Distinct tyrosine kinase activation and Triton X-100 insolubility upon Fc gamma RII or Fc gamma RIIIB ligation in human polymorphonuclear leukocytes. Implications for immune complex activation of the respiratory burst

Exogenous serpin B1 restricts immune complex-mediated NET formation via inhibition of a chymotrypsin-like protease and enhances microbial phagocytosis

Immune complex (IC)-driven formation of neutrophil extracellular traps (NETs) is a major contributing factor to the pathogenesis of autoimmune diseases including systemic lupus erythematosus (SLE). Exogenous recombinant human serpin B1 (rhsB1) can regulate NET formation; however, its mechanism(s) of action is currently unknown as is its ability to regulate IC-mediated NET formation and other neutrophil effector functions. To investigate this, we engineered or post-translationally modified rhsB1 proteins that possessed specific neutrophil protease inhibitory activities and pretreated isolated neutrophils with them prior to inducing NET formation with ICs derived from patients with SLE, PMA, or the calcium ionophore A23187. Neutrophil activation and phagocytosis assays were also performed with rhsB1 pretreated and IC-activated neutrophils. rhsB1 dose-dependently inhibited NET formation by all three agents in a process dependent on its chymotrypsin-like inhibitory activity, most likely cathepsin G. Only one variant (rhsB1 C344A) increased surface levels of neutrophil adhesion/activation markers on IC-activated neutrophils and boosted intracellular ROS production. Further, rhsB1 enhanced complement-mediated neutrophil phagocytosis of opsonized bacteria but not ICs. In conclusion, we have identified a novel mechanism of action by which exogenously administered rhsB1 inhibits IC, PMA, and A2138-mediated NET formation. Cathepsin G is a well-known contributor to autoimmune disease but to our knowledge, this is the first report implicating it as a potential driver of NET formation. We identified the rhsB1 C334A variant as a candidate protein that can suppress IC-mediated NET formation, boost microbial phagocytosis, and potentially impact additional neutrophil effector functions including ROS-mediated microbial killing in phagolysosomes.

Fast and furious: The neutrophil and its armamentarium in health and disease

Neutrophils are powerful effector cells leading the first wave of acute host-protective responses. These innate leukocytes are endowed with oxidative and nonoxidative defence mechanisms, and play well-established roles in fighting invading pathogens. With microbicidal weaponry largely devoid of specificity and an all-too-well recognized toxicity potential, collateral damage may occur in neutrophil-rich diseases. However, emerging evidence suggests that neutrophils are more versatile, heterogeneous, and sophisticated cells than initially thought. At the crossroads of innate and adaptive immunity, neutrophils demonstrate their multifaceted functions in infectious and noninfectious pathologies including cancer, autoinflammation, and autoimmune diseases. Here, we discuss the kinetics of neutrophils and their products of activation from bench to bedside during health and disease, and provide an overview of the versatile functions of neutrophils as key modulators of immune responses and physiological processes. We focus specifically on those activities and concepts that have been validated with primary human cells.

Neutrophils: Many Ways to Die

Neutrophils or polymorphonuclear leukocytes (PMN) are key participants in the innate immune response for their ability to execute different effector functions. These cells express a vast array of membrane receptors that allow them to recognize and eliminate infectious agents effectively and respond appropriately to microenvironmental stimuli that regulate neutrophil functions, such as activation, migration, generation of reactive oxygen species, formation of neutrophil extracellular traps, and mediator secretion, among others. Currently, it has been realized that activated neutrophils can accomplish their effector functions and simultaneously activate mechanisms of cell death in response to different intracellular or extracellular factors. Although several studies have revealed similarities between the mechanisms of cell death of neutrophils and other cell types, neutrophils have distinctive properties, such as a high production of reactive oxygen species (ROS) and nitrogen species (RNS), that are important for their effector function in infections and pathologies such as cancer, autoimmune diseases, and immunodeficiencies, influencing their cell death mechanisms. The present work offers a synthesis of the conditions and molecules implicated in the regulation and activation of the processes of neutrophil death: apoptosis, autophagy, pyroptosis, necroptosis, NETosis, and necrosis. This information allows to understand the duality encountered by PMNs upon activation. The effector functions are carried out to eliminate invading pathogens, but in several instances, these functions involve activation of signaling cascades that culminate in the death of the neutrophil. This process guarantees the correct elimination of pathogenic agents, damaged or senescent cells, and the timely resolution of the inflammation that is essential for the maintenance of homeostasis in the organism. In addition, they alert the organism when the immunological system is being deregulated, promoting the activation of other cells of the immune system, such as B and T lymphocytes, which produce cytokines that potentiate the microbicide functions.

Expression, Role, and Regulation of Neutrophil Fcγ Receptors

Neutrophils are best known for their critical role in host defense, for which they utilize multiple innate immune mechanisms, including microbe-associated pattern recognition, phagocytosis, production of reactive oxygen species, and the release of potent proteases, mediators, antimicrobials, and neutrophil extracellular traps. Beyond their well-established contribution to innate immunity, neutrophils were more recently reported to interact with various other cell types, including cells from the adaptive immune system, thereby enabling neutrophils to tune the overall immune response of the host. Neutrophils express different receptors for IgG antibodies (Fcγ receptors), which facilitate the engulfment of IgG-opsonized microbes and trigger cell activation upon cross-linking of several receptors. Indeed, FcγRs (via IgG antibodies) confer neutrophils with a key feature of the adaptive immunity: an antigen-specific cell response. This review summarizes the expression and function of FcγRs on human neutrophils in health and disease and how they are affected by polymorphisms in the FCGR loci. Additionally, we will discuss the role of neutrophils in providing help to marginal zone B cells for the production of antibodies, which in turn may trigger neutrophil effector functions when engaging FcγRs.

Multiple Variables at the Leukocyte Cell Surface Impact Fc γ Receptor-Dependent Mechanisms

Fc γ receptors (FcγR) expressed on the surface of human leukocytes bind clusters of immunoglobulin G (IgG) to induce a variety of responses. Many therapeutic antibodies and vaccine-elicited antibodies prevent or treat infectious diseases, cancers and autoimmune disorders by binding FcγRs, thus there is a need to fully define the variables that impact antibody-induced mechanisms to properly evaluate candidate therapies and design new intervention strategies. A multitude of factors influence the IgG-FcγR interaction; one well-described factor is the differential affinity of the six distinct FcγRs for the four human IgG subclasses. However, there are several other recently described factors that may prove more relevant for disease treatment. This review covers recent reports of several aspects found at the leukocyte membrane or outside the cell that contribute to the cell-based response to antibody-coated targets. One major focus is recent reports covering post-translational modification of the FcγRs, including asparagine-linked glycosylation. This review also covers the organization of FcγRs at the cell surface, and properties of the immune complex. Recent technical advances provide high-resolution measurements of these often-overlooked variables in leukocyte function and immune system activation.

