Immunoregulation by leukotrienes and other lipoxygenase metabolites

Food use and health effects of soybean and sunflower oils

This review provides a scientific assessment of current knowledge of health effects of soybean oil (SBO) and sunflower oil (SFO). SBO and SFO both contain high levels of polyunsaturated fatty acids (PUFA) (60.8 and 69%, respectively), with a PUFA:saturated fat ratio of 4.0 for SBO and 6.4 for SFO. SFO contains 69% C18:2n-6 and less than 0.1% C18:3n-3, while SBO contains 54% C18:2n-6 and 7.2% C18:3n-3. Thus, SFO and SBO each provide adequate amounts of C18:2n-6, but of the two, SBO provides C18:3n-3 with a C18:2n-6:C18:3n-3 ratio of 7.1. Epidemiological evidence has suggested an inverse relationship between the consumption of diets high in vegetable fat and blood pressure, although clinical findings have been inconclusive. Recent dietary guidelines suggest the desirability of decreasing consumption of total and saturated fat and cholesterol, an objective that can be achieved by substituting such oils as SFO and SBO for animal fats. Such changes have consistently resulted in decreased total and low-density-lipoprotein cholesterol, which is thought to be favorable with respect to decreasing risk of cardiovascular disease. Also, decreases in high-density-lipoprotein cholesterol have raised some concern. Use of vegetable oils such as SFO and SBO increases C18:2n-6, decreases C20:4n-6, and slightly elevated C20:5n-3 and C22:6n-3 in platelets, changes that slightly inhibit platelet generation of thromboxane and ex vivo aggregation. Whether chronic use of these oils will effectively block thrombosis at sites of vascular injury, inhibit pathologic platelet vascular interactions associated with atherosclerosis, or reduce the incidence of acute vascular occlusion in the coronary or cerebral circulation is uncertain. Linoleic acid is needed for normal immune response, and essential fatty acid (EFA) deficiency impairs B and T cell-mediated responses. SBO and SFO can provide adequate linoleic acid for maintenance of the immune response. Excess linoleic acid has supported tumor growth in animals, an effect not verified by data from diverse human studies of risk, incidence, or progression of cancers of the breast and colon. Areas yet to be investigated include the differential effects of n-6- and n-3-containing oil on tumor development in humans and whether shorter-chain n-3 PUFA of plant origin such as found in SBO will modulate these actions of linoleic acid, as has been shown for the longer-chain n-3 PUFA of marine oils.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of alveolar macrophage production of chemoattractants by leukotriene B4 and prostaglandin E2

Alveolar macrophages (AM) appear to influence the recruitment of neutrophils into the lung by the elaboration of both lipid and peptide chemotactic molecules for neutrophils. Little is known about the mechanisms that regulate production or release of chemotactic molecules by AM or the interaction between these classes of chemotactic molecules. We investigated the hypothesis that the lipid mediator leukotriene B4 (LTB4) has an in vitro regulatory action on the production of chemotactic proteins by AM. In these experiments, the chemotactic activity in AM culture supernatants was measured in a modified Boyden chamber. LTB4 treatment increased AM production of chemotactic activity in excess of what might be attributed to the amount of LTB4 measured in the culture supernatant after the incubation period. This effect was magnified by in vivo administration of endotoxin prior to AM harvesting. Pretreatment with LTB4 caused a sustained 250% increase in AM production of chemotactic activity, yet only negligible amounts of LTB4 were measured by gas chromatography/mass spectrometry in the LTB4-pretreated AM culture supernatants, indicating that LTB4 alone did not account for the chemotactic activity observed in our studies. A chemotactic peptide in LTB4-treated AM culture supernatant could be isolated and separated from LTB4 by molecular sieve chromatography. Purified column fractions contained 80% of the chemotactic activity of endotoxin-stimulated AM culture supernatant and had a molecular mass of 10,000 D. In contrast to LTB4, prostaglandin E2 (PGE2) suppressed chemotactic activity production by endotoxin-stimulated AM by 70%. Pretreatment with PGE2 was not effective; PGE2 had to be present in the AM culture medium during endotoxin exposure in order to exert a suppressive effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Leukotriene B4 up-regulates IL-6 rather than IL-1 synthesis in human monocytes

Leukotriene B4 (LTB4) preferentially induced IL-6 mRNA accumulation and IL-6 protein release as assessed by ELISA and the B9 cell bioassay. In contrast, minimal IL-1 mRNA or protein was induced by LTB4 either in the absence or presence of muramyl dipeptide. Supernatants of LTB4-treated monocytes consistently showed enhanced thymocyte costimulatory activity and this was abrogated by 75-80% by anti-IL-1 antibody. Baseline production of IL-1 appeared however to be sufficient for a synergistic stimulation of thymocytes in the presence of IL-6. Our results now help clarify that LTB4 stimulated preferentially IL-6 production and that the observed LTB4-induced augmentation in thymocyte responses to monocyte supernatants is due to augmented IL-6 contents in the presence of baseline minimal IL-1 production.

