2-Arachidonoyl-glycerol- and arachidonic acid-stimulated neutrophils release antimicrobial effectors against E. coli, S. aureus, HSV-1, and RSV

The endocannabinoid 2-AG is highly susceptible to its hydrolysis into AA, which activates neutrophils through de novo LTB(4) biosynthesis, independently of CB activation. In this study, we show that 2-AG and AA stimulate neutrophils to release antimicrobial effectors. Supernatants of neutrophils activated with nanomolar concentrations of 2-AG and AA indeed inhibited the infectivity of HSV-1 and RSV. Additionally, the supernatants of 2-AG- and AA-stimulated neutrophils strongly impaired the growth of Escherichia coli and Staphylococcus aureus. This correlated with the release of a large amount (micrograms) of α-defensins, as well as a limited amount (nanograms) of LL-37. All the effects of AA and 2-AG mentioned above were prevented by inhibiting LTB(4) biosynthesis or by blocking BLT(1). Importantly, neither CB(2) receptor agonists nor antagonists could mimic nor prevent the effects of 2-AG, respectively. In fact, qPCR data show that contaminating eosinophils express ∼100-fold more CB(2) receptor mRNA than purified neutrophils, suggesting that CB(2) receptor expression by human neutrophils is limited and that contaminating eosinophils are likely responsible for the previously documented CB(2) expression by freshly isolated human neutrophils. The rapid conversion of 2-AG to AA and their subsequent metabolism into LTB(4) promote 2-AG and AA as multifunctional activators of neutrophils, mainly exerting their effects by activating the BLT(1). Considering that nanomolar concentrations of AA or 2-AG were sufficient to impair viral infectivity, this suggests potential physiological roles for 2-AG and AA as regulators of host defense in vivo.

Oxidative stress-induced changes in pyridine nucleotides and chemoattractant 5-lipoxygenase products in aging neutrophils

Neutrophils spontaneously undergo apoptosis, which is associated with increased oxidative stress. We found that there is a dramatic shift in the formation of 5-lipoxygenase products during this process. Freshly isolated neutrophils rapidly convert leukotriene B(4) (LTB(4)) and 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) to their biologically inactive omega-oxidation products. However, omega-oxidation is impaired in neutrophils cultured for 24 h, when only 25% of the cells are nonapoptotic, resulting in the persistence of LTB(4) and a dramatic shift in 5-HETE metabolism to the potent granulocyte chemoattractant 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE). The reduced omega-oxidation activity seems to be due to a reduction in LTB(4) 20-hydroxylase activity, whereas the increased 5-oxo-ETE formation is caused by a dramatic increase in the 5-hydroxyeicosanoid dehydrogenase cofactor NADP(+). NAD(+), but not NADPH, also increased, as did the GSSG/GSH ratio, indicative of oxidative stress. The changes in 5-HETE metabolism and pyridine nucleotides were inhibited by antiapoptotic agents (GM-CSF, forskolin) and antioxidants (diphenylene iodonium, catalase, deferoxamine), suggesting the involvement of H(2)O(2) and possibly other reactive oxygen species. These results suggest that in severe inflammation, aging neutrophils that have evaded rapid uptake by macrophages may produce increased amounts of the chemoattractants 5-oxo-ETE and LTB(4), resulting in delayed resolution or exacerbation of the inflammatory process.

Activation of cytosolic phospholipase A2alpha in resident peritoneal macrophages by Listeria monocytogenes involves listeriolysin O and TLR2

