Increased Levels Of Leukotriene B4 Research Articles

Single-cell transcriptomics reveals variations in monocytes and Tregs between gout flare and remission.

Gout commonly manifests as a painful, self-limiting inflammatory arthritis. Nevertheless, the understanding of the inflammatory and immune responses underlying gout flares and remission remains ambiguous. Here, based on single-cell RNA-Seq and an independent validation cohort, we identified the potential mechanism of gout flare, which likely involves the upregulation of HLA-DQA1+ nonclassical monocytes and is related to antigen processing and presentation. Furthermore, Tregs also play an essential role in the suppressive capacity during gout remission. Cell communication analysis suggested the existence of altered crosstalk between monocytes and other T cell types, such as Tregs. Moreover, we observed the systemic upregulation of inflammatory and cytokine genes, primarily in classical monocytes, during gout flares. All monocyte subtypes showed increased arachidonic acid metabolic activity along with upregulation of prostaglandin-endoperoxide synthase 2 (PTGS2). We also detected a decrease in blood arachidonic acid and an increase in leukotriene B4 levels during gout flares. In summary, our study illustrates the distinctive immune cell responses and systemic inflammation patterns that characterize the transition from gout flares to remission, and it suggests that blood monocyte subtypes and Tregs are potential intervention targets for preventing recurrent gout attacks and progression.

The role of leukotriene inhibition using a 5-lipoxygenase (5-LO) inhibitor in a joint contracture model

PurposeArthrofibrosis is a common inflammatory complication of joint trauma and surgery. 5lipoxygenase (5-LO) is a key enzyme involved in inflammation. Inhibition of 5-LO has been shown to reduce inflammation in heart and lung models but has not been examined in a joint contracture model.MethodsTwenty-six rats underwent joint contracture. Six rats served as non-surgical controls. A 5-LO inhibitor, caffeic acid (CA), suspended in 10% ethanol was orally administered to 14 rats and ethanol without CA to the remaining 12 rats daily for 21 days. Leukotriene B4 (LTB4) levels were measured, both systemically and locally. 5-LO levels in the posterior capsule were quantified by measuring the ratio of the length of the posterior capsule demonstrating 5-LO immunostaining to the total length of the capsule.ResultsJoint contracture was successfully achieved in all rats who underwent manipulation. Levels of 5- LO measured in the posterior capsule were significantly increased in the animals who underwent surgery (56%/44–64) compared to the non-surgical control animals (7%/4–9). LTB4 levels were found to be significantly lower in the non-surgical control animals (107.79 ± 34.08 pg/ml) compared to all surgical animals (157.6 ± 55.3 pg/ml).ConclusionSurgical intervention resulted in increased 5-LO activity of the synovial surface of the posterior capsule and increased LTB4 levels in the patellar tendon—fat pad. Oral administration of the 5LO inhibitor, CA, was ineffective at reducing systemic and local LTB4 levels and preventing knee joint contracture. Inhibiting 5-LO activity may still be effective in preventing arthrofibrosis and warrants further investigation.

Abstract 16: LTA4 hydrolase inhibitor bestatin prevents intestinal tumors in APC mutant rodent models of FAP

