Delineation of the role of platelet-activating factor in the immunoglobulin G2 antibody response

Localized aggressive periodontitis (LAgP) is a chronic inflammatory disease characterized by severe destruction of periodontal tissues surrounding the first molars and incisors. LAgP subjects produce large amounts of immunoglobulin G2 (IgG2) antibody against oral pathogens, and this response is inversely correlated with the severity of disease. We previously demonstrated that platelet-activating factor (PAF) is required for optimal IgG2 responses. The present investigation was designed to determine the mechanism of IgG2 induction by PAF. Exogenous PAF acetylhydrolase suppressed approximately 80% of pokeweed mitogen-stimulated IgG2 production, confirming that PAF is essential for optimal responses. PAF-activated leukocytes produced gamma interferon (IFN-gamma), a Th1 cytokine that has been associated with IgG2 responses in previous studies. The monocyte-derived cytokines interleukin-12 (IL-12) and IL-18 are upstream of IFN-gamma production, and IgG2 production was suppressed by neutralizing antibodies against these proteins. In addition, PAF induced monocyte-derived dendritic cells (DC) but not macrophages (MPhi) to secrete IL-12 and IL-18. This observation was interesting because monocyte differentiation in LAgP subjects is skewed to the DC phenotype. Although other investigators have implicated IFN-gamma in IgG2 production, its precise role in this response is controversial. Our studies suggest that IFN-gamma induces isotype switching to IgG2 but only in concert with the Th2 cytokine IL-4. Thus, it appears that the unique PAF metabolism of LAgP monocytes or DC promotes Th1 responses that are essential for optimal IgG2 antibody production. As IgG2 antibodies opsonize oral bacteria and promote their clearance and destruction, these alterations in PAF metabolism may be essential for limiting disease severity in LAgP patients.

Dual signaling and effector pathways mediate human eosinophil activation by platelet-activating factor

Platelet-activating factor (PAF) induces various cellular functions in eosinophils including chemotaxis, adhesion, superoxide anion (O2-) production, and degranulation. While PAF shares many biological effects with other chemotactic factors such as N-formyl-methionyl-leucyl-phenylalanine, complement fragments, and lipid mediators, PAF is unique in that its action is relatively resistant to pertussis toxin (PTX), and in activating eosinophils more strongly than neutrophils. In this review we consider how PAF might activate human eosinophils in preference to neutrophils, and discuss possible mechanisms of PAF-induced activation of human eosinophils via two distinct signaling and effector pathways. Recently we analyzed O2- production by eosinophils using a sensitive, real-time chemiluminescence method. Our results showed that in human eosinophils PAF activates two distinct signaling and effector pathways coupled to the PAF receptor: one linked to PTX-sensitive G protein(s) and another to PTX-resistant G protein(s), phosphatidylinositol 3-kinase, and cellular adhesion. This activation of two different G proteins by the eosinophil PAF receptor may explain the strong and diverse biological responses of human eosinophils to PAF.

The mechanism for activation of the neutrophil NADPH-oxidase by the peptides formyl-Met-Leu-Phe and Trp-Lys-Tyr-Met-Val-Met differs from that for interleukin-8

Neutrophil chemotaxis has been shown to be regulated by two different signalling pathways that allow strong chemoattractants, such as bacterial-derived formylated peptides, to dominate over endogenous attractants, such as interleukin-8 (IL-8). Here we show that triggering of the formyl peptide receptor (FPR) with f-Met-Leu-Phe (fMLF) substantially reduced the neutrophil superoxide production induced by activation of the CXC receptors with IL-8. When the order of agonists was reversed, the cells were primed in their response to fMLF, suggesting that the signalling hierarchy between strong, so-called end-type (i.e. fMLF) and weak or intermediate-type (i.e. IL-8) chemoattractants, is also operating during activation of the NADPH-oxidase. The same result was obtained when fMLF was replaced with the hexapeptide, WKYMVM, specific for the formyl peptide-like receptor 1 (FPRL1). There were additional differences between the agonist receptor pairs fMLF/FPR, WKYMVM/FPRL1 and IL-8/CXCR. In contrast to FPR and FPRL1, no reserve pool of CXCR was present in subcellular granules and it was impossible to prime the oxidative response transduced through CXCR by the addition of priming agents such as tumour necrosis factor-alpha and platelet-activating factor. Moreover, the cytoskeleton-disrupting substance, cytochalasin B, had no effect either on IL-8-triggered oxidase activation or on CXCR reactivation. A pertussis toxin-sensitive G-protein is involved in signalling mediated through both FPR and CXCR, and the signalling cascades include a transient intracellular calcium increase, as well as downstream p38 MAPK and phosphoinositide 3-kinase activation. The data presented in this study provide support for two different signalling pathways to the neutrophil NADPH-oxidase, used by ligand binding to FPR/FPRL1 or CXCR, respectively.