Eicosanoid production by macrophages is an early response to microbial infection that promotes acute inflammation. The intracellular pathogen Listeria monocytogenes stimulates arachidonic acid release and eicosanoid production from resident mouse peritoneal macrophages through activation of group IVA cytosolic phospholipase A2 (cPLA2alpha). The ability of wild type L. monocytogenes (WTLM) to stimulate arachidonic acid release is partially dependent on the virulence factor listeriolysin O; however, WTLM and L. monocytogenes lacking listeriolysin O (DeltahlyLM) induce similar levels of cyclooxygenase 2. Arachidonic acid release requires activation of MAPKs by WTLM and DeltahlyLM. The attenuated release of arachidonic acid that is observed in TLR2-/- and MyD88-/- macrophages infected with WTLM and DeltahlyLM correlates with diminished MAPK activation. WTLM but not DeltahlyLM increases intracellular calcium, which is implicated in regulation of cPLA2alpha. Prostaglandin E2, prostaglandin I2, and leukotriene C4 are produced by cPLA2alpha+/+ but not cPLA2alpha-/- macrophages in response to WTLM and DeltahlyLM. Tumor necrosis factor (TNF)-alpha production is significantly lower in cPLA2alpha+/+ than in cPLA2alpha-/- macrophages infected with WTLM and DeltahlyLM. Treatment of infected cPLA2alpha+/+ macrophages with the cyclooxygenase inhibitor indomethacin increases TNFalpha production to the level produced by cPLA2alpha-/- macrophages implicating prostaglandins in TNFalpha down-regulation. Therefore activation of cPLA2alpha in macrophages may impact immune responses to L. monocytogenes.

Involvement of cannabinoid receptor CB2 in dectin-1-mediated macrophage phagocytosis

Cannabinoid receptors are expressed in macrophages, but little is known of their roles. We here examined their involvement in phagocytosis. The presence of 2-arachidonylglycerol, an endocannabinoid, augmented the phagocytosis of zymosan by mouse macrophages, while the phagocytosis of Escherichia coli, Staphylococcus aureus, apoptotic cells or latex beads remained unaffected. An agonist of the cannabinoid receptors CB1 and CB2 also stimulated the phagocytosis of zymosan. The stimulatory effect of 2-arachidonylglycerol was abolished when phagocytosis reactions were carried out in the presence of an antagonist of CB2 but not of CB1. Furthermore, the phagocytosis of zymosan in the presence of 2-arachidonylglycerol was severely inhibited by the addition of a beta-glucan-containing carbohydrate or antibody neutralizing dectin-1, a beta-glucan-recognizing phagocytosis receptor. These results suggested that the activation of CB2 in macrophages leads to the stimulation of dectin-1-mediated phagocytosis.

Arvanil and anandamide up-regulate CD36 expression in human peripheral blood mononuclear cells

In this study we analysed the regulation of gene expression by arvanil and anandamide in human peripheral blood mononuclear cells (PBMCs) to clarify their immunosuppressive properties. PBMCs were activated, leading to CD36 down regulation, that was normalized by arvanil and anandamide. We used microarray technology to identify a regulatory pattern associated with cell proliferation in the presence of both substances. CD3-CD28 stimulated PBMCs showed a pattern of up-regulated and down-regulated genes after treatment with these substances. We selected and analysed several genes chosen by their function in the regulation of cell proliferation. We showed a transcriptional control of the CD36 gene by arvanil and anandamide associated with an increased protein expression, thus suggesting a possible role of CD36 in anandamide and arvanil anti-inflammatory pattern.

Hierarchy of eosinophil chemoattractants: role of p38 mitogen-activated protein kinase

Several chemoattractants can regulate the recruitment of eosinophils to sites of inflammation, but the hierarchy among them is unknown. We observed here that eosinophil chemotaxis towards eotaxin or 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) was amplified up to sixfold in the presence of prostaglandin (PG) D2. This effect was only seen in eosinophils, and not in neutrophils or basophils. Pretreatment with the chemoattractant receptor-homologous molecule expressed on TH2 cells (CRTH2) antagonist ramatroban prevented the PGD2 enhancement of eosinophil migrations. In contrast, eotaxin or 5-oxo-ETE inhibited the migration of eosinophils towards PGD2. 5-oxo-ETE enhanced the chemotaxis to eotaxin, while eotaxin had no effect on 5-oxo-ETE-induced migration. 5-oxo-ETE induced the phosphorylation of p38 mitogen-activated protein kinase, and inhibition of p38 mitogen-activated protein kinase by SB-202190 converted the effect of 5-oxo-ETE on the chemotaxis to PGD2 from inhibition to enhancement. The presence of blood or plasma markedly decreased the sensitivity of eosinophils to eotaxin or 5-oxo-ETE, while responses to PGD2 were unaltered. In conclusion, PGD2 might be an initial chemoattractant, since it maintains its potency in the circulation and augments the responsiveness of eosinophils to other chemoattractants. In contrast, eotaxin seems to be an end-point chemoattractant, since it has reduced efficacy in blood and is capable of down-modulating eosinophil responsiveness to other chemoattractants.

