HE ACUTE RESPIRATORY DIStress syndrome (ARDS) is a serious form of acute lung injury and has a mortality rate of at least 30%. 1,2 Although the most obvious clinical abnormalities are referable to the lung, the most common cause of death is dysfunction of other organs, termed multiple organ dysfunction syndrome (MODS). [1][2][3] Multiple organ dysfunction syndrome is often irreversible, with mortality ranging from 60% to 98%. [4][5][6] To date, there is neither an effective treatment for MODS nor an effective means for preventing its onset.Mechanical ventilation is essential for patients with ARDS. However, animal and clinical studies have shown that mechanical ventilation can worsen preexisting lung injury and produce ventilator-induced lung injury (VILI). The spectrum of VILI includes not only air leaks and increases in endothelial and epithelial permeability, but also includes increases in pulmonary and systemic inflammatory mediators. [7][8][9] The importance of VILI has recently been highlighted by clinical trials demonstrating that protective ventilatory strategies were associated with decreased serum cytokine and chemokine levels, 10,11 decreased levels of organ dysfunction, 11,12 and decreased mortality in patients with Author Affiliations are listed at the end of this article.

Pre-B cell colony-enhancing factor (PBEF) is a highly conserved 52-kDa protein, originally identified as a growth factor for early stage B cells. We show here that PBEF is also upregulated in neutrophils by IL-1β and functions as a novel inhibitor of apoptosis in response to a variety of inflammatory stimuli. Induction of PBEF occurs 5-10 hours after LPS exposure. Prevention of PBEF translation with an antisense oligonucleotide completely abrogates the inhibitory effects of LPS, IL-1, GM-CSF, IL-8, and TNF-α on neutrophil apoptosis. Immunoreactive PBEF is detectable in culture supernatants from LPS-stimulated neutrophils, and a recombinant PBEF fusion protein inhibits neutrophil apoptosis. PBEF is also expressed in neutrophils from critically ill patients with sepsis in whom rates of apoptosis are profoundly delayed. Expression occurs at higher levels than those seen in experimental inflammation, and a PBEF antisense oligonucleotide significantly restores the normal kinetics of apoptosis in septic polymorphonuclear neutrophils. Inhibition of apoptosis by PBEF is associated with reduced activity of caspases-8 and -3, but not caspase-9. These data identify PBEF as a novel inflammatory cytokine that plays a requisite role in the delayed neutrophil apoptosis of clinical and experimental sepsis.

Circulating neutrophils from patients with SIRS or from patients who have undergone major elective surgery show delayed expression of constitutive programmed cell death, and antiapoptotic factors are present in the general circulation. While prolonged neutrophil survival may represent an appropriate adaptive response to injury, the presence of activated and apoptosis-resistant cells in an antiapoptotic environment may contribute to the systemic inflammatory injury characteristic of SIRS and predispose to the development of the multiple organ dysfunction syndrome.

Issue" section, a figure was inadvertently included with the paragraph titled "Thyrotopin receptor can be so insensitive", regarding the article by Takao Ando and colleagues. This figure should have been included with the paragraph titled "RAGE against an immune response", regarding the paper by Peter Nawroth and colleagues. We apologize for any confusion this may have caused. The online version of this section has been corrected. Figure 6PBEF is expressed and is biologically active in neutrophils harvested from critically ill septic patients. (A) PBEF mRNA in neutrophils from eight critically ill septic patients was expressed at higher levels than in control (Con) or LPS-stimulated neutrophils. Blots were reprobed with GAPDH to confirm comparability of loading. (B) Expression of PBEF mRNA transcripts in septic and LPS-treated neutrophils was evaluated by real-time PCR, normalizing expression to that for GAPDH. Expression was induced by LPS (*P < 0.05 versus unstimulated cells) and even more in septic neutrophils (**P < 0.05 versus both LPS-stimulated cells and unstimulated cells). (C) Immunoreactive PBEF was detectable by Western blot in supernatants from LPS-treated and septic neutrophils following 21 hours of in vitro culture in serum-free medium; antisense pretreatment blocked the secretion of PBEF. DMEM denotes medium only; studies were repeated three times, and a representative blot is shown. S, sense; A/S, antisense. (D) Neutrophils from 16 septic critically ill patients were incubated for 5 hours with PBEF antisense or the sense or nonsense controls, and apoptosis was evaluated 21 hours later. Antisense treated cells, but not controls, showed increased rates of apoptosis (*P = 0.002 versus no oligonucleotide [no oligo]; ANOVA). (E) Supernatants from control PMN had minimal effects on the apoptosis of resting PMN (black bar). In contrast, supernatants from septic PMN or septic PMN incubated with PBEF sense oligonucleotides significantly inhibited the apoptosis of control PMN (*P < 0.05), whereas supernatants from antisense-treated septic PMNs induced significantly less inhibition ( † P < 0.05 versus sense or no oligonucleotide; P = NS versus controls, n = 5).