Beneficial effects of intraluminal nitroglycerin in intestinal ischemia-reperfusion injury in rats

BACKGROUND

We examined the effects of intraluminal nitroglycerin (NTG) on various physiologic functions and intestinal pathology in intestinal ischemia-reperfusion (IR) injury in rats.

MATERIAL AND METHODS

Intraluminal NTG (0.15-3.75 mg/kg) was administered at different doses and stages during the experimental disease, and intestinal permeability and histology, bile flow, and systemic hemodynamics were measured.

RESULTS

Prophylactic intraluminal NTG treatment at 0.75 mg/kg, but not at 0.15 mg/kg, significantly attenuated the deleterious changes in intestinal barrier function and mucosal injury caused by IR. However, administration of NTG after ischemia was not effective, even up to 3.75 mg/kg. In vitro intestinal NTG metabolism was significantly decreased following intestinal ischemia. Intraluminal NTG at 0.75 mg/kg significantly attenuated the reduction in bile flow that accompanied IR. Reperfusion induced a precipitous and sustained decrease in mean arterial pressure, which was blunted by intraluminal NTG.

CONCLUSIONS

Intraluminal NTG produced several beneficial local and systemic effects in a rat model of intestinal IR. In this disease model, 0.75 mg/kg intraluminal NTG did not exacerbate, but rather reduced, the hypotensive effects induced by IR.

Antibodies against platelet-activating factor and platelet-activating factor–like lipids are raised in women with primary recurrent abortion

OBJECTIVE

The purpose of this study was to determine the antibody levels against platelet-activating factor (PAF), PAF-like lipids lysophosphatidylcholine (LPC), cardiolipin (CL), and oxidized low-density lipoprotein (LDL) in recurrent abortion.

STUDY DESIGN

Eigthy-five women with a history of at least 3 recurrent spontaneous abortions (55 women with primary abortion [31.4+/-5.1 years old]; 30 women with secondary abortion [33+/-4.5 years old]) were compared with 48 age-matched control subjects (33+/-4.4 years old) who had delivered without complications. Antibodies were measured using enzyme-linked immunosorbent assay (ELISA).

RESULTS

Antibodies against PAF and antibodies against oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (oxPAPC) were raised significantly in the group with primary abortion, as compared to control subjects (P<.05) and not significantly higher than in secondary abortion; antibodies against oxidized LDL, LPC, or CL levels did not differ between groups.

CONCLUSION

Antibodies against platelet-activating factor and antibodies against platelet-activating factor-like lipid oxPAPC are associated with primary recurrent abortion and may function as novel disease markers. Whether these antibodies also are pathogenic (eg, by interacting with endothelial cells in placenta or by interfering with platelet-activating factor during embryonal development) remains to be shown.

Recombinant platelet-activating factor acetylhydrolase to prevent acute respiratory distress syndrome and mortality in severe sepsis: Phase IIb, multicenter, randomized, placebo-controlled, clinical trial

OBJECTIVE

Platelet-activating factor (PAF) is a potent proinflammatory mediator implicated in the pathogenesis of both severe sepsis and acute respiratory distress syndrome. One of the regulatory pathways for PAF involves degradation to the inactive metabolite lyso-PAF by the enzyme PAF acetylhydrolase (PAF-AH). Because reduced concentrations of the natural form of PAF-AH have been reported in septic patients, the present study was conducted to determine whether treatment with recombinant human PAF-AH (rPAF-AH, Pafase) was safe when administered after the onset of severe sepsis and whether it decreases the prevalence of acute respiratory distress syndrome and 28-day all-cause mortality.

DESIGN

A prospective, randomized, double-blind, placebo-controlled, multicenter trial.

SETTING

Thirty-three medical and surgical intensive care units located in the United States.

PATIENTS

A total of 127 patients with severe sepsis, but without established acute respiratory distress syndrome, were enrolled in the study. Randomization occurred within 12 hrs of the onset of severe sepsis. Patients then received 1.0 mg/kg rPAF-AH (n = 45), 5.0 mg/kg rPAF-AH (n = 39), or placebo (n = 43) administered intravenously, once daily, for five consecutive days.

MEASUREMENTS AND MAIN RESULTS

Demographic and baseline clinical characteristics of the three treatment groups were similar, except for a significantly higher prevalence of respiratory tract infections as the cause of severe sepsis in patients treated with 1.0 mg/kg rPAF-AH. There were no treatment-related deaths, and the overall prevalence of adverse events was similar among rPAF-AH-treated and placebo-treated patients. There were no significant differences in the prevalence of acute respiratory distress syndrome among the three treatment groups. However, 28-day all-cause mortality was 21% in the 1.0 mg/kg rPAF-AH group, 28% in the 5.0 mg/kg rPAF-AH group, and 44% in the placebo group (overall chi-square p =.07; 1.0 mg/kg rPAF-AH vs. placebo, p =.03). A trend toward reduced multiple organ dysfunction also was observed in the 1.0 mg/kg rPAF-AH group compared with the placebo group (p =.11).

CONCLUSION

The results from this study indicate that rPAF-AH was well tolerated and should be pursued as a potential new treatment to decrease mortality in patients with severe sepsis.

