Beta2-integrin adhesion caused by eotaxin but not IL-5 is blocked by PDE-4 inhibition and beta2-adrenoceptor activation in human eosinophils

We investigated the effect and mechanism(s) of PDE-4 treatment with concurrent beta2-adrenoceptor stimulation on human eosinophil adhesion mediated by beta2-integrin in vitro. Eosinophils were pretreated with either rolipram, a PDE-4 inhibitor, alone or combined with salmeterol, a beta2-adrenoceptor agonist, before activation with either eotaxin or IL-5. Beta2-integrin mediated adhesion was assessed as adherence to BSA, an established surrogate for ICAM-1. Rolipram caused progressive blockade (77.7 +/- 6.2%) of adhesion elicited by eotaxin. Maximal blockade of IL-5-activated adhesion by rolipram was substantially less (29.9 +/- 5.2%). Salmeterol + rolipram synergistically enhanced the blockade of eotaxin-activated adhesion. Eotaxin also caused approximately 50% increase in surface CD11b expression, which was blocked additively by rolipram + salmeterol. By contrast, CD11b upregulation caused by IL-5 was not blocked by rolipram + salmeterol. Rolipram also attenuated cPLA2 phosphorylation caused by eotaxin but did not block IL-5-induced phosphorylation. We conclude that rolipram blocks expression of CD11b and inhibits cPLA2 phosphorylation in human eosinophils, thus blocking eotaxin-induced adhesion of beta2-integrin. IL-5-induced adhesion likely utilizes a different upstream mechanism in regulation of integrin adhesion.     

Inhibition by prostaglandins of leukotriene B4 release from activated neutrophils.

Chemoattractant N-formylmethionylleucylphenylalanine (fMet-Leu-Phe) in the presence of cytochalasin B stimulates the release of leukotriene B4 (LTB4), superoxide (O2-), and N-acetylglucosaminidase from elicited rat peritoneal and human peripheral neutrophils [PMN (polymorphonuclear leukocytes)]. Prostaglandins E1 and E2 (PGE1 and PGE2) inhibit LTB4 release from PMN in a dose-related manner with an IC50 of 1 X 10(-8) M. This action is associated with increased levels of cyclic AMP. The inhibitory activity of a variety of PGs on LTB4 production by rat peritoneal PMN parallels their affinity for PGE receptors in other tissues. O2- release is also suppressed by low levels of PGE1 and PGE2 in a dose-related manner and this inhibition is enhanced by theophylline. In contrast, lysosomal enzyme release is only minimally affected by physiological levels of PGs. These data are consistent with an action of PGs at the level of the PG receptor on LTB4 and O2- release from the fMet-Leu-Phe-stimulated rat peritoneal PMN. In addition, the fMet-Leu-Phe-induced adherence of PMN to endothelial cells and inhibition of this phenomenon by PGs may now be explained by PG-mediated inhibition of LTB4 formation.     

Additive blockade of beta 2-integrin adhesion of eosinophils by salmeterol and fluticasone propionate.

Migration of human eosinophils is regulated by integrin expression, conformational change, and activation of cytosolic phospholipase A2 (cPLA2). Corticosteroids have been shown to inhibit cPLA2 hydrolysis in human eosinophils. The objective of this study was to determine the mechanisms of fluticasone propionate (FP) alone or in combination with salmeterol (SM) in blocking adhesion mediated by beta 2-integrin in human eosinophils. Human eosinophils were isolated by negative magnetic selection. beta 2-integrin-mediated eosinophil adhesion was measured by residual eosinophil peroxidase activity. Eosinophils were pretreated for 12 h to 24 h with FP and with or without SM for 30 min. Both SM alone and FP alone inhibited eosinophil adhesion in concentration- and time-dependent manner. SM alone modestly (approximately 30%) inhibited interleukin (IL)-5-induced eosinophil adhesion. Blockade of IL-5-induced eosinophil adhesion caused by 10(-7) M FP at 24 h was augmented by 10(-7) M SM from 41.5% to 72.5%. Similar blockade was also observed for eotaxin-induced eosinophil adhesion. Neither SM, FP, nor FP + SM blocked either: 1) upregulation of CD11b surface expression; or 2) phosphorylation of cPLA2. Blockade of beta 2-integrin-mediated eosinophil adhesion by fluticasone propionate is augmented by salmeterol. Decreased adhesion results from augmented blockade of nuclear translocation of cytosolic phospholipase A2 caused by addition of salmeterol to fluticasone.     