5-Lipoxygenase products regulate basophil functions: 5-Oxo-ETE elicits migration, and leukotriene B4 induces degranulation

BACKGROUND

5-Lipoxygenase (5-LO) products have been strongly implicated in the pathogenesis of allergic diseases. In addition to their physiologic effects on residential cells, 5-LO products are capable of stimulating various eosinophil functions. However, little is known regarding the effects of 5-LO products on basophil functions.

OBJECTIVE

This study was designed to elucidate the effects of the main 5-LO products (ie, leukotriene [LT] B(4), LTD(4), and 5-oxo-6,8,11,14-eicosatetraenoic acid [5-oxo-ETE]), as well as their receptor expression on human basophils.

METHODS

We studied the effects of 5-LO products on Ca(2+) mobilization, migration, CD 11b expression, and degranulation of human basophils. Expression of the receptors for LTC(4)/D(4)/E(4) (cysteinyl leukotriene 1 [CysLT(1)] and CysLT(2)), LTB4 (BLT(1) and BLT(2)), and 5-oxo-ETE (oxoeicosanoid [OXE]) was assessed by means of real-time PCR and flow cytometry.

RESULTS

At the mRNA level, basophils strongly expressed OXE and predominantly expressed CysLT(1) and BLT(2). The expression level of OXE mRNA in basophils was approximately 20-fold higher than in neutrophils and similar to that in eosinophils. At the protein level, basophils expressed CysLT(1), CysLT(2), BLT(1), and OXE, but not BLT(2). All products elicited a transient increase of cytosolic calcium, with the order of magnitude being LTB(4)>5-oxo-ETE>LTD(4). 5-Oxo-ETE induced a strong basophil migratory response that was almost equivalent to that of prostaglandin D(2). LTB(4) elicited significant degranulation of IL-3-primed basophils. In contrast, no functional significance was observed for LTD(4).

CONCLUSION

Among 5-LO products, 5-oxo-ETE induces a potent basophil migratory response, and LTB(4) elicits degranulation under certain conditions. Our results strongly suggest that 5-oxo-ETE might afford opportunities for therapeutic targeting in allergic inflammation.

Reduced endocannabinoid immune modulation by a common cannabinoid 2 (CB2) receptor gene polymorphism: possible risk for autoimmune disorders

Immune system responsiveness results from numerous factors, including endogenous cannabinoid signaling in immunocytes termed the "immunocannabinoid" system. This system can be an important signaling pathway for immune modulation. To assess the immunomodulating role of the cannabinoid 2 (CB2) receptor, we sought polymorphisms in the human gene, identified a common dinucleotide polymorphism, and investigated its effect on endocannabinoid-induced inhibition of T lymphocyte proliferation. The CB2 cDNA 188-189 GG/GG polymorphism predicts the substitution of glutamine at amino acid position 63 by arginine. T lymphocytes from CB2 188-189 GG/GG homozygotes had approximately twofold reduction of endocannabinoid-induced inhibition of proliferation compared with cells from CB2 188-189 AA/AA homozygotes. In GG/GG subjects, the reduced endocannabinoid inhibitory response was highly significant for N-arachidonylglycine and nearly significant for 2-arachidonylglycerol, and a specific CB2 receptor antagonist partially blocked these effects. Also, patients with autoimmune diseases had an increased prevalence of the homozygous GG/GG genotype. Collectively, these results demonstrate reduced endogenous fatty acid amide immunomodulatory responses in individuals with the CB2 188-189 GG/GG genotype and suggest that this CB2 gene variation may be a risk factor for autoimmunity. The results also support the proposition that the CB2 receptor may represent a novel pharmacological target for selective agonists designed to suppress autoreactive immune responses while avoiding CB1 receptor-mediated cannabinoid adverse effects.

