis no specific antigen can be found on the surface of neoplastic cells but another type, 'weak antigen' appears, which originates from the alteration of a cell surface glycoprotein beta 1-6 saccharide chain branching that is directly related to the increased immune reactivity. The inhibition of downregulation enhances the elimination of neoplastic cells whose membrane surface glycoproteins are altered.

Cyclic AMP-mediated modulation of immunoglobulin production in B cells by prostaglandin E1

We had previously demonstrated in a transformed human B cell line, LA350, the existence of an inverse relationship between cyclic adenosine monophosphate (cAMP) content and immunoglobulin secretion using the cAMP-elevating agents such as cholera toxin and forskolin. In this paper we report that cAMP acting as a second messenger for prostaglandin exerts a similar effect on the antibody response of B lymphocytes. Incubation of the cells with PGE1 in the presence of the phosphodiesterase inhibitor isobutylmethylxanthine (IBMX) produced a concentration- and time-dependent elevation of intracellular cAMP. Significant increases of cAMP production were observed at physiologically relevant levels of PGE1 (10(-7) and 10(-8) M). Immunoglobulin production, whether measured as the total number of immunoglobulin-secreting cells by a reverse hemolytic plaque assay or as specific immunoglobulin production (IgM) by an enzyme-linked immunoadsorbent assay, was suppressed in a dose-dependent fashion by the presence of IBMX. This suppression of immunoglobulin production was significantly enhanced by the presence of PGE1. Phorbol myristate acetate-induced IgM production was also inhibited by the presence of PGE1. These results imply that prostaglandins regulate B cell activation and immunoglobulin production by signal transduction mechanisms involving cyclic nucleotides.

Characterization and purification of an immunosuppressive factor produced by a small cell lung cancer cell line

The present study was undertaken to determine whether small cell lung cancer (SCLC) cell lines produce immunosuppressive factors and, if they do, to characterize the factors. The supernatants of SCLC cell lines, H69 and N857, inhibited not only the blastogenic response of human peripheral blood lymphocytes (PBL) to phytohemagglutinin or concanavalin A, but also the cytotoxic activity of lymphokine-activated killer cells. Neither was inhibited by supernatants from non-SCLC cell lines PC9, QG56, and A549. The immunosuppressive activity of H69 supernatant was stable upon heating to 56 degrees C for 60 min, but labile when heated to 70 degrees C for 10 min. The activity was abolished after dialysis at pH 2.0 or pH 11.0, but not at pH 4.5 or pH 9.0. Digestion with trypsin or proteinase eliminated the immunosuppressive activity, whereas treatment with neuraminidase, mixed glycosidase, DNase or RNase had no effect, suggesting that the immunosuppressive activity in H69 supernatant is due to a protein factor. This H69-derived immunosuppressive factor was isolated by ion exchange chromatography using a gradient of 0.04 to 0.08 M NaCl solution. Gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed the factor to have molecular weights of 98 kD and 102 kD, respectively. These results suggest that SCLC cells produce a potent immunosuppressive factor which may account for the immune deficiency in SCLC patients.

Indomethacin increases the sensitivity of the monocyte migration inhibition assay

In ophthalmo-immunological investigations only small samples of ocular tissues and fluid are available and assays which are feasible with very small volumes or cell numbers are mandatory. Indomethacin, which is known to augment the immune response both in vivo and in vitro was therefore tested for its effect on the monocyte migration inhibition (MIF) assay using low cell or antigen doses. The sensitivity of the MIF assay may be greatly increased by adding indomethaci during the first step of the assay. Titration of either the antigen dose, the mononuclear cells number or both per assay, resulted in a 10-50-fold increase in sensitivity of the assay, with a broad inter-individual variability. Increasing the sensitivity of the MIF assay with indomethacin has clear advantages with regard to the number of cells required but also confronts us with a new problem: activation of specific cells that circulate at very low frequencies in non-immunized individuals. The enhanced response could be reversed to some extent by adding prostaglandin E2 together with indomethacin to the first step of the assay. Moreover, adding leukotriene B4 to the first step of the assay had an enhancing effect over a limited concentration range. We conclude that in the presence of indomethacin, the MIF assay provides a highly sensitive technique for the demonstration of cellular immune responses in small samples of biological fluids containing very small numbers of antigen-specific lymphocytes.