No evidence for a putative involvement of platelet-activating factor in systemic lupus erythematosus without active nephritis

BACKGROUND

Platelet-activating factor (PAF) seems to be implicated in systemic lupus erythematosus (SLE) patients with associated renal diseases.

AIMS

In this study, we ensured the role of PAF in SLE patients without renal complications.

METHODS

Blood PAF and acetylhydrolase activity, plasma soluble phospholipase A(2), and the presence of antibodies against PAF were investigated in 17 SLE patients without active nephritis and in 17 healthy controls.

RESULTS

Blood PAF levels were not different (p=0.45) between SLE patients (6.7+/-2.8 pg/ml) and healthy subjects (9.6+/-3.1 pg/ml). Plasma acetylhydrolase activity (the PAF-degrading enzyme) was significantly (p=0.03) elevated in SLE patients (57.8+/-6.4 nmol/min/ml) as compared with controls (37.9+/-2.6 nmol/min/ml). Plasma soluble phospholipase A(2) (the key enzyme for PAF formation) was not different (p=0.6) between SLE patients (59.1+/-5.1 U/ml) and controls (54.7+/-2.4 U/ml). Antibodies against PAF were detected only in 3/17 SLE patients. Flow cytometry analysis did not highlight PAF receptors on circulating leukocytes of SLE patients.

CONCLUSION

This clinical study highlights no evidence for a putative important role of PAF in SLE patients without active nephritis.

Neutrophil apoptosis is delayed by trauma patients' plasma via a mechanism involving proinflammatory phospholipids and protein kinase C

BACKGROUND

Delayed apoptosis of primed neutrophils (PMNs) may facilitate PMN-mediated tissue injury leading to multiple organ failure (MOF). We previously reported delayed apoptosis and priming of PMNs in severely injured patients at risk for MOF. Our in vitro and in vivo data have implicated phospholipids in PMN cytotoxicity following trauma and shock. The phospholipid signaling pathway remains to be elucidated, but may involve protein kinase C (PKC). We hypothesized that circulating platelet-activating factor (PAF) and PAF-like proinflammatory phospholipids mediate delayed postinjury PMN apoptosis and that PKC is integral to the signaling pathway.

METHODS

Blood was drawn from severely injured patients (n = 6; mean injury severity score = 21 and transfusion = 10 units) at 6 h postinjury. The plasma fraction was isolated and incubated (5% CO(2), 37 degrees C, 24 h) with PMNs harvested from healthy volunteers. Some PMNs were preincubated with a PAF receptor antagonist (WEB 2170, 400 microM) or a PKC inhibitor (Bis I, 1 microM). Apoptotic index (% PMNs undergoing apoptosis) was assessed morphologically.

RESULTS

Trauma patients' plasma delayed PMN apoptosis compared with plasma from controls. The PMN apoptotic index was not altered by WEB 2170 or Bis I alone; however, WEB 2170 or Bis I pretreatment abrogated delayed PMN apoptosis in response to trauma patients' plasma.

CONCLUSION

Trauma patients' plasma delays apoptosis of PMNs. Our data implicate PAF-like phospholipids in this effect, and PKC appears to be integral in the signaling process. Further elucidation of specific lipids and signaling pathways may reveal clinically accessible therapeutic targets to prevent PMN-mediated hyperinflammation.

Membrane and intracellular platelet-activating factor receptor expression in leukemic blasts of patients with acute myeloid and lymphoid leukemia

Platelet-activating factor (PAF), a phospholipid mediator with a wide range of actions on mature leukocytes, acts through PAF-receptors (PAF-Rs) on the membranes of responsive cells. No results are available concerning the putative presence of PAF-Rs on leukemic blasts. Using multiparameter flow cytometry, we assessed intracellular and membrane PAF-Rs on blast cells of acute myeloid leukemic (AML) and acute lymphoid leukemic (ALL) patients. Membrane PAF-Rs were documented in 7/15 cases of ALL and 0/28 cases of AML. Putative intracellular PAF-Rs were found in blasts of 8/8 ALL and 13/13 AML patients. Vitamin D(3) and dimethyl sulfoxide that induced the expression of PAF-Rs on the membrane of the human promyelocytic leukemia cell line, HL60, failed to induce their expression on the membranes of CD34(+) AML blasts. The lack of membrane PAF-Rs on the membranes of AML blasts confirms that these receptors represent a marker of mature cells and that their membrane induction is a consequence of cell maturation and differentiation.