[Skin allergy to hydrocortisone hemisuccinate in a patient with asthma]

INTRODUCTION

Corticosteroids are the basis of treatment of asthma; they interrupt the development of inflammation. However, corticosteroids can also be at the origin of severe allergical reactions.

CASE REPORT

A 40 Year-old woman, during hospitalisation for severe acute asthma, presented with an allergy to hydrocortisone hemisuccinate (HCHS) in the form of generalised pruritus with, on examination, cutaneous mucosal lesions in the form of purpura and ecchymoses on the abdomen and the upper and lower limbs. The substitution of HCHS led to the return to normal.

COMMENTS

Allergic reactions to corticosteroids, generally paradoxical, were for many Years ignored and their existence was controversial. They were usually secondary to the administration of injectable substances containing hydrocortisone hemisuccinate or methylprednisolone. Their physiopathology remains a mystery. Their management requires the immediate and permanent withdrawal of the product implied, antihistamine and adrenalin in the case of shock and symptomatic treatment.

Preparation of monoclonal antibodies reactive to the endogenous small molecule, anandamide

The development of an easy and inexpensive immunoassay to measure the limited quantities of endogenous cannabinoids found in the body would be beneficial for both cannabinoid researchers and clinicians. This report describes the hapten design and carrier molecule strategy that we used to generate a panel of monoclonal antibodies (mAB) to the endogenous cannabinoid anandamide (N-arachidonylethanolamide, AEA). We designed and successfully prepared a hapten, N-arachidonyl-7-amino-6-hydroxy-heptanoic acid (AHA), which retained the basic characteristic features of anandamide--the carboxamide, the hydroxyl and the lipophilic arachidonyl moiety with its skipped double bond system, while still allowing attachment to protein. In addition, a secondary alcohol structure was added to reduce the potential for biological hydrolysis of the hapten. Because of the diverse responses obtained after coupling this hapten to four different carriers, we determined that the type of carrier molecule used was particularly important for generating anti-anandamide antibodies. Described in this report are the characteristics of a panel of 11 mAB, generated from four separate fusions, with a range of relative affinities and cross reactivities. Excellent selectivity for anandamide vs. two other endogenous cannabinoids and arachidonic acid was achieved this strategy (cross-reactivities <5%). In addition, at least one mAB maintained specificity for anandamide compared to two very closely related fatty acid amide molecules. However, the IC50 values in a standard enzyme-linked immunosorbent assay (ELISA) format (ca. 2-3 microM) indicate that improvement in antibody affinities or assay format will be required for an immunoassay to measure endogenous levels. Such work is underway.

Allergen-induced mediator release tests

The diagnosis of allergic reactions in clinical practice is based on both clinical history and the determination of specific immunoglobulin E (IgE), either in the serum or on skin mast cells. However, for various reasons, identification of the causative factors is not possible in all the cases. Moreover, not all allergies are IgE-dependent. In an attempt to find sensitive, specific and cost-effective methods to investigate hypersensitivity reactions, in vitro tests were developed at a very early stage. Allergen-induced mediator release assays analyze the mediator released from effector cells, mainly peripheral blood cells, when stimulated in vitro with serial dilutions of the putative allergens. Described initially as research tools, they could well become diagnostic tests. However, relatively few high quality reports have been published so far. In this review, we will detail allergen-dependent histamine, tryptase, arachidonic acid metabolite, e.g. cysteinyl leukotrienes and 15-hydroxyeicosatetraenoic mediator release tests.

Modulation of the host response in periodontal therapy

This paper was prepared by the Research, Science, and Therapy Committee of the American Academy of Periodontology to provide the dental profession an overview of current and potential methods to modulate the host response in the treatment of periodontal diseases. Specifically, it discusses components of periodontal disease pathogenesis (i.e., immune and inflammatory responses, excessive production of matrix metalloproteinases and arachidonic acid metabolites, and regulation of bone metabolism) and their modulation.

