Role Of Platelet-activating Factor Research Articles

Targeting Trypanosoma cruzi Platelet-activating Factor Receptors: Scope for the Development of Novel Drugs to Treat Chagas Disease

Chagas Disease (CD), a tropical parasitic disease caused by the flagellate protozoan Trypanosoma cruzi, accounts for the highest burden of parasitic diseases in the Western hemisphere. Current drug treatments for CD are highly toxic and often ineffective, particularly for the chronic stage of the disease, a fact that clearly emphasizes the importance of identification/validation of molecular targets for the development of new drugs to treat the disease. Here, we review in details the evidences that suggest the existence of specific receptors for platelet-activating factor (PAF) in T. cruzi, the role of PAF on the control of parasite differentiation and the potential of exploring these putative receptors as new targets for the chemotherapy of CD.

Platelet-activating Factor Nasal Challenge Induces Nasal Congestion and Reduces Nasal Volume in Both Healthy Volunteers and Allergic Rhinitis Patients

Platelet-activating factor (PAF) is a lipid mediator produced by most inflammatory cells. Clinical and experimental findings suggest that PAF participates in allergic rhinitis (AR) pathogenesis. The aim was to assess the PAF ability to induce clinical response in nasal airway after local stimulation. Ten nonatopic healthy volunteers (HVs) and 10 AR patients out of pollen season were enrolled. PAF increasing concentrations (100, 200, and 400 nM) were instilled into both nasal cavities (0, 30, and 60 minutes, respectively). Nasal symptoms (congestion, rhinorrhea, sneezing, itching, and total 4 symptom score and nasal volume between the 2nd and 5th cm (Vol(2-5)) using acoustic rhinometry (AcR), were assessed at -30, 0, 30, 60, 90, 120, and 240 minutes. PAF increased individual and total nasal symptom score in both HVs and seasonal AR (SAR) patients from 30 to 120 minutes (maximum score at 120', p < 0.05). Nasal obstruction was the most relevant and lasting nasal symptom. PAF also induced a significant reduction of Vol(2-5) at 90' (27%), 120' (38.7%), and 240' (36.4%). No differences in the response to PAF nasal challenge were observed between HVs and SAR subjects in either clinical symptoms or AcR. This is the first description of PAF effects on human nasal mucosa using a cumulative dose schedule and evaluated by both nasal symptoms and AcR. Nasal provocation with PAF showed long-lasting effects on nasal symptoms and nasal obstruction in HVs and in patients with SAR. Nasal challenge may be a useful tool to investigate the role of PAF in AR and the potential role of anti-PAF drugs.

Amyloid toxicity and platelet‐activating factor signaling

Amyloidosis is the accumulation of insoluble proteinaceous aggregates in vivo and is implicated in many neurodegenerative diseases, including Alzheimer's, Huntington's, and Parkinson's diseases. This article briefly reviews the current knowledge of amyloid aggregate toxicity and inflammatory signaling in the nervous system. In particular, we focus our attention on the role of platelet-activating factor (PAF) as mediator of amyloid cytotoxicity.

Loss of the platelet activating factor receptor in mice augments PMA-induced inflammation and cutaneous chemical carcinogenesis

Although platelet-activating factor (PAF) is a well-known acute inflammatory mediator, little is known regarding the role of PAF in chronic inflammation. Phorbol esters are known to stimulate PAF production. Moreover, the ability of repeated applications of phorbol esters to induce a sustained inflammatory response is crucial to their tumorigenic activity. We therefore examined whether PAF acts as a mediator of phorbol ester-induced inflammation and tumorigenesis. While PAF receptor knockout mice (PAFR(-/-)) showed an expected but modest reduction in the acute inflammatory response to phorbol 12-myristate 13-acetate (PMA), these mice exhibited a surprising increase in inflammation following chronic PMA application. This increased inflammation was documented by a number of findings that included: increased skin thickness, increased myeloperoxidase activity and expression and increased expression of known inflammatory mediators. Interestingly, vehicle-treated PAFR(-/-) mice also exhibited modest increases in levels of inflammatory markers. This suggests that the platelet activating factor receptor (PAFR) acts to suppress chronic inflammation in response to other stimuli, such as barrier disruption. The idea that chronic PAFR activation is anti-inflammatory was documented by repetitive topical PAFR agonist administration that resulted in reduced myeloperoxidase activity in skin. We next utilized a 7,12-dimethylbenz(a)anthracene/PMA carcinogenesis protocol to demonstrate that PAFR(-/-) mice exhibit significantly increased tumor formation and malignant progression compared with wild-type control mice. These studies provide evidence for two important, unexpected and possibly interrelated pathological roles for the PAFR: first, the PAFR acts to suppress PMA-induced chronic inflammation; secondly, the PAFR acts to suppress neoplastic development in response to chemical carcinogens.