Abstract Colorectal cancer (CRC) is the third most common cancer in the United States with 145,600 new cases and 51,020 deaths estimated to occur in 2019. Leukotriene B4 (LTB4), the product of the enzyme leukotriene A4 hydrolase (LTA4H), reportedly plays a role in carcinogenesis. LTA4H over expression and increased LTB4 levels are found in CRC tissues and correlate with both disease stage and reduced survival. Thus, we used a preclinical rodent model to assess repurposing bestatin (Ubenimex), a potent orally-active reversible small molecule inhibitor of LTA4H, for prevention of CRC in high-risk FAP patients. Six week old Apcmin/+ male and female mice (n≥15) were assigned to control and treatment groups; groups received the same diet either with 1000 ppm bestatin (treatment) or no bestatin (control) for 14 weeks at which point mice were euthanized and intestines were evaluated for tumors. Control mice developed colonic tumors with multiplicity of 1.35±0.16 (Mean±SEM) in males and 0.86±0.13 in females. Colonic tumor incidence was 91% and 73% in the male and female mice respectively. Additionally, control mice developed 30.52±1.66 (male) and 29.57±2.74 (female) small intestinal polyps (SIP). Dietary bestatin significantly reduced colon tumor multiplicity. Bestatin treated male mice had 55% fewer colonic tumors (0.60±0.21; p<0.01) and female mice 59% fewer (0.35±0.12; p<0.008) compared to their respective controls. Importantly colonic tumor incidence was inhibited by >50% in both genders. Bestatin administration was reduced colonic tumor incidence by 56% (p<0.001) in male and 52% (p<0.026) in female mice. Small intestinal polyps were also significantly reduced in treated mice compared to controls. Male mice developed 29% less SIP (21.67±2.32; p<0.006) while female had 46% fewer SIP (16.00±1.98; p<0.0005) compared to controls. The polyposis in rat coli (PIRC) model replicates CRC in FAP patients. PIRC rats (n=6) at 8 weeks of age were assessed for polyp number by colonoscopy, and assigned to control and bestatin (1000 ppm) groups for 8 weeks. Colonic polyp inhibition in each rat was evaluated by colonoscopy after treatment. Bestatin treatment led to strong suppression of colonic polyps; significantly fewer (~72% less; p<0.005) colonic polyps were seen in bestatin-treated PIRC rats. Pharmacokinetic analysis demonstrated that dietary bestatin resulted in significant bestatin levels in both serum (15μg/mL) and colonic tissue (up to 250 μg/g). LTB4 levels in both plasma and colon tumors were also significantly lowered by ~70% (p<0.004) and ~26% (p<0.01) respectively. Colonic tumors from the treated animals also showed an increase in NK and NKT cells suggesting immune-modulatory effects of the agent. In summary, bestatin demonstrated excellent safety, pharmacokinetics, and chemopreventive effects against CRC in preclinical models and warrants further validation clinically. Citation Format: Venkateshwar Madka, Gopal Pathuri, Hariprasad Gali, Nandini Kumar, Nagendra Sastri Yarla, Anh Bao, Adam S. Asch, Chinthalapally V. Rao. LTA4 hydrolase inhibitor bestatin prevents intestinal tumors in APC mutant rodent models of FAP [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 16.

Early and Sustained Increases in Leukotriene B4 Levels Are Associated with Poor Clinical Outcome in Ischemic Stroke Patients

Leukotriene B4 (LTB4) has been implicated in ischemic stroke pathology. We examined the prognostic significance of LTB4 levels in patients with acute middle cerebral artery (MCA) infarction and their mechanisms in rat stroke models. In ischemic stroke patients with middle cerebral artery infarction, plasma LTB4 levels were found to increase rapidly, roughly doubling within 24 h when compared to initial post-stroke levels. Further analyses indicate that poor functional recovery is associated with early and more sustained increase in LTB4 rather than the peak levels. Results from studies using a rat embolic stroke model showed increased 5-lipoxygenase (5-LOX) expression in the ipsilateral infarcted cortex compared with sham control or respective contralateral regions at 24 h post-stroke with a concomitant increase in LTB4 levels. In addition, neutrophil influx was also observed in the infarcted cortex. Double immunostaining indicated that neutrophils express 5-LOX and leukotriene A4 hydrolase (LTA4H), highlighting the pivotal contributions of neutrophils as a source of LTB4. Importantly, rise in plasma LTB4 levels corresponded with an increase in LTB4 amount in the infarcted cortex, thereby supporting the use of plasma as a surrogate for brain LTB4 levels. Pre-stroke LTB4 loading increased brain infarct volume in tMCAO rats. Conversely, administration of the 5-LOX-activating protein (FLAP) inhibitor BAY-X1005 or B-leukotriene receptor (BLTR) antagonist LY255283 decreased the infarct volume by a similar extent. To conclude, targeted interruption of the LTB4 pathway might be a viable treatment strategy for acute ischemic stroke.

Is leukotriene B4 one of the keloid marker? a fibroblast keloid study

Keloid pathogenesis occurs due to the duration of prolonged inflammatory phase and increased production of various growth factors such as TGF-β1 which may cause increasing fibroblast proliferation and collagen synthesis. Existence of one of the chemical mediators released during inflammation, leukotriene B4 (LTB4), in keloid pathogenesis specifically in the phases of inflammation and proliferation, is still unclear. The purpose of the study is to analyze the levels of LTB4 in keloid. Methods: Fibroblast culture that was done by explanting keloid and normal skin of a keloid patient. Measurement of LTB4 on keloid and normal fibroblast was done by Elisa method. This experiment was run in triplicate. Statistical test was conducted by t test for the unpaired data and Anova test. The experiment was done at cell culture laboratory of Medical Faculty of Padjadjaran University Bandung. Levels of LTB4 in keloid fibroblast was higher than that of normal skin fibroblast (mean 23143.27 vs 18191.85 pg/ml; p<0.05). Conclusion, increased LTB4 levels in keloid fibroblast showed the existence of LTB4 role in the prolonged inflammatory process in keloid pathogenesis.

