Phagocytic function of polymorphonuclear leukocytes and the RES in endotoxemia

Leucocytes and cardiopulmonary bypass: in vitro production of oxygen free radicals and trapping in the reperfused myocardium

The production of oxygen free radicals (OFR) by leucocytes was evaluated ex vivo by chemiluminescence (CL) before, during and after routine coronary artery bypass surgery (group A, n=11). The possibility of leucocyte trapping in the coronary circulation during the early reperfusion period was also investigated (group B, n=9). In group A, arterial blood samples were taken immediately before the start of surgery during anaesthesia, five minutes before and five and 30 minutes after the start of cardiopulmonary bypass (CPB), five minutes before and five and 30 minutes after the start of reperfusion of the heart, and then four and 24 hours after the end of CPB. In group B, arterial and coronary sinus blood samples were simultaneously drawn five and 30 minutes after the release of the aortic crossclamp. All blood samples were corrected for haemodilution. In group A, both CL and the level of circulating leucocytes declined during CPB. The lowest value of CL was measured 30 minutes after the start of CPB (69± 2% of baseline values) (mean±SEM). The lowest level of leucocytes was found after 30 minutes of CPB: 2.6±0.4 (109/l) vs 4.2±0.5 before surgery. Twenty-four hours after CPB, CL was increased to 170±49% and a leucocytosis was present (12.2±1.1). In group B, after five minutes of reperfusion the number of circulating leucocytes in arterial blood was 3.8±0.9 x 10 9/l as compared to 2.2±0.5 x 109/l in the coronary sinus (p<0.0017). However, no such difference was found after 30 minutes of reperfusion. The decreased CL during CPB was probably due to in vivo activation and exhaustion of leucocytes. The postischaemic trapping of these cells may play a pathogenetic role in reperfusion injury.

Immature circulating neutrophils in sepsis have impaired phagocytosis and calcium signaling

Patients with sepsis commonly develop leukocytosis, which is presumed to reflect a host response to infection. Effective phagocytosis by neutrophils is crucial in the clearance of invading microbes. However, efficacy of phagocytosis in sepsis is controversial. We hypothesized that host phagocytic capacity in sepsis can be affected by immature neutrophils that are released into the circulation. Circulating neutrophils were evaluated in 16 patients with severe sepsis and 5 healthy donors. Immature neutrophils were identified by the cell morphology. Phagocytosis was evaluated by micromanipulation technique and simultaneous cytosolic-free Ca2+ imaging. Leukocytosis was present in 12 of 16 patients. Nine of the 12 patients with leukocytosis and 3 of 4 patients with normal white blood cell counts had increased circulating immature neutrophils (mean, 39.3% +/- 20.7%; normal <or=5%). Quantification of the phagocytic activity revealed a significantly reduced phagocytic index of immature neutrophils as compared with mature neutrophils from both sepsis patients and healthy donors (25% +/- 5% vs. 69% +/- 8% and 42% +/- 6%; P < 0.05). As compared with mature neutrophils, the number of internalized zymosan particles within immature neutrophils was also significantly lower. Mature neutrophils from patients and healthy donors displayed a single rapid transient Ca signal during phagocytosis in contrast with weak signals from immature neutrophils. Our preliminary results show that phagocytic capacity of immature neutrophils is lower as compared with mature neutrophils. An increase in immature neutrophils in severe sepsis may undermine the overall phagocytic efficacy of a host despite observed leukocytosis.

Omeprazole treatment diminishes intra- and extracellular neutrophil reactive oxygen production and bactericidal activity

OBJECTIVE

Neutrophils play a crucial role in host defense against infectious disease. The objective was to analyze the effect of omeprazole treatment on indexes of neutrophil function in healthy subjects.

DESIGN

Open.

SETTING

University hospital.

SUBJECTS

Ten healthy subjects.

INTERVENTION

Analysis of blood samples before and after omeprazole administration.