Clinical Significance and Expression of PAF and TNF-alpha in Seminal Plasma of Leukocytospermic Patients

Objective. Discuss the changes and roles of PAF in the reproductive tract infection by observing the expression of platelet activating factor (PAF) and tumor necrosis factor α (TNF-α) in seminal plasma of patients with leukocytospermia. Methods. The seminal plasma was obtained from 22 cases of leukocytospermia and 15 cases of normal males; the peroxidase dyeing method was adopted for seminal plasma white blood count; the ELISA was adopted to test PAF and TNF-α concentration in seminal plasma. Result. PAF concentration (2.14 ± 0.43 ng/mL) of leukocytospermia group was significantly lower than the normal group (6.21 ± 1.38 ng/mL, P < 0.01) while TNF-α (5.51 ± 1.46 ng/mL) was significantly higher than that of normal group (3.48 ± 1.08 ng/mL). There was negative correlation between PAF and TNF-α , (r = −0.68, P < 0.01); the same situation existed in PAF and WBC (r = −0.62, P < 0.01); but TNF-α was positively correlated to WBC (r = 0.77, P < 0.01). Conclusion. (1) Low expression of PAF and high expression of TNF-α in leukocytospermia affect the sperm motility, which is one of the reasons that leads to infertility. (2) Lower expression of PAF has its particularity during the reproductive tract infection.

Esophageal disease: updated information on inflammation

The following on esophageal disease provides updated information the mucosal defense against acid and acid-pepsin injury; the roles of platelet activating factor, mast cells, proinflammatory cytokines, and chemokines in inflammation; differences and similarities in erosive and nonerosive esophagitis; acid and vanilloid receptors in esophageal mucosa; and bile acid receptors in esophageal epithelium.

Adhesion of Streptococcus pneumoniae to human airway epithelial cells exposed to urban particulate matter

Epidemiologic studies report an association between pneumonia and urban particulate matter (PM) less than 10 microns (μm) in aerodynamic diameter (PM(10)). Streptococcus pneumoniae is a common cause of bacterial pneumonia worldwide. To date, the mechanism whereby urban PM enhances vulnerability to S pneumoniae infection is unclear. Adhesion of S pneumoniae to host cells is a prerequisite for infection. Host-expressed proteins, including the receptor for platelet-activating factor (PAFR), are co-opted by S pneumoniae to adhere to lower airway epithelial cells. To define whether inhalable urban PM enhances the adhesion of S pneumoniae to airway epithelial cells. A549 cells were cultured with PM(10) from Leicester (United Kingdom [UK]) and PM(10) and PM less than 2.5 μm in aerodynamic diameter (PM(2.5)) from Accra (Ghana), then infected with S pneumoniae strain D39. Pneumococcal adhesion to human primary bronchial epithelial cells was also assessed. Bacterial adhesion was determined by quantitative culture and confocal microscopy. The role of oxidative stress was assessed by N-acetyl cysteine, and the role of PAFR was assessed by mRNA transcript level, receptor expression, and receptor blocking. PM(10) (UK) increased S pneumoniae adhesion to both A549 airway epithelial cells and human primary bronchial epithelial cells. PM(10) (Ghana) and PM(2.5) (Ghana) also increased adhesion. Culture of A549 cells by PM(10) (UK) increased PAFR mRNA transcript level and PAFR expression. PM(10) (UK)-stimulated adhesion to A549 cells was attenuated by a PAFR blocker and N-acetyl cysteine. Urban PM increases adhesion of S pneumoniae to human airway epithelial cells. PM-stimulated adhesion is mediated by oxidative stress and PAFR.