A review of mechanism of action of aspirin and its potential as an immunomodulating agent

The basic aspects of PG immune function interactions are presented and discussed herein. Specifically, the findings of many of the studies summarized suggest the possibility that pharmacologic actions of aspirin may play a role in enhancing the immune response to viral infections. Mechanisms proposed for ASA include: PG inhibition via the cyclooxygenase pathway, an interaction with cyclic nucleotides, altered cellular interactions with PG's, altered leukocyte migration, activation of complement components, stimulation of monocytopoiesis, and induction of interferon. Since dual effects for ASA have been observed for several of these mechanisms, it is clear that its role in modulating the immune response to viral infections is very complex. This delineation of a role for ASA, that would seem to constitute a defense against viral infections leads to an area worthy of study and surveillance.

The role of arachidonic acid metabolites in mononuclear phagocytic cell interactions

Numerous investigations support the theory that arachidonic acid metabolites play a critical role in dictating the progression of chronic immune reactions. With regard to macrophage-mediated inflammatory responses, enzymatic oxygenation of arachidonic acid via the lipoxygenase or cyclooxygenase pathway can result in the production of compounds that may potentiate or suppress the inflammatory lesion. We recently have presented data demonstrating that lipoxygenase derived leukotriene B4 and C4 can induce the release of IL-1 by macrophages, while PGE2 and PGI2 can suppress the production of IL-1. Macrophages are central to the induction of immune responses and the progression of chronic inflammatory reactions. Therefore, an understanding of the role that macrophage-derived arachidonic acid metabolites play in the initiation, maintenance, and resolution of chronic immune responses is essential. As shown in Figure 3, there are a number of chemical signals that occur between macrophages and lymphocytes that are critical for immune cell communication. The investigations described above have demonstrated that the macrophage may regulate the production and expression of any or all of these signals, such that the inflammatory response is potentiated, sustained, suppressed, or resolved. A better comprehension of the activity of these potent arachidonate derivates will undoubtedly aid in the therapeutic manipulation of inflammatory disease.

Nonsteroidal anti-inflammatory drugs and immunologic function. Overview of the European experience

A large number of nonsteroidal anti-inflammatory drugs are available in Europe. There appears to be little difference in overall clinical effectiveness of these drugs, despite individual patient variation, suggesting a common mode of action. Occasionally, a nonsteroidal anti-inflammatory drug will show some evidence of a more impressive anti-rheumatic effect, perhaps related to a more prolonged or different mode of action. The evidence for an immunologic effect of nonsteroidal anti-inflammatory drugs is largely derived from in vitro studies. In patients with rheumatoid arthritis treated with piroxicam, there are no overall changes in lymphocyte numbers or T4/T8 ratios, but numbers of activated cells expressing la decrease and rheumatoid factor titers may also fall. It is suggested that this is not a direct immunosuppressive effect, but one that is related to local inhibition of polymorphonuclear leukocyte-derived free radical production within the joint, which may lower the antigenic load of IgG altered by free radicals, with subsequent diminished immune stimulation.

Renal arachidonic acid metabolism and cellular changes in the rabbit renal vein constricted kidney: inflammation as a common process in renal injury models

The process of renal inflammation was examined using the partial renal vein constricted rabbit kidney ( RVC ) as a model. Forty eight hours of partial renal vein constriction in the rabbit was associated with an increase in prostaglandin (PG) and thromboxane (Tx) production. The ex vivo perfused RVC kidney showed an enhanced time-dependent increase in PG and Tx production in response to bradykinin stimulation when compared with the unaltered contralateral ( CLK ) or normal kidney. At 6 hrs of perfusion bradykinin stimulation released 2950 +/- 350 ng PGE2, 61 +/- 15 ng TxB2 from the RVC , and 225 +/- 85 ng PGE2 and undetectable TxB2 from the CLK . Histological examination of the RVC cortex showed an increase in fibroblast-like cells, a modest increase in the interstitial space and an appearance of macrophages and lymphocytes not seen in the normal or CLK . Endotoxin has been reported to stimulate macrophages in culture to produce PGE2 and TxB2. Endotoxin (100 ng) stimulation of the perfused RVC kidney caused an immediate, followed by a chronically increasing, release of PGs and Tx. Two hours after endotoxin injection 50 ml of effluent from the RVC contained 1450 +/- 107 ng PGE2 and 15.0 +/- 4.5 ng TxB2. Other animals of renal inflammation (e.g., the hydronephrotic kidney, chronic glomerulonephritis) also show the histological appearance of macrophages. In addition, hydronephrotic kidneys undergo fibroblast proliferation and changes in arachidonic acid metabolism similar to that we observed in the RVC . This work suggests that the inflammatory process (mononuclear cell infiltration, fibroblast-like cell proliferation, and accompanying changes in arachidonate metabolism is common among different forms of renal injury.