[Heart surgery, cardiopulmonary bypass, and organic inflammatory response. Part II: changes in leukocytes, arachidonic acid derivatives, and hormones]

The use of cardiopulmonary bypass for surgical cardiac procedures is characterized by a whole-body inflammatory reaction due to the contact of blood through nonendothelialized surfaces; this stimulates the organism to recognize the cardiopulmonary bypass system as "nonself" and to activate specific (immune) and nonspecific (inflammatory) responses. These responses are then related with postoperative damage to many body systems of the body, like pulmonary, renal or brain dysfunction, excessive bleeding and postoperative sepsis. In this paper, present knowledge on untoward responses of the patient to cardiopulmonary bypass in cardiac surgery is reviewed and discussed, particularly focusing on the perturbation of the leukocytes, of the hormones and of the products of the arachidonic acid cascade.

Dietary Platycladus orientalis seed oil suppresses anti-erythrocyte autoantibodies and prolongs survival of NZB mice

Dietary fish oils rich in 20:5(5,8,11,14,17) and 22:6(4,7,10,13,16,19) are known to replace arachidonic acid [20:4(5,8,11,14)] and to improve the immunopathology of New Zealand mice. However, in humans, similar dietary strategies may be impractical because of the high levels of fish oils required. In contrast, we believe that beneficial effects in humans may be attainable using new exotic fatty acids. Toward this end, we have focused on 5,11,14-eicosatrienoic acid [5,11,14-ETA, 20:3(5,11,14)]. This fatty acid is structurally analogous to 20:4(5,8,11,14) but lacks the delta-8 double bond essential for conversion to eicosanoids. To examine our hypothesis, diets containing the oil of Platycladus orientalis containing 3% 5,11,14-ETA, a matched control oil, fish oil, or safflower oil were fed to NZB mice. There was a dramatic delay in both the onset and the titer of direct Coombs' tests in mice fed P. orientalis oil. These were directly reflected by the abundance of 5,11,14-ETA in serum lipids. Most striking was the accumulation of 5,11,14-ETA in serum and tissue phospholipids. Though constituting only 3% of dietary fatty acids, 5,11,14-ETA was the most abundant long chain polyunsaturated fatty acid in the serum phospholipids, suggesting that it very successfully competed with 20:4 as a constituent of membrane lipids. 5,11,14-ETA was incorporated into all tissue phospholipids examined except brain phosphatidyl inositol. Among tissues, liver showed the highest incorporation of 5,11,14-ETA into phosphatidylcholine (PC), phosphatidylserine (PS), and phosphatidylinositol (PI), yet spleen PE had a higher quantity of ETA than other tissues. Lesser arachidonate in spleen PS, heart PC, and heart PI showed the evidence of replacement by 5,11,14-ETA. The data presented illustrates how new nutrition can modify autoimmune responses and emphasizes the need for further studies based on new nutritional strategies.

Arachidonic acid metabolites in normal and autoimmune mice do not influence lymphocyte-high endothelial venule interactions

In peripheral lymphoid organs the number of lymphocytes and the proportion of functional lymphocyte subsets are regulated by multiple factors including the control of lymphocyte migration by selective lymphocyte-high endothelial venule (HEV) interactions. In this study, prostaglandin E2 (PGE2) levels from normal and autoimmune mouse lymph node cells were measured. The contribution of eicosanoids to lymphocyte-HEV interactions in normal (CBA/T6) and autoimmune (MRL/n) mice was examined. There was no association between PGE2 production in normal or autoimmune mice and the age of onset of disease activity in the latter strains. Arachidonic acid metabolites, in particular PGE2 and leukotriene B4 (LTB4), did not have any effects on lymphocyte-HEV binding. Likewise, lymphocytes treated in vivo and/or in vitro with arachidonic acid metabolite inhibitors (acetyl salicylic acid, indomethacin, BW755C) did not alter lymphocyte-HEV binding interactions in both normal and autoimmune mice. No clinical significance could be attributed to lymph node PGE2 production and the age of onset of autoimmune disease. In summary, these findings cast doubt on the role of arachidonic acid metabolites in lymphocyte-HEV binding interactions.