Role of platelet-activating factor in the pathogenesis of 5-fluorouracil-induced intestinal mucositis in mice

Gastrointestinal mucositis is a common side effect of cancer chemotherapy. Platelet-activating factor (PAF) is produced during gut inflammation. There is no evidence that PAF participates in antineoplastic-induced intestinal mucositis. This study evaluated the role of PAF in 5-fluorouracil (5-FU)-induced intestinal mucositis using a pharmacological approach and PAF receptor knockout mice (PAFR(-/-)). Wild-type mice or PAFR(-/-) mice were treated with 5-FU (450mg/kg, i.p.). Other mice were treated with saline or BN52021 (20mg/kg, s.c.), an antagonist of the PAF receptor, once daily followed by 5-FU administration. After the third day of treatment, animals were sacrificed and tissue samples from the duodenum were removed for morphologic evaluation. In addition, myeloperoxidase activity and the cytokine concentration were measured. 5-FU treatment decreased the duodenal villus height/crypt depth ratio, increased MPO activity, and increased the concentration of TNF-α, IL-1β and KC in comparison with saline-treated animals. In PAFR(-/-) mice and PAFR antagonist-treated mice, 5-FU-dependent intestinal damage was reduced and a decrease in duodenal villus height/crypt depth ratio was attenuated. However, the 5-FU-dependent increase in duodenum MPO activity was not affected. Without PAFR activation, 5-FU treatment did not increase the TNF-α, IL-1β and KC concentration. In conclusion, our study establishes the role of PAFR activation in 5-FU-induced intestinal mucositis. This study implicates treatment with PAFR antagonists as novel therapeutic strategy for this condition.

Endothelial progenitor cells express PAF receptor and respond to PAF via Ca 2+-dependent signaling

Endothelial progenitor cell (EPC) therapy is a promising approach to promote angiogenesis and endothelial repair in patients with cardiovascular diseases (CVD). However, their release of proinflammatory mediators may compromise the therapeutic efficacy. Little is known about the role of Platelet-Activating Factor (PAF) in EPC functional response. Here, we investigated the expression of PAF receptor (PAF-R) in early EPC and the release of PAF under stimulation with factors involved in endothelial dysfunction. Results indicated that early EPC express the PAF-R and respond to PAF signaling via a transient increase of cytoplasmic Ca 2+ concentration. EPC release PAF in a time dependent manner upon stimulation with tumor necrosis factor-α (TNF-α) or high-glucose concentration with a peak at 30 min and 10 min ( p < 0.01 vs. control), respectively. PAF, starting at concentration of 50 ng/ml, exerted a detrimental effect on EPC number with a concomitant increase of p38 activity. Furthermore, both the reduction of early EPC number and the enhanced p38 activity induced by PAF were abolished by CV3988, a PAF receptor antagonist. These novel findings, revealing that early EPC respond to PAF signaling, unveil an inflammatory pathway that may play a crucial role in the outcome of cardiovascular cell therapy with EPC.

Anaphylaxis: An Update on its Understanding and Management

Anaphylaxis is the most concerning manifestation of hypersensitivity. Recent thorough investigations on the pathophysiology of anaphylaxis achieved important advances in its understanding, regarding in particular the emerging role of mediators such as platelet activating factor (PAF) and sphyngosine 1 phosphate (S1P) and the improved knowledge on the actors of the signaling cascade, from the contact between the specific allergen and the IgE fixed on the Fc-epsilon-RI receptor to the opening of calcium channels. These advances may provide new diagnostic and therapeutical tools. In particular, a role for PAF and S1P as laboratory markers of anaphylaxis is likely to be developed, and innovative preventive strategies able to induce a negative signaling are currently under evaluation. Also, using well known preventive treatments, such as allergen specific immunotherapy may offer new perspectives for the management of patients at risk of potentially fatal reaction to foods. In fact, controlled studies demonstrated that sublingual immunotherapy is able to significantly increase the tolerance to the causative foods, fulfilling the need and protecting the allergic subject from anaphylaxis caused by accidental ingestion of small food amounts. The article also presented some promising patents on anaphylaxis.

Role of Platelet-Activating Factor in Cell Death Signaling in the Cornea: A Review

Platelet-activating factor (PAF) is a potent bioactive lipid generated in the cornea after injury whose actions are mediated through specific receptors. Studies from our laboratory have shown that PAF interactions with its receptors activate several transmembrane signals involved in apoptosis. Continuous exposure to PAF during prolonged inflammation increases keratocyte apoptosis and inhibition of epithelial adhesion to the basement membrane. As a consequence, there is a marked delay in wound healing, which is not countered by the action of growth factors. While apoptosis of stroma cells is rapid and potent, epithelial cells as well as myofibroblasts, which appear in the stroma during the repair phase, are resistant to apoptosis. However, PAF accelerates apoptosis of corneal epithelial cells exposed to oxidative stress by stimulating phospholipase A2, producing an early release of cytochrome C from mitochondria and activating caspase-3. In myofibroblasts, PAF has a synergistic action with tumor necrosis factor-alpha (TNF-alpha), increasing apoptosis of the cells to 85%. PAF antagonists block the effects of PAF and could have a therapeutic role in maintaining a healthy and transparent cornea.