The effects of prostaglandins on the proliferation of cultured human T lymphocytes

The effects of PGE2 on cultured T lymphocytes (CTC) stimulated by either Con A, PHA, or lectin-free IL-2 were studied. PGE2, in a concentration ranging from 100 to 1 ng/ml, consistently and significantly inhibited the proliferation of CTC induced by either PHA or Con A. PGF2 alpha was essentially without effect. Although the degree of inhibition of PHA-treated CTC was increased with suboptimal amounts of PHA, significant inhibition still resulted with optimal PHA concentrations. PGE2, but not PGF2 alpha, was also effective in significantly inhibiting the proliferation of IL-2-treated CTC in a dose-related fashion; however, the addition of suboptimal amounts of IL-2 did not result in greater increases in the degree of inhibition by PGE2. Depleting the CTC of either OKT-4 or OKT-8 phenotypic cells did not abrogate this PGE2 inhibitory effect, indicating that PGE2 does not suppress the proliferative response solely by the activation of suppressor cells with the OKT-8 phenotype. PGE2 also was found to inhibit the production of IL-2 by fresh lymphocytes treated by either optimal or suboptimal amounts of PHA, however, this decrease in production by PGE2 was not necessarily associated with a decrease in the proliferation of these stimulated lymphocytes. Only with low PHA concentrations, where IL-2 production was markedly reduced and barely detectable, was lymphocyte proliferation appreciably reduced by PGE2. In additional experiments, LiCl was added to PGE2 containing cultures to determine whether LiCl could modulate the inhibitor effect of PGE2 of either PHA- or IL-2-stimulated CTC. In these studies, LiCl, in concentrations of 1-10 mM was found to lessen or completely abrogate the reduced PHA proliferative response induced by PGE2. This effect was more pronounced with suboptimal concentrations of PHA than with optimal PHA amounts. In contrast, the PGE2-induced inhibition of IL-2-stimulated CTC was not modified or altered by the addition of LiCl. Thus, these results suggest that LiCl acts at the level of IL-2 production instead of IL-2 action, and that PGE2 inhibits IL-2-induced proliferation of CTC by a different or additional mechanism than for PHA-treated cells. In conclusion, these results, taken as a whole, indicate that PGE2 suppresses the proliferation of stimulated CTC by at least two different mechanisms: 1) by reducing the production of IL-2 by stimulated lymphocytes; and 2) by directly acting on the responding CTC.(ABSTRACT TRUNCATED AT 400 WORDS)

Endogenous inhibition of autologous lymphocyte antibody-dependent cellular cytotoxicity

Previous reports have indicated that prostaglandins can inhibit certain immune mechanisms, particularly mitogen responsiveness and cell-mediated cytotoxicity of virus-infected or tumor cells. In this study an endogenous self-inhibitory mechanism for antibody-dependent cellular cytotoxicity (ADCC) with normal human peripheral blood mononuclear cells is described. This inhibition could be abrogated by the prostaglandin synthetase inhibitor indomethacin or by removing nylon wool-adherent cells but not platelets. ADCC inhibition was restored by adding exogenous PGE1, PGE2, or supernatant fluid from cultured plastic-adherent mononuclear cells. In contrast, supernatant fluid from adherent mononuclear cells cultured with indomethacin was not inhibitory for ADCC. These results suggest that peripheral blood mononuclear cells contain adherent cells, probably monocytes, which produce prostaglandins that inhibit the ADCC effector activity of normal peripheral blood lymphocytes. This may explain, in part, the wide variability of ADCC effector cell activity that has been reported previously. Monocyte proportions and/or activity may have profound effects on tests of ADCC effector cell activity in various disease states.