[Arachidonic acid derivatives in periodontitis]

A myriad of mediators of inflammation are involved in the onset and progress of periodontal disease. The exact roles of some of them are understood nowadays. In this paper, the current knowledge on the products of the arachidonic acid cascade (i.e. prostaglandins and leukotrienes) is reviewed. The main interests of these mediators are in their potential in diagnosing the phases of activity of periodontitis and the therapeutic prospects that their inhibition open up.

Role of eicosanoids as mediators of inflammation in inflammatory bowel disease

An unknown initiating event in inflammatory bowel disease (IBD) activates the immune system, which is followed by infiltration of the intestinal mucosa with inflammatory cells and the production of soluble mediators of inflammation. These mediators of inflammation include the metabolites of arachidonic acid. The results of research on arachidonic acid metabolites are reviewed, and it is concluded that the major arachidonic metabolites in human IBD mucosa are the lipoxygenase products leukotriene B4 (LTB4) and 5-hydroxy-6,8,11,14-eicosatetraenoic acid. These metabolites are found in much higher concentrations in mucosa from patients with IBD than from healthy controls. Significantly more chemotactic activity is found in IBD mucosa than in healthy mucosa, and most of this activity is attributable to LTB4. Enhanced synthesis of LTB4 could account for much of the inflammatory response in IBD. Inhibition of the lipoxygenase pathway could be the mechanism that accounts for the therapeutic efficacy of mesalazine.

Human monocytes exposed to Biostim (RU 41740) alter lymphocyte mitogenesis: mechanisms of action

The immunomodulatory agent RU 41740 (Biostim), which is derived from Klebsiella pneumoniae, may augment mitogenic responses of purified human blood lymphocytes. In non-purified preparations, however, responses may be sharply reduced due to the fact that Biostim induces monocytes to secrete immunosuppressive factors. This investigation has shown that both these biological activities can be exerted by a single, major glucoprotein fraction of Biostim termed F1. The Biostim-induced suppression of mitogen responses was not blocked by antibodies directed against IFN alpha or IFN gamma, thus speaking against IFN as being a mediator of suppression. Reduced suppression, however, was observed in the presence of drugs which inhibit arachidonic acid transformation. The cyclo-oxygenase inhibitors meclofenamic acid and indomethacin, which diminish biosynthesis of prostaglandins, could partially block the Biostim-induced suppression. Such an effect was not observed with 5,8,11-eicosatrynoic acid (ETI) which is an inhibitor of 12-lipoxygenase and leukotriene biosynthesis. Combinations of ETI and meclofenamic acid, however, were more potent than the latter tested separately. Another drug termed diclofenac Na, which apart from being an inhibitor of cyclo-oxygenase, rapidly clears cells of free arachidonic acid by binding to triglycerides, was found to be the most potent in preventing Biostim-induced suppression of mitogen responses. It is concluded that Biostim-exposed monocytes liberate increased amounts of immunosuppressive eicosanoids such as prostaglandins.

Mediators of human mast cells and human mast cell subsets

Although a great deal has been learned about the mediators produced by mast cells, the ultimate biologic function(s) of mast cell remains a mystery. Histamine, LTC4, PAF, and possibly tryptase (C3a generation) all enhance vasopermeability. Mediators with anticoagulant activities such as heparin and tryptase (fibrinogenolysis) and antithrombotic activity, PGD2, would appear to facilitate dispersion in tissues of the plasma ultrafiltrate brought there by the subgroup of mediators that enhance vasopermeability. In contrast, PAF causes platelet aggregation and chymase may cause arteriolar vasoconstriction (decreasing the volume of plasma reaching venules) by generation of angiotensin II. Assessment of any differential production of mediators by different types of mast cells will be of obvious importance in sorting out the physiologic responses to mast cell activation as well as the pathophysiology of allergic reactions.

