Down-regulation of the CD62L antigen as a possible mechanism for neutrophilia during inflammation

Whole body and hematopoietic ADAM8 deficiency does not influence advanced atherosclerotic lesion development, despite its association with human plaque progression

Although A Disintegrin And Metalloproteinase 8 (ADAM8) is not crucial for tissue development and homeostasis, it has been implicated in various inflammatory diseases by regulating processes like immune cell recruitment and activation. ADAM8 expression has been associated with human atherosclerosis development and myocardial infarction, however a causal role of ADAM8 in atherosclerosis has not been investigated thus far. In this study, we examined the expression of ADAM8 in early and progressed human atherosclerotic lesions, in which ADAM8 was significantly upregulated in vulnerable lesions. In addition, ADAM8 expression was most prominent in the shoulder region of human atherosclerotic lesions, characterized by the abundance of foam cells. In mice, Adam8 was highly expressed in circulating neutrophils and in macrophages. Moreover, ADAM8 deficient mouse macrophages displayed reduced secretion of inflammatory mediators. Remarkably, however, neither hematopoietic nor whole-body ADAM8 deficiency in mice affected atherosclerotic lesion size. Additionally, except for an increase in granulocyte content in plaques of ADAM8 deficient mice, lesion morphology was unaffected. Taken together, whole body and hematopoietic ADAM8 does not contribute to advanced atherosclerotic plaque development, at least in female mice, although its expression might still be valuable as a diagnostic/prognostic biomarker to distinguish between stable and unstable lesions.

Depletion of blood neutrophils from patients with sepsis: treatment for the future?

Organ failure arising from severe sepsis accounts for nearly 6 million deaths worldwide per annum. At present there are no specific pharmacological agents available for its treatment and identifying a suitable therapeutic target is urgently needed. Neutrophils appear to be contributing directly to pulmonary damage in severe forms of lung injury and indirectly to the failure of other organs. Blood neutrophils from patients with sepsis possess a phenotype that is indicative of activation and our results show that neutrophils isolated from patients with sepsis exhibit a supranormal adherence to endothelial monolayers treated with pro-inflammatory cytokines. Additional studies reveal that the patients' cells are highly efficient at releasing IL-8. We also demonstrate that organ function is improved upon removing neutrophils from the circulation. In this article we propose that in severe sepsis there is a subpopulation of neutrophils which is actively engaged in pathological insult. The phenotypic characterisation of this subset may provide a novel therapeutic strategy for sepsis that could lead to patient benefit.

Regulation of neutrophil trafficking from the bone marrow

Neutrophils are an essential component of the innate immune response and a major contributor to inflammation. Consequently, neutrophil homeostasis in the blood is highly regulated. Neutrophil number in the blood is determined by the balance between neutrophil production in the bone marrow and release from the bone marrow to blood with neutrophil clearance from the circulation. This review will focus on mechanisms regulating neutrophil release from the bone marrow. In particular, recent data demonstrating a central role for the chemokines CXCL12 and CXCL2 in regulating neutrophil egress from the bone marrow will be discussed.

Citrullination of CXCL8 increases this chemokine's ability to mobilize neutrophils into the blood circulation

BACKGROUND

During the first line defense of an infected host, circulating neutrophils invade the inflamed tissue, whereas mature neutrophils from the bone marrow pool migrate into the blood circulation and from there reinforce tissue infiltration. The CXC chemokine CXCL8, also know as interleukin-8, is a potent attractant of neutrophils. Recently, we discovered a new natural post-translational modification of CXCL8, i.e. the deimination of arginine into citrulline by peptidylarginine deiminases.

DESIGN AND METHODS

The ability to provoke leukocytosis was assessed by intravenous administration of citrullinated CXCL8 in rabbits. Adsorption of citrullinated CXCL8 to the Duffy antigen/receptor for chemokines on human or rabbit erythrocytes was evaluated using a competitive binding assay. Finally, surface expression of adhesion molecules was studied after stimulating neutrophils with citrullinated CXCL8.

