Neutrophils can Promote Clotting via FXI and Impact Clot Structure via Neutrophil Extracellular Traps in a Distinctive Manner in vitro

Neutrophils and neutrophil extracellular traps (NETs) have been shown to be involved in coagulation. However, the interactions between neutrophils or NETs and fibrin(ogen) in clots, and the mechanisms behind these interactions are not yet fully understood. In this in vitro study, the role of neutrophils or NETs on clot structure, formation and dissolution was studied with a combination of confocal microscopy, turbidity and permeation experiments. Factor (F)XII, FXI and FVII-deficient plasmas were used to investigate which factors may be involved in the procoagulant effects. We found both neutrophils and NETs promote clotting in plasma without the addition of other coagulation triggers, but not in purified fibrinogen, indicating that other factors mediate the interaction. The procoagulant effects of neutrophils and NETs were also observed in FXII- and FVII-deficient plasma. In FXI-deficient plasma, only the procoagulant effects of NETs were observed, but not of neutrophils. NETs increased the density of clots, particularly in the vicinity of the NETs, while neutrophils-induced clots were less stable and more porous. In conclusion, NETs accelerate clotting and contribute to the formation of a denser, more lysis resistant clot architecture. Neutrophils, or their released mediators, may induce clotting in a different manner to NETs, mediated by FXI

The tumor necrosis factor receptor and human neutrophil function. Deactivation and cross-deactivation of tumor necrosis factor-induced neutrophil responses by receptor down-regulation.

Despite numerous reports, the role of tumor necrosis factor (TNF) in polymorphonuclear leukocyte (PMN) function remains controversial. We found TNF to be a potent, pertussis toxin-independent stimulator of PMN adhesion (ED50 2.6 pM). TNF-stimulated PMN under adherent conditions released up to 65% of their transcobalamine content (ED50 3.9 pM) and increased their burst activity 10-fold (ED50 3.2 pM) as measured by the hexose monophosphate shunt, whereas PMN held in suspension hardly degranulated at all and only little burst activity was demonstrable. However, preincubation of PMN with TNF in suspension led to a decrease in cellular adhesiveness, degranulation, and burst activity in response to a secondary stimulus of TNF under adherent conditions, although cells remained fully responsive toward phorbol myristate acetate. A concomitant dose-dependent decline of TNF receptor numbers that correlated well with the inhibition of PMN function (r = 0.91) suggests receptor down-regulation as the mechanism of functional PMN deactivation. Remarkably, preincubation with other PMN stimuli such as N-formyl-methionyl-leucyl-phenylalanine, platelet-activating factor, leukotriene B4, complement component fragment 5a (C5a)/C5a (desarginated), and endotoxin also led to a reduction of TNF-specific PMN responses (cross-deactivation) from 35% (LTB4) to 90% (endotoxin), corresponding with the down-regulation of TNF receptors. Deactivation and receptor down-regulation are independent of pertussis toxin-sensitive G proteins and protein kinase C but seemed to depend on changes in calcium metabolism. Granulocyte hyporesponsiveness towards TNF in sepsis (with elevated blood levels of endotoxin and TNF) might be a mechanism of self-protection or, to the contrary, might impair a possibly central mode of host defense

The cell surface glycoprotein Mac-1 (CD11b/CD18) mediates neutrophil adhesion and modulates degranulation independently of its quantitative cell surface expression.

Abstract It has previously been shown that during degranulation Mac-1 (CD11b/CD18)--a glycoprotein that plays a central role in neutrophil adhesion-is up-regulated on PMN surfaces. It has been assumed that this quantitative change in adhesion Ag expression on the cell surface would in turn lead to increased cellular adhesiveness. In contrast, we found that at an incubation temperature of 16 degrees C, stimulated neutrophil adhesion to plastic tissue culture dishes in the presence of FMLP (2.5 x 10(-6) M), TNF (10 ng/ml), or PAF (1 x 10(-4) M) occurred without cellular degranulation or Mac-1 surface up-regulation as measured cytofluorometrically. As shown by functional inhibition studies employing monoclonal antibodies 60.3 (anti-CD18) and 60.1 (anti-CD11b), adhesion at 16 degrees C, where no CD11b/CD18 up-regulation was seen, is mediated by CD11b/CD18 just as it is at 37 degrees C, where degranulation and CD11b/CD18 up-regulation could be demonstrated. The physiologic importance of these findings was underscored by experiments done on endothelial monolayers, which showed that PMN association with endothelial cells is absolutely independent from the quantitative up-regulation of Mac-1 on PMN surfaces. When neutrophils were stimulated at 37 degrees C by endotoxin, an agent that does not induce aggregation (a form of intercellular adhesion), Mac-1 surface expression increased only after cells had become adherent, whereas cells held in suspension to prevent cell-substrate adhesion neither degranulated nor up-regulated their Mac-1 surface expression. Thus, not only is adherence independent of degranulation and Mac-1 cell surface up-regulation, but both degranulation and Mac-1 surface up-regulation appear to depend on the process of adhesion. Correspondingly, incubation of neutrophils with antibodies 60.1 and 60.3 inhibited not only adhesion of cells stimulated with FMLP at 37 degrees C but degranulation as well. These results indicate that Mac-1 influences degranulation as well as it controls adhesion not by its mere quantity on the cell surface, but rather by an yet undefined molecular modulation.</jats:p