MEASUREMENTS AND MAIN RESULTS

Neutrophil Escherichia coli phagocytosis was assessed by microscopy and flow cytometry. Intracellular production of reactive oxygen intermediates was measured by flow cytometry. Extracellular reactive oxygen intermediate production was assessed with a cytochrome c reduction assay. Neutrophil bactericidal capacity and intracellular concentrations of Ca2+ were determined by fluorometry. Four hours after a single 40-mg dose of omeprazole, intra- and extracellular reactive oxygen intermediate production by neutrophils was significantly reduced compared with pretreatment values: -30% (24% to 42%) (median and range) and -22% (21% to 68%; p <.05 for both). The intracellular Ca2+ concentrations in resting neutrophils were significantly increased (+33%, 21% to 39%, compared with pretreatment concentrations, p <.001) and neutrophilic bactericidal activity was decreased (-30%, 19% to 47%, compared with pretreatment concentrations, p <.0001). Intracellular Ca2+ concentrations correlated with intracellular reactive oxygen intermediate production and neutrophilic bactericidal capacity (r =.730 and r =.618, p <.05 for both, respectively). In contrast, phagocytosis rates were not impaired by omeprazole.

CONCLUSIONS

Our results imply that omeprazole impairs production of reactive oxygen intermediates by neutrophils. Whether specific impairments of neutrophil host defenses occur in vivo remains uncertain. Reduced bactericidal activity is associated with an increase of intracellular Ca2+ concentrations in resting neutrophils.

Activation of adherent vascular neutrophils in the lung during acute endotoxemia

BACKGROUND

Neutrophils constitute the first line of defense against invading microorganisms. Whereas these cells readily undergo apoptosis under homeostatic conditions, their survival is prolonged during inflammatory reactions and they become biochemically and functionally activated. In the present study, we analyzed the effects of acute endotoxemia on the response of a unique subpopulation of neutrophils tightly adhered to the lung vasculature.

METHODS

Rats were treated with 5 mg/kg lipopolysaccharide (i.v.) to induce acute endotoxemia. Adherent neutrophils were isolated from the lung vasculature by collagenase digestion and sequential filtering. Agarose gel electrophoresis, RT-PCR, western blotting and electrophoretic mobility shift assays were used to evaluate neutrophil activity.

RESULTS

Adherent vascular neutrophils isolated from endotoxemic animals exhibited decreased apoptosis when compared to cells from control animals. This was associated with a marked increase in expression of the anti-apoptotic protein, Mcl-1. Cells isolated 0.5-2 hours after endotoxin administration were more chemotactic than cells from control animals and expressed increased tumor necrosis factor-alpha and cyclooxygenase-2 mRNA and protein, demonstrating that they are functionally activated. Endotoxin treatment of the animals also induced p38 and p44/42 mitogen activated protein kinases in the adherent lung neutrophils, as well as nuclear binding activity of the transcription factors, NF-kappaB and cAMP response element binding protein.

CONCLUSION

These data demonstrate that adherent vascular lung neutrophils are highly responsive to endotoxin and that pathways regulating apoptosis and cellular activation are upregulated in these cells.

Down-regulation of CXCR1 and CXCR2 expression on human neutrophils upon activation of whole blood by S. aureus is mediated by TNF-alpha

It was suggested that bacterial products can inhibit the expression of leucocyte chemokine receptors during sepsis and affect leucocyte functions in septic syndrome. Superantigens and toxins produced by Staphylococcus aureus are capable of activating leucocytes via binding to MHC-II antigens on monocytes and T-cell receptor molecules on T lymphocytes. It was recently shown that staphylococcal enterotoxins directly down-regulate the expression of CC chemokine receptors on monocytes through binding to MHC class II molecules. We studied the effects of killed S. aureus on the expression of interleukin-8 receptors, CXCR1 and CXCR2, on polymorphonuclear leucocytes (PMN), which are known to lack the expression of MHC-II antigens. It was shown that S. aureus down-regulated the cell-surface expression of CXCR1 and CXCR2 on PMN in the whole blood and total blood leucocyte fraction containing PMN and monocytes, but did not modulate IL-8 receptor expression in purified PMN suspension. Antibody to TNF-alpha abrogated down-regulation of IL-8 receptors induced by S. aureus. In contrast, LPS reduced CXCR1 and CXCR2 expression in purified PMN and whole blood in a TNF-alpha-independent manner. We further showed that TNF-alpha-induced decrease of CXCR1 and CXCR2 expression was associated with lower IL-8 binding and lower CXCR1 and CXCR2 mRNA levels, and was abrogated by protease inhibitors. We suggest that during septicemia, S. aureus may inhibit neutrophil responsiveness to IL-8 and other CXC chemokines via TNF-alpha- mediated down-regulation of CXCR1 and CXCR2.