TREM-1 regulates neutrophil chemotaxis by promoting NOX-dependent superoxide production

Neutrophil migration across tissue barriers to the site of injury involves integration of complex danger signals and is critical for host survival. Numerous studies demonstrate that these environmental signals fundamentally alter the responses of extravasated or "primed" neutrophils. Triggering receptor expressed on myeloid cells 1 (TREM-1) plays a central role in modulating inflammatory signaling and neutrophil migration into the alveolar airspace. Using a genetic approach, we examined the role of TREM-1 in extravasated neutrophil function. Neutrophil migration in response to chemoattractants is dependent upon multiple factors, including reactive oxygen species (ROS) generated either extracellularly by epithelial cells or intracellularly by NADPH oxidase (NOX). We, therefore, questioned whether ROS were responsible for TREM-1-mediated regulation of migration. Thioglycollate-elicited peritoneal neutrophils isolated from wild-type (WT) and TREM-1-deficient mice were stimulated with soluble and particulate agonists. Using electron paramagnetic resonance spectroscopy, we demonstrated that NOX2-dependent superoxide production is impaired in TREM-1-deficient neutrophils. Consistent with these findings, we confirmed with Clark electrode that TREM-1-deficient neutrophils consume less oxygen. Next, we demonstrated that TREM-1 deficient neutrophils have impaired directional migration to fMLP and zymosan-activated serum as compared to WT neutrophils and that deletion or inhibition of NOX2 in WT but not TREM-1-deficient neutrophils significantly impaired direction sensing. Finally, TREM-1 deficiency resulted in decreased protein kinase B (AKT) activation. Thus, TREM-1 regulates neutrophil migratory properties, in part, by promoting AKT activation and NOX2-dependent superoxide production. These findings provide the first mechanistic evidence as to how TREM-1 regulates neutrophil migration.

Neutrophil CD16b crosslinking induces lipid raft-mediated activation of SHP-2 and affects cytokine expression and retarded neutrophil apoptosis

Two different types of FcRs for IgG are constitutively expressed on the surface of human neutrophils, namely, FcγRIIA (CD32a) and FcγRIIIB (CD16b). Unlike FcγRIIA, FcγRIIIb is GPI anchored to the cell membrane and its signal transduction is still ambiguous. To further understand the signal transduction of CD16b, we compared neutrophil cytokine expression and apoptosis by the cross-linking of CD32a and CD16b respectively. We found that both CD32a and CD16b crosslinking can activate neutrophils, but did not exactly share cytokine expression profiles. On the other hand, CD16b cross-linking retarded neutrophil apoptosis while CD32a promoted it. By interrupting the lipid raft with methyl-β-cyclodextrin (MβCD) and inhibiting the ITAM-SYK pathway with an SYK inhibitor (piceatannol), we found reduced apoptosis was at least partially mediated by lipid raft structure, but not the ITAM-SYK pathway. Additionally, CD16b but not CD32a cross-linking triggered SHP-2 phosphorylation and led to its translocation into lipid rafts. SHP-2 phosphorylation and translocation were inhibited by MβCD. Moreover, pre-inhibition of SHP-2 by a specific inhibitor (SHP099) converted IL-10 and SOCS3 expression level and promoted neutrophil apoptosis after CD16b crosslinking. In conclusion, these results, for the first time, collectively indicate that SHP-2 is activated by CD16b crosslinking in neutrophils and functions as a component of the raft-mediated signaling pathway.

Neutrophil FcγRIIA promotes IgG-mediated glomerular neutrophil capture via Abl/Src kinases

The kidney glomerular capillaries are frequent sites of immune complex deposition and subsequent neutrophil accumulation in post-infectious and rapidly progressive glomerulonephritis. However, the mechanisms of neutrophil recruitment remain enigmatic, and there is no targeted therapeutic to avert this proximal event in glomerular inflammation. The uniquely human activating Fc receptor FcγRIIA promotes glomerular neutrophil accumulation and damage in anti-glomerular basement membrane-induced (anti-GBM-induced) glomerulonephritis when expressed on murine neutrophils. Here, we found that neutrophils are directly captured by immobilized IgG antibodies under physiological flow conditions in vitro through FcγRIIA-dependent, Abl/Src tyrosine kinase-mediated F-actin polymerization. Biophysical measurements showed that the lifetime of FcγRIIA-IgG bonds increased under mechanical force in an F-actin-dependent manner, which could enable the capture of neutrophils under physiological flow. Kidney intravital microscopy revealed that circulating neutrophils, which were similar in diameter to glomerular capillaries, abruptly arrested following anti-GBM antibody deposition via neutrophil FcγRIIA and Abl/Src kinases. Accordingly, inhibition of Abl/Src with bosutinib reduced FcγRIIA-mediated glomerular neutrophil accumulation and renal injury in experimental, crescentic anti-GBM nephritis. These data identify a pathway of neutrophil recruitment within glomerular capillaries following IgG deposition that may be targeted by bosutinib to avert glomerular injury.

Reprint of Neutrophil cell surface receptors and their intracellular signal transduction pathways

Neutrophils play a critical role in the host defense against bacterial and fungal infections, but their inappropriate activation also contributes to tissue damage during autoimmune and inflammatory diseases. Neutrophils express a large number of cell surface receptors for the recognition of pathogen invasion and the inflammatory environment. Those include G-protein-coupled chemokine and chemoattractant receptors, Fc-receptors, adhesion receptors such as selectins/selectin ligands and integrins, various cytokine receptors, as well as innate immune receptors such as Toll-like receptors and C-type lectins. The various cell surface receptors trigger very diverse signal transduction pathways including activation of heterotrimeric and monomeric G-proteins, receptor-induced and store-operated Ca(2+) signals, protein and lipid kinases, adapter proteins and cytoskeletal rearrangement. Here we provide an overview of the receptors involved in neutrophil activation and the intracellular signal transduction processes they trigger. This knowledge is crucial for understanding how neutrophils participate in antimicrobial host defense and inflammatory tissue damage and may also point to possible future targets of the pharmacological therapy of neutrophil-mediated autoimmune or inflammatory diseases.

Neutrophil cell surface receptors and their intracellular signal transduction pathways

Neutrophils play a critical role in the host defense against bacterial and fungal infections, but their inappropriate activation also contributes to tissue damage during autoimmune and inflammatory diseases. Neutrophils express a large number of cell surface receptors for the recognition of pathogen invasion and the inflammatory environment. Those include G-protein-coupled chemokine and chemoattractant receptors, Fc-receptors, adhesion receptors such as selectins/selectin ligands and integrins, various cytokine receptors, as well as innate immune receptors such as Toll-like receptors and C-type lectins. The various cell surface receptors trigger very diverse signal transduction pathways including activation of heterotrimeric and monomeric G-proteins, receptor-induced and store-operated Ca^2 + signals, protein and lipid kinases, adapter proteins and cytoskeletal rearrangement. Here we provide an overview of the receptors involved in neutrophil activation and the intracellular signal transduction processes they trigger. This knowledge is crucial for understanding how neutrophils participate in antimicrobial host defense and inflammatory tissue damage and may also point to possible future targets of the pharmacological therapy of neutrophil-mediated autoimmune or inflammatory diseases.

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Neutrophils are crucial players in innate and adaptive immunity.

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Neutrophils also participate in autoimmune and inflammatory diseases.

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Various neutrophil receptors recognize pathogens and the inflammatory environment.

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The various cell surface receptors trigger diverse intracellular signaling.

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Neutrophil receptors and signaling are potential targets in inflammatory diseases.