The IL-1 family and inflammatory diseases

IL-1 and its related family member IL-18 are primarily proinflammatory cytokines by their ability to stimulate the expression of genes associated with inflammation and autoimmune diseases. For IL-1 (IL-1alpha and IL-1beta), the most salient and relevant properties are the initiation of cyclooxygenase type 2 (COX-2), type 2 phospholipase A and inducible nitric oxide synthase (iNOS). This accounts for the large amount of prostaglandin-E2 (PGE2), platelet activating factor and nitric oxide (NO) produced by cells exposed to IL-1 or in animals or humans injected with IL-1. Another important member of the proinflammatory IL-1 family is IL-18. IL-18 is also an important player in autoimmune disease because of its ability to induce IFNgamma, particularly in combination with IL-12 or IL-15. Both IL-1 and IL-18 increase the expression of adhesion molecules such as intercellular adhesion molecule-1 (ICAM-1) on mesenchymal cells and vascular-cell adhesion molecule-1 (VCAM-1) on endothelial cells. This latter property promotes the infiltration of inflammatory and immunocompetent cells into the extravascular space. IL-1 and IL-18 are also an angiogenic factors by increasing the expression of vascular endothelial growth factor; IL-1 and IL-18 thus play a role in pannus formation and blood vessel supply. The strongest case for the importance of IL-1 in disease processes come from the administration of the IL-1 receptor antagonist, also a member of the IL-1 family and IL-18 binding protein (IL-18BP), a constitutively expressed and secreted protein that binds and neutralizes IL-18. Data from the human genome project have revealed other members of the IL-1 family. However, these appear to be antagonists rather than agonists. IL-1 also acts as an adjuvant during antibody production and stimulates bone marrow stem cells for differentiation in the myeloid series. IL-1 is distinct from tumor necrosis factor (TNF); IL-1 and TNFalpha share several biological properties but the salient difference is that TNF receptor signaling induces programmed cell death whereas IL-1 receptor signaling does not. In fact, IL-1 is a hematopoietic growth factor and IL-1 was administered to humans to reduce the nadir of white blood cells and platelets in patients during bone-marrow transplantation. This property, of IL-1 is not observed in the responses to TNFalpha. Furthermore, in animal models of destructive rheumatoid arthritis, IL-1 is necessary but TNFalpha is not.

Endotoxin, but not platelet-activating factor, activates nuclear factor-kappaB and increases IkappaBalpha and IkappaBbeta turnover in enterocytes

Bacterial endotoxin (lipopolysaccharide; LPS) and platelet-activating factor (PAF) are important triggers of bowel inflammation and injury. We have previously shown that LPS activates the transcription factor nuclear factor (NF)-kappaB in the intestine, which up-regulates many pro-inflammatory genes. This effect partly depends on neutrophils and endogenous PAF. However, whether LPS and PAF directly activate NF-kappaB in enterocytes remains controversial. In this study, we first investigated the effect of LPS and PAF on NF-kappaB activation in IEC-6 (a non-transformed rat small intestinal crypt cell line) cells, by electrophoresis mobility shift assay and supershift, and found that LPS, but not PAF, activates NF-kappaB mostly as p50-p65 heterodimers. The effect was slower than tumour necrosis factor (TNF). Both LPS and TNF induce the expression of the NF-kappaB-dependent gene inducible nitric oxide synthase (iNOS), which occurs subsequent to NF-kappaB activation. We then examined the effect of LPS and TNF on the inhibitory molecules IkappaBalpha and IkappaBbeta. We found that TNF causes rapid degradation of IkappaBalpha and IkappaBbeta. In contrast, LPS did not change the levels of IkappaBalpha and IkappaBbeta up to 4 hr (by Western blot). However, in the presence of cycloheximide, there was a slow reduction of IkappaBalpha and IkappaBbeta, which disappeared almost completely at 4 hr. These observations suggest that LPS causes slow degradation and synthesis of IkappaBalpha and IkappaBbeta and therefore activates NF-kappaBeta via at least two mechanisms: initially, through an IkappaB-independent mechanism, and later, via an increased turnover of the inhibitor IkappaB. NF-kappaBeta activation precedes the gene expression of iNOS (assayed by reverse transcription-polymerase chain reaction), suggesting that LPS up-regulates iNOS via this transcription factor.

Evaluation of lipopolysaccharide-induced activation of equine neutrophils

OBJECTIVE

To evaluate lipopolysaccharide (LPS)-induced activation of equine neutrophils in blood.

SAMPLE POPULATION

Blood samples from 5 healthy adult Thoroughbreds.

PROCEDURES

Neutrophil integrin (CD11/CD18) expression, size variation, degranulation, and deformability were measured with and without incubation with LPS. Time and concentration studies were done. The mechanism of endotoxin-induced neutrophil activation was investigated by inactivating complement or preincubating neutrophils with inhibitors of tumor necrosis factor-alpha (TNF-alpha) synthesis, prostaglandin-leukotriene synthesis, or platelet-activating factor.

RESULTS

Incubation of equine neutrophils with LPS increased cell surface expression of CD11/CD18, decreased neutrophil deformability, increased and decreased neutrophil size, and induced neutrophil degranulation. The LPS-induced neutrophil activation was attenuated by addition of inhibitors of TNF-alpha and prostaglandin-leukotriene synthesis.