15-HETE "modulates" expression of C3b receptor (CR1) antigen on peripheral blood B-lymphocytes

We have studied the effect of the lipoxygenase metabolite, 15-HETE, on the expression of the human C3b receptor (CR1) by a B-lymphocyte enriched population of human peripheral blood leukocytes. The number of CR1 antigenic sites expressed by B-lymphocytes isolated from HLA typed donors was determined by equilibrium binding studies using an 125 I-labelled mouse monoclonal anti CR1 antibody before and after 16 hrs incubation in RPMI alone or containing 10(-6)M, 10(-7)M or 10(-8)M final concentration of 15-HETE. In B44- subjects CR1 expression on B cells increased 63% after incubation in RPMI alone. This increase was inhibited in the presence of 10(-6)M and 10(-7)M 15-HETE (23% and 30% increase respectively). In contrast, B44+ individuals showed a smaller increase in CR1 numbers when incubated in RPMI alone. In the presence of 15-HETE CR1 antigenic sites continued to increase. When B44+ subjects were classified as A29+ or A29-, donors that were A29+ B44+ accounted for the augmentation observed while A29- B44+ individuals did not differ from individuals that were A29- B44-.

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.

Arachidonic acid-related elicitors of the hypersensitive response in potato and enhancement of their activities by glucans from Phytophthora infestans (Mont.) deBary

The dose response for elicitation of the hypersensitive reaction in potato tuber discs by arachidonic acid (AA) suggested saturation at higher concentrations. Glucans from Phytophthora infestans, inactive themselves as elicitors of the hypersensitive reaction, enhanced sesquiterpene accumulation and hypersensitive browning elicited by AA. Significant activity (seven times control values) was observed with 33 pmol AA/3.0-cm potato disc in the presence of glucans. Glucans did not affect accumulation of steroid glycoalkaloids, influence the timing or relative amounts of sesquiterpenes which accumulate, or affect recovery of AA added to potato discs. Glucans enhanced activity whether added to potato discs 18 h prior to AA, at the same time as AA, or 18 h after AA. Elicitor activity in the presence of glucans was evident with 20-carbon unsaturated fatty acids that had little or no elicitor activity in the absence of glucans. The position of double bonds had considerable influence on the specific activity of unsaturated fatty acids. The most active had a minimum of three double bonds in a methylene-interrupted series beginning with delta 5, e.g., delta 5,8,11. A delta 5 double bond conferred significant activity even if it was not part of a methylene-interrupted series. The 20-carbon chain length appeared optimal for elicitor activity. The 22-carbon chain acids had low activity, and 16- and 18-carbon acids were inactive. A free carboxyl group or easily transesterified group appeared necessary for activity. Arachidonyl alcohol had very low activity and arachidonyl cyanide was inactive. AA-containing phosphatidylcholine, lysophosphatidylcholine and monoacylglycerol were at least as active as free AA, AA-containing diacylglycerols were slightly less active than free AA, and triarachidonyl glycerol was inactive.

Inhibition of the late phase response to anti-IgE in humans by indomethacin

The hypothesis of cyclooxygenase derivates of arachidonic acid as putative mediators of late phase skin reactions (LPR) was evaluated by studying the effect of indomethacin and naproxen on anti-IgE elicited skin reactions in healthy volunteers. Indomethacin 50 mg t.i.d., 48 h prior to and up to 24 h following challenge with anti-IgE 1/3300 (v/v), produced a slight attenuation of the flare response and a 35% inhibition of the LPR (P less than 0.05) at 1-24 h as compared with placebo (n = 11). Naproxen, 250 mg, b.i.d. showed analogous anti-LPR effect (n = 4, P less than 0.05). Intradermally (i.d.) injected indomethacin, 75 micrograms (7 X 10(-3) mol/l), attenuated the flare and LPR to anti-IgE 1/330 at 1-6 h (n = 12, P less than 0.01). Indomethacin, oral and i.d., enhanced the LPR to various dilutions of anti-IgE in 30% of the individuals. The results suggest that prostaglandins and thromboxanes participate in the development of an LPR in human skin.