Spontaneous helper factor production by nonadherent rabbit lymphoid cells and its feedback regulation by adherent cells

Normal, unstimulated rabbit lymphoid cells, when depleted of adherent cells, produced soluble helper factor activity that augmented antibody formation by rabbit spleen cells primed against sheep red blood cells (SRBC). Adherent cells inhibited the production of the helper factor by nonadherent cells via a soluble product. Thus unseparated (adherent cell-containing) appendix, lymph node, and spleen cell cultures did not produce the helper factor. On the other hand, the activity of the helper factor required the presence of adherent cells in the assay cultures. Peritoneal exudate cells, predominantly esterase positive, also inhibited the production of the helper factor if they were first exposed to the helper factor-containing culture supernatant. These results imply that a helper factor may participate in the feedback regulation of its own production via an adherent cell population.

Melanin: the organizing molecule

The hypothesis is advanced that (neuro)melanin (in conjunction with other pigment molecules such as the isopentenoids) functions as the major organizational molecule in living systems. Melanin is depicted as an organizational "trigger" capable of using established properties such as photon-(electron)-phonon conversions, free radical-redox mechanisms, ion exchange mechanisms, and semiconductive switching capabilities to direct energy to strategic molecular systems and sensitive hierarchies of protein enzyme cascades. Melanin is held capable of regulating a wide range of molecular interactions and metabolic processes primarily through its effective control of diverse covalent modifications. To support the hypothesis, established and proposed properties of melanin are reviewed (including the possibility that (neuro)melanin is capable of self-synthesis). Two "melanocentric systems"--key molecular systems in which melanin plays a central if not controlling role--are examined: 1) the melanin-purine-pteridine (covalent modification) system and 2) the APUD (or diffuse neuroendocrine) system. Melanin's role in embryological organization and tissue repair/regeneration via sustained or direct current is considered in addition to its possible control of the major homeostatic regulatory systems--autonomic, neuroendocrine, and immunological.

Augmentation of prostaglandin and thromboxane production in vitro by monocytes exposed to histamine-induced suppressor factor (HSF)

A possible mechanism to explain the suppression of mitogen-induced lymphocyte proliferation in vitro by histamine-stimulated mononuclear cells was investigated. In initial experiments, the inhibitory action of histamine-induced suppressor factor (HSF) on lymphocyte proliferation was documented to be reduced by the addition of indomethacin (1 microgram/ml). Moreover, the addition of exogeneous PGE2 (10(-7)-10(-8) M) to mononuclear cell cultures reconstituted HSF activity in the presence of indomethacin. In order to ascertain the nature of the target cell responding to HSF, control and suppressor supernatants were incubated with human lymphocytes or monocytes (5 X 10(6) cells/ml) for 24 hr. Following incubation, the supernatants were assayed for their content of prostaglandin E2, F2 alpha, and thromboxane B2. Monocytes (but not lymphocytes) incubated with supernatants containing HSF increased their production of prostaglandin E2, F2 alpha, and thromboxane B2 by 169, 53, and 49%, respectively. Suppressor supernatants were generated with histamine or an H-2 agonist (dimaprit) and chromatographed by gel filtration on Sephadex G-100. The elution profiles for the factor(s) inducing suppression of lymphocyte proliferation (25-40,000 daltons) and augmenting PGE2 production (25,000 daltons) overlapped but were not identical. Collectively, these data suggest that HSF-mediated inhibition of lymphocyte proliferation may occur in part through the augmented production of prostaglandins and/or thromboxane B2 by human monocytes.

Prostaglandin E inhibits the production of human interleukin 2

Prostaglandins of the E type specifically inhibited the production of interleukin 2 (IL-2) by normal human lymphocytes, whereas PG synthetase inhibitors such as indomethacin and fentiazac raised IL-2 production above normal levels. Removal of adherent cells from mononuclear cell populations also resulted in enhanced IL-2 production. The resultant nonadherent cell population lost sensitivity to the enhancement effect of PG synthetase inhibitors, suggesting that a PGE-producing adherent cell plays a major role in the regulation of IL-2.