CONCLUSIONS AND CLINICAL RELEVANCE

Equine neutrophils are readily activated in vitro by LPS, resulting in increased expression of integrin adhesion molecules, decreased deformability, variation in neutrophil size, and degranulation. The tests used to detect activated neutrophils in this study may be useful in detecting in vivo neutrophil activation in horses with sepsis and endotoxemia.

Measurement of the activation of equine platelets by use of fluorescent-labeled annexin V, anti-human fibrinogen antibody, and anti-human thrombospondin antibody

OBJECTIVE

To investigate the potential use of fluorescent-labeled annexin V, anti-human fibrinogen antibody, and anti-human thrombospondin antibody for detection of the activation of equine platelets by use of flow cytometry.

SAMPLE POPULATION

Platelets obtained from 6 Thoroughbreds.

PROCEDURE

Flow cytometry was used to assess platelet activation as indicated by detection of binding of fluorescent-labeled annexin V, anti-human fibrinogen antibody, and anti-thrombospondin antibody to unactivated and ADP-, collagen-, platelet activating factor (PAF)-, and A23187-activated equine platelets. Human platelets were used as control samples. Determination of 14C-serotonin uptake and release was used to assess the extent of platelet secretion.

RESULTS

Anti-human thrombospondin antibody failed to bind to equine platelets. Annexin V bound to platelets activated with PAF or A23187 when platelets had undergone secretion. Anti-human fibrinogen antibody bound to ADP-, PAF-, and A23817-activated platelets, but binding was not dependent on platelet secretion. The extent of binding of anti-fibrinogen antibody was less in equine platelets, compared with that for human platelets, despite maximal stimulation.

CONCLUSIONS AND CLINICAL RELEVANCE

Activation of equine platelets can be detected by use of fluorescent-labeled annexin V and anti-human fibrinogen antibody but not by use of anti-human thrombospondin antibody. These flow cytometric techniques have the potential for detection of in vivo platelet activation in horses at risk of developing thrombotic disorders.

Platelet-activating factor drives eotaxin production in an allergic pleurisy in mice

1. The activation of eosinophils via G-protein-coupled seven transmembrane receptors play a necessary role in the recruitment of these cells into tissue. The present study investigates a role for PAF in driving eotaxin production and eosinophil recruitment in an allergic pleurisy model in mice. 2. The intrapleural injection of increasing doses of PAF (10(-11) to 10(-9) moles per cavity) induced a dose- and PAF receptor-dependent recruitment of eosinophils 48 h after stimulation. 3. Intrapleural injection of PAF induced the rapid (within 1 h) release of eotaxin into the pleural cavity of mice and an anti-eotaxin antibody effectively inhibited PAF-induced recruitment of eosinophils. 4. Eosinophil recruitment in the allergic pleurisy was markedly inhibited by the PAF receptor antagonist UK-74,505 (modipafant, 1 mg kg(-1)). Moreover, recruitment of eosinophils in sensitized and challenged PAF receptor-deficient animals was lower than that observed in wild-type animals. 5. Blockade of PAF receptors with UK-74,505 suppressed by 85% the release of eotaxin in the allergic pleurisy. 6. Finally, the injection of a sub-threshold dose of PAF and eotaxin cooperated to induce eosinophil recruitment in vivo. 7. In conclusion, the production of PAF in an allergic reaction could function in multiple ways to facilitate the recruitment of eosinophils -- by facilitating eotaxin release and by cooperating with eotaxin to induce greater recruitment of eosinophils.

In vitro evaluation of the role of platelet-activating factor and interleukin-8 in Mannheimia haemolytica-induced bovine pulmonary endothelial cell injury

OBJECTIVE

To develop an in vitro model of the bovine alveolar-capillary interface and to evaluate the roles of interleukin-8 (IL-8) and platelet-activating factor (PAF) in neutrophil-mediated endothelial injury induced by infection with Mannheimia haemolytica.

SAMPLE POPULATION

Cultured bovine pulmonary microvascular endothelial cells, freshly isolated bovine neutrophils, and monocyte-derived bovine macrophages.

PROCEDURE

A coculture system was developed in which endothelial cells were grown to confluence in tissue culture inserts, neutrophils were added to the inserts, and macrophages were added to tissue culture wells. Mannheimia haemolytica-derived lipopolysaccharide (LPS) or supernatant was added to activate macrophages, and inhibitors of PAF or IL-8 were added to the insert. Endothelial cell cytotoxicity and permeability (ie, albumin leakage) and neutrophil activation (ie, adhesion, degranulation [lactoferrin expression], and superoxide production) were assessed.

RESULTS

The addition of M haemolytica-derived LPS to bovine macrophages in the coculture system resulted in significant increases in endothelial cell cytotoxicity and permeability and neutrophil degranulation and adhesion. Inhibition of IL-8 reduced endothelial cell permeability and neutrophil degranulation induced by exposure to M haemolytica-derived supernatant, whereas inhibition of PAF decreased superoxide release by neutrophils.