Altered formation of leukotriene B4 in vitro by synovial fluid neutrophils in rheumatoid arthritis

The synthesis of products of the 5-lipoxygenase pathway by synovial fluid (SF) and peripheral blood neutrophils of 12 patients with rheumatoid arthritis was compared in 3 experimental conditions using high performance liquid chromatographic analysis. Major differences were observed when blood and SF neutrophils were incubated with ionophore A23187, the formation of all 5-lipoxygenase products being lower (p less than 0.0005) in the SF neutrophils. Addition of exogenous arachidonic acid to the A23187 stimulated cells partially overcame the difference in 5-lipoxygenase product synthesis between the 2 neutrophil populations. In contrast, upon incubation with arachidonic acid alone, SF neutrophils produced significantly larger amounts of 5-lipoxygenase products. The increased reactivity of the SF neutrophil 5-lipoxygenase to arachidonic acid and the decreased 5-lipoxygenase product synthesis upon A23187 stimulation may be the consequence of the previous activation of the cells and 5-lipoxygenase product synthesis in situ.     

Telmisartan inhibits beta2-integrin MAC-1 expression in human T-lymphocytes

OBJECTIVE: The pathogenesis of atherosclerosis, a chronic inflammatory disease, is influenced by the renin-angiotensin system and especially by angiotensin II subtype 1 (AT1) receptor activation. Although pro-inflammatory properties of angiotensin II as well as anti-inflammatory effects of AT1 receptor antagonists are well known, the underlying mechanisms are poorly understood. METHOD AND RESULTS: In a prospective double-blind study, patients with hypertension and coronary artery disease were treated with either 40 mg telmisartan (n = 21) or placebo (n = 21) for 12 weeks. General markers of inflammation, such as high-sensitivity C-reactive protein (hs-CRP) and interleukin-6 (IL-6), and cell adhesion molecules, such as soluble intercellular adhesion molecule (s-ICAM-1) and the leucocyte adhesion molecule soluble-L-selectin (sL-selectin), as well as the lymphocytic expression of the beta2 integrin MAC-1, were assessed before and after treatment. Telmisartan therapy significantly decreased the lymphocyte beta2 integrin MAC-1 expression, whereas hs-CRP, IL-6, s-ICAM and sL-selectin remained unaltered. In-vitro experiments were conducted to clarify the mode of action. Cultured human lymphocytes were stimulated with either angiotensin II or phorbol-12-myristate-13-acetate (PMA)/ionomycin, alone or after pretreatment with telmisartan. Whereas angiotensin II exerted no effect on beta2-integrin MAC-1 expression in lymphocytes, telmisartan dose-dependently inhibited beta2-integrin expression in lymphocytes in the absence or presence of angiotensin II. CONCLUSION: The AT1 receptor antagonist telmisartan inhibits the expression of the pro-inflammatory beta2-integrin MAC-1 expression in lymphocytes independently of angiotensin II, suggesting an AT1 receptor-independent atheroprotective effect of this AT1 receptor antagonist.     

Prostaglandin E2 and leukotriene B4 synthesis by peripheral leucocytes in alcoholics.

Alcohol inhibits phospholipase (PL) activity in a number of animal models. We have therefore measured prostaglandin E2 (PGE2) and leukotriene B4 (LTB4), liberated by stimulated peripheral blood mononuclear cells (PBMC) and neutrophils respectively in chronic alcoholics and in control subjects. Peripheral blood mononuclear cells from alcoholics produced less PGE2 (p less than 0.01) and neutrophils produced less LTB4 (p less than 0.025). Reduced PGE2 production by PBMC of alcoholics was corrected by the addition of exogenous arachidonic acid (p less than 0.005) whilst neutrophil LTB4 production remained lower in the alcoholics (p less than 0.01). Percutaneous liver biopsies were undertaken in the 20 alcoholics having abnormal liver function tests. Prostaglandin E2 biosynthesis was lower in PBMC from patients with alcoholic hepatitis than with alcoholic cirrhosis (p less than 0.05). Analysis of PBMC fatty acid composition demonstrated that endogenous arachidonate and linoleate contents were not significantly different in alcoholics and controls. Cells from controls and alcoholics were incubated with 0, 50 and 150 mmol/l ethanol for two hours but there was no alteration in PGE2 or LTB4 biosynthesis. In summary, we found reduced eicosanoid production by peripheral leucocytes in alcoholics, supporting the hypothesis that chronic alcohol consumption either inhibits membrane bound phospholipase activity or enhances, alternatively, catabolism of eicosanoids. This phenomenon is more marked in alcoholic patients with hepatitis than in those with cirrhosis alone.     