RESULTS

Citrullination of CXCL8 significantly increased this chemokine's ability to recruit neutrophils into the blood circulation. In addition, the competitive binding properties of CXCL8 for the Duffy antigen/receptor for chemokines were impaired upon citrullination. Since the Duffy antigen/receptor for chemokines is an important scavenging receptor for CXCL8 in the blood stream, citrullination may delay CXCL8 clearance from the circulation. Furthermore, the shedding of CD62L (L-selectin) and the upregulation of CD11b (beta2-integrin) protein expression on CXCL8-induced neutrophils were improved by deimination of CXCL8, possibly contributing to the neutrophil egress from the bone marrow. Conversely, surface expression of CD15, the neutrophilic ligand of endothelial selectins, was equally well upregulated by intact and citrullinated CXCL8.

CONCLUSIONS

These data show that citrullination of CXCL8 enhances leukocytosis, possibly through impaired chemokine clearance from the blood circulation and prolonged presentation to the bone marrow.

Neutrophil mobilization and clearance in the bone marrow

The bone marrow is the site of neutrophil production, a process that is regulated by the cytokine granulocyte colony-stimulating factor (G-CSF). Mature neutrophils are continually released into the circulation, with an estimated 10(11) neutrophils exiting the bone marrow daily under basal conditions. These leucocytes have a short half-life in the blood of approximately 6.5 hr, and are subsequently destroyed in the spleen, liver and indeed the bone marrow itself. Additionally, mature neutrophils are retained in the bone marrow by the stromal cell-derived factor (SDF-1alpha)/chemokine (C-X-C motif) receptor 4 (CXCR4) chemokine axis and form the bone marrow reserve. Following infection or inflammatory insult, neutrophil release from the bone marrow reserve is substantially elevated and this process is mediated by the co-ordinated actions of cytokines and chemokines. In this review we discuss the factors and molecular mechanisms regulating the neutrophil mobilization and consider the mechanisms and functional significance of neutrophil clearance via the bone marrow.

The appearance of L-selectin(low) polymorphonuclear leukocytes in the circulating pool of peripheral blood during myocardial infarction correlates with neutrophilia and with the size of the infarct

BACKGROUND

It is assumed that not only leukocytosis, but also the activation of white blood cells (WBC) may play a role in the pathogenesis and prognosis of patients with myocardial infarction (MI). Activation of WBC includes upregulation of CD11b/CD18 and downregulation of CD62L (L-selectin) antigens.

HYPOTHESIS

The activation of WBC is associated with the appearance of a larger MI.

METHODS

CD11b/CD18 and CD62L were measured on the surface of WBC on Day 1 and Day 3 from the onset of MI. The size of the infarct with estimated by calculating the area under the curve of the creatine kinase enzyme, which was measured every 6 h.

RESULTS

A negative correlation was noted between the absolute polymorphonuclear count and the availability of the CD62L on these cells during Day 1 (r = -0.46, p = 0.003) and Day 3 (r = -0.35, p = 0.05). There was a positive correlation between the size of MI and the WBC count (r = 0.46, p = 0.004) and a negative correlation with CD62L on polymorphonuclears (r = -0.35, p = 0.03). During Day 3, the CD11b/CD18 on the polymorphonuclears increased despite a decrement in the absolute number of these cells.

CONCLUSION

The neutrophilia during the early phases of acute MI correspond to the appearance of the L-selectin(low) population of polymorphonuclear leukocytes. There is a correlation between the appearance of this population and the size of the infarct.