Ablation of 5-lipoxygenase mitigates pancreatic lesion development

BackgroundPancreatic ductal adenocarcinoma (PDAC), which continues to have a dismal prognosis, is associated with a pronounced fibroinflammatory response. Inflammation in vivo can be mediated by 5-lipoxygenase (5LO), an enzyme that converts omega-6 fatty acids (FA) to eicosanoids, including leukotriene B4 (LTB4). We have previously shown that diets rich in omega-6 FA increase pancreatic lesions and mast cell infiltration in EL-Kras mice. In this study, we evaluated the role of 5LO in generating higher levels of LTB4 from human cells and in mediating lesion development and mast cell infiltration in EL-Kras mice. Materials and methodsHuman pancreatic ductal epithelial and cancer cells were treated with omega-6 FA in vitro. EL-Kras mice lacking 5LO (EL-Kras/5LO−/−) mice were generated and fed standard chow or omega-6 FA diets. Pancreatic lesion frequency and mast cell infiltration were compared with EL-Kras/5LO+/+ mice. Human PDAC tumors were evaluated for 5LO expression and mast cells. ResultsHuman pancreatic ductal epithelial and pancreatic cancer cells treated with omega-6 FA generated increased LTB4 levels in vitro. EL-Kras/5LO−/− mice developed fewer pancreatic lesions and had decreased mast cell infiltration when compared with EL-Kras/5LO+/+ mice. Human PDAC tumors with increased 5LO expression demonstrate increased mast cell infiltration. Additionally, diets rich in omega-6 FA failed to increase pancreatic lesion development and mast cell infiltration in EL-Kras/5LO−/− mice. ConclusionsThe expansion of mutant Kras-induced lesions via omega-6 FA is dependent on 5LO, and 5LO functions downstream of mutant Kras to mediate inflammation, suggesting that 5LO may be a potential chemopreventive and therapeutic target in pancreatic cancer.

Relationship between salivary leukotriene B4 levels and salivary mucin or alveolar bone resorption, in subjects with periodontal health and disease

Here we determine the salivary levels of leukotriene B4 (LTB4 ) and its relation with salivary mucin and alveolar bone level. LTB4 is a membrane-derived lipid mediator formed from arachidonic acid. It is among the most potent stimulants of polymorphonuclear leukocytes providing the first host defense against infections. Leukotrienes also induce bone resorption. Because LTB4 is present in the oral cavity the aim of the present study was to explore the role of LTB4 in patients with periodontal disease. Eighty-one subjects were clinically examined and distributed into four groups, namely, clinically healthy, mild, moderate and severe periodontitis, according to periodontal status, classified into values of clinical attachment level and probing pocket depth. Unstimulated saliva was collected for 5min. Salivary LTB4 was determined by an immune assay method, mucin was determined by a colorimetric method and radiographic assessment used to determine alveolar bone level. Patients with mild periodontitis showed a decrease in salivary LTB4 levels while patients with severe periodontitis showed increased LTB4 levels. A significant positive correlation was observed between salivary LTB4 and clinical attachment level, salivary mucin concentration or alveolar bone level. The close relation between salivary LTB4 and mucin levels suggested that LTB4 might be involved in the defense mechanism of the oral cavity. The correlation of LTB4 with the alveolar bone level indicates that they are one of the mediators responsible for bone resorption.