CONCLUSIONS AND CLINICAL RELEVANCE

In vitro activation of bovine macrophages by M haemolytica-derived LPS resulted in neutrophil activation and neutrophil-mediated endothelial damage. Neutrophil-mediated endothelial injury and neutrophil degranulation were, at least in part, mediated by IL8, whereas PAF promoted superoxide release by neutrophils in this in vitro system designed to mimic the in vivo events that occur during the early stages of bovine pneumonic pasteurellosis.

Platelet-activating factor, a molecular sensor for cellular damage, activates systemic immune suppression

Ultraviolet (UV) radiation plays a critical role in the induction of nonmelanoma skin cancer. UV radiation is also immune suppressive, and the immune suppression induced by UV irradiation has been identified as a major risk factor for skin cancer induction. Previously, we showed that UV exposure activates a cytokine cascade involving prostaglandin (PG)E(2), interleukin (IL)-4, and IL-10 that induces immune suppression. However, the earliest molecular events that occur immediately after UV exposure, especially those upstream of PGE2, are not well defined. UV-irradiated keratinocytes secrete the inflammatory phospholipid mediator, platelet-activating factor (PAF). Because PAF upregulates the production of immunomodulatory compounds, including PGE2, we tested the hypothesis that UV-induced PAF activates cytokine production and initiates UV-induced immune suppression. Both UV and PAF activated cyclooxygenase (COX)-2 and IL-10 reporter gene construct transcription. PAF mimicked the effects of UV in vivo and suppressed delayed-type hypersensitivity (DTH). Furthermore, immune suppression was blocked when UV-irradiated mice were injected with PAF receptor antagonists. In addition to the well-known role of PAF as a proinflammatory lipid mediator, we propose that the PAF receptor senses cellular damage through the recognition of PAF and/or PAF-like molecules, such as oxidized phosphatidylcholine, which activates cytokine transcription and induces systemic immune suppression.

Promotion of platelet aggregation by sera from brucellosis patients with antiphosphatidylcholine antibodies

Results obtained in this study suggest that in human brucellosis there is an antibody response against platelet-activating factor (PAF) and phosphatidylcholine (PC). The specificity of the antiphospholipid response was determined by inhibition assays. The PAF molecule was able to inhibit the anti-PC activity of the brucellosis-control serum. This inhibition capacity of PAF was similar to that of the phosphorylcholine (PYC) group. These results suggest that the inhibition activity could be attributed to the PYC group present in both PAF and PC molecules. Consequently, these findings support an immunodominant role of PYC in the antiphospholipid response of brucellosis. Furthermore, sera from patients infected with Brucella organisms were able to cause platelet aggregation, as were brucella phospholipids, suggesting a possible role of the antiphospholipid antibodies and phospholipids in the inflammatory response in brucellosis.

Activation-induced mobilization of secretory vesicles in bovine neutrophils

OBJECTIVE

To characterize mobilization of secretory granules in bovine neutrophils.

SAMPLE POPULATION

Neutrophils obtained from four 6- to 18-month-old Holstein cattle.

PROCEDURE

Mobilization of secretory granules in bovine neutrophils was determined by measuring changes in cell-surface alkaline phosphatase activity on cells treated with various inflammatory mediators. Subcellular distribution of the alkaline phosphatase activity was determined by analysis of bovine neutrophil homogenates fractionated on density gradients.

RESULTS

Alkaline phosphatase-containing secretory granules of bovine neutrophils were readily mobilized by a number of inflammatory agents, including platelet-activating factor, interleukin-8, tumor necrosis factor-alpha, lipopolysaccharide, leukotriene B4, and zymosan-activated plasma. In contrast, N-formyl-methionyl-leucyl-phenylalanine did not have a significant effect. Phorbol myristate acetate induced a biphasic response with up-regulation of cell-surface alkaline phosphatase at low doses and a return to baseline or even a reduction in cell-surface alkaline phosphatase at higher doses (> or = 10 ng/ml). Subcellular fractionation of bovine neutrophil homogenates revealed that alkaline phosphatase activity resided in light-density membrane vesicles (ie, location of secretory granules), which were distinct from specific, azurophil, and large granules.

CONCLUSIONS AND CLINICAL RELEVANCE

Bovine neutrophils respond to various inflammatory mediators by mobilizing alkaline phosphatase-containing secretory granules. This suggests that the process is an important early step in the host-defense response of bovine neutrophils.

Platelet activating factor antagonism reduces the systemic inflammatory response in a murine model of acute pancreatitis

BACKGROUND

The platelet activating factor (PAF) antagonist, Lexipafant, has been used in experimental models and clinical trials to treat severe acute pancreatitis (AP). The purpose of this study was to determine whether Lexipafant reduces the local and systemic components of AP in a murine model of mild, edematous AP.