Expression of priming-associated cellular markers on neutrophils during an exacerbation of COPD

Chronic inflammation of the airways is a hallmark of chronic obstructive pulmonary disease (COPD). We investigated the kinetics of priming of inflammatory cells in peripheral blood during exacerbations of COPD and during the resolution phase. Modulation of the leukocyte compartment as a consequence of systemic activation by cytokines/chemokines was determined by measuring the expression of priming-associated epitopes by novel antibodies designated A17 and A27. Furthermore, H2O2 was determined in breath condensate as a read out for local inflammation. Leukocytes were obtained from COPD patients (GOLD II-IV) during and after an exacerbation of their disease. During an exacerbation the expression of priming epitopes on leukocytes was increased. This priming phenotype disappeared upon treatment with intravenous corticosteroids. Similarly, H2O2 levels in breath condensate were also increased during an exacerbation and decreased upon treatment. We conclude that the activation status of neutrophils in the systemic compartment can be used as a read-out for systemic innate immune signals involved in the pathogenesis of COPD. The correlation between H2O2 in exhaled air with A27 priming on neutrophils showed that local inflammation has systemic effects on cells of the innate immune system.

The CXC chemokine MIP-2 stimulates neutrophil mobilization from the rat bone marrow in a CD49d-dependent manner

The acute release of neutrophils from the bone marrow is a critical step in their trafficking to sites of inflammation. This process is stimulated by systemically acting inflammatory mediators, such as the CXC chemokines. In this study we have used a novel in situ perfusion system of the rat femoral bone marrow to directly investigate the role of specific adhesion molecules in chemokine-stimulated neutrophil mobilization. We show here that neutrophils mobilized in response to rat macrophage inflammatory protein-2 (MIP-2) shed l-selectin and expressed significantly higher levels of CD11b and CD49d. However, inhibition of l-selectin sheddase activity with KD-IX-73-4 had no effect on the number of neutrophils mobilized in response to rat MIP-2. Blockade of CD18, using a neutralizing monoclonal antibody (mAb), did not inhibit neutrophil mobilization but unexpectedly increased the rate and number of neutrophils released from the bone marrow in response to chemokine, suggesting that CD18 could play a role in neutrophil retention within the bone marrow. Blockade of CD49d using either a selective mAb or a specific antagonist resulted in a dramatic inhibition (> 75%) of the chemokine-stimulated neutrophil mobilization from the bone marrow. These data reveal contrasting roles for CD18 and CD49d in the retention and release of neutrophils from the bone marrow.

Endotoxin down-modulates P-selectin glycoprotein ligand-1 (PSGL-1, CD162) on neutrophils in humans

P-selectin glycoprotein ligand-1 (PSGL-1, CD162), the counter-receptor for P-selectin and possibly E- and L-selectin, mediates rolling of leukocytes during inflammation and, thus, plays a pivotal role in hemostasis and inflammation. PSGL-1 is constitutively expressed on circulating leukocytes. Until recently, PSGL-1 has been considered not to be regulated upon cell activation. As modulation of PSGL-1 has only recently been reported for three proinflammatory substances, PSGL-1 regulation was examined during systemic inflammation in humans. Nine healthy human volunteers received a bolus of 2 ng/kg LPS i.v. Endotoxin infusion down-modulated PSGL-1 expression on neutrophils, with a maximum at 6-8 hr (-22%; P =0.001 vs. baseline and placebo), which correlated with peak neutrophilia. Similar PSGL-1 down-regulation was observed on monocytes. sPSGL-1 plasma levels increased trendwise after LPS infusion (+12% at 6 hr; P =0.10). In vitro LPS stimulation of whole blood significantly down-regulated PSGL-1 on neutrophils (-43%) and monocytes (-35%) as early as 2 hr ( P <0.05; n =5) in both EDTA and lepirudin anticoagulated samples. In summary, PSGL-1 is down-modulated on neutrophils and monocytes during endotoxemia in humans. PSGL-1 down-regulation could potentially facilitate the development of neutrophilia.

Neutrophil and monocyte adhesion molecules in bronchopulmonary dysplasia, and effects of corticosteroids

AIMS

To study a longitudinal change in the expression of adhesion molecules CD11b, CD18, and CD62L on neutrophils and monocytes in very low birth weight babies who develop respiratory distress syndrome, to compare these levels between bronchopulmonary dysplasia (BPD) and non-BPD infants, and to assess the effect of corticosteroid treatment on these adhesion molecules.