Assessment of neutrophil function in patients with septic shock: comparison of methods

Patients with septic shock are shown to have decreased neutrophil phagocytic function by multiple assays, and their assessment by whole-blood assays (fluorescence-activated cell sorter analysis) correlates with assays requiring isolated neutrophils (microscopic and spectrophotometric assays). For patients with similar underlying conditions but without septic shock, this correlation does not occur.

Effects of colloidal resuscitation fluids on reticuloendothelial function and resistance to infection after hemorrhage

The effects of three resuscitation fluids, hydroxyethyl starch (HES), Haemaccel, and fresh autologous blood, on reticuloendothelial system phagocytic and catabolic functions and resistance to infection after 40% hemorrhages in BALB/c mice were studied. The mice, anesthetized with isoflurane, were bled over a 10-min period, left hypovolemic for 30 min, and then resuscitated with their shed blood or the same volume of asanguineous fluid. Normothermia was maintained throughout the experiments. The uptake and catabolism of intravenously injected double-labelled sheep erythrocytes (51Cr-125I-SRBC) in liver and spleen were determined at 1 and 48 h after hemorrhage. No significant changes in the uptake or catabolism of SRBC in liver or spleen were found at 1 h after hemorrhage and resuscitation with any of the fluids. However, at 48 h a significant increase in liver uptake of SRBC was seen in animals resuscitated with either Haemaccel or HES compared to that in animals resuscitated with shed blood or in animals subjected to a sham operation. The increase in liver uptake was accompanied by a small decrease in spleen uptake in animals resuscitated with Haemaccel but not with HES. No great changes in catabolic activity were seen at 48 h, although activity levels tended to be higher in animals resuscitated with Haemaccel. Separate groups of animals were challenged by an intraperitoneal injection with live Escherichia coli at 1 or 48 h after hemorrhage and resuscitation. Sixty-four percent of the animals resuscitated with shed blood survived the challenge with E. coli at 1 h after hemorrhage, whereas only 10 and 0% survival was seen for animals resuscitated with Haemaccel and HES, respectively. At 48 h survival was 80% for shed-blood-resuscitated animals and 60 and 70% for Haemaccel- and HES-resuscitated animals, respectively.

Hemodynamic and metabolic effects of vasopressin blockade in endotoxin shock

BACKGROUND

Arginine vasopressin V1 receptor antagonist (AVPRA) was administered to investigate the influence of vasopressin blockade on hemodynamics and metabolism during endotoxin shock.

METHODS

Anesthetized rats were divided into four groups: control (0.9% saline solution, n = 5), drug control (AVPRA, n = 5), endotoxin (endotoxin, 5 mg/kg, n = 10), and pretreatment (AVPRA and endotoxin, n = 10). Hemodynamics and oxygen transport were evaluated for 2 hours. Terminal arterial and portal venous concentrations of endotoxin, pyruvate, lactate, and ketone bodies were determined.

RESULTS

The endotoxin group maintained blood pressure levels similar to those of control animals. AVPRA pretreatment decreased vascular resistance and resulted in lower blood pressure than endotoxin alone. Endotoxin decreased oxygen consumption and the oxygen extraction ratio and increased arterial lactate concentration and the lactate/pyruvate ratio. Endotoxin also decreased arterial ketone body concentration and markedly decreased ketone body availability in the mesenteric circulation. AVPRA pretreatment improved oxygen consumption, oxygen extraction ratio, and ketone body availability; arterial lactate concentration, lactate/pyruvate ratio, and arterial ketone body concentration were not affected. Pretreatment with AVPRA also decreased arterial and portal venous concentrations of endotoxin.

CONCLUSIONS

Vasopressin receptor blockade during endotoxemia resulted in lower blood pressure than endotoxin alone. Vasopressin receptor blockade also maintained oxygen extraction ratio and ketone body availability in the mesenteric circulation. Vasopressin may play a key role in the response to endotoxemia.