Leukotriene A4 hydrolase in the human B-lymphocytic cell line Raji: indications of catalytically divergent forms of the enzyme

Leukotriene A4 hydrolase was purified 1400-fold, with an approximate yield of 25%, to apparent homogeneity from the human B-lymphocytic cell line Raji. The purification included ammonium sulfate precipitations followed by anion exchange, hydrophobic interaction, and molecular exclusion fast protein liquid chromatography. Kinetic properties at 2 degrees C varied between different enzyme preparations. Two patterns were observed, one with a Km of about 12 microM and Vmax of about 1.1 mumol LTB4/mg protein/min which correlated well with the properties of the human leukocytic LTA4 hydrolase. In other enzyme preparations a higher catalytic activity was observed. These enzyme batches did not obey Michaelis-Menten kinetics but were compatible with a mixture of enzymatic species. Heat treatment (60 degrees C) led to a time-dependent decline in catalytic activity. However, certain enzyme preparations contained a subfraction of enzymatic activity which was more resistant to heat treatment, yielding a biphasic inactivation pattern. It is thus suggested, on the basis of the kinetic properties and the heat-inactivation pattern, that these enzyme preparations contained an addition form of LTA4 hydrolase.

Effect of dietary fats on the fatty acid compositions of serum and immune tissues in chickens

The purpose of the present study was to measure the effect of dietary fat source on the fatty acid composition of immune cells in chickens. One-day-old female chicks were fed corn and soybean meal-based diets containing 7% of either lard, corn oil, canola oil, linseed oil (LO), or menhaden fish oil (FO). After being fed experimental diets for 3 to 4 wk, samples of serum, thymus glands, bursa of Fabricius glands, and splenocytes were collected. All samples were frozen and stored at -80 C until lipid analysis. Results indicate that the fatty acid composition of the sera and immune tissues of chickens reflected the fat in the diet. The relative content of long-chain polyunsaturated fatty acids varied considerably among immune tissues, with, from greatest to least, spleen, bursa, and thymus. The young chick demonstrated a substantial capacity to elongate and desaturate linoleic (C18:2n-6) and alpha-linolenic acids (C18:3n-3). Feeding chicks fats rich in n-3 fatty acids (e.g., LO or FO) decreased significantly (P less than .05) the level of arachidonic acid (C20:4n-6) present in the serum and immune tissues by 50 to 75%. The levels of eicosapentaenoic acid (EPA, C20:5n-3) and docosahexaenoic acid (DHA, C20:6n-3) were substantially increased (P less than .05) by FO and LO feeding. However, LO, which is rich in C18:3n-3, was generally only one-half to one-quarter as effective as FO in elevating EPA and DHA levels in immune tissues. The implications for these changes in serum and immune tissue fatty acid profiles are discussed briefly.

Effects of monocyte-lymphocyte interaction on the synthesis of leukotriene B4

Human monocytes in monolayers were challenged with the calcium ionophore A23187. Methanol trapping of the products in the cell-free supernatants, followed by analysis on HPLC and by ultraviolet spectroscopy, revealed the presence of two compounds, which exhibited a conjugated-triene spectrum and chromatographed with the compounds formed when synthetic leukotriene (LT) A4 was added to warm acidified methanol. Furthermore, addition of purified LTA4 hydrolase to the cell-free supernatant of monocytes, stimulated with the ionophore A23187, resulted in increased levels of LTB4. These results indicate that monocytes release LTA4 extracellularly after activation with the calcium ionophore. Incubation of monocytes together with monoclonal lymphocytic cells, of both B and T cell lineage, yielded increased levels of LTB4 whereas the non-enzymatic isomers of this compound, i.e. delta 6-trans-LTB4 and 12-epi-delta 6-trans-LTB4, declined. In addition, the sum of LTB4 and its non-enzymatically formed isomers increased in mixed cultures of monocytes and monoclonal lymphocytic cells as compared to monocytes alone. The present study indicates that activated monocytes release LTA4, which is converted into LTB4 by monoclonal lymphocytic cells. Furthermore, the increase of the total amounts of leukotrienes on incubation of monocytes with lymphocytic cells, suggests the presence of an additional mechanism leading to activation of the 5-lipoxygenase pathway in monocytes.

Comparison of the immunosuppressive activities of the antimycotic agents itraconazole, fluconazole, ketoconazole and miconazole on human T-cells

Four antifungal agents have been screened in vitro for their immunosuppressive effects on proliferative responses in human mixed lymphocyte cultures (MLC). A hierarchy of inhibitory activity was observed, where itraconazole was greater than ketoconazole greater than miconazole greater than fluconazole, with itraconazole as suppressive as cyclosporin A, and fluconazole completely without suppressive activity. The mechanism of inhibition did not involve blockade of T-cell growth factor production and, consistent with this, interleukin-2-dependent T-cell clone proliferation was blocked by these agents in the same order of decreasing activity as in MLC. The secretion of cytokines without known T-cell growth factor activity (interferon-gamma, tumour necrosis factor-alpha) was also not significantly blocked by these agents. These results therefore demonstrate that antifungal azole drugs may be variably strongly immunosuppressive for human T-lymphocyte proliferation in vitro, but none appear to be so via a mechanism involving inhibition of cytokine secretion.