Mast cells: makers and breakers of allergic inflammation

Recent findings have developed, changed, challenged and extended the established view of mast cell biology and of their role in inflammation. The purpose of this review is to present and discuss recent research in this area relating to allergic inflammation. Mast cells are traditionally viewed only as IgE-activated histamine-providing effector cells of allergic inflammation. Yet, recent findings also support a role for mast cells in the sensitization to allergens, and early released human mast cell tryptase has been shown to break down IgE, hence breaking the key maker of allergic inflammation. Furthermore, mast cells demonstrate proinflammatory action through nonhistamine and non-IgE-mediated routes. For example, the role of platelet-activating factor in contributing to allergic inflammation and anaphylaxis in mice is now starting to be shown in humans. Most surprisingly, mast cells have also emerged as modulators and downregulators of allergic inflammation. For example, the newly discovered siglec-8 receptor might act as an inhibitor of mast cell degranulation and thus of mast cell-mediated allergic inflammation. Also, mast cell-derived IL-10 is shown to be a modulator of allergic inflammation, demonstrated in a murine model of contact hypersensitivity. Understanding the mast cell's divergent phenotypes based on situation and setting is required to truly discover their role in allergic inflammation.

The Novel Role of Platelet-Activating Factor in Protecting Mice against Lipopolysaccharide-Induced Endotoxic Shock

BackgroundPlatelet-activating factor (PAF) has been long believed to be associated with many pathophysiological processes during septic shock. Here we present novel activities for PAF in protecting mice against LPS-mediated endotoxic shock.Principal Findings In vivo PAF treatment immediately after LPS challenge markedly improved the survival rate against mortality from endotoxic shock. Administration of PAF prominently attenuated LPS-induced organ injury, including profound hypotension, excessive polymorphonuclear neutrophil infiltration, and severe multiple organ failure. In addition, PAF treatment protects against LPS-induced lymphocytes apoptosis. These protective effects of PAF was correlated with significantly decreases in the production of the inflammatory mediators such as TNF-α, IL-1β, IL-12, and IFN-γ, while increasing production of the anti-inflammatory cytokine IL-10 in vivo and in vitro.ConclusionsTaken together, these results suggest that PAF may protect mice against endotoxic shock via a complex mechanism involving modulation of inflammatory and anti-inflammatory mediators.

PAF receptor activation in hippocampal plasticity induced by SE

One of the defining characteristics of epilepsy is abberant mossy fiber sprouting (MFS) in the dentate gyrus. These axonal projections within the granule cell layer of the dentate gyrus create a hyperexcitable network and lead to spontaneous seizures. Growth‐associated protein 43 (GAP‐43), a presynaptic marker that is expressed during development and axonal growth, has been preveiously implicated in the abnormal MFS found in epileptic models. The purpose of our study is to investigate the role of platelet activating factor (PAF) receptor‐mediated signaling in abnormal MFS by evaulating GAP‐43 immunoreactivity. PAF is a mediator of inflammation, a potent gene expression inducer and a modulator of long term potentiation (LTP), synaptic plasticity, and memory formation. PAF abnormally accumulates in the brain during seizures, or injuries, contributing to neuroinflammation and neurotoxicity. Using the novel PAF receptor antagonist, LAU‐0901, in the rat pilocarpine model of epilepsy, we found a positive correlation between a decrease in spontenous seizure activity and an increase GAP‐43 immunoreacitivy in our treated group, suggesting that PAF receptor activation is involved in the abberant plasticity associated with epilepsy.Source of support: This work was supported by NIH/NCRR grant P20 RR016816.