Deficient induction of leukotriene synthesis in human neutrophils by lipoxygenase-deficient platelets

The effect of human platelets with deficient lipoxygenase activities on leukotriene B4 (LTB4) synthesis by neutrophils was studied. When arachidonic acid (AA) metabolites obtained from the incubation of washed normal neutrophils and platelets with N- formylmethionylleucylphenylalanine (FMLP), cytochalasin B, and AA were analyzed by reversed-phase high-performance liquid chromatography, the synthesis of 5-lipoxygenase products, including LTB4, was remarkably stimulated by platelets, with their maximal effect at a ratio of platelets to neutrophils of 15:1. However, the use of lipoxygenase- deficient platelets obtained from four patients with myeloproliferative disorders instead of normal platelets showed the deficient production of 5-lipoxygenase-derived products, whereas platelets with normal lipoxygenase activities obtained from MPD patients stimulated the 5- lipoxygenase pathway similarly to the way in which normal platelets did. The addition of 12-hydroperoxyeicosatetraenoic acid (12-HPETE), a labile AA metabolite via the platelet lipoxygenase pathway, could activate the 5-lipoxygenase pathway in neutrophils incubated with FMLP, cytochalasin B and AA, but its stable end product, 12- hydroxyeicosatetraenoic acid, could not. Thus, it is suggested that lipoxygenase-deficient platelets did not sufficiently stimulate LTB4 synthesis during platelet-neutrophil interactions because of defective formation of 12-HPETE. This altered interaction between platelets and neutrophils through the lipoxygenase pathway might result in deficient responses at sites of thrombosis or inflammation in patients with deficient platelet lipoxygenase activities.     

Enhanced generation of leukotriene B4 by neutrophils stimulated by unopsonized zymosan and by calcium ionophore after exercise-induced asthma

The generation of LTB4 by peripheral blood neutrophils (PMN) isolated before and for as long as 6 h after exercise-induced asthma (EIA) has been analyzed. Three and 6 h after the development of EIA, PMN isolated from 10 asthmatic subjects and stimulated in vitro by 2 x 10(8) and 4 x 10(8) zymosan particles per 2 x 10(6) PMN demonstrated a 12- and 4-fold enhancement, respectively, in the production of immunoreactive LTB4 as compared with PMN isolated before exercise. At 6 h after EIA, there was a redistribution of generated LTB4 such that 30 to 40% of LTB4 produced by zymosan-activated PMN was released extracellularly as compared with 10% before exercise. There was no significant enhancement in the generation of LTB4 by unstimulated PMN at any time point after exercise. Resolution by reverse-phase high performance liquid chromatography (HPLC) of products from [3H]arachidonic-acid-labeled and zymosan-activated PMN demonstrated that, in addition to LTB4, there was enhanced metabolism to 6-trans-LTB4, omega-oxidation metabolites of LTB4 and 5-HETE. Stimulation of PMN with 10 microM A23187 revealed a 2-, 6-, and 5-fold enhancement in the production of LTB4, 6-trans-LTB4, and 5-HETE, respectively, at 6 h after EIA, as measured by integrated ultraviolet absorbance after HPLC. There was no significant enhancement in LTB4 generation by PMN in 6 asthmatic subjects after methacholine-induced bronchospasm, and after exercise in 6 subjects who did not develop asthma. The augmentation of PMN LTB4 generation in EIA correlated with the extent of the early decrease in SGaw.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of humoral immunity on leukotriene B4 production by neutrophils in response to Trichomonas vaginalis stimulation

