Evaluation of the safety, reactogenicity and immunogenicity of FluBlok® trivalent recombinant baculovirus-expressed hemagglutinin influenza vaccine administered intramuscularly to healthy adults 50-64 years of age.

BACKGROUND: Alternative methods for influenza vaccine production are needed to ensure adequate supplies. METHODS: Healthy adults 50-64 years were assigned randomly to receive one intramuscular injection of trivalent recombinant hemagglutinin (rHA) or U.S. licensed trivalent inactivated vaccine (TIV) containing H1, H3 and B antigens (Ag) derived from 2007 to 2008 influenza virus strains A/Solomon Islands/03/2006 (H1N1), A/Wisconsin/67/2005 (H3N2), and B/Malaysia/2506/2004. Each rHA dose contained 45 µg HA/strain of the 2007-2008 FDA-recommended Ag vs. 15 µg/strain for TIV. Antibody (Ab) responses were measured using a hemagglutination-inhibition (HAI) assay at baseline and 28 days post-vaccination. Respiratory samples for viral culture were collected from subjects with influenza-like illness (ILI) during the 2007-2008 season in the U.S. RESULTS: 601 subjects were enrolled. Vaccines were well tolerated. Seroconversion (the percentage of subjects with either (a) a pre-vaccination HAI titer ≤ 10 and a post-vaccination HAI titer ≥ 40 or (b) a pre-vaccination titer ≥ 10 and a minimum four-fold rise in post-vaccination HAI antibody titer) in the TIV and rHA groups, respectively, was obtained in 66% vs. 72% for H1; 44% vs. 61% for H3; and 41% vs. 41% for B. Proportions achieving titers ≥ 40 were 96% vs. 96% for H1, 75% vs. 85% for H3, and 94% vs. 93% vs. B. Geometric mean titer ratios at day 28 (TIV/rHA) were 0.77 for H1; 0.58 for H3; and 1.05 for B, respectively. ILI frequencies were low and similar in both groups. CONCLUSIONS: Both vaccines were safe and immunogenic. Ab responses vs. H1 and H3 Ags were significantly higher in the rHA group, with similar responses to B. Furthermore, the FluBlok group had a statistically significantly higher seroconversion rate against influenza A/H3N2 compared to the TIV group.

Comparative immunogenicity of recombinant influenza hemagglutinin (rHA) and trivalent inactivated vaccine (TIV) among persons > or =65 years old.

Alternative substrates for influenza vaccine production are needed to ensure adequate supplies. We evaluated the relative safety and immunogenicity of recombinant hemagglutinin (rHA) or trivalent inactivated vaccine (TIV) among 869 > or =65-year-old subjects in a randomized clinical trial. Virologic surveillance for influenza-like illness (ILI) was conducted during the 2006-2007 epidemic. Vaccines were well tolerated. Seroconversion rates vs. influenza A/H1N1 and H3N2 antigens were superior in the rHA group, but were inferior vs. influenza B; however, results for influenza B are confounded since the vaccine antigens were different. ILI frequencies were low and similar in both groups. Studies assessing relative immunogenicity of vaccines using identical B Ags are warranted.

Role of intracellular chloride in the reversible activation of neutrophil beta 2 integrins: a lesson from TNF stimulation.

The process of beta(2) integrin activation, which enhances the interaction of these heterodimers with ligands, plays a crucial role in the adherence-dependent neutrophilic polymorphonuclear leukocytes' (PMN) responses to TNF. Our previous observation, showing that a marked decrease of the high basal Cl(-) content (Cl(-)(i)) is an essential step in the TNF-induced activation of PMN, stimulated this study, which investigates the role of alterations of Cl(-)(i) in the activation of beta(2) integrins triggered by TNF. Here we show that TNF enhances the expression of activation-specific neoepitopes of beta(2) integrins, namely, epitope 24, a unique epitope present on all three leukocyte integrin alpha subunits, and epitope CBRM1/5, localized to the I domain on the alpha-chain of Mac-1 (CD11bCD18). Moreover, we demonstrate that the conformational changes underlying the expression of the neoepitopes are dependent on a drop in Cl(-)(i) because 1) inhibition of Cl(-)(i) decrease is invariably accompanied by inhibition of beta(2) integrin activation, 2) Cl(-)(i) decrease induced by means other than agonist stimulation, i.e., by placing PMN in Cl(-)-free buffers, activates beta(2) integrins, and 3) restoration of the original Cl(-)(i) levels is accompanied by deactivation of beta(2) integrins. We also show that Cl(-)(i) decrease is required for TNF-induced cytoplasmic alkalinization, but such a rise in pH(i) does not seem to be relevant for beta(2) integrin activation. The results of our study emphasize the role of Cl(-) as a new PMN "second messenger."