CX3CL1/CX3CR1 regulates nerve injury-induced pain hypersensitivity through the ERK5 signaling pathway

Peripheral nerve injury induces the cleavage of CX3CL1 from the membrane of neurons, where the soluble CX3CL1 subsequently plays an important role in the transmission of nociceptive signals between neurons and microglia. Here we investigated whether CX3CL1 regulates microglia activation through the phosphorylation of extracellular signal-regulated protein kinase 5 (ERK5) in the spinal cord of rats with spinal nerve ligation (SNL). ERK5 and microglia were activated in the spinal cord after SNL. The knockdown of ERK5 by intrathecal injection of antisense oligonucleotides suppressed the hyperalgesia and nuclear impact of nuclear factor-κB induced by SNL. The blockage of CX3CR1, the receptor of CX3CL1, significantly reduced the level of ERK5 activation following SNL. In addition, the antisense knockdown of ERK5 reversed the CX3CL1-induced hyperalgesia and spinal microglia activation. Our study suggests that CX3CL1/CX3CR1 regulates nerve injury-induced pain hypersensitivity through the ERK5 signaling pathway.

The role of calcium signaling in phagocytosis

Immune cells kill microbes by engulfing them in a membrane-enclosed compartment, the phagosome. Phagocytosis is initiated when foreign particles bind to receptors on the membrane of phagocytes. The best-studied phagocytic receptors, those for Igs (FcgammaR) and for complement proteins (CR), activate PLC and PLD, resulting in the intracellular production of the Ca(2+)-mobilizing second messengers InsP3 and S1P, respectively. The ensuing release of Ca(2+) from the ER activates SOCE channels in the plasma and/or phagosomal membrane, leading to sustained or oscillatory elevations in cytosolic Ca(2+) concentration. Cytosolic Ca(2+) elevations are required for efficient ingestion of foreign particles by some, but not all, phagocytic receptors and stringently control the subsequent steps involved in the maturation of phagosomes. Ca(2+) is required for the solubilization of the actin meshwork that surrounds nascent phagosomes, for the fusion of phagosomes with granules containing lytic enzymes, and for the assembly and activation of the superoxide-generating NADPH oxidase complex. Furthermore, Ca(2+) entry only occurs at physiological voltages and therefore, requires the activity of proton channels that counteract the depolarizing action of the phagocytic oxidase. The molecules that mediate Ca(2+) ion flux across the phagosomal membrane are still unknown but likely include the ubiquitous SOCE channels and possibly other types of Ca(2+) channels such as LGCC and VGCC. Understanding the molecular basis of the Ca(2+) signals that control phagocytosis might provide new, therapeutic tools against pathogens that subvert phagocytic killing.

FcgammaRIIA and FcgammaRIIIB mediate nuclear factor activation through separate signaling pathways in human neutrophils

Receptors for IgG Abs (Fcgamma receptors) are capable of triggering diverse cell responses in leukocytes. In neutrophils, two Fcgamma receptors, namely FcgammaRIIA and FcgammaRIIIB, are constitutively expressed. The signaling pathways that regulate FcgammaRIIA-mediated phagocytosis have been relatively well described. However, the different signaling pathways that lead to NF activation after engagement of each Fcgamma receptor have only been partially described. To address this problem, neutrophils were stimulated by cross-linking selectively each type of Fcgamma receptor with specific mAbs, and NF activation was then analyzed. FcgammaRIIIB, but not FcgammaRIIA, promoted a robust increase in phosphorylated ERK in the nucleus, and also efficient phosphorylation of the NF Elk-1. Complete mAb 3G8 (anti-FcgammaRIIIB) induced a higher response than did F(ab')(2) fragments of mAb 3G8, suggesting a possible synergistic effect of both FcgammaR receptors. However, mAb IV.3 (anti-FcgammaRIIA) alone did not cause an increase of phosphorylated ERK in the nucleus. FcgammaRIIIB-induced nuclear phosphorylation of ERK, and of Elk-1, was not affected by Syk, PI3K, or MEK inhibitors. In contrast, FcgammaRIIA- or FcgammaRIIIB-mediated phosphorylation of cytoplasmic ERK depended on Syk, PI3K, and MEK. Also, ERK, but not MEK, was constitutively present in the nucleus, and FcgammaRIIIB cross-linking did not increase the levels of nuclear ERK or MEK. These data clearly show that different neutrophil Fcgamma receptors possess different signaling capabilities. FcgammaRIIIB, but not FcgammaRIIA, activates a unique signaling pathway leading to the nuclear-restricted phosphorylation of ERK and Elk-1, independently of Syk, PI3K, or MEK.

Platelet FcgammaRIIA binds and internalizes IgG-containing complexes

OBJECTIVE

The physiologic role of platelet FcgammaRIIA, the only Fc receptor for IgG on human platelets, is largely unknown. FcgammaRIIA is also expressed on phagocytes such as monocytes and neutrophils, where it mediates the binding and internalization of both soluble IgG-containing complexes and IgG-coated cells. We previously reported the creation and characterization of a transgenic mouse that expresses human FcgammaRIIA on platelets and macrophages at levels comparable to that seen in humans. Using the transgenic mouse model, we observed that FcgammaRIIA mediates the clearance of IgG-coated cells. With the hypothesis that FcgammaRIIA on platelets may serve to remove IgG complexes from the circulation, we studied the capacity of human platelet FcgammaRIIA to bind and internalize such complexes.

METHODS

We demonstrated by flow cytometry and electron microscopy that human platelets at 37 degrees C can bind and endocytose IgG complexes. We also utilized platelets from FcgammaRIIA transgenic mice to study endocytosis of IgG complexes by platelet FcgammaRIIA.

RESULTS

Wild-type mouse platelets do not express Fcgamma receptors. While platelets from wild-type mice did not bind or endocytose IgG complexes, the presence of transgenic FcgammaRIIA on mouse platelets allowed the platelets to bind and endocytose IgG complexes.

CONCLUSION

Our data indicate that platelet FcgammaRIIA binds and internalizes IgG complexes and suggest that human platelets may function to clear soluble IgG complexes from the circulation.

Surfactant protein A regulates IgG-mediated phagocytosis in inflammatory neutrophils

Surfactant proteins (SP)-A and SP-D have been shown to affect the functions of a variety of innate immune cells and to interact with various immune proteins such as complement and immunoglobulins. The goal of the current study is to test the hypothesis that SP-A regulates IgG-mediated phagocytosis by neutrophils, which are major effector cells of the innate immune response that remove invading pathogens by phagocytosis and by extracellular killing mediated by reactive oxygen and nitrogen. We have previously shown that SP-A stimulates chemotaxis by inflammatory, but not peripheral, neutrophils. To evaluate the ability of SP-A to modulate IgG-mediated phagocytosis, polystyrene beads were coated with BSA and treated with anti-BSA IgG. SP-A significantly and specifically enhanced IgG-mediated phagocytosis by inflammatory neutrophils, but it had no effect on beads not treated with IgG. SP-A bound to IgG-coated beads and enhanced their uptake via direct interactions with the beads as well as direct interactions with the neutrophils. SP-A did not affect reactive oxygen production or binding of IgG to neutrophils and had modest effects on polymerization of actin. These data suggest that SP-A plays an important role in mediating the phagocytic response of neutrophils to IgG-opsonized particles.