MATERIALS AND METHODS

Forty-eight female Swiss-Webster mice were divided into four groups. Group 1 received 50 microl of saline ip every hour for 6 h (sham). Group 2 received saline treatment, plus Lexipafant (25 mg/kg dose ip, every 3 h starting 1 h after the first saline injection) (sham/Lex). Group 3 received cerulein (50 microg/kg dose ip, every hour for 6 h) (AP). Group 4 received AP, plus therapeutic treatment with Lexipafant (AP/Lex). Animals were sacrificed 3 h after the last injection. Serum cytokine levels were determined by ELISA. Standard assays were performed for serum amylase activity and lung myeloperoxidase activity (MPO). Histology was scored by two blinded investigators.

RESULTS

Serum cytokines (TNFalpha, IL-1beta), lung MPO, and serum amylase activity were reduced by PAF antagonism. Histology showed a trend toward improvement with Lexipafant, but did not reach statistical significance.

CONCLUSION

The PAF antagonism reduces the severity of systemic inflammation when given after the induction of mild AP in mice. These results suggest that Lexipafant may be useful in the treatment of mild pancreatitis after its clinical onset.

Cardiac functional and structural alterations induced by endotoxin in rats: Importance of platelet-activating factor

OBJECTIVE

In this study, we evaluated the time course of the alterations in left ventricular (LV) dimensions, LV wall thickness, and LV systolic function in rats with endotoxemia by using echocardiography as well as myocardial histopathologic assessments. Our second goal was to examine whether pretreatment with a platelet-activating factor (PAF) antagonist would ameliorate the lipopolysaccharide (LPS)-induced cardiovascular collapse during the early phase.

DESIGN

A prospective, controlled, in vivo animal laboratory study.

SETTING

Research laboratory at a university.

SUBJECTS

Male, Wistar rats (8-9 wks old; n = 83).

INTERVENTIONS

In pentobarbital-anesthetized rats, the right carotid artery was cannulated to measure the arterial blood pressure and to sample blood. The right jugular vein also was catheterized for the administration of drugs. LPS (2 mg/kg) derived from Klebsiella pneumoniae or physiologic saline was administered in the presence or absence of pretreatment with TCV-309, a specific potent PAF antagonist. Echocardiographic studies were performed with an 8- to 13-MHz transducer.

MEASUREMENTS AND MAIN RESULTS

LPS administration immediately induced progressive hypotension. The maximal hypotensive response was observed at 10 mins after LPS infusion with mean arterial pressure decreasing from 119 +/- 2 to 56 +/- 3 mm Hg (p < .001). LV end-diastolic internal dimensions decreased from 6.4 +/- 0.1 to 3.1 +/- 0.1 mm (p < .001) at 30 mins after LPS and remained significantly reduced compared with control rats. LV end-systolic dimensions also decreased dramatically from 3.5 +/- 0.2 to 0.5 +/- 0.1 mm (p < .001) at 30 mins after LPS and remained significantly reduced throughout the experiment. LV fractional shortening increased from 45 +/- 1% to 84 +/- 2% (p < .001) at 30 mins after LPS and remained elevated compared with control rats. LV wall thickness increased strikingly from 15 mins until 2 hrs after LPS infusion. Pathologic studies demonstrated marked congestion of capillaries and mild edema in the LV myocardium. The hematocrit increased after the administration of LPS. LPS markedly increased sympathetic tone as demonstrated by the elevation of plasma concentrations of epinephrine and norepinephrine. There was no elevation of concentrations of nitrite and nitrate. Pretreatment with TCV-309, a specific potent PAF antagonist, reduced LPS-induced hypotension and attenuated LV functional and structural changes. TCV-309 administration reduced the LPS-induced adrenergic activation and hemoconcentration.

CONCLUSIONS

The hypotension that occurred during the initial phase of LPS-induced shock was accompanied by LV functional and structural alterations. The marked increase in LV wall thickness can be ascribed to the congestion of capillaries and edema in the LV myocardium. Pretreatment with a PAF antagonist reduced LPS-induced alterations. PAF may play a pivotal role during the initial phase of LPS-induced cardiovascular responses.

Platelet-activating factor in infants at risk for necrotizing enterocolitis

BACKGROUND

Platelet-activating factor (PAF) is a heterogeneous phospholipid that has been implicated as participating in a number of perinatal disease processes including necrotizing enterocolitis (NEC).

METHODS

Baseline blood levels of PAF and related lipids (PAF-LL) were measured for 164 infants at risk for NEC from 3 neonatal intensive care units. Serial levels were obtained from the 11 infants in whom NEC developed.

RESULTS

The mean peak PAF-LL in the infants without NEC was 2.03 +/- 1.96 ng/mL. Infants with stage II (n = 6) and III (n = 5) NEC had elevated peak PAF-LL values (mean peak value 13.6 +/- 6.9 ng/mL). No PAF-LL measurements obtained from infants during stage II or III NEC were <2.03 ng/mL. Three infants had PAF-LL elevations before the development of any clinical or radiographic evidence of NEC. PAF-LL level increased as the severity of NEC increased and decreased with its resolution. Setting a PAF-LL level of 10.2 ng/mL as a cutoff for NEC had a positive predictive value of 100%.

CONCLUSIONS

PAF-LL determinations can complement clinical and radiographic studies to diagnose and follow the progression of NEC. PAF-LL may have a role in the evolution of NEC.