Phosphorylation of 5-Lipoxygenase at Ser523 by Protein Kinase A Determines Whether Pioglitazone and Atorvastatin Induce Proinflammatory Leukotriene B4 or Anti-Inflammatory 15-Epi-Lipoxin A4 Production

The 5-lipoxygenase (5LO) produces leukotriene B(4) and 15-epilipoxin-A(4) (15-epi-LXA(4)). Phosphorylation at Ser(523) by protein kinase A (PKA) prevents 5LO shift to the perinuclear membrane. Atorvastatin and pioglitazone up-regulate 15-epi-LXA(4) production in the heart. We assessed whether phosphorylation of 5LO by PKA determines whether 5LO interacts with the membranous cytosolic phospholipase A(2) (cPLA(2)) to produce leukotriene B(4) or with cyclooxygenase-2 (COX2) to produce 15-epi-LXA(4). Rats received either pioglitazone, atorvastatin, pioglitazone plus atorvastatin, vehicle, or LPS. Rat myocardial cells were incubated with pioglitazone plus atorvastatin, pioglitazone plus atorvastatin plus H-89 (PKA inhibitor), H-89, or vehicle for 8 h. Pioglitazone and atorvastatin did not affect total 5LO expression. However, both increased 5LO levels in the cytosolic fraction. H-89 caused a shift of 5LO to the membranous fraction in atorvastatin- and pioglitazone-treated rats. Pioglitazone and atorvastatin increased phospho-5LO levels. H-89 attenuated this increase. Both pioglitazone and atorvastatin increased COX2 levels in the cytosolic fraction and the membranous fraction. H-89 prevented this increase. Pioglitazone and atorvastatin increased cPLA(2) expression in the membranous fraction. This effect was not attenuated by H-89. Pioglitazone plus atorvastatin increased 15-epi-LXA(4) levels. H-89 attenuated the effect of pioglitazone plus atorvastatin. Pioglitazone plus atorvastatin plus H-89 increased leukotriene B(4) levels. Coimmunoprecipitation showed that without H-89, atorvastatin and pioglitazone induced an interaction between 5LO and COX2 in the cytosolic fraction, whereas when H-89 was added, 5LO interacted with cPLA(2) on the membranous fraction. The 5LO phosphorylation determines whether 15-epi-LXA(4) (anti-inflammatory) or leukotriene B(4) (inflammatory mediator) is produced.

Phosphorylation of 5‐lipoxygenase by protein kinase A determines whether leukotriene B4 or 15‐epilipoxin A4 mediators are produced in the heart

5-lipoxygenase (5LO) produces both 15-epilipoxin-A4 (15ELX), an antiinflammatory mediator, and leukotriene-B4 (LTB4). Phosphorylation at Ser523 by protein kinase A prevents 5LO translocation to the perinuclear membrane. Atorvastatin (ATV) and pioglitazone (PIO) upregulate 15ELX. We assessed whether 5LO phosphorylation (P5LO) by PKA determines whether the cells produce LTB4 or 15ELX. Methods: Rats received either oral PIO (10 mg/kg/d); ATV (10 mg/kg/d); PIO+ATV; or vehicle; 5) or iv lipopolysacharide (LPS) (10 mg/kg). Rat myocardial cells were incubated with ATV+PIO, ATV+PIO+H89 (PKA inhibitor), H89, or vehicle for 8h. Results: ATV (1347±27%), PIO (1407±47%), ATV+PIO (1629±11%), and LPS (185±9%) increased P5LO (p<0.001). ATV+PIO increased P5LO (2069±93%). H89 attenuated the effect of ATV+PIO (409±18%)(p<0.001). ATV+PIO increased 15ELX (2.19±0.04 vs 0.87±0.03 ng/ml in sham). H89 attenuated the effect of PIO+ATV (1.66±0.06) (p<0.001). PIO+ATV (35.58±0.86 pg/ml) and H89 (35.56±0.89) had no effect on LTB4 (sham 36.44±0.25). PIO+ATV+H89 increased LTB4 levels (64.51±0.61) (p<0.001). Immunofluorescence shows that ATV+PIO increased cytosolic expression of 5LO. H89 alone had no effect, whereas in the ATV+PIO+H89 5LO translocated to the perinuclear membrane. Conclusions: Phosphorylation of 5LO determines whether 15ELX (anti-inflammatory) or LTB4 (inflammatory mediator) are produced.

Tepoxalin inhibits inflammation and microvascular dysfunction induced by abdominal irradiation in rats.