METHODS

Of 40 eligible neonates, 11 neonates were oxygen dependent at 36 weeks (BPD 36 weeks), 16 infants were oxygen dependent at 28 days, but not at 36 weeks (BPD d28), and 13 infants did not develop BPD. Seventeen neonates received a six day course of steroid treatment. Expression of CD11b, CD18, and CD62L was measured on neutrophils and monocytes in arterial blood on days 1, 3, 7, 14, 21, and 28, and before and 2-3 days after initiation of dexamethasone treatment by flow cytometry.

RESULTS

CD18 expression on neutrophils and monocytes and CD62L on neutrophils, measured as mean fluorescent intensity, was significantly decreased in BPD neonates compared to non-BPD neonates on days 1-28. Dexamethasone treatment significantly decreased CD11b, CD18, and CD62L expression on neutrophils, and CD11b and CD18L expression on monocytes.

CONCLUSIONS

Decreased CD18 expression on neutrophils and monocytes, and decreased CD62L expression on neutrophils, measured as mean fluorescent intensity during the first four weeks of life in micropremies may be risk factors and early predictors of BPD. Dexamethasone use was associated with decreased expression of CD11b, CD18, and CD62L.

Hematopoietic stem cells and hematopoiesis

BACKGROUND

The highly orchestrated process of blood cell development and homeostasis is termed "hematopoiesis." Understanding the biology of hematopoietic stem cells as well as hematopoiesis is important to developing improved treatments for hematologic malignancies, congenital disorders, chemotherapy-related cytopenias, and blood and marrow transplants.

METHODS

The author reviews the current state of the art regarding hematopoietic stem cells and hematopoiesis.

RESULTS

Several new concepts, including stem cell plasticity, suggest the possibility that stem cells may have the ability to differentiate into other tissues in addition to blood cells.

CONCLUSIONS

While much is known about hematopoietic stem cells and hematopoiesis, much remains to be clarified about the environmental and genetic processes that govern the growth and development of the blood system. In addition, careful studies remain to be conducted to determine whether hematopoietic stem cells can differentiate into extra-hematopoietic tissues.

The usefulness of an inflammation meter to detect the presence of infection/inflammation in elderly patients

BACKGROUND

Medical personnel who work in small geriatric institutions most frequently do not have access to realtime laboratory facilities.

METHODS

In order to present a new method to determine the presence of an inflammatory response and for the assessment of its intensity, 118 patients aged 77 +/- 6 years with various bacterial infections were evaluated as well as 129 elderly individuals with various stressful conditions but no acute infections who served as controls. The leukocyte and erythrocyte adhesiveness/aggregation tests were performed by using a simple slide test and image analysis. The availability of the CD11b/CD18 and CD62L antigen on the leukocytes' surface was measured by whole blood flow cytometry, and the quantitative C-reactive protein by using laser nephelometry and specific antihuman C-reactive protein antibodies.

RESULTS

A significant difference was noted between patients and controls for all variables obtained by the slide test and image analysis. In addition, a highly significant correlation was noted between the number of leukocytes counted on the slides and white blood cell count, between the leukocyte adhesiveness/aggregation test and quantitative C-reactive protein, and between the degree of erythrocyte adhesiveness/aggregation and either the Westergren sedimentation or fibrinogen concentration.

CONCLUSIONS

By using our low-cost and real-time slide test, any medical or paramedical personnel can get relevant information regarding the presence of an acute phase response at the point of care.

Effects of indomethacin on the L-selectin expression in humans

Based on an in vitro study and an uncontrolled in vivo trial we examined the effects of indomethacin on the expression of L-selectin by leukocytes in healthy volunteers. Eight subjects received infusions of 0.7 mg/kg indomethacin and placebo t.i.d. (three times daily) in a randomized, controlled trial. Indomethacin decreased the mean fluorescence intensity of the L-selectin expression on isolated neutrophils incubated with toxic indomethacin concentrations. However, indomethacin did not lower the L-selectin expression in whole blood or in-vivo. Thus, therapeutic doses of the cyclo-oxygenase inhibitor indomethacin do not lower the L-selectin expression on leukocytes. Hence, the inhibition of cyclo-oxygenase cannot explain the previously observed dexamethasone-induced decrease in L-selectin.