TNF-Induced shedding of TNF receptors in human polymorphonuclear leukocytes: role of the 55-kDa TNF receptor and involvement of a membrane-bound and non-matrix metalloproteinase.

A down-modulation of both the 55-kDa (TNF-R55) and the 75-kDa (TNF-R75) TNF receptors is observed in neutrophils exposed to a variety of stimuli. Proteolytic cleavage of the extracellular region of both receptors (shedding) and, with TNF, internalization of TNF-R55 and shedding of TNF-R75 are the proposed mechanisms. We have characterized the TNF-induced shedding of TNF receptors in neutrophils and determined the nature of the involved proteinase. Neutrophils exposed to TNF release both TNF receptors. A release of TNF receptors comparable to that observed with TNF was induced with TNF-R55-specific reagents (mAbs and a mutant of TNF) but not with the corresponding TNF-R75-specific reagents. A hydroxamic acid compound (KB8301) almost completely inhibited shedding of TNF-R55 and to a lesser degree shedding of TNF-R75. KB8301 also inhibited FMLP-induced shedding to a similar extent. Shedding was also inhibited by 1,10-phenanthroline, but this effect was considered nonspecific as the compound, at variance with KB8301, almost completely inhibited TNF and FMLP-induced PMN activation. Diisopropylfluorophosphate partially inhibited shedding of TNF-R75, suggesting the contribution of a serine proteinase to the release of this receptor. Shedding activity was not affected by matrix metalloproteinases inhibitors nor was it released in the supernatants of FMLP-stimulated neutrophils. These results suggest that TNF induces release of its receptors, that such a release is mediated via TNF-R55, and that a membrane-bound and non-matrix metalloproteinase is involved in the process. The possibility that ADAM-17, which we show to be expressed in neutrophils, might be the involved proteinase is discussed.

Expression and characterization of recombinant human eosinophil peroxidase. Impact of the R286H substitution on the biosynthesis and activity of the enzyme.

Hereditary eosinophil peroxidase deficiency is a genetic abnormality characterized by a decrease or absence of peroxidase activity and a reduction of the granule matrix volume. Recently, we identified two mutations associated with eosinophil peroxidase deficiency in a subject and his siblings, i.e. a base insertion causing the appearance of a premature stop codon and a base transition causing the replacement of an Arg at codon 286 with a His (R286H). In this article we report the stable expression of both the recombinant wild-type and the R286H eosinophil peroxidase precursor in the K-562 cell line, and the effects of the R286H substitution on the structure and function of the eosinophil peroxidase precursor. Heme group incorporation into both the recombinant wild-type and the recombinant R286H eosinophil peroxidase precursor was comparable, as was the stability of both proteins. Instead, the recombinant R286H eosinophil peroxidase precursor exhibited marked alterations of the catalytic properties and an increased sensitivity to four peroxidase inhibitors with respect to both the recombinant wild-type eosinophil peroxidase precursor and the native enzyme. In addition, the recombinant wild-type, but not the R286H, eosinophil peroxidase precursor was immunoprecipitated by two anti-(eosinophil peroxidase) mAbs. Altogether, our results suggest a protein misfolding of the R286H eosinophil peroxidase precursor which might account for its altered catalytic properties and the absence of expression of some epitopes.

Triggering of chloride ion efflux from human neutrophils as a novel function of leukocyte beta 2 integrins: relationship with spreading and activation of the respiratory burst.

PMN residing on immobilized fibronectin have been shown to respond to TNF with an intense and long lasting Cl- efflux that leads to a marked decrease of the unusually high basal Cl- content of these phagocytes. The finding that this Cl- efflux depends, at least in part, on beta2 integrin engagement stimulated the present investigation, which addresses the question as to whether beta2 integrins per se, in the absence of PMN agonists, are able to generate signals triggering Cl- efflux. We induced beta2 integrin cross-linking by plating PMN onto surface-bound mAbs directed against either the common beta-chain (CD18) or the individual alpha-chains (CD11a, CD11b, CD11c) of LFA-1, CR3, and gp150/95. Anti-CD18 mAbs triggered a marked release of Cl- ions, which was accompanied by spreading and activation of the respiratory burst. Cross-linking of gp150/95 and LFA-1 generated the most powerful signals for the activation of Cl- efflux. The results of three independent experimental approaches, i.e., kinetic studies, use of Cl- transport inhibitors, and modulation of Cl- efflux with different amounts of anti-beta2 integrin mAbs, indicated that Cl- efflux regulates both spreading and respiratory burst triggered by beta2 integrin cross-linking. Cl- efflux appears to be independent on either alterations of [Ca2+]i or changes in the plasma membrane potential and shows sensitivity to a raise in pHi. This study uncovers a new signaling ability of beta2 integrins and contributes to highlight the role of Cl- efflux in the outside-in signal transduction pathway regulating adherence-dependent PMN responses.