Antiendothelial cell antibodies mediate enhanced leukocyte adhesion to cytokine-activated endothelial cells through a novel mechanism requiring cooperation between Fc{gamma}RIIa and CXCR1/2

Antiendothelial cell antibodies (AECAs) are commonly detectable in diseases associated with vascular injury, including systemic lupus erythematosus (SLE), systemic sclerosis, Takayasu arteritis, Wegener granulomatosis, Behçet syndrome, and transplant arteriosclerosis. Here, we explore the hypothesis that these antibodies might augment polymorphonuclear leukocyte (PMN) adhesion to endothelium in inflammation. Initially, we established that a mouse IgG mAb bound to endothelial cells (ECs) significantly increased PMN adhesion to cytokine-stimulated endothelium in an FcgammaRIIa-dependent manner. Neutralizing antibodies, and adenoviral transduction of resting ECs, demonstrated that the combination of E-selectin, CXCR1/2, and beta(2) integrins is both necessary and sufficient for this process. We observed an identical mechanism using AECA IgG isolated directly from patients with SLE. Assembled immune complexes also enhanced PMN adhesion to endothelium, but, in contrast to adhesion because of AECAs, this process did not require CXCR1/2, was not inhibited by pertussis toxin, and was FcgammaRIIIb rather than FcgammaRIIa dependent. These data are the first to demonstrate separate nonredundant FcgammaRIIa and FcgammaRIIIb-mediated mechanisms by which EC-bound monomeric IgG and assembled immune complexes amplify leukocyte adhesion under dynamic conditions. Furthermore, the observation that FcgammaRIIa and CXCR1/2 cooperate to enhance PMN recruitment in the presence of AECAs suggests a mechanism whereby AECAs may augment tissue injury during inflammatory responses.

Reactive oxygen and nitrogen species as signaling molecules regulating neutrophil function

As a cornerstone of the innate immune response, neutrophils are the archetypical phagocytic cell; they actively seek out, ingest, and destroy pathogenic microorganisms. To achieve this essential role in host defense, neutrophils deploy a potent antimicrobial arsenal that includes oxidants, proteinases, and antimicrobial peptides. Importantly, oxidants produced by neutrophils, referred to in this article as reactive oxygen (ROS) and reactive nitrogen (RNS) species, have a dual function. On one hand they function as potent antimicrobial agents by virtue of their ability to kill microbial pathogens directly. On the other hand, they participate as signaling molecules that regulate diverse physiological signaling pathways in neutrophils. In the latter role, ROS and RNS serve as modulators of protein and lipid kinases and phosphatases, membrane receptors, ion channels, and transcription factors, including NF-kappaB. The latter regulates expression of key cytokines and chemokines that further modulate the inflammatory response. During the inflammatory response, ROS and RNS modulate phagocytosis, secretion, gene expression, and apoptosis. Under pathological circumstances such as acute lung injury and sepsis, excess production of ROS may influence vicinal cells such as endothelium or epithelium, contributing to inflammatory tissue injury. A better understanding of these pathways will help identify novel targets for amelioration of the untoward effects of inflammation.

Differential kinase requirements in human and mouse Fc-gamma receptor phagocytosis and endocytosis

Fc gamma receptors (FcgammaRs) contribute to the internalization of large and small immune complexes through phagocytosis and endocytosis, respectively. The molecular processes underlying these internalization mechanisms differ dramatically and have distinct outcomes in immune clearance and modulation of cell function. However, it is unclear how the same receptors (FcgammaR) binding to identical ligands (IgG) can elicit such distinct responses. We and others have shown that Syk kinase, Src-related tyrosine kinases (SRTKs) and phosphatidyl inositol 3-kinases (PI3K) play important roles in FcgammaR phagocytosis. Herein, we demonstrate that these kinases are not required for FcgammaR endocytosis. Endocytosis of heat-aggregated IgG (HA-IgG) by COS-1 cells stably transfected with FcgammaRIIA or chimeric FcgammaRI-gamma-gamma (EC-TM-CYT) was not significantly altered by PP2, piceatannol, or wortmannin. In contrast, phagocytosis of large opsonized particles (IgG-sensitized sheep erythrocytes, EA) was markedly reduced by these inhibitors. These results were confirmed in primary mouse bone marrow-derived macrophages and freshly isolated human monocytes. Levels of receptor phosphorylation were similar when FcgammaRIIA was cross-linked using HA-IgG or EA. However, inhibition of FcgammaR phosphorylation prevented only FcgammaR phagocytosis. Finally, biochemical analyses of PI3K(p85)-Syk binding indicated that direct interactions between native Syk and PI3K proteins are differentially regulated during FcgammaR phagocytosis and endocytosis. Overall, our results indicate that FcgammaR endocytosis and phagocytosis differ dramatically in their requirement for Syk, SRTKs, and PI3K, pointing to striking differences in their signal transduction mechanisms. We propose a competitive inhibition-based model in which PI3K and c-Cbl play contrasting roles in the induction of phagocytosis or endocytosis signaling cascades.

Selective recruitment of src family kinase Hck by leukocyte integrin αMβ2but not αLβ2or αXβ2

Integrins are type I heterodimeric (alpha/beta) cell adhesion molecules. They trigger cell-signaling by recruiting cytosolic molecules to their cytoplasmic tails. Integrin alpha cytoplasmic tail contributes towards integrin function specificity, an important feature of integrins having different alpha subunits but sharing the same beta subunit. Herein, we show that the src family kinase Hck co-capped selectively with leukocyte integrin alpha(M)beta(2) but not alpha(L)beta(2) or alpha(X)beta(2). This was disrupted when the alpha(M) cytoplasmic tail was substituted with that of alpha(L) or alpha(X). Co-capping was recovered by alpha(L) or alpha(X) cytoplasmic tail truncation or forced separation of the alpha and beta cytoplasmic tails via salt-bridge disruption.

CD16b associates with high-density, detergent-resistant membranes in human neutrophils

CD16b is unique in that it is the only Fc receptor linked to the plasma membrane by a GPI (glycosylphosphatidylinositol) anchor. GPI-anchored proteins often preferentially localize to DRMs (detergent-resistant membranes) that are rich in sphingolipids and cholesterol and play an important role in signal transduction. Even though the responses to CD16b engagement have been intensively investigated, the importance of DRM integrity for CD16b signalling has not been characterized in human neutrophils. We provide direct evidence that CD16b constitutively partitions with both low- and high-density DRMs. Moreover, upon CD16b engagement, a significant increase in the amount of the receptor is observed in high-density DRMs. Similarly to CD16b, CD11b also resides in low- and high-density DRMs. In contrast with CD16b, the partitioning of CD11b in DRMs does not change in response to CD16b engagement. We also provide evidence for the implication of Syk in CD16b signalling and its partitioning to DRMs in resting and activated PMNs (polymorphonuclear neutrophils). Additionally, DRM-disrupting agents, such as nystatin and methyl-beta-cyclodextrin, alter cellular responses to CD16b receptor ligation. Notably, a significant increase in the mobilization of intracellular Ca2+ and in tyrosine phosphorylation of intracellular substrates after CD16b engagement is observed. Altogether, the results of this study provide evidence that high-density DRMs play a role in CD16b signalling in human neutrophils.