Diagnostic et traitement de la carence en fer sans anémie [Diagnosis and treatment of iron deficiency without anaemia]

Iron deficiency (ID) without anaemia frequently remains undiagnosed when symptoms are attributed to ID with anaemia. Serum ferritin is the primary diagnostic parameter, whereas &lt;10 microg/l represent depleted iron stores, 10-30 microg/l can confirm ID without anaemia and 30-50 microg/l might indicate functional ID. In case of increased CRP or ALT, normal/elevated ferritin should be interpreted with caution. IV iron is indicated if oral iron is not effective or tolerated. At ferritin &lt;10 microg/l, a cumulative dose of 1000 mg iron and at ferritin 10-30 microg/l, a cumulative dose of 500 mg is advised. At ferritin 30-50 microg/l a first dose of 200 mg might be considered. Ferritin shall be reassessed not sooner than 2 weeks after the last oral or 8-12 weeks after the last IV iron administration

Inhibition of leukocyte L-selectin function with a monoclonal antibody attenuates reperfusion injury to the rabbit ear

Abstract The leukocyte adhesion molecule L-selectin mediates neutrophil adhesive interactions with endothelial cells and is in part responsible for neutrophil rolling. We examined the role of L-selectin in ischemia- reperfusion injury of rabbit ears using a monoclonal antibody (MoAb) directed to a functional epitope of L-selectin. Arterial blood flow to the rabbit ear was occluded for six hours with ambient temperature at 23 degrees C to 24 degrees C. Rabbits were treated at reperfusion with saline (n = 8), the L-selectin function-blocking LAM1–3 MoAb (2 mg/kg), or the nonfunction-blocking LAM1–14 MoAb (2 mg/kg). Tissue injury was determined by measuring edema and necrosis. Edema in the LAM1–3 MoAb- treated group (peak = 25 +/- 4 mL) was significantly less (P &lt; .05) than in saline-treated (peak = 40 +/- 8 mL) and LAM1–14 MoAb-treated (peak = 41 +/- 6 mL) groups. Tissue necrosis at 7 days was not observed in the LAM1–3 MoAb-treated group, whereas significant necrosis (P &lt; .05) was seen in the saline- (8% +/- 3% necrosis) and LAM1–14 MoAb- treated (7% +/- 3% necrosis) group. We conclude that blocking L- selectin ameliorates necrosis and edema after ischemia and reperfusion in the rabbit ear, presumably by blocking neutrophil rolling.</jats:p

Inhibition of leukocyte L-selectin function with a monoclonal antibody attenuates reperfusion injury to the rabbit ear

The leukocyte adhesion molecule L-selectin mediates neutrophil adhesive interactions with endothelial cells and is in part responsible for neutrophil rolling. We examined the role of L-selectin in ischemia- reperfusion injury of rabbit ears using a monoclonal antibody (MoAb) directed to a functional epitope of L-selectin. Arterial blood flow to the rabbit ear was occluded for six hours with ambient temperature at 23 degrees C to 24 degrees C. Rabbits were treated at reperfusion with saline (n = 8), the L-selectin function-blocking LAM1–3 MoAb (2 mg/kg), or the nonfunction-blocking LAM1–14 MoAb (2 mg/kg). Tissue injury was determined by measuring edema and necrosis. Edema in the LAM1–3 MoAb- treated group (peak = 25 +/- 4 mL) was significantly less (P &lt; .05) than in saline-treated (peak = 40 +/- 8 mL) and LAM1–14 MoAb-treated (peak = 41 +/- 6 mL) groups. Tissue necrosis at 7 days was not observed in the LAM1–3 MoAb-treated group, whereas significant necrosis (P &lt; .05) was seen in the saline- (8% +/- 3% necrosis) and LAM1–14 MoAb- treated (7% +/- 3% necrosis) group. We conclude that blocking L- selectin ameliorates necrosis and edema after ischemia and reperfusion in the rabbit ear, presumably by blocking neutrophil rolling.</jats:p