Neutrophils are the predominant inflammatory cells found in vaginal discharges from patients with Trichomonas vaginalis infection. In this study, we investigated the effect of humoral immunity on leukotriene B4 (LTB4) generation by neutrophils in the inflammatory response of vaginal trichomoniasis. As quantitated by a radioimmunoassay, no release of LTB4 was detected from neutrophils (5 x l0⁶/ml) interacted with trichomonads (1 times 10⁶/ml). However, specific immunoglobulin G(IgG) but not F(ab¹)₂, at a titre of 1:256 directed against T. vaginalis, augmented LTB4 production (1·4 ± 0·4 ng/ml, n= 5) by neutrophils, suggesting that this enhancement is Fey receptor-mediated. Moreover, addition of the specific IgG (1 mglml) to C2-deficient serum or Factor B-deficient serum, but not C5-deficient serum, significantly increased LTB4 production by neutrophils in response to trichomonad stimulation. This indicates that the complement common pathway activation is crucial for the amplification of host defence mechanisms against T. vaginalis. An LTB4 receptor antagonist, SC-41930, completely abolished neutrophil chemotactic activity induced by LTB4. Taken together, these results indicate that humoral immunity could promote the interaction of neutrophils with T. vaginalis and augment the inflammatory response through the amplification of LTB4 production.     

Potentiation and inhibition of migration of human neutrophils by auranofin.

OBJECTIVES--As auranofin resembles some neutrophil activating sulphur containing compounds, it was decided to investigate whether it had activating effects on neutrophil migration in addition to the published inhibitory effects. METHODS--The Boyden chamber assay was used to determine the migration velocity of human neutrophils. The difference between chemotaxis and chemokinesis was established with a chequerboard assay. RESULTS--Low concentrations of auranofin stimulated human neutrophil migration; concentrations of auranofin higher than 1 mumol/l were inhibitory. Inhibitors of leukotriene formation, or of protein kinase C, had the same effect on auranofin induced potentiation of migration as on fMLP activated migration. Auranofin, at a concentration of 100 nmol/l, caused a transient increase in the cGMP level of neutrophils. The auranofin induced increase in migration was strongly inhibited by methylene blue and by LY83583, two inhibitors of cGMP accumulation. CONCLUSIONS--The auranofin induced enhancement of migration is partly due to a chemokinetic effect, but mainly due to a chemotactic effect. The potentiating effect of auranofin on migration is not specifically due to the ability of the drug to inhibit protein kinase C activity or to generate leukotrienes. These results suggest that the enhancement of neutrophil migration by low levels of auranofin is related to the enhancement of cGMP levels in neutrophils.     

Inhibitory effect of loratadine on leukotriene B4 production by neutrophils either alone or during interaction with human airway epithelial cells

Leukotriene B4 (LTB4), an inflammatory mediator, is a potent chemoattractant for neutrophils (PMN) that plays an important role in the late reaction in asthma. Human airway epithelial cells (HAEC) can interact with PMN to increase LTB4 production. The aim of this study was to determine the influence of loratadine, an antihistaminic drug, on the production of LTB4 by PMN either alone or during interaction with transformed HAEC. The effect of tumour necrosis factor-alpha (TNF-alpha) was also examined. LTB4 production was measured by RP-HPLC after cell stimulation with calcium ionophore. Loratadine (0.25-25 microM) induced a significant and dose-dependent decrease of LTB4 production by PMN alone whereas it was up-regulated by TNF-alpha. As reported by others, we confirmed the increase of LTB4 release when PMN were cocultured with HAEC as compared to PMN alone. Addition of loratadine to HAEC before co-culture with PMN induced a significant decrease of LTB4 formation by cell interaction. This effect was noted when HAEC were washed following incubation with loratadine, demonstrating a direct action of the drug on this cell type. Moreover, the TNF-alpha-induced stimulation of LTB4 release that we demonstrated in PMN-HAEC interaction was also inhibited by loratadine. These results indicate that loratadine might reduce inflammatory reaction by a direct effect on PMN LTB4 production but also through an influence on HAEC during interaction with PMN.     

Generation of leukotriene B4 by human lung fragments and purified human lung mast cells

Leukotriene B4 (LTB4) is a potent stimulus for neutrophil chemotaxis, aggregation, and activation. Although this mediator has been postulated as a possible stimulus for the neutrophil accumulation seen after mast cell triggering in vivo, the ability of human mast cells to produce this leukotriene has never been described. The purpose of this study was to investigate the ability of purified human lung mast cells and mast cells in lung fragments to generate leukotriene B4 after immunologic (anti-IgE) and nonimmunologic (calcium ionophore, A23187) activation. Release of LTB4 was quantitated by 2 specific radioimmunoassays with biochemical characterization by high performance liquid chromatography. In a first series of experiments using radioimmunoassay 1, purified human lung mast cells (n = 10) released LTB4 in response to both an immunologic and nonimmunologic stimulus in a time- and dose-dependent manner. In response to an optimum concentration of anti-IgE (3 micrograms/ml), mast cells of 4.5 to 98% purity, generated 6.2 +/- 1.7 ng immunoreactive LTB4 (iLTB4)/10(6) mast cells. HPLC characterization revealed that 30 +/- 0.3% of the iLTB4 coeluted with standard synthetic LTB4 in these studies. In a second series of experiments using radioimmunoassay 2, mast cell activation resulted in the release of 0.5 to 1 ng iLTB4/10(6) mast cells with greater than 75% coeluting with synthetic LTB4. Thus, we estimate that human lung mast cells can generate approximately 1 to 2 ng of LTB4 per million mast cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of gold compounds on leukotriene B4, leukotriene C4 and prostaglandin E2 production by polymorphonuclear leukocytes