Impairment of SHP-1 down-regulation in the lipid rafts of human neutrophils under GM-CSF stimulation contributes to their age-related, altered functions

It has been shown that the functions and the rescue from apoptosis by proinflammatory mediators of polymorphonuclear leukocytes (PMN) tend to diminish with aging. Here, we investigated the role of protein tyrosine phosphatases (PTP), especially Src homology domain-containing protein tyrosine phosphatase-1 (SHP-1), in the age-related, altered PMN functions under granulocyte macrophage-colony stimulating factor (GM-CSF) stimulation. The inhibition of PTP suggested a differential effect of GM-CSF on phosphatase activity in modulating PMN functions with aging. The down-regulation of phosphatase activity of immunopurified SHP-1 from lipid rafts of PMN of young donors was found significantly altered at 1 min of stimulation with aging. In young donors, SHP-1 is displaced from lipid rafts at 1 min of stimulation, whereas in the elderly, SHP-1 is constantly present. We assessed in PMN lipid rafts the phosphorylation of tyrosine and serine residues of SHP-1, which regulates its activity. We observed an alteration in the phosphorylation of tyrosine and serine residues of SHP-1 in PMN of elderly subjects, suggesting that GM-CSF was unable to inhibit SHP-1 activity by serine phosphorylation. GM-CSF activates Lyn rapidly, and we found alterations in its activation and translocation to the lipid rafts with aging. We also demonstrate that SHP-1 in the PMN of elderly is constantly recruited to Lyn, which cannot be relieved by GM-CSF. In contrast, in the young, the resting recruitment could be relieved by GM-CSF. Our results suggest an alteration of the SHP-1 modulation by GM-CSF in lipid rafts of PMN with aging. These alterations could contribute to the decreased GM-CSF effects on PMN.

In vitro and in vivo evaluation of Adacolumn cytapheresis in healthy subjects

Adacolumn is a medical device for adsorptive cytapheresis. It has been developed for selective adsorption of granulocytes and monocytes from peripheral blood of patients with immune disorders, such as autoimmune diseases and chronic inflammatory diseases. A double blind sham-controlled crossover study design was used in order to evaluate in vivo biological responses of leukocytes as well as biocompatibility during and after Adacolumn cytapheresis in healthy volunteers. In addition, experiments were undertaken to further evaluate leukocyte reactions to Adacolumn carrier (G-1: cellulose diacetate) beads in vitro. Six healthy volunteers, 4 males and 2 females, with a mean age of 26.7 years were randomly assigned to one of the two treatment arms in a crossover fashion. Three subjects received a single Adacolumn treatment, followed by a single sham treatment at an interval of 7 days. The other three subjects received the two treatments in reverse order. All subjects were followed up 7 days after the last treatment. Additionally, in vitro investigations were carried out using blood from the healthy donors to examine the effect of G-1 beads on granulocyte functions. In vitro exposure of human peripheral blood to G-1 beads caused downregulation of L-selectin expression and upregulation of Mac-1 expression on granulocytes, leading to a marked reduction of adhesive capacity of granulocytes to endothelial cells. The exposure also led to decreased granulocyte chemotactic activity to IL-8. The number of granulocytes and monocytes clearly decreased during Adacolumn cytapheresis. Granulocytes showed marked phenotypic changes of L-selectin(Low) and Mac-1(Hi) after passing through Adacolumn in vivo. Expression of TNF-alpha and chemokine receptors was downregulated. In addition, TNF-alpha and IL-1beta producing capacity of peripheral blood leukocytes was decreased after Adacolumn cytapheresis and these changes lasted even one week after the cytapheresis. The level of complement fragments, C3a and C5a, increased, while bradykinin concentration did not change during Adacolumn cytapheresis. Exposure of human peripheral blood to G-1 beads, both in vitro and in vivo, caused a significant reduction of adhesive capacity and proinflammatory cytokine producing capacity of peripheral blood leukocytes. Such changes were not observed after sham apheresis. Despite complement activation, tolerability of Adacolum cytapheresis was not influenced. These findings may at least partly explain the beneficial effect of Adacolumn cytapheresis in the treatment of autoimmune diseases.

Albumin attenuates neutrophil activation induced by stimulators including antibodies against neutrophil-specific antigens

As neutrophil activation is related to several adverse transfusion reactions, we studied about the activation induced by anti-neutrophil antibodies and the stabilizing effects of albumin pretreatment by means of flow cytometry. Anti-neutrophil monoclonal antibody (anti-HNA-1a, 1b, 2a) alone induced CD11b expression and shedding of L-selectin, and anti-HNA-1a reinforced reactive oxygen species (ROS) production. Albumin pretreatment significantly reduced CD11b expression and L-selectin shedding induced by fMLP and ROS production induced by PMA, G-CSF combined with PMA or LPS-fMLP, or anti-HNA-1a combined with PMA. These findings suggest that anti-HNA-1a is related to adverse reactions and albumin has a regulating effect on neutrophil activation.

Signaling through CD16b in human neutrophils involves the Tec family of tyrosine kinases

Tec kinases belong to the second largest family of nonreceptor tyrosine kinases. Although these kinases are expressed in myeloid cells, little is known about their implication in neutrophil function. We recently reported the participation of Tec kinases in the responses of human neutrophils to the bacterial peptide N-formyl-l-methionyl-l-leucyl-l-phenylalanine via G-coupled protein receptors. In this study, we extended our investigations of Tec kinases to the signaling of the glycosylphosphatidylinositol-linked receptor CD16b, which is highly and specifically expressed in neutrophils. The results obtained indicate that Tec is translocated to the plasma membrane, phosphorylated, and activated upon CD16b cross-linking and that the activation of Tec is inhibited by Src-specific inhibitors as well as by the phosphatidylinositol-3 kinase inhibitor, wortmannin. As no specific inhibitor of Tec exists, the role of Tec kinases was further investigated using a-Cyano-b-hydroxy-b-methyl-N-(2,5-dibromophenyl)propenamide (LFM-A13), a compound known to inhibit Bruton's tyrosine kinase. We show that this compound also inhibits the kinase activity of Tec and provide evidence that the mobilization of intracellular calcium and the tyrosine phosphorylation of phospholipase Cgamma2 (PLCgamma2) induced upon CD16b engagement are inhibited by LFM-A13. We also show that Tec kinases are important for CD16b-dependent degranulation of neutrophils. In summary, we provide direct evidence for the implication of Tec in CD16b signaling and suggest that Tec kinases are involved in the phosphorylation and activation of PLCgamma2 and subsequently, in the mobilization of calcium in human neutrophils.

Leucoytapheresis with Adacolumn® enhances HCV-specific proliferative responses in patients infected with hepatitis C virus genotype 1

The most important aim in controlling virus infections is to destroy infected cells. Impaired cellular immunity in HIV and HCV infection leads to chronic infection. This study examined the effect of cytapheresis on the subsequent response to interferon/ribavirin treatment in patients infected with HCV. Adacolumn cytapheresis was carried out once a day for 5 consecutive days in patients who relapsed or did not respond to previous peginterferon and ribavirin combination treatment (n = 14: relapsers = 3, non-responders = 11). Peginterferon and ribavirin combination treatment was started after cytapheresis. During combination treatment, the proliferative response of peripheral blood mononuclear cells to HCV proteins (core, NS3, NS4, and NS5), tetanus toxoid, and phytohemagglutinin was measured, and compared to the early virological response. After treatment by leucocytapheresis, the proliferative response of peripheral blood mononuclear cells to HCV-core and tetanus toxoid increased significantly over the baseline (P < 0.05). A marked increase in the phytohemagglutinin response was observed after peginterferon and ribavirin combination treatment was started (P < 0.01 at week 5 and P < 0.005 at week 13). There were, however, no clear changes in the proliferative response to other antigens. Among the 14 patients, 12 (85.7%) achieved an early virological response by week 13 (12 weeks after the start of combination treatment). After treatment, nine patients (64.3%) had a significant proliferative response to HCV core antigen. Among the nine patients, eight patients (88.9%) achieved early virological response. The results indicate that activation of cellular immunity by leucocytapheresis facilitates an early virological response rate in HCV patients. This new therapy may, therefore, become an additional therapeutic measure for HCV.