Biochemical signal transmitted by Fc gamma receptors: phospholipase A2 activity of Fc gamma 2b receptor of murine macrophage cell line P388D1

The detergent lysate of the P388D1 macrophage cell line was subjected to affinity chromatography on two different media, Sepharose coupled to heat-aggregated human IgG (IgG-Sepharose) and Sepharose coupled to the phosphatidylcholine analog rac-1-(9-carboxyl)nonyl-2-hexadecylglycero-3-phosphocholine (PC-Sepharose). Both IgG- and phosphatidylcholine-binding proteins were further purified by Sephadex G-100 gel filtration and isoelectric focusing in the presence of 6 M urea. The isolated IgG-binding proteins specifically bound to IgG2a, but not to IgG2b, whereas the isolated phosphatidylcholine-binding proteins specifically bound to IgG2b but not to IgG2a. Phosphatidylcholine-binding proteins possessed a typical phospholipase A2 activity (phosphatide 2-acylhydrolase, EC 3.1.1.4), which was maximal (10 mumol/min per mg of protein) at pH 9.5, depended on Ca2+, and was specific for cleavage of fatty acid from the C-2 position of the glycerol backbone of phosphatidylcholine. The noted enzymatic activity was augmented 4-fold by preincubating phosphatidylcholine-binding proteins with heat-aggregated murine IgG2b but not with IgG2a. IgG-binding proteins, on the other hand, are devoid of any detectable phospholipase A2 activity. Thus, the functional significance of Fc gamma 2b receptor of P388D1 macrophage cell line would be the generation of phospholipase A2 activity at the cell surface upon specific binding to Fc gamma 2b fragment.

Metabolism of exogenous arachidonic acid by murine macrophage-like tumor cell lines

Murine macrophage-like cell lines, J774.2, P388D1, RAW264.7 and PU-5-1R, were incubated with exogenous arachidonic acid (AA). The major metabolites were identified by comigration with known standards in TLC and HPLC and by characteristic behavior following reduction. During a 30 min incubation J774.2 cells metabolized exogenous 14C-AA (10 microM) to PGE2 (14.8%), 12-hydroxy-5,8,10-heptadecatrienoic acid (HHT) (13.0%), thromboxane B2 (TXB2) (7.4%), PGD2 (4.4%) and PGF2 alpha (3.0%). The remainder was incorporated into phospholipids (39.0%), triglycerides (6.1%), and as yet unidentified metabolites (8.2%). No PGF1 alpha was found. Metabolism of exogenous AA was rapid, being less than 90% completed at 3.5 min. Metabolism of exogenous AA is not increased by the simultaneous addition of macrophage stimuli including the cation ionophore A-23187, particulate phagocytic stimuli and endotoxin. The synthesis of cyclooxygenase products was inhibited by low doses of indomethacin (ID50=0.6 microM) while the synthesis of TXB2 and HHT was selectively inhibited by benzylimidazole (ID50=9.5 microM). Identification of a probable lipoxygenase product is being pursued. The synthesis of this product is not inhibited by indomethacin and migrates with an Rf value close to 5,12-diHETE in TLC. P388D1 and RAW264.7 cells metabolize exogenous AA to the same products as J774.2, but in different proportions, while PU-5-1R does not produce cyclooxygenase metabolites to any appreciable extent.

Endogenous prostaglandin synthesis and the control of lymphocyte function

Prostaglandins serve an important regulatory role in immune responses. Much of their activity seems to involve regulating the early stages of lymphocyte or macrophage activation. Besides the capacity of prostaglandins to control lymphocyte activation directly by blocking transformation, at least one type, PGE2 can induce a class of glass-adherent T-cells to produce a suppressive peptide in vitro. The data we have obtained suggest the existence of a feedback loop in which PG production by an activated T-cell serves as the signal that induces a second T-cell to release a suppressor peptide. This peptide can then regulate the ability of the activated T-cell to pass through the cell cycle. Other examples of feedback loops have recently been postulated or shown to exist among immunocompetent cells. It remains to be shown how these various regulatory loops combine to form the integrated network that modulates immunoresponsiveness.