Peptide opioids and morphine effects on inflammatory process

Morphine was found to inhibit human granulocyte aggregation and ATP, thromboxane B2 (TxB2), and leukotriene B4 (LTB4) secretion during cell aggregation. None of the opioid peptides tested [(D-Ala2, D-Leu5)-enkephalin (DADL), (D-Ala2, N-Me-Phe4, Gly-ol5)-enkephalin (DAGO) or dynorphin 1-9 (Dyn 1-9)] was capable of mimicking morphine effects, while Dyn 1-9 per se induced TxB2 and LTB4 secretion from granulocytes. Morphine inhibition of both cell aggregation and ATP, but not of arachidonic acid metabolism product secretion, was prevented by naloxone. The naloxone-sensitive impairment by morphine of CD11b-CD18 complex surface expression observed could play a role in opioid inhibition of granulocyte activation.

PAF metabolism in resident and activated alveolar macrophages: role of protein kinase C

Platelet-activating factor (PAF) metabolism was studied in resident and activated alveolar macrophages. Macrophages were obtained from normal Sprague-Dawley rats and from rats previously injected with complete Freund's adjuvant. Macrophages were attached and stimulated for 90 min. Then, cell PAF was extracted and quantitated by thin-layer chromatography. We found that in both resident and activated macrophages, calcium ionophore A23187 was a potent stimulus for PAF production while phorbol myristate acetate (PMA) was not. PMA and ionophore acted synergistically to increase PAF content in resident macrophages. This synergism was not observed in activated macrophages. To examine if this difference between resident and activated macrophages was due to a difference in PAF degradation, we assayed acetylhydrolase, the PAF-degrading enzyme. We found that ionophore stimulated acetylhydrolase activity in activated macrophages, but not in resident macrophages. Furthermore, PMA potentiated the ionophore effect in activated macrophages. This synergism was less obvious in resident cells. We conclude that PAF metabolism is different in activated and resident alveolar macrophages. Protein kinase C may play an important role in acetylhydrolase regulation in these cells.

Dietary modulation of cytokine production and biologic functions

Cytokines play a key role as communication signals during both normal immunologic responses and pathologic conditions leading to infectious, inflammatory, and neoplastic diseases. Production and biologic function of cytokines are affected by changes in macro- and micronutrients. On the other hand, metabolic and catabolic consequences of the action of cytokines change nutrient status and the distribution of nutrients in tissues. The effect of some nutrients on cytokine production as well as some of the biologic effects of cytokines are mediated through metabolites of arachidonic acid (prostaglandins, leukotrienes, etc.). Other mechanisms involved in nutrient-induced changes of cytokines needs to be determined. Understanding the role of nutrients in cytokine production and biologic function during normal homeostasis, as well as under pathologic conditions, can help in designing proper dietary modification for the prevention and therapy of diseases.

Leukotriene B4 in atopic dermatitis: increased skin levels and altered sensitivity of peripheral blood T-cells

Employing a radioimmunoassay, de-proteinated suction blister fluid from 12 patients with active atopic dermatitis appeared to contain higher levels of the pro-inflammatory and immunomodulatory mediator leukotriene B4 (LTB4) than suction blister fluid from 12 non-atopic individuals. Indirect support for the identity of the mediator was obtained by HPLC of pooled samples. Nylon wool enriched T cells from six patients with atopic dermatitis and six non-atopic people preincubated with LTB4 (10(-10) M - 10(-8) M) expressed no statistically significant suppression in co-culture with mitogen stimulated autologous mononuclear cells, and there was no difference between atopic and non-atopic T cells in this respect. In contrast, LTB4 induced a dose-dependent reduction in the percentage of phenotypic Leu 2a (suppressor) cells leading to an increased helper/suppressor ratio in five atopic patients that was not observed in five non-atopics. Elevated skin levels of LTB4 may initiate or amplify dermal inflammation, and abnormal T cell response to the mediator may account for the increased helper/suppressor ratio characteristic of patients with atopic dermatitis.