Apoptosis of circulating neutrophils from patients with clinical sepsis is profoundly suppressed, through a mechanism that involves activation of nuclear factor-kappaB that is associated with reduced activity of caspases-9 and -3 and maintenance of mitochondrial transmembrane potential and that differs in important respects from the inhibitory effects seen following the exposure of healthy neutrophils to inflammatory stimuli.

Hypertonicity suppresses neutrophil functions by unknown mechanisms. We investigated whether osmotically induced cytoskeletal changes might be related to the hypertonic inhibition of exocytosis. Hyperosmolarity abrogated the mobilization of all four granule types induced by diverse stimuli, suggesting that it blocks the process of exocytosis itself rather than individual signaling pathways. Concomitantly, osmotic stress provoked a twofold increase in F-actin, induced the formation of a submembranous F-actin ring, and abolished depolymerization that normally follows agonist-induced actin assembly. Several observations suggest a causal relationship between actin polymerization and inhibition of exocytosis: 1) prestimulus actin levels were inversely proportional to the stimulus-induced degranulation, 2) latrunculin B (LB) prevented the osmotic actin response and restored exocytosis, and 3) actin polymerization induced by jasplakinolide inhibited exocytosis under isotonic conditions. The shrinkage-induced tyrosine phosphorylation and the activation of the Na(+)/H(+) exchanger were not affected by LB. Inhibition of osmosensitive kinases failed to prevent the F-actin change, suggesting that the osmotic tyrosine phosphorylation and actin polymerization are independent phenomena. Thus cytoskeletal remodeling appears to be a key component in the neutrophil-suppressive, anti-inflammatory effects of hypertonicity.

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Efficient expression of innate immunity is critically dependent upon the capacity of the neutrophil to be activated rapidly in the face of an acute threat and to involute once that threat has been eliminated. Here we report a novel mechanism regulating neutrophil survival dynamically through the tyrosine phosphorylation or dephosphorylation of caspase-8. Caspase-8 is tyrosine-phosphorylated in freshly isolated neutrophils but spontaneously dephosphorylates in culture, in association with the progression of constitutive apoptosis. Phosphorylation of caspase-8 on Tyr-310 facilitates its interaction with the Src-homology domain 2 containing tyrosine phosphatase-1 (SHP-1) and enables SHP-1 to dephosphorylate caspase-8, permitting apoptosis to proceed. The non-receptor tyrosine kinase, Lyn, can phosphorylate caspase-8 on Tyr-397 and Tyr-465, rendering it resistant to activational cleavage and inhibiting apoptosis. Exposure to lipopolysaccharide reduces SHP-1 activity and binding to caspase-8, caspase-8 activity, and rates of spontaneous apoptosis. SHP-1 activity is reduced and Lyn increased in neutrophils from patients with sepsis, in association with profoundly delayed apoptosis; inhibition of Lyn can partially reverse this delay. Thus the phosphorylation and dephosphorylation of caspase-8, mediated by Lyn and SHP-1, respectively, represents a novel, dynamic post-translational mechanism for the regulation of neutrophil apoptosis whose dysregulation contributes to persistent neutrophil survival in sepsis.