Role of platelet-activating factor in protecting against lipopolysaccharide-induced endotoxic shock (33.3)

Abstract AbstractPlatelet-activating factor (PAF) has been long believed to be associated with many pathophysiological processes during septic shock. Here we present novel activities for PAF in the LPS-mediated endotoxic shock. In vivo PAF treatment immediately after LPS challenge markedly improved the survival rate against mortality from endotoxic shock. In addition, this treatment prominently attenuated LPS-induced profound hypotension, excessive polymorphonuclear neutrophil infiltration, severe multiple organ failure, and lymphocyte apoptosis. These protective effects of PAF was correlated with significantly decreases in the production of the inflammatory mediators such as TNF-α, IL-1β, IL-12, and IFN-γ, while increasing production of the anti-inflammatory cytokine IL-10 in vivo and in vitro. In response to LPS, PAF inhibits ERK1/2 and p38 MAPK activation, which is critical for proinflammatory cytokines production. Furthermore, PAF upregulates SOCS1 and SOCS3, which are essential for cross-talk inhibition in LPS-induced cytokine signaling. Taken together, these results suggest that PAF may provide protection against endotoxic shock via a complex mechanism involving modulation of inflammatory and anti-inflammatory mediators, as well as balanced regulation between activation and subsequent deactivation of the signaling pathways in response to LPS.

Edematogenic Activity of Scorpion Venoms from the Buthidae Family and the Role of Platelet-Activating Factor and Nitric Oxide in Paw Edema Induced by Tityus Venoms

We compared the edematogenic activity of venoms of scorpions from the Buthidae family, Tityus bahiensis (Tbv), Tityus serrulatus (Tsv) and Rhopalurus rochai (Rrv). Three doses (20, 40 and 80 microg/kg sc) of each venom were administrated in hind paw of mice and edema was measured from 5 min to 24 h. Tbv and Tsv both induced edema of rapid onset (135% of increase at 15 min); Rrv induced only a mild edema (40% of increase). We then investigated the involvement of platelet-activating factor (PAF) and endogenous nitric oxide (NO) in Tbv and Tsv-induced paw edema. Pretreatment of mice with a PAF antagonist (WEB-2170) inhibited Tsv but not Tbv-induced edema. Pretreatment with a non selective inhibitor of NO-synthases (L: -NAME) inhibited or increased the edema depending on the dose and the time the edema was measured. In conclusion, the venoms from Tityus are stronger inducers of edema than the venom from the Rhopalurus scorpion. The venoms of Tityus species are similar in potency and time-course edema development. PAF is involved in the edema induced only by Tsv.

The Role of Platelet‐activating Factor in the Mammalian Female Reproductive Tract

Platelet-activating factor (PAF) is a potent lipid mediator produced by various cell types of mammals and is involved in an inflammatory-like process with increased vascular permeability. Platelet-activating factor exerts its actions through the activation of specific PAF receptors (PAF-R) found in cells and tissues of the female reproductive tract. The aim of this article was summarized briefly in the current research on the role of PAF in female reproductive functions. Platelet-activating factor has been implicated in processes of ovulation, implantation and parturition because of its angiogenic and growth factor properties. This factor is influenced by ovarian steroid hormones in bringing about changes in the uterus and is a candidate molecule for initial embryo-maternal dialogue. Tissue concentrations of PAF are regulated by the equilibrium between biosynthesis and degradation by PAF-acetylhydrolase (PAF-AH). Antagonists of PAF interfere with ovulation and implantation. Platelet-activating factor, its receptor, and PAF-AH activity play an important role in the maintenance of pregnancy.

Platelet-Activating Factor, PAF Acetylhydrolase, and Severe Anaphylaxis

Vadas P, Gold M, Perelman B, et al. N Engl J Med. 2008;358(1):28–35 PURPOSE OF THE STUDY. To characterize the roles of platelet-activating factor (PAF) and PAF acetylhydrolase, the enzyme that inactivates PAF, in humans. STUDY POPULATION. The population was a variety of pediatric and adult patients with different levels of allergic disease along with nonallergic controls. METHODS. Serum PAF levels and activity of PAF acetylhydrolase were measured in 41 patients with anaphylaxis and in 23 control patients. Serum PAF acetylhydrolase activity was also measured in 9 patients with peanut allergy who had fatal anaphylaxis and compared with that in 26 nonallergic pediatric control patients, 49 nonallergic adult control patients, 63 children with mild peanut allergy, 24 patients with nonfatal anaphylaxis, 10 children who died of nonanaphylactic causes, 15 children with life-threatening asthma, and 19 children with non–life-threatening asthma. RESULTS. Mean serum PAF levels were significantly higher in patients with anaphylaxis than in patients in the control groups and were correlated with the severity of anaphylaxis. The proportion of subjects with elevated PAF levels increased from 4% in the control groups to 20% in the group with grade 1 anaphylaxis, 71% in the group with grade 2 anaphylaxis, and 100% in the group with grade 3 anaphylaxis. There was an inverse correlation between PAF levels and serum PAF acetylhydrolase activity. The proportion of patients with low PAF acetylhydrolase activity increased with the severity of anaphylaxis. Serum PAF acetylhydrolase activity was significantly lower in patients with fatal peanut anaphylaxis than in control patients. CONCLUSIONS. Serum PAF levels were directly correlated and serum PAF acetylhydrolase activity was inversely correlated with the severity of anaphylaxis. PAF acetylhydrolase activity was significantly lower in patients with fatal anaphylactic reactions to peanuts than in patients in any of the control groups. Failure of PAF acetylhydrolase to inactivate PAF may contribute to the severity of anaphylaxis. REVIEWER COMMENTS. PAF is 1 of the proinflammatory mediators that are released systemically by the degranulation of mast cells and basophils. Although PAF is not the only mediator that plays a role in anaphylaxis, these results suggest that PAF is very important. Therefore, it may be useful to develop new pharmaceutical agents that block its actions. Additional research is also needed to determine if PAF and PAF acetylhydrolase measurements may be used as a screening tool to select patients at highest risk for fatal anaphylaxis.