Comparison of eicosanoid generation by highly purified human Langerhans cells and keratinocytes

The present study was conducted to investigate the eicosanoid metabolism of highly enriched human Langerhans cells and keratinocytes. Arachidonic acid (100 microM) was added to the cells which were then stimulated with 1 microM calcium ionophore A 23187 for 10 and 30 min. The supernatants were examined for cyclooxygenase and lipoxygenase products using different chromatographic systems and radioimmunoassays. Compounds were identified by comparison with authentic standards. The major cyclooxygenase product of both cell types was prostaglandin D2, with minor amounts of prostaglandin E2. The main products of the lipoxygenase pathway were 5-hydroxyeicosatetraenoic acid (5-HETE), 12-HETE, 15-HETE, and their corresponding hydroperoxy derivatives, with small amounts of leukotrienes B4 and C4. The major differences in the metabolism of the two cell types were related to faster kinetics of generation of the mediators and a more complete conversion of arachidonic acid by the LC. Because eicosanoids have been implicated to be potent mediators of inflammation and immunomodulators, the present data underline the potential contributory role of epidermal cells to eicosanoid-associated pathologic processes.

Elevated white blood cell synthesis of leukotriene C4 in chronic myelogenous leukaemia but not in polycythaemia vera

Leukotriene (LT) formation was studied in ionophore A23187-stimulated white blood cell (WBC) preparations from patients with chronic myelogenous leukaemia (CML; n = 14), polycythaemia vera (PV; n = 10) and two control groups consisting of patients with non-malignant inflammatory disease (n = 4) and normal healthy donors (n = 25). The synthesized products were identified and quantitated using high-performance liquid chromatography combined with computerized UV-spectroscopy. White blood cell preparations from the CML patients produced more LTC4 (40.2 +/- 7.9 pmol/10(6) WBC, mean +/- SEM) than WBC from the healthy donors (9.0 +/- 1.8), P less than 0.0005. In contrast, the formation of LTB4 was normal and there was no increase in the total leukotriene synthesis (the sum of LTC4, LTB4, 20-OH-LTB4 and the delta 6-trans-isomers of LTB4). The ratio between leukotrienes C4 and B4 was strongly elevated in the CML group; 1.67 +/- 0.25 v. 0.37 +/- 0.07 in the controls, P less than 0.0005. No significant correlation was observed between the levels of LTC4 and the number of known LTC4 producing cells (such as monocytes, eosinophils and basophils) in the CML WBC preparations. In contrast, a correlation was found between the sum of neutrophilic granulocytes and metamyelocytes in these suspensions and the amount of LTB4 formed; r = 0.600, P less than 0.05. A number of other laboratory or clinical variables of the CML patients (including total white blood cell and platelet counts, differential counts, previous cytotoxic treatment, time from diagnosis, time from last treatment, post study survival and age) did not significantly correlate with the formation of leukotrienes. No abnormality in the production of LTB4 or LTC4 was observed in granulocyte and WBC preparations from the patients with polycythaemia vera and non-malignant inflammatory disease, respectively. The results indicate a selectively increased LTC4 producing capacity in CML.

Inhibition of Ehrlich ascites tumor in vivo by PAF-antagonists

Several lines of evidence support that PAF modulates the inflammatory and immune responses, and that tumors may inhibit both these processes. In the present study we analysed the effect of PAF antagonists on the growth of Ehrlich Ascites Tumor (EAT) in vivo. Mice were inoculated intraperitoneally with 1 x 10(3) EAT cells and the tumor growth evaluated by counting the number of peritoneal cells, 1,6 and 10 days after tumor implantation. BN 52021 was administered intraperitoneally, intravenously or subcutaneously once or twice a day, at 1.0, 2.5, 5.0 and 20.0 mg/kg. Control animals received 0.1 ml of the vehicle in the same schedule. It was found that i.p. and i.v. administration of BN 52021 (5 mg/kg, twice a day) significantly inhibited EAT growth (80.8% and 56.0% respectively). Other routes and doses were less effective. Another PAF antagonist, SRI 63441 (5 mg/kg, i.p., twice a day) also inhibited EAT growth (80.4%). The BN 52021 added to EAT cells in culture, at concentration of 10(-3) and 10(-4) M, did not affect the viability and proliferation of tumors cells. In an attempt to understand the mechanism of this inhibition, we analyzed the peritoneal macrophages for spreading ability and H2O2 release. It was found that 24 h after tumor implantation there was an increase in the spreading ability of peritoneal macrophages (75%) and that, as the tumor grew, the spreading index fell to control levels ( less than 10%). (5 mg/kg/twice a day) the spreading remained elevated (50-60%) at all the times examined. Release of H2O2, measured by horseradish peroxidase-phenol red oxidation, was below detectable levels throughout tumor growth.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitors of arachidonic acid lipoxygenase impair the stimulation of inositol phospholipid hydrolysis by the T lymphocyte mitogen phytohaemagglutinin