Role of the 75-kDa TNF receptor in TNF-induced activation of neutrophil respiratory burst.

The exclusive role of the 55-kDa TNF receptor (TNF-R55) as the signaling receptor in TNF-induced activation of respiratory burst by human polymorphonuclear leukocytes residing on biologic surfaces has been inferred from results obtained with receptor-specific monoclonal and polyclonal Abs. In this work, we confirm this assumption by a more direct approach, i.e., by using receptor-specific TNF mutants (p55TNF and p75TNF) and, as a novel contribution, we show that cooperation of the 75-kDa TNF receptor (TNF-R75) is required for a full blown response to the cytokine. This conclusion stems from three sets of data: 1) none of the TNF-R55-specific agonists used, i.e., mAbs or p55TNF, induced a respiratory burst comparable with that induced by TNF; 2) selective down-modulation of TNF-R75 resulted in a diminished response to TNF but not to TNF-R55-specific agonists or to the chemotactic peptide FMLP; and 3) mAbs that either block or stabilize binding of TNF to TNF-R75 inhibited the response to the cytokine, suggesting that cooperation requires not only TNF binding to the receptor but also an appropriate dissociability from it. The inhibitory effect of the Abs increased as the cytokine concentrations decreased, indicating that cooperation by TNF-R75 becomes more relevant at low TNF doses. Such a cooperation does not seem to rely on the activation of a TNF-R75-linked signaling pathway independent of TNF-R55, since the response to p55TNF and p75TNF given in combination was not higher than the response to p55TNF alone. The possible mechanisms of cooperation are discussed.

Report of a US public health service workshop on hypotonic-hyporesponsive episode (HHE) after pertussis immunization.

Hypotonic-hyporesponsive episode (HHE) is a term used to describe a somewhat heterogenous group of clinical disorders that have been reported primarily in association with whole-cell pertussis vaccination. A 1991 review by the Institute of Medicine determined that the evidence available was indeed consistent with a causal relation between whole-cell pertussis-diphtheria-tetanus immunization and HHE, but that the evidence was insufficient to indicate a causal relationship between HHE and the subsequent development of permanent neurologic damage. More recent data from clinical trials conducted in Europe suggest that HHE also occurs after vaccination with acellular pertussis vaccines. The US Food and Drug Administration, in collaboration with the US Public Health Service, sponsored a workshop on HHE in Rockville, Maryland, on June 19, 1997. The primary goals of the workshop were to develop a case definition of HHE and to evaluate the general design and feasibility of possible studies of HHE using the federal Vaccine Adverse Event Reporting System (VAERS), a national passive surveillance system. The goals of such studies would be to understand better the acute HHE event and to evaluate the possibility of long-term sequelae. Case Definition. There has been no generally accepted definition of HHE, and a standard definition would be useful for vaccine safety work and would potentially facilitate interstudy comparisons of the growing number of licensed vaccines containing acellular pertussis components. The workshop defined HHE as an event of sudden onset occurring within 48 hours of immunization, with duration of the episode ranging from 1 minute to 48 hours, in children younger than 10 years of age. All of the following must be present: 1) limpness or hypotonia, 2) reduced responsiveness or hyporesponsiveness, and 3) pallor or cyanosis or failure to observe or to recall skin coloration. HHE is not considered to have occurred if there is a known cause for these signs (eg, postictal), if urticaria is present during the event, if normal skin coloration is observed throughout the episode, or if the child is simply sleeping. This inclusive (sensitive) case definition will allow investigators, through the technique of stratification according to certain characteristics (eg, time from vaccination to onset of HHE), to attempt to hone the definition and make it more specific. Refinement of the definition of HHE has been hindered by the lack of information on its pathophysiology and by the lack of pathognomonic signs, symptoms, and diagnostic tests. Another hindrance is that by the time the child presents for medical evaluation, the signs of HHE often have normalized. Moreover, different mechanisms may be involved in different individuals whose events meet this workshop's HHE definition. Further Study of HHE. Probably the most important question about HHE is whether it has any permanent sequelae. The workshop assessed the possible contribution VAERS-based studies could make to answering this question and found substantial methodologic problems; however, ongoing studies in Sweden and The Netherlands have the potential to provide useful information on this question. The most useful contribution of VAERS data would be in a descriptive study of HHE, with a possible case-control study of factors that may affect the risk of HHE after vaccination, rather than a study of possible permanent sequelae. The workshop participants felt that a detailed descriptive study of approximately 100 HHE events reported during a 1- to 2-year period could provide a more in-depth description of HHE cases in greater numbers than has been published previously, but the study would not address the issue of long-term sequelae of HHE. Better descriptive data may lead to new hypotheses concerning risk factors, etiology, and pathophysiology of HHE that might be evaluated further by studying subsequent cases and controls from VAERS or from other sources, depending on the hypoth