Enhancement of the antibody-dependent cellular cytotoxicity of low-fucose IgG1 Is independent of FcgammaRIIIa functional polymorphism

PURPOSE

The most common polymorphic variant of Fcgamma receptor type IIIa (FcgammaRIIIa), FcgammaRIIIa-158F, has been associated with inferior clinical responses to anti-CD20 chimeric IgG1 rituximab compared with FcgammaRIIIa-158V. As we previously found that removal of fucose residues from the oligosaccharides of human IgG1 results in enhanced antibody-dependent cellular cytotoxicity, we compared the effects of the FcgammaRIIIa gene (FCGR3A) polymorphism on normal and low-fucose versions of rituximab on antibody-dependent cellular cytotoxicity.

EXPERIMENTAL DESIGN

The polymorphism at position 158 of FcgammaRIIIa was determined for the peripheral blood mononuclear cells (PBMCs) of 20 healthy donors. The PBMCs were then used as effector cells to compare the antibody-dependent cellular cytotoxicity of rituximab and a low-fucose version, KM3065. The contributions of the different cell types within the PBMC to antibody-dependent cellular cytotoxicity were examined.

RESULTS

We found KM3065-mediated antibody-dependent cellular cytotoxicity was increased 10 to 100-fold compared with rituximab for each of the 20 donors. In contrast to rituximab, KM3065 antibody-dependent cellular cytotoxicity enhancement was similar for both FCGR3A alleles and thus independent of genotype. In addition, antibody-dependent cellular cytotoxicity of both KM3065 and rituximab requires natural killer cells but not monocytes nor polymorphonuclear cells. The antibody-dependent cellular cytotoxicity (ADCC) of each of the 20 donors correlated with the natural killer cell numbers present in the PBMCs. Importantly, using KM3065, the ADCC mediated by effector cells bearing the lower affinity variant FcgammaRIIIa-158F was significantly increased compared with rituximab-mediated ADCC using effector cells bearing the higher affinity FcgammaRIIIa-158V receptors.

CONCLUSIONS

The use of low-fucose antibodies might improve the therapeutic effects of anti-CD20 therapy for all patients independent of FcgammaRIIIa phenotype beyond that currently seen with even the most responsive patients.

Possible role of factor XIII subunit A in Fcγ and complement receptor-mediated phagocytosis

Besides its traditional role in hemostasis, factor XIII subunit A (FXIII-A) is supposed to function as a cellular transglutaminase and to be involved in certain intracellular processes, including cytoskeletal remodeling. To investigate its intracellular role, the aim of the present study was to follow changes in FXIII-A production in combination with the receptor-mediated phagocytic activities of monocytes/macrophages and to examine the phagocytic functions of monocytes in patients with FXIII-A deficiency. Human blood monocytes were isolated from the buffy coats of healthy volunteers and cultured for 4 days. The FcgammaR-mediated phagocytosis of sensitized erythrocytes (EA) and the complement receptor (CR)-mediated phagocytosis of complement-coated yeast particles were studied during monocyte/macrophage differentiation. Changes in the gene expression of FXIII-A were detected by real-time quantitative RT-PCR. FXIII-A protein production was investigated with fluorescent image analysis at single cell level and Western immunoblot analysis. Both the FcgammaR and CR-mediated phagocytosis increased during culturing, which peaked on day 3. The phagocytic activity of the cells could be markedly inhibited with monodansylcadaverine, an inhibitor of the transglutaminase-induced crosslinking of proteins. The phagocytosis of EA, complement-coated and uncoated yeast particles was found to be strongly diminished in monocytes of FXIII-A deficient patients. The phagocytic functions of cultured cells showed a change in parallel with the alterations in FXIII-A mRNA expression, as well as with that in FXIII-A in protein synthesis detected by image and Western immunoblot analyses in concert. Our results suggest that FXIII-A plays a role in the Fcgamma and complement receptor-mediated phagocytic activities of monocytes/macrophages.

Cross-talk between Fc receptors and integrins

Fc receptors (FcRs) and integrins are both key players of immune responses. These receptors are capable of independent signaling that leads to various cell functions. Recently, it is becoming clear that these receptors are also capable of modulating each other's responses. This modulation is achieved by direct physical interactions of the receptors on the cell surface, or by one receptor modifying the signaling pathway of the other receptor. Receptor co-localization and resonance energy transfer studies have shown that Fc receptors and integrins interact on the cell surface. Biochemical and functional studies have shown that signaling from Fc receptors modulates integrin adhesiveness through a process called "inside-out signaling". Other studies also show that the signaling from integrins modulates Fc receptor responses such as adhesion to immune complexes and cell mediated antibody-dependent cytotoxicity. This bi-directional cross-talk between Fc receptors and integrins is very important for the final cell function. Here, we review the latest information about interactions between Fc receptors and integrins.

Increased H(2)O(2) counteracts the vasodilator and natriuretic effects of superoxide dismutation by tempol in renal medulla

A membrane-permeable SOD mimetic, 4-hydroxytetramethyl-piperidine-1-oxyl (tempol), has been used as an antioxidant to prevent hypertension. We recently found that this SOD mimetic could not prevent development of hypertension induced by inhibition of renal medullary SOD with diethyldithiocarbamic acid. The present study tested a hypothesis that increased H2O2 counteracts the effects of tempol on renal medullary blood flow (MBF) and Na+ excretion (UNaV), thereby restraining the antihypertensive effect of this SOD mimetic. By in vivo microdialysis and Amplex red H2O2 microassay, it was found that interstitial H2O2 levels in the renal cortex and medulla in anesthetized rats averaged 55.91 +/- 3.66 and 102.18 +/- 5.16 nM, respectively. Renal medullary interstitial infusion of tempol (30 micromol x min-1x kg-1) significantly increased medullary H2O2 levels by 46%, and coinfusion of catalase (10 mg x min-1x kg-1) completely abolished this increase. Functionally, removal of H2O2 by catalase enhanced the tempol-induced increase in MBF, urine flow, and UNaV by 28, 41, and 30%, respectively. Direct delivery of H2O2 by renal medullary interstitial infusion (7.5-30 nmol x min-1x kg-1) significantly decreased renal MBF, urine flow, and UNaV, and catalase reversed the effects of H2O2. We conclude that tempol produces a renal medullary vasodilator effect and results in diuresis and natriuresis. However, this SOD mimetic increases the formation of H2O2, which constricts medullary vessels and, thereby, counteracts its vasodilator actions. This counteracting effect of H2O2 may limit the use of tempol as an antihypertensive agent under exaggerated oxidative stress in the kidney.