Inflammatory cells contribute to the acute and sub-acute sequelae of radiation therapy. Tepoxalin, an inhibitor of cyclooxygenase and 5-lipoxygenase that suppresses NF-kappaB activation, has potent anti-inflammatory activity. To assess the effects of tepoxalin on radiation-induced inflammatory damage, and determine its mechanisms of action. Leucocyte rolling, adhesion and emigration, and albumin leakage were determined by intra-vital microscopy in rat mesenteric venules. NF-kappaB activation was measured by electrophoretic mobility shift assays, and endothelial intercellular adhesion molecule-1 expression by the radiolabelled antibody technique. Groups of irradiated rats were treated with tepoxalin, N-acetyl-L-cysteine, zileuton (lipoxygenase inhibitor), or vehicle. Irradiated animals had a marked increase in the number of rolling, adherent and emigrated leucocytes in mesenteric venules, and in microvascular permeability. Tepoxalin prevented leucocyte adhesion and the increase in permeability after radiation. Tepoxalin did not inhibit radiation-induced NF-kappaB activation or intercellular adhesion molecule-1 up-regulation, while N-acetyl-L-cysteine, which attenuated NF-kappaB activation, had no effect on leucocyte recruitment. In contrast, tepoxalin inhibited the increase in leukotriene B4 levels after radiation, and the anti-inflammatory effects of the drug were mimicked by zileuton. Tepoxalin affords significant protection against radiation-induced inflammation and microvascular dysfunction in splanchnic organs through a mechanism dependent on leukotriene synthesis inhibition.

Effect of a 5‐lipoxygenase inhibitor and leukotriene antagonist (PF 5901) on antigen‐induced airway responses in neonatally immunized rabbits

1. The effect of a single intratracheal dose (10 mg) of PF 5901 (2-[3(1-hydroxyhexyl) phenoxymethyl] quinoline hydrochloride, a specific inhibitor of the 5-lipoxygenase pathway of arachidonic acid metabolism and a leukotriene D4 antagonist) on airway changes induced in response to Alternaria tenuis aerosol challenge was assessed in adult rabbits neonatally immunized. Leukotriene generation was determined in vivo by measuring leukotriene B4 (LTB4) levels in bronchoalveolar lavage (BAL) fluid and ex vivo by measuring calcium ionophore-stimulated production of LTB4 in whole blood. 2. While PF 5901 (10 mg) had no significant effect on the acute bronchoconstriction induced by antigen, this dose was sufficient to inhibit significantly the increase in airway responsiveness to inhaled histamine 24 h following antigen challenge (P < 0.05). 3. Total leucocyte infiltration into the airways induced by antigen, as assessed by bronchoalveolar lavage, was significantly inhibited by pretreatment with PF 5901 (10 mg). However, the pulmonary infiltration of neutrophils and eosinophils induced by antigen was unaltered by prior treatment with PF 5901 (10 mg). 4. PF 5901 (10 mg) had no effect on ex vivo LTB4 synthesis in whole blood. However, the antigen-induced increase in LTB4 levels in BAL 24 h following challenge was significantly inhibited (P < 0.05). 5. We suggest from the results of the present study that the antigen-induced airway hyperresponsiveness to inhaled histamine in immunized rabbits is mediated, at least in part, by products of the 5-lipoxygenase metabolic pathway, and is not dependent on the extent of eosinophil or neutrophil influx into the airway lumen.

Eicosanoids in hypoxic insult to neonatal rabbit bowel.

Eicosanoids, derivatives of arachidonic acid, play a role in several inflammatory diseases of the bowel. To determine whether prostaglandin E2 (PGE2), leukotriene B4 (LTB4), and leukotriene C4D4E4 (LTC4D4E4), have a role in hypoxic insult to the intestine, we examined the levels of these mediators in a hypoxic neonatal rabbit model. One group of animals underwent hypoxic insult postnatally, the second group did not undergo hypoxia and served as a control. The levels of PGE2, LTB4, and LTC4D4E4 were determined by radioimmunoassay. PGE2 in the hypoxic group was 1,779 +/- 142 pg/mg protein (mean +/- SD) as opposed to 2,380 +/- 197 pg/mg protein in the control group (p less than 0.02). LTB4 level was 5,446 +/- 3,492 pg/mg protein in the hypoxic rabbits and 3,362 +/- 2,570 pg/mg protein in the control group (p less than 0.03). There was no statistically significant difference in the level of LTC4D4E4 between the two groups. Our study shows that hypoxia shifts the arachidonic acid metabolism toward enhanced lipoxygenase activity with a resultant increase in LTB4 levels and a concomitant decrease in cyclooxygenase activity with reduced PGE2 levels in the bowel. The shift in the balance between these eicosanoids may play a role in the pathogenesis of ischemic-hypoxic bowel diseases by enhancing the inflammatory response in the intestine, and simultaneously, diminishing cytoprotection.