The effects of auranofin (AF) and sodium aurothiomalate (GSTM) on the production of specific arachidonic acid metabolites by chemotactic tripeptide activated polymorphonuclear leukocytes has been investigated using radioimmunoassay techniques. AF insignificantly enhanced the production of leukotrienes B4 and C4 at a concentration of 0.5 microgram Au/ml. However, at increasing concentrations, this drug suppressed the production of these metabolites in a dose dependent manner. In contrast, GSTM did not affect the production of either leukotriene at the concentrations tested. Of particular interest, prostaglandin E2 production was not affected by either gold compound. Both leukotrienes and prostaglandins are metabolized from arachidonic acid and are potent mediators of inflammation. The inhibition of leukotriene production may be another mechanism by which AF manifests its antiinflammatory effects in patients with rheumatoid arthritis.     

Prolongation of survival of human polymorphonuclear neutrophils by granulocyte-macrophage colony-stimulating factor is caused by inhibition of programmed cell death.

In the absence of appropriate stimuli, polymorphonuclear neutrophils (PMN) undergo programmed cell death (PCD), also termed apoptosis. We show that granulocyte-macrophage colony-stimulating factor (GM-CSF), but not the chemotactic factors formyl-methionyl-leucyl-phenylalanine (FMLP), recombinant human (rh) C5a, transforming growth factor (TGF)-beta, and interleukin-8 (IL-8), or other cytokines including IL-3, IL-4, IL-6, and G-CSF, maintains viability of PMN in culture by preventing these cells from undergoing PCD. Prevention from PCD by GM-CSF was associated with induction of RNA and protein synthesis in PMN. Inhibition of RNA and protein synthesis by actinomycin-D and cycloheximide impeded the protection of apoptosis by GM-CSF. Similarly, neutralization of GM-CSF biologic activity by a specific antiserum abrogated GM-CSF-mediated inhibition of PCD.     

Glucocorticoid-induced lymphoma cell growth inhibition: the role of leukotriene B4

Glucocorticoid-sensitive murine S49.1 lymphoma cells respond in a biphasic way to the steroid challenge. The first effect of corticosteroids is to induce a reversible growth inhibition, which is probably permissive for the following cytolysis. Distinct mechanisms for the two effects are likely. Since dilution of S49.1 lymphoma cultures resulted in a drastic reduction of the proliferation rate, which could be overcome by the addition of conditioned medium, the proliferation appears to depend on the presence of autocrine growth factors. Therefore, the cytostatic effect of corticosteroids could possibly be attributable to an interference with the production of endogenous growth factors. Analysis of the growth-promoting activity in culture supernatant showed that the critical growth factor in diluted cultures is an arachidonic acid metabolite, the leukotriene B4. The role of leukotriene B4 in S49.1 cell proliferation received further support from the finding that while nordihydroguaiaretic acid, an inhibitor of the lipoxygenase pathway which is necessary for leukotriene formation blocked lymphoma multiplication, indomethacin, an inhibitor of cyclooxygenase activity, did not affect proliferation. Quantitation of the leukotriene B4 content of dexamethasone-treated vs. untreated cultures revealed an almost complete inhibition of leukotriene production, pointing to the significance of this mechanism for the glucocorticoid-induced lymphoma growth inhibition. Moreover, these findings offer a new approach to increase the therapeutic effectiveness of glucocorticoid therapy of steroid-sensitive leukemias and lymphomas.     