FcgammaR polymorphisms: Implications for function, disease susceptibility and immunotherapy

Leukocyte Fcgamma receptors (FcgammaR) confer potent cellular effector functions to the specificity of IgG. FcgammaR-induced leukocyte functions, including antibody-dependent cellular cytotoxicity, phagocytosis, superoxide generation, degranulation, cytokine production and regulation of antibody production, are essential for host defense and immune regulation. The efficacy of IgG-induced FcgammaR function displays inter-individual heterogeneity due to genetic polymorphisms of three FcgammaR subclasses, FcgammaRIIa (CD32a), FcgammaRIIIa (CD16a), and FcgammaRIIIb (CD16b). FcgammaR polymorphisms have been associated with infectious and autoimmune disease, or with disease severity. FcgammaR polymorphisms may furthermore serve as markers for therapeutic efficacy and side-effects of treatment with monoclonal antibodies. In this review, FcgammaR function and the relevance of FcgammaR polymorphisms as prognostic markers for inflammatory disease and antibody-based immunotherapy are discussed.

Immunoblotting and sequential lysis protocols for the analysis of tyrosine phosphorylation-dependent signaling

In stimulated neutrophils, the majority of tyrosine-phosphorylated proteins are concentrated in Triton X-100 or NP-40 insoluble fractions. Most immunobiochemical studies, whose objective is to study the functional relevance of tyrosine phosphorylation are, however, performed using the supernatants of cells that are lysed in non-ionic detergent-containing buffers (RIPA lysis buffers). This observation prompted us to develop an alternative lysis protocol. We established a procedure involving the sequential lysis of neutrophils in buffers of increasing tonicities that not only preserve and solubilize tyrosine-phosphorylated proteins but also retain their enzymatic activities. The sequential lysis of neutrophils in hypotonic, isotonic and hypertonic buffers containing non-ionic detergents resulted in the solubilization of a significant fraction of tyrosine-phosphorylated proteins. Furthermore, we observed in neutrophils in which CD32 was cross-linked that the tyrosine kinase activity of Lyn was enhanced in the soluble fraction recovered from the hypertonic lysis but not in that derived from the first hypotonic lysis. Furthermore, we detected tyrosine kinase activity and the presence of the tyrosine kinase Syk in association with CD32 in the soluble hypertonic lysis fraction. This fraction also contained most of the tyrosine-phosphorylated proteins including Cbl, Syk and CD32 itself. The results of this study provide a new experimental procedure for the investigation of tyrosine phosphorylation pathways in activated human neutrophils which may also be applicable to other cell types.

Expression profile of leukocyte genes activated by anti-neutrophil cytoplasmic autoantibodies (ANCA)

BACKGROUND

Anti-neutrophil cytoplasmic autoantibodies (ANCA) induce neutrophil activation in vitro with release of injurious products that can mediate necrotizing vasculitis in vivo. The importance of ANCA IgG F(ab')2-antigen binding versus Fcgamma receptor engagement in this process is controversial. We propose that ANCA-antigen binding affects cell signaling pathways that can result in changes of gene expression.

METHODS

Microarray GeneChip analysis and real-time, quantitative PCR (TaqMan(R)) was used to probe for transcripts in leukocytes from patients (in vivo gene expression study) and in leukocytes treated with ANCA IgG or ANCA-F(ab')2 (in vitro gene expression study).

RESULTS

Microarray gene chip analysis showed that ANCA IgG and ANCA-F(ab')2 stimulate transcription of a distinct subset of genes, some unique to whole IgG, some unique to F(ab')2 fragments, and some common to both. DIF-2, COX-2, and IL-8 were identified as genes responsive to ANCA signaling and were selected for in depth evaluation. In vitro DIF-2 and IL-8 were increased by both ANCA IgG and F(ab')2, but COX-2 only by MPO-ANCA F(ab')2. In vivo DIF-2 levels were increased in leukocytes of ANCA patients, which correlated strongly with disease activity and ANCA titer. DIF-2 was not increased in patients in remission or in disease control patients (systemic lupus erythematosus and IgA nephropathy). COX-2 gene expression was significantly increased in patients with active disease, while IL-8 was increased in remission.

CONCLUSIONS

The data indicate that leukocyte genes are activated in vitro by both ANCA Fc and ANCA F(ab')2 pathways and that in vitro activation mimics changes in circulating leukocytes of patients with ANCA disease. Increased levels of DIF-2 in patient leukocytes strongly correlate with severity of disease in kidney tissue. The observations indicate a previously unrecognized role for DIF-2 in ANCA-mediated inflammation, which raises the possibility that DIF-2 has an important role in other types of inflammation.

Enhanced expression and activity of protein-tyrosine kinases establishes a functional signaling pathway only in FcepsilonRIhigh Langerhans cells from atopic individuals

The trimeric high-affinity IgE receptor (FcepsilonRI) on human epidermal Langerhans cells mediates IgE-dependent antigen uptake and subsequent antigen focusing. Its expression is upregulated on Langerhans cells (FcepsilonRIhigh Langerhans cells) and inflammatory dendritic epidermal cells (FcepsilonRIhigh inflammatory dendritic epidermal cells) in the skin of patients with atopic dermatitis. In the absence of the amplifying beta-chain in these cells, FcepsilonRI signaling (indicated by calcium mobilization and activation of the transcription factor nuclear factor-kappaB) is only detectable in FcepsilonRIhigh Langerhans cells from atopics, but not FcepsilonRIlow Langerhans cells from nonatopics. Therefore we investigated protein-tyrosine kinases putatively involved in FcepsilonRI signaling in Langerhans cells and asked whether differences in their expression and FcepsilonRI-induced activity could explain the dichotomic responses observed in atopic vs nonatopic individuals. First, we found the src protein-tyrosine kinases p53/56lyn, p59fyn, p56/59hck, p55c-fgr, and p60c-src to be expressed in Langerhans cells from all donors. In addition, whereas p56lck was lacking, p72syk and the negative regulatory p50csk were detected. Upon terminal maturation of Langerhans cells in vitro, no significant change of the protein- tyrosine kinase expression profile except downregulation of p56/59hck was observed. In contrast, significant upregulation of all protein-tyrosine kinase expressed except p50csk was detected in FcepsilonRIhigh Langerhans cells, but not in FcepsilonRIhigh inflammatory dendritic epidermal cells. Finally, the important protein-tyrosine kinases substrate phospholipase C-gamma1, which is also essential for downstream calcium mobilization, was only phosphorylated upon FcepsilonRI triggering in FcepsilonRIhigh Langerhans cells from atopics, but not in FcepsilonRIlow Langerhans cells from nonatopics. Therefore, upregulation of FcepsilonRI and protein-tyrosine kinase expression as well as subsequent protein-tyrosine kinase activity may explain, at least in part, that an efficient signaling pathway in terms of calcium mobilization is restricted to FcepsilonRIhigh Langerhans cells from atopic individuals. Key words:

Early events in the activation of Fc gamma RIIA in human neutrophils: stimulated insolubilization, translocation to detergent-resistant domains, and degradation of Fc gamma RIIA

The signal transduction mechanisms associated with the ligation of FcgammaRIIA in human neutrophils are as yet only incompletely characterized. In the present study, we have investigated the distribution and fate of FcgammaRIIA following its cross-linking. The results obtained indicate that cross-linking of FcgammaRIIA led, within a few seconds, to its translocation into a nonionic detergent-insoluble fraction. This was followed, within a couple of minutes, by a substantial loss of immunoreactive FcgammaRIIA in the cells. The stimulated degradation of FcgammaRIIA was blocked by the Src kinase inhibitor PP1 but not by wortmannin, ST-638, piceatannol, or cytochalasin B. Cross-linked FcgammaRIIA could be solubilized by saponin (in the presence of Nonidet P-40) and by beta-octylglucoside. Sucrose gradient analysis of the distribution of FcgammaRIIA revealed that its cross-linking led to its translocation into the pellets and not the light buoyant density fractions classically associated with lipid rafts. Disruption of cholesterol-containing membrane microdomains with filipin prevented the degradation of FcgammaRIIA but did not inhibit the stimulation of the pattern of tyrosine phosphorylation or the mobilization of calcium that followed FcgammaRIIA cross-linking. These data suggest that both cholesterol-rich domains and Src kinases are required for the degradation of the activated FcgammaRIIA and provide new insights into the early events following FcgammaRIIA cross-linking.