Eicosanoids in Hypoxic Insult to Neonatal Rabbit Bowel

SummaryEicosanoids, derivatives of arachidonic acid, play a role in several inflammatory diseases of the bowel. To determine whether prostaglandin E2 (PGE2), leukotriene B4 (LTB4), and leukotriene C4D4E4 (LTC4D4E4), have a role in hypoxic insult to the intestine, we examined the levels of these mediators in a hypoxic neonatal rabbit model. One group of animals underwent hypoxic insult postnatally, the second group did not undergo hypoxia and served as a control. The levels of PGE2, LTB4, and LTC4D4E4 were determined by radioimmunoassay. PGE2 in the hypoxic group was 1,779± 142 pg/mg protein (mean± SD) as opposed to 2,380± 197 pg/mg protein in the control group (p &lt; 0.02). LTB4 level was 5,446± 3,492 pg/mg protein in the hypoxic rabbits and 3,362± 2,570 pg/mg protein in the control group (p &lt; 0.03). There was no statistically significant difference in the level of LTC4D4E4 between the two groups. Our study shows that hypoxia shifts the arachidonic acid metabolism toward enhanced lipoxygenase activity with a resultant increase in LTB4 levels and a concomitant decrease in cyclooxygenase activity with reduced PGE2 levels in the bowel. The shift in the balance between these eicosanoids may play a role in the pathogenesis of ischemic‐hypoxic bowel diseases by enhancing the inflammatory response in the intestine, and simultaneously, diminishing cytoprotection.

Epidermal Cell—Polymorphonuclear Leukocyte Cooperation in the Formation of Leukotriene B4 by Transcellular Biosynthesis

The cellular origin of Leukotriene B4, a potent pro-inflammatory agent that is present in psoriatic lesions, has not been completely ascertained. The present study was performed in order to assess the possible contribution of epidermal cells to leukotriene B4 synthesis through 5-lipoxygenase or by means of transcellular metabolism of the epoxide intermediate leukotriene A4 from activated polymorphonuclear leukocytes. The metabolism of exogenous arachidonic acid in fresh human epidermal cell, polymorphonuclear leukocyte or mixed suspensions was determined by means of high-performance liquid chromatography. Epidermal cells transformed arachidonic acid mainly into 12-hydroxy-eicosatetraenoic acid and prostaglandin E2. Formation of prostaglandins F2 alpha and D2, 12-hydroxy-eptadecatrienoic acid, and 15- and 11-hydroxy-eicosatetraenoic acids was also detected. We did not detect any eicosanoid derived from 5-lipoxygenase pathway. Mixed suspensions of polymorphonuclear leukocytes and epidermal cells (ratio 1:4) produced 1.72 times more leukotriene B4 than leukocytes alone under the same experimental conditions. Epidermal cells incubated with 5 microM authentic leukotriene A4 for 3 min yielded 2.954 +/- 0.27 pmoles/10(6) cells of leukotriene B4, which was characterized by co-elution with authentic standard and its ultraviolet absorption spectrum. These data demonstrate the existence of a leukotriene A4 epoxide hydrolase activity in human epidermal cells. Our results suggest that epidermal cells could cooperate in leukotriene B4 biosynthesis by transcellular metabolism of leukotriene A4 in lesions of psoriasis, and possibly other inflammatory dermatoses characterized by increased leukotriene B4 levels and prominent polymorphonuclear leukocyte infiltrates.

Leukotriene B4 levels from stimulated neutrophils from healthy and allergic subjects: effect of platelets and exogenous arachidonic acid.

Leukotriene B4 (LTB4) levels were measured in peripheral blood neutrophils from allergic and healthy donors after stimulation by calcium ionophore A 23187. This level was higher in neutrophils from allergic subjects than in neutrophils from healthy subjects in the presence as well as in the absence of exogenous arachidonic acid. Platelets from allergics increased LTB4 levels from neutrophils from allergics but not levels in those from healthy donors. Moreover, platelets from healthy subjects reduced LTB4 in neutrophils from both groups. These results suggest that biochemical differences exist in neutrophils and platelets from allergics which contribute to changes in arachidonic acid metabolism via the 5-lipoxygenase pathway. In addition, they support the concept that platelets may play an important role in the regulation of neutrophil LTB4 levels, possibly by affecting the 5-lipoxygenase activity during the course of allergic inflammatory reactions.