Biochemical and molecular characterization of hereditary myeloperoxidase deficiency.

Hereditary myeloperoxidase (MPO) deficiency is a neutrophil disorder characterized by the lack of peroxidase activity. Cytochemical, biochemical, spectroscopic, immunocytochemical, and genetic studies were carried out on a 5-year-old MPO-deficient subject and on her parents. The father was also MPO-deficient, whereas the mother had 24% of normal MPO activity. Although the typical absorption spectrum of MPO was absent in both the father and daughter, the father's neutrophils, and not those of the daughter, contained material antigenically related to MPO. In the MPO gene of the father, two mutations were found, each located in a different allele: a T --> C transition, causing the nonconservative replacement M251T and a 14-base deletion within exon 9. The M251T substitution occurred in the carboxy-terminal region of the light chain that is included in the heme pocket. The daughter inherited the 14-base deletion from her father. The study of the MPO mRNAs present in liquid cultures of granulocyte precursors surprisingly showed that the same genetic defect, ie, the 14-base deletion, seemed to exhibit different mRNA phenotypes in the father and the daughter. In fact, mRNA derived from the 14-base-deleted allele was not found in the father and an aberrantly spliced MPO mRNA with a 77-base deletion of exon 9, which includes the 14-base deletion and leads to the generation of a premature stop codon, was found in the daughter. The possibility that Delta77 mRNA could derive from other mutations linked to the Delta14 allele was dismissed because no sequence differences were found in the region (exons and exon-intron junctions). Our data indicate that the alteration of the mRNA context caused by the 14-base deletion provide a basis for the 77-base deletion in the mRNA processing. Since the granulocyte precursors from the liquid cultures of the father were more differentiated than those from the daughter, the observed different behavior of the 14-base-deleted allele in the father and daughter may be the result of a differentiation-stage dependent control of altered spliced mRNA, which may be tolerated during the early stages of differentiation but degraded at later stages. In the liquid cultures of the daughter's cells, in addition to the mRNA with the 77-base deletion, a mRNA with the wild type sequence was also found. This mRNA was inherited from the mother, since no mutations were found in her MPO cDNA and MPO gene. The MPO defect might be caused by a regulatory mutation that induces the MPO gene switch off at an early stage of granulocyte differentiation.

Influenza pandemic preparedness plan for the United States.

In preparation for the next influenza pandemic, a comprehensive and action-oriented plan is presently under development that focuses on six major areas: (1) improvements in ongoing virologic and disease-based surveillance systems; (2) vaccination of high-priority target groups, and, given sufficient vaccine supplies, the entire US population; (3) liability programs for vaccine manufacturers and health care providers; (4) research to improve detection of new variants and to accelerate the availability of existing and novel vaccines and antiviral agents; (5) integrated, multicomponent communication systems for rapid information dissemination and exchange; and (6) emergency preparedness plans to provide for adequate medical care and maintenance of essential community services. The sudden and unpredictable emergence of pandemic influenza and its potential for causing severe health and social consequences dictate the need for close collaboration among a wide variety of organizations in both the public and private sectors.

Biologically active polypeptides in the venom of the jellyfish Rhopilema nomadica.

A tropical jellyfish, Rhopilema nomadica (Scyphozoa, Rhizostomeae) has recently invaded the eastern Mediterranean. Its painful stings have been the bane of bathers and fishermen from Egypt to Turkey. This paper reports on the presence of haemolytic activity and alpha-chymotrypsin-like serine protease activity in the venom of the R. nomadica nematocysts. In addition, the presence of phospholipase A2 activity, which has been described previously, is confirmed. Some properties of these activities are defined.