Piriprost and nordihydroguiaretic acid (NDGA), specific inhibitors of arachidonate lipoxygenase, inhibited phytohaemagglutinin (PHA)-stimulated breakdown of inositol lipids in human T lymphocytes. The dual inhibitors eicosatetraynoic acid (ETYA) and BW 755C, which inhibit both lipoxygenase and cyclooxygenase, also had similar actions, whereas indomethacin and acetylsalicyclic acid, which inhibit cyclooxygenase alone, did not. The effects of lipoxygenase inhibitors and dual inhibitors were reversible. These agents did not inhibit phosphatidylinositol-4,5-bisphosphate-specific phospholipase C (PIP2-PLC) in vitro. Bromophenacyl bromide, and irreversible inhibitor of phospholipase A2, also abolished PHA-stimulated inositol lipid breakdown without affecting PIP2-PLC in vitro. The results are consistent with a role for the PHA-stimulated generation of arachidonic acid and its conversion to lipoxygenase metabolites (e.g. leukotrienes and/or hydroxyeicosatetraenoic acids) as intermediate steps in the signal transduction pathway between cell-surface mitogen receptors and the stimulation of PIP2-PLC in lymphocytes.

Recombinant interleukin-1 beta stimulates eicosanoid production in rat primary culture astrocytes

Astrocytes may play a prominent role in the initiation of immunoinflammatory responses in the central nervous system. They can be induced to synthesize eicosanoids but how immunologically relevant molecules modulate this process is not known. We examined the influence of recombinant interleukin-1 (rIL-1), an immunomodulating monokine on the release of arachidonic acid metabolites. IL-1 (1-30 U) induced a dose-related elaboration predominantly of the cyclo-oxygenation products prostaglandin E and thromboxane B2. Preincubation of rIL-1 with a specific antibody abrogated and heat-inactivation destroyed this activity. Both mepacrine and the isoquinolinesulfonamide H7 blocked the stimulatory effect dose-dependently, indicating involvement of protein kinase C in this novel biologic activity of IL-1. In central nervous system inflammation, IL-1-evoked release from astrocytes of arachidonic acid-derived metabolites may influence the severity of phlogistic responses and modulate local immune reactivity.

Asbestos fibers and silica particles stimulate rat alveolar macrophages to release tumor necrosis factor. Autoregulatory role of leukotriene B4

Alveolar macrophages (AM) can play a crucial role in the pathogenesis of pulmonary disease via their ability to produce potent inflammatory and fibrogenic mediators. We found that rat AM cultured with 1 to 100 micrograms/ml of silica particles or asbestos fibers produced tumor necrosis factor (TNF) and leukotriene B4 (LTB4) in a concentration-dependent fashion, whereas latex beads, an inert phagocytic stimulus, failed to induce significant augmentation of either TNF or LTB4. In a time course study, AM stimulated for 2 h with silica or asbestos produced an increased amount of LTB4, which preceded the rise in TNF activity detected 7 and 24 h after culture initiation. The induction appears to involve the synthesis of new protein since actinomycin D and cycloheximide abrogate the majority of the stimulatory effect. We next examined the role of LTB4 in mineral-dust-induced TNF production. The lipoxygenase inhibitors nordihydroguaiaretic acid (NDGA) and AA861 used at 1 to 50 micrograms/ml reduced in a concentration-dependent fashion asbestos- or silica-stimulated TNF release. On the other hand, "reconstitutive" experiments in which we added exogenous LTB4 (10(-14) to 10(-8) M) to AM treated with lipoxygenase inhibitors showed partial restoration of TNF production induced by chrysotile or silica, with peak effect at 10(-10)M LTB4. The present study demonstrated that AM incubated in the presence of chrysotile A or silica can produce both LTB4 and TNF and that endogenous lipoxygenase metabolites as well as exogenous LTB4 can act to amplify TNF production. These observations suggest a common mechanism by which asbestos and silica may modulate the production of inflammatory and fibrogenic cytokines.

Regulation of murine hematopoiesis by arachidonic acid metabolites

Arachidonic acid metabolites have been shown to exert a variety of regulatory effects on cellular activation and proliferation. Recently, a role for these products as regulators of hematopoiesis was suggested and evidence provided that products of the lipoxygenase pathway, specifically leukotrienes, are essential for human myeloid colony formation in vitro. In this report the broader role of these metabolites in hematopoiesis was examined using murine bone marrow stem cell assays for both myeloid and lymphoid cell lines. The effects of lipoxygenase and/or cyclooxygenase pathway inhibitors on stem cell colony formation were evaluated and compared to qualitative and quantitative changes in arachidonic acid metabolism that occurred in similarly treated bone marrow cell cultures. Interruption of the lipoxygenase pathway by esculetin or nordihydroguaiaretic acid resulted in decreased colony formation in both lymphoid and myeloid stem cells. This inhibition of colony growth was partly reversed by the addition of leukotrienes and was particularly evident in B-cell progenitor cultures to which was added LTB4. Inhibition of the cyclooxygenase pathway by indomethacin or ibuprofen had a slight stimulatory effect on myeloid colony formation, while slightly inhibiting the formation of lymphoid colonies. These results support a direct role for lipoxygenase products in myeloid colony formation and lymphoid stem cell proliferation. A more complex role for cyclooxygenase metabolites in the hematopoietic process appears probable.