The Endothelin-Converting Enzyme-1/Endothelin-1 Pathway Plays a Critical Role in Inflammation-Associated Premature Delivery in a Mouse Model

Premature delivery occurs in 12% of all births and accounts for nearly half of long-term morbidity. Current therapeutic approaches to preterm delivery are ineffective and present serious risks to both mother and fetus. The single most common cause of preterm birth is infection. Previous in vitro investigations have shown that endothelin-1 (ET-1) is induced by inflammatory cytokines and that it increases myometrial smooth muscle tone. Furthermore, we have previously shown that both the endothelin-converting enzyme-1 (ECE-1) inhibitor, phosphoramidon, as well as a novel ET-1 receptor A antagonist synthesized by our group, control premature delivery in a mouse model of inflammation-associated preterm delivery. In the current work, we show that levels of both ET-1 and ECE-1 are increased in gestational tissues in E16.5 mice induced to deliver prematurely after lipopolysaccharide administration. We also show that premature delivery is controlled by treatment with the selective endothelin receptor A antagonist BQ-123 in a dose-dependent manner. Finally, we show here for the first time that premature delivery can be controlled using RNA silencing, by hydrodynamic transfection of E15 mice with ECE-1 RNAi. Taken together, these data support a critical role for the ECE-1/ET-1 system in inflammation-associated premature delivery. The ability to control premature delivery by antagonizing or silencing the ECE-1/ET-1 system offers a novel approach to an unmet clinical need.

The impact of platelet-activating factor (PAF)-like mediators on the functional activity of neutrophils: anti-inflammatory effects of human PAF-acetylhydrolase.

Platelet-activating factor (PAF) is a proinflammatory agent in infectious and inflammatory diseases, partly due to the activation of infiltrating phagocytes. PAF exerts its actions after binding to a monospecific PAF receptor (PAFR). The potent bioactivity is reflected by its ability to activate neutrophils at picomolar concentrations, as defined by changes in levels of intracellular Ca(2+) ([Ca(2+)](i)), and induction of chemotaxis and actin polymerization at nanomolar concentration. The role of PAF in neutrophil survival is, however, less well appreciated. In this study, the inhibitory effects of synthetic PAFR-antagonists on various neutrophil functions were compared with the effect of recombinant human plasma-derived PAF-acetylhydrolase (rPAF-AH), as an important enzyme for PAF degradation in blood and extracellular fluids. We found that endogenously produced PAF (-like) substances were involved in the spontaneous apoptosis of neutrophils. At concentrations of 8 microg/ml or higher than normal plasma levels, rPAF-AH prevented spontaneous neutrophil apoptosis (21 +/- 4% of surviving cells (mean +/- SD; control) versus 62 +/- 12% of surviving cells (mean +/- SD; rPAF-AH 20 microg/ml); P < 0.01), during overnight cultures of 15 h. This effect depended on intact enzymatic activity of rPAF-AH and was not due to the resulting product lyso-PAF. The anti-inflammatory activity of rPAF-AH toward neutrophils was substantiated by its inhibition of PAF-induced chemotaxis and changes in [Ca(2+)](i). In conclusion, the efficient and stable enzymatic activity of rPAF-AH over so many hours of coculture with neutrophils demonstrates the potential for its use in the many inflammatory processes in which PAF (-like) substances are believed to be involved.