Syncope after immunization.

OBJECTIVE: To describe the individual characteristics, clinical features, and morbidity associated with syncope following immunization. DESIGN: Large case series. SETTING: United States, 1990 through 1995. SUBJECTS: Reports to the national Vaccine Adverse Event Reporting System (VAERS), a passive surveillance system. An additional 3 reports of head injury (documented by medical records) were obtained through the National Vaccine Injury Compensation Program. MAIN OUTCOME MEASURES: Syncope, syncope and hospitalization, or syncope and head injury within 12 hours of vaccination. RESULTS: A total of 697 cases of syncope after vaccination was reported. Age younger than 20 years was reported for 77.4%; 57.5% were female. Hospitalization was reported in 9.6%. Of the 571 syncope events with known time, 511 occurred 1 hour or less after vaccination. Of these, 323 (63.2%) occurred 5 minutes or less, 454 (88.8%) occurred 15 minutes or less, and 500 (97.8%) occurred 30 minutes or less after vaccination. Tonic or clonic movements, which have been associated with the anoxia of vasovagal syncope, were reported in 30.4% of syncopal episodes occurring 15 minutes or less after and in 12.8% of those occurring 15 minutes or longer after vaccination (P < .001). Six patients suffered skull fracture, cerebral bleeding, or cerebral contusion after falls; 3 of these patients required neurosurgery. Falls occurred 15 minutes or less after vaccination, in or near the clinic or office. Ages ranged from 12 to 28 years; 5 of 6 were male. Follow-up revealed substantial residual impairment in 2 patients. CONCLUSIONS: Prevention of injury from syncope after vaccination and of syncope itself may be possible in many cases. Vaccinators should be aware that patients exhibiting presyncopal signs and symptoms around the time of immunization need to be evaluated carefully and may need to be assisted to sit or lie down after immunization until free of symptoms.

Outbreak of paralytic poliomyelitis in a highly immunized population in Jordan.

Between November 1991 and March 1992, 37 cases of paralytic poliomyelitis occurred in Jordan, where none had been reported since 1988. Of these, 17 (50%) of 34 patients had received at least three doses of oral poliovirus vaccine (OPV3). The first and 2 subsequent case-patients were children of Pakistani migrant workers, and the first 8 and a total of 27 (75%) case-patients resided in or near the Jordan Valley. A seroepidemiologic study of 987 children in all regions of Jordan was performed to assess OPV3 coverage and immune response to OPV. Although OPV3 coverage by 12 months of age was high (96%) in the general population, coverage was lower among Pakistani (21%), Bedouin (63%), and Gypsy (9%) children (P < .001). Seroprevalences for poliovirus type 3 were 71% in the Jordan Valley versus 81% in other regions after 3 doses of OPV (P < .06) and 77% in the Jordan Valley versus 98% in other regions after 5 doses of OPV (P < .001). This outbreak demonstrates the importance of achieving high seroimmunity to infection in all geographic areas to prevent the reintroduction and spread of imported strains of wild poliovirus.

Outbreaks of paralytic poliomyelitis, 1976-1995.

During 1976-1995, 48 outbreaks of paralytic poliomyelitis with a cumulative total of approximately 17,000 cases were reported worldwide. Outbreaks occurred on most continents, affected from 0.1 to 52 persons per 100,000 total population (median, 4.4), lasted 2-25 months (median, 7), typically involved unvaccinated or inadequately vaccinated subgroups within highly immunized communities, and were primarily caused by poliovirus type 1 (74%). Cases in developing countries occurred predominantly among children <2 years of age, while those in industrialized countries tended to occur in older persons who had escaped natural infection earlier in life and who had not been vaccinated or had received poliovirus vaccine of inadequate potency. Partial genomic sequencing studies indicated that at least 15 outbreaks resulted from importation of wild polioviruses, primarily from the Indian subcontinent. These findings illustrate the potential for wide dissemination of wild poliovirus infection and underscore the critical need for maintaining high levels of immunity in all countries and for more aggressive vaccination efforts in areas in which polio is endemic.

Increased immunogenicity of oral poliovirus vaccine administered in mass vaccination campaigns compared with the routine vaccination program in Jordan.