Dysregulation of arachidonic acid release and metabolism by atopic mononuclear cells

We studied the ability of monocytes to metabolize [3H]arachidonic acid (AA) provided exogenously by activated T cells, and the extent to which dexamethasone suppressed eicosanoid production by normal and atopic cells. [3H]AA metabolites were identified using a reverse-phase high pressure liquid chromatography system (HPLC). Unstimulated and PHA-stimulated T cells from normal and atopic subjects exhibited a similar uptake and time-dependent release of radiolabel, 90% of which was identified as free AA. The addition of autologous normal and atopic monocytes to these cultures enhanced the release of radiolabel, even in the absence of stimulation with mitogen. Atopic T cell/monocyte cultures released significantly (P = 0.046) more radiolabel than normal cells when stimulated with PHA. Furthermore, the monocytes from both normal and atopic subjects metabolized T cell derived [3H]AA into cyclo-oxygenase (CO) and lipoxygenase (LO) products. Under unstimulated conditions, atopic cells produced significantly (P = 0.04) less CO products than normal cells. In contrast, under PHA and calcium ionophore-stimulated conditions, the atopic cells produced significantly (P = 0.048) more prostaglandins than normal donor cells. Furthermore, although the total release of radioactivity was comparable in both groups, significantly less (P = 0.02) free AA remained in ionophore-stimulated culture supernatants from atopic cells. In order to study the regulation of AA release by normal and atopic T cells, dexamethasone (1 microM) was added to T cell cultures. Dexamethasone inhibited the release of [3H]AA from normal T cells to a significantly (P = 0.003) greater extent than it did to atopic cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Leukotrienes and macrophage activation: augmented cytotoxic activity and enhanced interleukin 1, tumor necrosis factor and hydrogen peroxide production

Leukotrienes (LT), and in particular LTB4, are potent inflammatory mediators and immunomodulators. In its interactions with leukocytes, LTB4 can activate numerous functions of neutrophils and modulate the activities of various lymphocyte subsets. LTB4 can also augment macrophage and monocyte cytotoxic activities and enhance their production of hydrogen peroxide and the monokines interleukin 1 and tumor necrosis factor. These observations allow a more detailed understanding of the effects of LTB4 on cellular immune and inflammatory functions.

Primary rat astroglial cultures can generate leukotriene B4

Astrocytes are important elements of cellular immune responses in the central nervous system. Eicosanoids exhibit immunomodulatory properties. We studied whether astroglial cells have the capacity to convert arachidonic acid via the lipoxygenase pathway to leukotriene B4 (LTB4). Calcium ionophore A23187 evoked a dose-related release of LTB4 into supernatants of primary culture rat astrocytes. This stimulatory effect was abrogated by the addition of the lipoxygenase inhibitors BW755c and nordihydroguaretic acid. Astrocyte production of the phlogistic and immunoregulatory mediator LTB4 may be one mechanism by which these cells influence immunity and inflammation in the central nervous system.

Effect of arachidonic acid metabolites on thymocyte proliferation

The influences of prostaglandin E2 (PGE2), 15-hydroxyeicosatetraenoic acid (15-HETE) and leukotrienes (LT) on the proliferative response of mature (PNA-) and immature (PNA+) mouse thymocytes was investigated. Both PNA+ and PNA- thymocytes proliferated when cultured with concanavalin A plus interleukin-2. PGE2 in concentrations of 10(-6) to 10(-9) M caused significant inhibition of proliferation of both PNA+ and PNA- thymocytes in these cultures. In contrast, the lipoxygenase products 15-HETE, LTB4, LTC4 and LTD4 caused marked increases in proliferation of PNA+ thymocytes while having no effect on PNA- cells. Therefore, the effect of leukotrienes on thymocyte proliferation depends upon the level of cell maturation and mainly affects immature PNA+ thymocytes.

The oxidant defence system in water-buffaloes (Bubalus bubalis) experimentally infected with Anaplasma marginale

The glutathione (GSH) -oxidant defence system protects the erythrocytes and leucocytes from oxidative damage. Leucocyte -superoxide dismutase (SOD), GSH-peroxidase (GSH-px), GSH-reductase (GR), GSH-S-transferase (GSH-S-t) and arginase were examined in samples from buffaloes infected with Anaplasma marginale. All the enzymes, except arginase, were also studied in the red cell haemolysates from these animals. GSH-S-t, GSH- and glutathione-reductase (GR) levels in leucocytes decreased in infected animals suggesting a decline in the efficiency of the GSH-oxidant defence system. SOD levels increased but there was no change in leucocyte-arginase activity due to infection. Infection caused no significant changes in red cell SOD, GSH-px, GR and GSH. However, GSH-S-t significantly decreased (P less than 0.05).