CXCR2-specific chemokines mediate leukotriene B4-dependent recruitment of neutrophils to inflamed joints in mice with antigen-induced arthritis

OBJECTIVE: To investigate the mechanism underlying neutrophil migration into the articular cavity in experimental arthritis and, by extension, human inflammatory synovitis. METHODS: Antigen-induced arthritis (AIA) was generated in mice with methylated bovine serum albumin (mBSA). Migration assays and histologic analysis were used to evaluate neutrophil recruitment to knee joints. Levels of inflammatory mediators were measured by enzyme-linked immunosorbent assay. Antibodies and pharmacologic inhibitors were used in vivo to determine the role of specific disease mediators. Samples of synovial tissue and synovial fluid from rheumatoid arthritis (RA) or osteoarthritis patients were evaluated for CXCL1 and CXCL5 expression. RESULTS: High levels of CXCL1, CXCL5, and leukotriene B4 (LTB4) were expressed in the joints of arthritic mice. Confirming their respective functional roles, repertaxin (a CXCR1/CXCR2 receptor antagonist), anti-CXCL1 antibody, anti-CXCL5 antibody, and MK886 (a leukotriene synthesis inhibitor) reduced mBSA-induced neutrophil migration to knee joints. Repertaxin reduced LTB4 production in joint tissue, and neutrophil recruitment induced by CXCL1 or CXCL5 was inhibited by MK886, suggesting a sequential mechanism. Levels of both CXCL1 and CXCL5 were elevated in synovial fluid and were released in vitro by RA synovial tissues. Moreover, RA synovial fluid neutrophils stimulated with CXCL1 or CXCL5 released significant amounts of LTB4. CONCLUSION: Our data implicate CXCL1, CXCL5, and LTB4, acting sequentially, in neutrophil migration in AIA. Elevated levels of CXCL1 and CXCL5 in the synovial compartment of RA patients provide robust comparative data indicating that this mechanism plays a role in inflammatory joint disease. Together, these results suggest that inhibition of CXCL1, CXCL5, or LTB4 may represent a potential therapeutic strategy in RA.     

Expression of β2-integrin on leukocytes in liver cirrhosis

AIM: To analyze beta2-integrin expression on blood leukocytes in liver cirrhosis. METHODS: In 40 patients with liver cirrhosis and 20 healthy individuals, the evaluation of expression of CD11a (LFA-1alpha), CD11b (Mac-1alpha), CD11c (alphaX) and CD49d (VLA-4alpha) on peripheral blood leukocytes was performed using flow cytometry. The analysis was carried out in groups of patients divided into B and C according to Child-Pugh's classification. RESULTS: An increased CD11a, CD11b, CD11c and CD49d integrin expression was observed on peripheral blood leukocytes in liver cirrhosis. The integrin levels were elevated as the advancement of liver failure progressed. The highest expression of integrins occurred predominantly on monocytes. A slight expression of VLA-4 was found on lymphocytes and granulocytes and it increased together with liver failure. A positive correlation was noted between median intensity of fluorescence (MIF) expression on polymorphonuclear cells of CD11a and CD11c and CD49d (r = 0.42, P < 0.01; r = 053, P < 0.01, respectively) in liver cirrhosis stage C. However, no correlation was observed between integrin expression on leukocytes. The concentrations of sICAM-1, sVCAM-1, and TNFalpha, were significantly elevated in liver cirrhosis. CONCLUSION: beta2-integrin expression on leukocytes increases in liver cirrhosis decompensated as the stage of liver failure increases, which is a result of permanent activation of leukocytes circulating through the inflamed liver environment. beta2-integrin expression on circulating leukocytes can intensify liver cirrhosis.     

In vivo production of leukotriene B4 and leukotriene C4 in rabbit colitis. Relationship to inflammation

Leukotriene B4, a proinflammatory compound, recently has been identified as the major metabolite of arachidonic acid in tissue incubations of human and animal colitis. To determine the relationship of inflammation to the in vivo production of leukotrienes, rabbit colitis was induced by formalin enema followed by intravenous infusion of immune complexes, and serial samples were collected by rectal dialysis. Leukotrienes B4 and C4 were measured by radioimmunoassay after high-pressure liquid chromatography. Prostaglandin E2 was assayed after Sephadex chromatography. Leukotrienes were not detected in control animals. Eicosanoid production progressively increased during development of inflammation and correlated with severity of inflammatory cell infiltration (p less than 0.01). Methylprednisolone decreased prostaglandin E2 but did not significantly reduce leukotrienes or inflammation. These data demonstrate that in vivo production of leukotrienes B4 and C4 correlates with indices of inflammation, consistent with the concept that these eicosanoids contribute to the inflammation of colitis.