To compare the immunogenicity of routine versus mass campaign doses of oral poliovirus vaccine (OPV), serum neutralizing antibodies were measured in 254 children before and after two mass vaccination campaigns in Jordan. Precampaign seroprevalences to poliovirus types 1, 2, and 3 in children who had received three, four, or five routine doses of OPV were compared with postcampaign seroprevalences in children who had received one, two, or three routine doses plus two mass campaign doses. Seroprevalences were consistently higher in subgroups that received two doses through mass campaigns than in subgroups that received all doses through the routine program, especially for poliovirus type 3. Geometric mean titers were also consistently higher for mass campaign subgroups, particularly for poliovirus type 3. The findings suggest that adding further doses of OPV to the routine schedule is unlikely to have as great an impact on the immune state of children as administering the same number of doses during mass campaigns.

Humoral and mucosal immunity in infants induced by three sequential inactivated poliovirus vaccine-live attenuated oral poliovirus vaccine immunization schedules. Baltimore Area Polio Vaccine Study Group.

The relative immunity induced by sequential administration of inactivated poliovirus vaccine (IPV) produced in human diploid cells and live attenuated oral poliovirus vaccine (OPV) was evaluated by randomization of 510 infants to receive IPV and OPV sequentially according to one of three experimental schedules, IPV only, or OPV only. The antibody response to two IPV doses was lower than expected. However, for each of the IPV-OPV sequential schedules, the first OPV dose significantly enhanced seroconversion rates and geometric mean microneutralization antibody titers. Three months after the final dose, 96%-99%, 99%-100%, and 81%-100% of infants had antibodies to poliovirus types 1, 2, and 3, respectively, and subjects with two or more prior OPV doses were significantly less likely than those with none or one prior OPV dose to excrete virus in feces after an OPV challenge. Sequential IPV-OPV immunization is now recommended for routine use in the United States. The optimal schedule consists of two IPV doses followed by two OPV doses.

The effect of diarrhea on oral poliovirus vaccine failure in Brazil.

The effect of diarrhea on oral poliovirus vaccine (OPV) failure was evaluated using data from Brazil, where 728 infants were immunized at birth (OPV1) and approximately 6 (OPV2), 10 (OPV3), and 14 (OPV4) weeks. Recent diarrhea history was significantly associated with increased vaccine failure only after OPV2 for poliovirus types 2 and 3. In multivariate models, controlling for breast feeding, season of vaccine administration (type 3 only), maternal antibody (type 3 only), and immunization campaign exposure (type 3 only) strengthened this effect. Diarrhea at OPV receipt was associated with vaccine failure to poliovirus types 1 and 3 only after OPV2. These data support the current recommendation that children with diarrhea receive OPV and be reimmunized once their illness resolves. Expanding this recommendation to include children with a recent diarrhea history should be considered. While the effect of diarrhea on vaccine failure may be limited to OPV2, programmatic realities may preclude dose-specific recommendations.

Chloride ion efflux regulates adherence, spreading, and respiratory burst of neutrophils stimulated by tumor necrosis factor-alpha (TNF) on biologic surfaces.

Chloride ion efflux is an early event occurring after exposure of neutrophilic polymorphonuclear leukocytes (PMN) in suspension to several agonists, including cytokines such as tumor necrosis factor-alpha (TNF) and granulocyte/macrophage-colony stimulating factor (Shimizu, Y., R.H. Daniels, M.A. Elmore, M.J. Finnen, M.E. Hill, and J.M. Lackie. 1993. Biochem. Pharmacol. 9:1743-1751). We have studied TNF-induced Cl- movements in PMN residing on fibronectin (FN) (FN-PMN) and their relationships to adherence, spreading, and activation of the respiratory burst. Occupancy of the TNF-R55 and engagement of beta 2 integrins cosignaled for an early, marked, and prolonged Cl- efflux that was accompanied by a fall in intracellular chloride levels (Cl-i). A possible causal relationship between Cl- efflux, adherence, and respiratory burst was first suggested by kinetic studies, showing that TNF-induced Cl- efflux preceded both the adhesive and metabolic response, and was then confirmed by inhibition of all three responses by pretreating PMN with inhibitors of Cl- efflux, such as ethacrynic acid. Moreover, Cl- efflux induced by means other than TNF treatment, i.e., by using Cl(-)-free media, was followed by increased adherence, spreading, and metabolic activation, thus mimicking TNF effects. These studies provide the first evidence that a drastic decrease of Cl-i in FN-PMN may represent an essential step in the cascade of events leading to activation of proadhesive molecules, reorganization of the cytoskeleton network, and assembly of the O2(-)-forming NADPH oxidase.