Mast cell polymorphisms. Present concepts, future directions

Although mast cells are widely distributed in the body, their functions are poorly known. The elucidation of mast cell function is complicated by growing evidence that mast cells are heterogeneous. Recent studies of mast cell ontogeny suggest that microenvironmental stimuli control the phenotypic expression of parts of the genome leading to subtype differences in a common lineage. Mast cells influence cell proliferation, differentiation, and activation in a range of target cells, although until recently they were considered important only in immediate hypersensitivity. However, they function in delayed-type hypersensitivity, potentiate cytotoxicity of eosinophils and macrophages, and are cytotoxic for certain targets themselves. Mast cell mediators influence blood flow and vascular permeability and facilitate angiogenesis. Numerous mast cell mediators are immunoregulatory. In vitro experiments have begun to investigate the role of mast cells in fibrotic diseases. Further knowledge of mast cell heterogeneity will provide the basis for new therapies in inflammatory diseases of the intestine and other organs.

Astrocytes as eicosanoid-producing cells

A variety of prostaglandins and leukotrienes, together with thromboxane and prostacyclin metabolites, can be detected in central nervous tissues and in cerebrospinal fluid. Defined cultures of astrocytes have revealed these cells to be a major source of eicosanoids. In common with other eicosanoid-producing cells, agents such as calcium ionophores and phorbol esters are potent stimuli for promoting release. While in other tissues agonists for receptors linked to calcium mobilisation prompt eicosanoid release, this does not seem to be the case in astrocytes, though a range of such receptors are present. The notable exceptions to this observation are adenosine triphosphate and adenosine diphosphate, presumably acting through P2 purinergic receptors. Many cell types in the CNS are targets for eicosanoids, possessing receptors linked to adenylate cyclase or phospholipase C. An appreciation of the functional significance of activation of these receptors is just now beginning. Eicosanoids have effects in the CNS that involve not only the vascular supply but also synaptic modulation and immune regulation.

Effects of piroxicam and D-penicillamine on T lymphocyte subpopulations, natural killer cells and rheumatoid factor production in rheumatoid arthritis

The effects of piroxicam and D-penicillamine on T lymphocytes, NK cell activity and rheumatoid factor production as well as clinical parameters were studied in patients with rheumatoid arthritis. The level of total rheumatoid factor fell during treatment with D-penicillamine (p less than 0.02) and there was a positive correlation (K greater than 0.50, p less than 0.05) between this fall in rheumatoid factor and the improvement of several clinical activity parameters. No significant change was observed in the level of rheumatoid factor during treatment with piroxicam. Natural killer cell activity decreased from 21.1 +/- 2.5 to 15.8 +/- 1.9 after treatment with piroxicam for 3 weeks (p less than 0.05) as compared with changes in the controls. No change in natural killer cell activity was seen after treatment with D-penicillamine. Moreover, no significant changes in the numbers of T4+ and T8+ lymphocytes nor in the numbers of HLA-DR positive T cells were seen in the two treatment groups. Both laboratory and clinical activity parameters improved during the treatment with D-penicillamine, while only subjective parameters improved during treatment with piroxicam.

Studies on the effects of disease-modifying antirheumatic drugs on lipoxygenase product synthesis in human neutrophils in vitro

The disease-modifying antirheumatic drugs sodium aurothiomalate, D-penicillamine and chloroquine phosphate were tested on leukotriene (LT) synthesis in human blood polymorphonuclear leukocytes stimulated with either the ionophore A23187, zymosan or f-Met-Leu-Phe. Lipoxygenase products were analyzed by reversed-phase high-performance liquid chromatography. The study demonstrated that the drugs can either inhibit or enhance 5-lipoxygenase product synthesis in human leukocytes, depending on the stimulus used to activate the cells and the drug concentration. The data also suggested that increased substrate availability accounted for the stimulatory effects of the drugs on leukotriene synthesis.

In vitro effects of fluconazole (UK-49,858) and ketoconazole on mouse lymphocyte proliferation and on Candida blastospore destruction by human polymorphonuclear leukocytes

The effects of fluconazole, a novel antifungal compound with a bis-triazole structure, were compared with those of ketoconazole on mitogen-induced DNA synthesis by cultured mouse lymphocytes, and on the destruction of fungal (Candida albicans) blastospores by human polymorphonuclear leukocytes. Fluconazole had little or no effect on concanavalin A- or lipopolysaccharide-induced lymphocyte proliferation at concentrations at which ketoconazole caused marked inhibition of the response to both these mitogens. Similarly, fungal cell killing by polymorphonuclear leukocytes was substantially depressed by ketoconazole but was unaffected by fluconazole. In addition, therefore, to having excellent in vivo antifungal activity, fluconazole, unlike ketoconazole, has been shown to have no inhibitory effect in two in vitro assays of immune function.