Targeted disruption of the leukotriene B(4) receptor in mice reveals its role in inflammation and platelet-activating factor-induced anaphylaxis

Leukotrienes are derived from arachidonic acid and serve as mediators of inflammation and immediate hypersensitivity. Leukotriene B(4) (LTB(4)) and leukotriene C(4) (LTC(4)) act through G protein-coupled receptors LTB(4) receptor (BLTR) and Cys-LTR, respectively. To investigate the physiological role of BLTR, we produced mice with a targeted disruption of the BLTR gene. Mice deficient for BLTR (BLTR(-/-)) developed normally and had no apparent hematopoietic abnormalities. Peritoneal neutrophils from BLTR(-/-) mice displayed normal responses to the inflammatory mediators C5a and platelet-activating factor (PAF) but did not respond to LTB(4) for calcium mobilization or chemotaxis. Additionally, LTB(4) elicited peritoneal neutrophil influx in control but not in BLTR(-/-) mice. Thus, BLTR is the sole receptor for LTB(4)-induced inflammation in mice. Neutrophil influx in a peritonitis model and acute ear inflammation in response to arachidonic acid was significantly reduced in BLTR(-/-) mice. In mice, intravenous administration of PAF induces immediate lethal anaphylaxis. Surprisingly, female BLTR(-/-) mice displayed selective survival (6 of 9; P = 0.002) relative to male (1 of 11) mice of PAF-induced anaphylaxis. These results demonstrate the role of BLTR in leukotriene-mediated acute inflammation and an unexpected sex-related involvement in PAF-induced anaphylaxis.

Clinical importance of antibodies against platelet activating factor in antiphospholipid syndrome manifestations

BACKGROUND

We assessed whether antibodies against platelet activating factor (PAF) are related to the presence of antiphospholipid syndrome (APS) clinical manifestations, in particular thrombosis, in patients with connective tissue diseases.

MATERIALS AND METHODS

Anti-PAF, anticardiolipin (aCL), antibeta2 glycoprotein I (antibeta2GPI) and antiphosphatidylcholine (anti-PC) antibodies were determined in 52 patients with APS, 29 patients with systemic lupus erythematosus (SLE) aCL but without APS, 30 patients with SLE without aCL, and 30 patients with scleroderma. A new enzyme-linked immunosorbent assay (ELISA) was developed for determining anti-PAF antibodies in a bovine serum-free fashion.

RESULTS

The ELISA showed high specificity. Homologous inhibition experiments showed 60-70% inhibition. Anti-PAF antibodies were found in 18/52 APS patients, 10/29 SLE/aCL+ patients, 9/30 SLE/aCL- patients and 3/30 scleroderma patients. Anti-PAF antibodies were significantly associated with anti-PC antibodies (odds ratio [OR] 12. 7, P < 0.01), and there was a modest association with immunoglobulin G (IgG) aCL (OR 3.1, P > 0.10), but not with IgM aCL or antibeta2GPI. Three SLE/aCL+ patients and five SLE/aCL- patients had clinical manifestations characteristic of APS. All these patients had anti-PAF antibodies, while none had high titres of aCL or antibeta2GPI antibodies and only one had anti-PC antibodies. Among the combined APS and SLE groups, the presence of anti-PAF antibodies was significantly associated with clinical manifestations which are characteristic of APS (OR 2.6, P = 0.02). The effect was independent of IgG aCL and antibeta2GPI antibodies.

CONCLUSIONS

Anti-PAF antibodies are common in APS and SLE and comprise an independent factor for the development of thrombosis. Several patients experiencing thromboses have anti-PAF antibodies without other antiphospholipid specificities.

Lipoprotein-associated phospholipase A(2), platelet-activating factor acetylhydrolase: a potential new risk factor for coronary artery disease

A specific and robust immunoassay for the lipoprotein-associated phospholipase A(2) (Lp-PLA(2)), platelet-activating factor acetylhydrolase, is described for the first time. The immunoassay was used to evaluate possible links between plasma Lp-PLA(2) levels and atherosclerosis risk amongst susceptible individuals. Such an investigation was important because Lp-PLA(2) participates in the oxidative modification of low density lipoprotein by cleaving oxidised phosphatidylcholines, generating lysophosphatidylcholine and oxidised free fatty acids. The majority of Lp-PLA(2) was found associated with LDL (approximately 80%) and, as expected, enzyme levels were significantly positively correlated to LDL cholesterol. Plasma Lp-PLA(2) levels were significantly elevated in patients with angiographically proven coronary artery disease (CAD) when compared with age-matched controls, even though LDL cholesterol levels did not differ significantly. Indeed, when included in a general linear model with LDL cholesterol and other risk factors, Lp-PLA(2) appeared to be an independent predictor of disease status. We propose, therefore, that plasma Lp-PLA(2) mass should be viewed as a potential novel risk factor for CAD that provides information related to but additional to traditional lipoprotein measurements.