Polymorphonuclear leucocyte dysregulation in patients with gram-negative septicaemia assessed by flow cytometry

Flow cytometry was used to study phagocytic function and release of reactive oxygen intermediates (ROI) following phagocytosis by granulocytes in 14 patients (six female, eight male) with gram-negative septicaemia prior to, during, and after therapy compared with a group of healthy controls. Phagocytic capacity was assessed by measuring uptake of fluorescein isothiocyanate (FITC)-labelled bacteria. Reactive oxygen generation after phagocytosis was measured by the quantification of dihydrorhodamine 123 converted to rhodamine 123 intracellulary. Compared with results in healthy controls granulocytes of septicaemic patients exhibited a decreased capacity to phagocytize Escherichia coli and to generate reactive oxygen products. Both phagocytosis and ROI production increased after initiation of therapy and normalized within 7 days of treatment. The results suggest that granulocytes do not only participate in, but are also a target of, the septic host inflammatory response.

Are soluble factors relevant for polymorphonuclear leukocyte dysregulation in septicemia?

Polymorphonuclear leukocytes (PMNs) of twelve patients with gram-negative septicemia exhibited a decreased capacity to phagocytize Escherichia coli and generate reactive oxygen products which normalized within 7 days of treatment. Ex vivo exchange of plasma from age-, sex-, and blood-group-identical normal controls resulted in an increase of both phagocytic capacity and reactive oxygen intermediate generation in PMNs of septicemic patients and transiently reduced phagocytosis and reactive oxygen intermediate production in PMNs of normal controls. These results suggest that extrinsic factors are crucial for PMN function.

Effect of cefodizime and ceftriaxone on phagocytic function in patients with severe infections

Thirty patients with severe bacterial infections were treated with 50 mg of cefodizime per kg of body weight once daily or 50 mg of ceftriaxone per kg once daily for 10 +/- 3 days. The effect of cefodizime and ceftriaxone on the phagocytic capacity and generation of reactive oxygen intermediates after phagocytosis by granulocytes was assessed prior to, during, and after therapy. Flow cytometry was used to study phagocytic capacity by measuring the uptake of fluorescein-labeled bacteria. The generation of reactive oxygen intermediates after phagocytosis was estimated by the quantification of the intracellular conversion of dihydrorhodamine 123 to rhodamine 123. Prior to therapy, patients in both groups exhibited a decreased capacity to phagocytize Escherichia coli and subsequently to generate reactive oxygen intermediates. Granulocyte function increased after the initiation of therapy and normalized within 7 days for the ceftriaxone-treated patients and within 3 days for the cefodizime group (P < 0.05). In the cefodizime group, an enhancement of phagocytic capacity was observed 14 days after the initiation of therapy (P < 0.05). Prior to therapy, phagocytic capacity was significantly correlated with the generation of reactive oxygen products (r = 0.674 and P < 0.005).

Alveolar cell pattern and chemiluminescence response of blood neutrophils and alveolar macrophages in sheep after endotoxin injection

In order to study the pathomechanisms of the Adult Respiratory Distress Syndrome in an acute animal model, we monitored the alveolar cell pattern and the stimulatory chemiluminescence responses of blood neutrophils and alveolar macrophages in sheep after Escherichia coli endotoxin injection (2 micrograms/kg of body weight). Using appropriate bronchoalveolar lavage techniques, thereby avoiding local inflammation, it was demonstrated that endotoxin injection did not cause any recruitment of neutrophils into the alveoli for a period of up to 24 hours. Following endotoxin injection, blood neutrophils showed a maximal stimulatory response after 5 minutes, and alveolar macrophages after 4 hours. It is concluded that if neutrophils are responsible for initiating the increase in microvascular permeability, then this action must be purely intravascular.

Continuous removal of leucocytes during early gram-negative septicemia reduces plasma levels of endotoxin and improves cardiac performance

The effect of filter leucapheresis as treatment of gram-negative septicemia was studied in an experimental porcine model. In 7 matched pairs of animals, one of the animal groups received filter leucapheresis starting 2 h after the induction of septicemia. The other animal group acted as a non-treated control. A calculated mean number of 15 x 10(9) white blood cells were removed. Animals submitted to leucapheresis showed lower levels of circulating endotoxin, diminished degree of granulocyte activation and higher cardiac output when compared to the non-treated controls. The increased cardiovascular performance indicated a beneficial effect of selective leucafiltration during early gram-negative septicemia. Lower levels of circulating endotoxin and less active PMNs might contribute to these changes.