A novel metabolic pathway for leukotriene B4 in different cell types: primary reduction of a double bond

Addition of leukotriene B4 together with trace amounts of tritiated leukotriene B4 to different cell types, such as bone marrow-derived macrophages, T-lymphocytes, mesangial cells or fibroblast tumor cells, led to the formation of several hitherto unknown degradation products within hours. None of them could be identified as 20-hydroxy- or 20-carboxyleukotriene B4, known to be produced by polymorphonuclear leukocytes. The primarily formed transient leukotriene B4 metabolite was less polar than leukotriene B4 and was detectable by measuring its ultraviolet absorbance at 232 nm or its radioactivity. Mass spectral analysis showed very similar fragmentation spectra of leukotriene B4 and its primary metabolite. The most abundant ion and the main fragments of the new metabolite were increased by two mass units compared to leukotriene B4. These observations suggest that, in a variety of cells, leukotriene B4 is first reduced to a 5,12-dihydroxyeicosatrienoic acid, which is further converted to secondary hydrophilic degradation products. This raises the question of the major route of leukotriene B4 metabolism in vivo.

Lymphocyte subpopulations in bronchoalveolar lavage in Sjögren's syndrome. Evidence for an expansion of cytotoxic/suppressor subset in patients with alveolar neutrophilia

We initiated this study to determine the cellular composition and T-lymphocyte subpopulations of fluid from bronchoalveolar lavage from 15 patients with primary Sjögren's syndrome (1SS), six patients with secondary Sjögren's syndrome associated with primary biliary cirrhosis (2SS-PBC), eight patients with secondary Sjögren's syndrome associated with collagen-vascular diseases (2SS-CVD), and 12 normal subjects. All were nonsmokers who were free of clinical pulmonary symptoms and had normal findings on chest roentgenograms. Lymphocyte subsets were identified by mouse monoclonal antibodies that were specific for T-cells, helper/inducer, and suppressor/cytotoxic (namely, OKT3, OKT4, and OKT8). Patients with 1SS, patients with 2SS-PBC, and patients with 2SS-CVD had a significantly increased percentage of lymphocytes in fluid from bronchoalveolar lavage (respectively, 21.6 +/- 3.7 percent, 24.3 +/- 6.1 percent, and 25.6 +/- 3.9 percent) compared with the normal value of control subjects (9.9 +/- 1.5 percent). In addition, two of the 15 patients with 1SS and five of the eight patients with 2SS-CVD demonstrated an increased percentage of alveolar neutrophils. The predominant T-cell subset in patients with 1SS was T4+, and the mean T4:T8 ratio was normal. The percentage of T4+ cells was increased in patients with 2 SS-PBC, resulting in an increased T4:T8 ratio. In contrast, patients with 2 SS-CVD demonstrated a markedly increased percentage of T8+ cells, reflected by a shift in the T4:T8 ratio which was inverted. Patients with Sjögren's syndrome and with neutrophilia on bronchoalveolar lavage had a marked expansion of the T8+ lymphocyte subpopulation, where as patients with Sjögren's syndrome and with pure lymphocytosis on bronchoalveolar lavage showed predominantly T4+ cells. In addition, we found a strong positive correlation between the number of neutrophils and the number of T8+ cells in bronchoalveolar lavage from patients with Sjögren's syndrome (r = 0.74; p less than 0.05). Until the functional activities of OKT4+ and OKT8+ cells are better defined, the role that these cells play in the pathogenesis of pulmonary disease in Sjögren's syndrome remains unclear.

Leukotriene production by cultured astroglial cells

Astrocytes metabolize arachidonic acid via the cyclooxygenase pathway to prostanoids. We examined whether primary culture astrocytes from neonatal rat brain can be induced to generate and release the lipoxygenase derivative leukotriene C4 (LTC4). While there was only minute constitutive production of immunoreactive LTC4 this metabolite was liberated by astroglial cells in response to calcium ionophore A23187. The phorbol diester 12-O-tetradecanoylphorbol 13-acetate (TPA) failed to precipitate leukotriene release. However, when threshold doses of A23187 were added to astrocyte cultures challenged with TPA, LTC4 was recovered from their supernatants. It is suggested that leukotriene generation by astrocytes bears relevance to immunoinflammatory responses in the central nervous system and may be involved in brain edema formation.

Platelet-activating factor (PAF) receptor antagonists inhibit mitogen-induced human peripheral blood T-cell proliferation

The addition of L-652,731 and L-653,150, two synthetic PAF-specific receptor antagonists, to 72 hour cultures of phytohemagglutinin (PHA)-stimulated human peripheral blood mononuclear leukocytes (PBML) caused a dose-dependent inhibition of (3H)-thymidine incorporation into T-cells (IC50: 25 microM and 3.2 microM, respectively). This inhibition was not reversed by exogenous interleukin (IL)-1 and IL-2. PAF receptor antagonists did not affect the expression of IL-2 receptors (TAC-antigen) on T-cells. Exogenous PAF which by itself had no significant effect on PHA-stimulated PBML proliferation, only partially reversed the inhibition of proliferation caused by PAF receptor antagonists. These results may suggest the involvement of endogenously produced PAF in the regulation of immune reactions.