Selective recruitment of T-cell subsets to the udder during staphylococcal and streptococcal mastitis: analysis of lymphocyte subsets and adhesion molecule expression

During bacterial infection of the bovine mammary gland, large numbers of leukocytes migrate into the udder, resulting in the establishment of a host response against the pathogen. Currently, the specific leukocyte populations mediating this immune response are not well defined. In the studies described here, we analyzed blood and milk from healthy cows and cows with naturally occurring mastitis to determine if distinct alphabeta and gammadelta T-lymphocyte subsets were involved in the response of the udder to a mastitis pathogen and if the type of mastitis pathogen influenced the subset composition of these responding leukocytes. Although blood samples from cows with confirmed staphylococcal and streptococcal mastitis were characterized by increased numbers of gammadelta T cells, the most dramatic changes in leukocyte distributions occurred in milk samples from these cows, with a 75% increase in alphabeta T-cell levels and a 100% increase in gammadelta T-cell levels relative to the levels in milk samples from healthy animals. Interestingly, the increase in alphabeta T-cell numbers observed in milk from cows with staphylococcal mastitis was primarily due to increased numbers of CD4(+) T cells, while the increase in alphabeta T-cell numbers observed in cows with streptococcal mastitis was due to a parallel increase in both CD4(+) and CD8(+) T-cell numbers. The increased numbers of gammadelta T cells in milk from cows with staphylococcal and streptococcal mastitis were due to a selective recruitment of a distinct gammadelta T-cell subset (GD3.1(+)), while no change in the numbers of GD197(+) gammadelta T cells was observed. We also analyzed adhesion protein expression on blood and milk leukocytes and found that, in comparison to the situation for healthy cows, L-selectin was down-regulated and CD18 was up-regulated on leukocytes from cows with mastitis. Thus, shedding of L-selectin and up-regulation of CD18 by neutrophils may provide a sensitive indicator of early inflammatory responses during bovine mastitis. Overall, these studies suggest that distinct alphabeta and gammadelta T-cell subsets are involved in the host defense of the udder against mastitis infection and that selective recruitment of these T-cell subsets depends on the infectious agent involved.

Regulation of adhesion molecules during human endotoxemia. No acute effects of aspirin

Gram-negative septic shock is mediated in part by endotoxin (lipopolysaccharide; LPS), and animal models have shown that blockade of even single adhesion molecules considerably improves survival. Thus interference with the adhesion cascade may provide a useful therapeutic approach in human sepsis. Young healthy men (n = 30) each received a bolus of 4 ng/kg LPS intravenously to study the effects of endotoxemia on adhesion processes in humans and to identify potential targets for pharmacologic intervention. One third of subjects received pretreatment with 1,000 mg aspirin and 1,000 mg paracetamol to study potential antiinflammatory effects of aspirin or effects of antipyresis. Circulating neutrophils dropped by -80% at 67 min after LPS, monocytes by -96% at 90 min, and lymphocytes by -85% at 240 min. L-selectin expression decreased, particularly on monocytes. Circulating (c)E-selectin levels increased by 820%, von Willebrand factor-Ag (vWF), soluble thrombomodulin, circulating (c)P-selectin, circulating intercellular adhesion molecule-1 (cICAM-1), and circulating vascular cell adhesion molecule-1 (cVCAM-1) by a mean of 65 to 98% (p < 0.001 for all), but cL-selectin by only 15%. Urinary excretion of soluble adhesion molecules was negligible. Aspirin had no influence on the LPS-induced changes of adhesion parameters, but paracetamol blunted the relative increase in vWF while having no effects on the other parameters measured. The consistent, profound, and early upregulation of cE-selectin during endotoxemia indicates that cE-selectin may be a better surrogate marker to monitor the activation status of endothelial cells in systemic inflammation than the other markers measured. Although aspirin did not have any antiinflammatory effects in this model, paracetamol lowered the relative increase in vWF.