Macrophage function in the Schistosoma mansoni egg-induced pulmonary granuloma. Role of arachidonic acid metabolites in macrophage Ia antigen expression

The ability of arachidonic acid (AA) metabolites to regulate I-region-associated (Ia) antigen expression on macrophages from schistosome-egg-induced pulmonary granulomas was examined. The prostaglandin (PG) analog 15-S-15-CH3-PGE1 (M-PGE1) and PGF2 alpha were found to modulate the kinetics of Ia expression when administered in vivo. Methyl-PGE1 significantly suppressed Ia antigen expression by hypersensitivity granuloma macrophages, while PGF2 alpha appeared to potentiate the expression. Lymphokine-induced Ia antigen expression by cultured granuloma macrophages was likewise dramatically inhibited by M-PGE1. Further analysis using systemically administered inhibitors of AA metabolism demonstrated that the cyclooxygenase inhibitor indomethacin caused augmentation of Ia expression. In contrast, lipoxygenase inhibitors significantly reduced both Ia expression and granuloma size. The role of AA metabolites in modulating chronic inflammation is discussed.

Leukotrienes and lipoxygenase factors: mediators and modulators of the allergic reaction

Lipoxygenase factors of arachidonic acid (mono- and di-Hetes) are not only mediators but also modulators of inflammatory reactions. They have chemotactic and spasmogenic properties; the latter are similar to those induced by the slow reacting-substance of anaphylaxis (SRS-A). The eosinophil chemotactic factor has been identified as a lipoxygenase product. Among the chemically mono- and di-Hetes the 5-S-12-R di-Hete (LTB4) and the 5-S 12S di-Hete demonstrated the most pronounced eosinophil chemotactic activity. The phospholipase-arachidonic acid sequence is involved in the IgE induced activation and secretion of human basophils. With arachidonic acid analogs the lipoxygenase transformation pathway is inhibited.

Indomethacin modification of immediate-type immunologic airway responses in allergic asthmatic and non-asthmatic subjects: evidence for altered arachidonic acid metabolism in asthma

To examine the role of arachidonic acid metabolism in the modulation of immediate-type immunologic airway responses, we compared the effects of indomethacin (50 mg every 6 h for 96 h) and placebo on responses to antigen inhalation challenge in allergic asthmatic subjects and a group of nonasthmatic subjects with allergic rhinitis. Sensitivity to antigen was determined for changes in one-second forced expiratory volume, specific airway conductance, and expiratory flow at 25% of the forced vital capacity measured from partial flow-volume curves. The groups differed in terms of prechallenge pulmonary function and non-immunologic airway reactivity as determined by methacholine challenge, but were comparable with respect to intradermal sensitivity to ragweed antigen. After placebo, asthmatic subjects demonstrated approximately 3.5-fold greater sensitivity to antigen than that of nonasthmatic subjects. Indomethacin had no effect on prechallenge pulmonary function in either group. However, after indomethacin, non-asthmatic subjects had a significant increase in antigen sensitivity. Indomethacin had no effect on antigen sensitivity in asthmatic subjects as measured by one-second forced expiratory volume or expiratory flow at 25% of the forced vital capacity, and produced a slight but significant decrease as measured by specific airway conductance. Indomethacin failed to alter methacholine sensitivity in atopic, non-asthmatic subjects. These findings indicate that products of arachidonic acid metabolism participate in vivo in the modulation of airway responses to immediate-type immunologic stimuli, and that this participation differs in asthmatic and non-asthmatic subjects.

Phospholipase A2 and arachidonic acid: a common link in the generation of the eosinophil chemotactic factor (ECF) from human PMN by various stimuli

An eosinophil chemotactic factor (ECF) of low molecular weight can be generated and released from human polymorphonuclear neutrophils by the calcium ionophore, phagocytosis of zymosan particles, arachidonic acid, and phospholipase A2. Since the activation of cells by the ionophore and during the phagocytic event leads to phospholipid turnover, with the subsequent generation of arachidonic acid, it is reasonable that phospholipase A2 represents the common link for ECF production. The kinetics of ECF release by phospholipase A2 is similar to the pattern observed with the various stimuli. After a rapid rise in activity a decline occurred at later times of secretion, suggesting a mechanism of inactivation. During subcellular fractionation of cells an ECF-generating component was enriched in the 200,00 g supernatant fraction, which represents the cytosol. Addition of arachidonic acid or phospholipase A2 induced ECF generation. On gel filtration analysis the ECF-generating component revealed a molecular weight of about 80,000 daltons. It is suggested that this component represents a lipoxygenase.