Preservation of the pattern of tyrosine phosphorylation in human neutrophil lysates. II. A sequential lysis protocol for the analysis of tyrosine phosphorylation-dependent signalling

In stimulated neutrophils, the majority of tyrosine phosphorylated proteins are concentrated in Triton X-100 or NP-40 insoluble fractions. Most immunobiochemical studies, whose objective is to study the functional relevance of tyrosine phosphorylation are, however, performed using the supernatants of cells lysed in non-ionic detergent-containing buffers (RIPA lysis buffers). This observation prompted us to develop an alternative lysis protocol. We established a procedure involving the sequential lysis of neutrophils in buffers of increasing tonicities that not only preserved and solubilized tyrosine phosphorylated proteins but also retained their enzymatic activities. The sequential lysis of neutrophils in hypotonic, isotonic and hypertonic buffers containing non-ionic detergents resulted in the solubilisation of a significant fraction of tyrosine phosphorylated proteins. Furthermore, we observed that in monosodium urate crystals-stimulated neutrophils, Lyn activity was enhanced in the soluble fraction recovered from the hypertonic fraction, but not from that of the first hypotonic lysis. The distribution of tyrosine phosphorylated proteins between the NP-40 soluble and insoluble fractions was both substrate- and agonist-dependent. In neutrophils stimulated with fMet-Leu-Phe, MSU crystals or by CD32 ligation, the tyrosine phosphorylated proteins were mostly insoluble. On the other hand, in GM-CSF-treated cells, the phosphoproteins were more equally distributed between the two fractions. The results of this study provide a new experimental procedure for the investigation of tyrosine phosphorylation pathways in activated human neutrophils which may also be applicable to other cell types.

Signaling mechanism for equine neutrophil activation by immune complexes

Neutrophils (PMN) are critical host defense cells that have a role in the pathophysiology of a variety of inflammatory diseases, particularly those diseases associated with antigen-antibody immune complexes (IC) deposited in tissues. Activation of PMN by IC is most efficient if the IC are presented immobilized on a surface. Adhesion to the immobilized IC is important for subsequent activation of PMN effector functions, such as generation of reactive oxygen metabolites. Adhesion of human PMN to immobilized IC requires the expression and activation of adhesion receptors called integrins. Of the integrins expressed on PMN, the beta 2 family has been found to be of particular importance for PMN function. The mechanism of beta 2 integrin activation during adhesion to IC has been studied in human PMN, but not in equine PMN. We show here that adhesion of equine PMN to immobilized IC requires beta 2 integrins. Like adhesion, IC-induced respiratory burst activity is dependent on beta 2 integrins. Furthermore, the signaling pathway triggering beta 2 integrin-dependent adhesion of equine PMN to IC and subsequent generation of respiratory burst activity is inhibited by the specific phosphatidylinositol 3-kinase (PI3K) antagonists wortmannin and LY294002 with IC(50) (concentration at which 50% inhibition is achieved) similar to the published values for inhibition of PI3K enzymatic activity. In contrast, PMA-induced activation of beta 2 integrin-dependent adhesion and respiratory burst activity are wortmannin and LY294002 insensitive. These data demonstrate that like in human PMN, IC-induced activation of beta 2 integrins and beta 2 integrin-dependent functions in equine PMN is dependent on PI3K activity.

Signal transduction pathways involved in soluble fractalkine-induced monocytic cell adhesion

Fractalkine displays features that distinguishes it from the other chemokines. In particular, besides its chemoattractant action it promotes, under physiologic flow, the rapid capture and the firm adhesion of a subset of leukocytes or intervenes in the neuron/microglia interaction. This study verified that indeed the human monocytic MonoMac6 cell line adheres to fibronectin-coated filters in response to soluble fractalkine (s-FKN). s-FKN stimulates, with distinct time courses, extracellular signal-related kinases (ERK1 and ERK2) and stress-activated protein kinases (SAPK1/JNK1 and SAPK2/p38). Both p60 Src and p72 Syk were activated under s-FKN stimulation with a rapid kinetic profile compatible with a downstream regulation on the mitogen-activated protein kinase (MAPK) congeners. The use of specific tyrosine kinase inhibitors revealed that the ERK pathway is strictly controlled by Syk, whereas c-Src up-regulated the downstream SAPK2/p38. In contrast, the SAPK1/JNK1 pathway was not regulated by any of these nonreceptor tyrosine kinases. The s-FKN-mediated increased adherence of MonoMac6 cells was partially inhibited by SB202190, a broad SAPKs inhibitor, PD98059, an MEK inhibitor, LY294002, a phosphatidyl inositol 3-kinase inhibitor, and a pertussis toxin-sensitive G protein. These data highlight that the integration of a complex array of signal transduction pathways is necessary to complete the full s-FNK-dependent adherence of human monocytic cells to fibronectin. (Blood. 2001;97:2031-2037)

Signal transduction involved in MCP-1-mediated monocytic transendothelial migration

Monocyte chemoattractant protein-1 (MCP-1) is a major chemoattractant for monocytes and T lymphocytes. The MonoMac6 cell line was used to examine MCP-1 receptor-mediated signal transduction events in relation to MCP-1-mediated monocytic transendothelial migration. MCP-1 stimulates, with distinct time courses, extracellular signal-related kinases (ERK1 and ERK2) and stress-activated protein kinases (SAPK1/JNK1 and SAPK2/p38). SAPK1/JNK1 activation was blocked by piceatannol, indicating that it is regulated by Syk kinase, whereas SAPK2/p38 activation was inhibited by PP2, revealing an upstream regulation by Src-like kinases. In contrast, ERK activation was insensitive to PP2 and piceatannol. Pertussis toxin, a blocker of Go/Gi proteins, abrogated MCP-1-induced ERK activation, but was without any effect on SAPK1/JNK1 and SAPK2/p38 activation. These results underscore the major implication of Go/Gi proteins and nonreceptor tyrosine kinases in the early MCP-1 signaling. Furthermore, MCP-1-mediated chemotaxis and transendothelial migration were significantly diminished by a high concentration of SB202190, a broad SAPK inhibitor, or by SB203580, a specific inhibitor of SAPK2/p38, and abolished by pertussis toxin treatment. Altogether, these data suggest that coordinated action of distinct signal pathways is required to produce a full response to MCP-1 in terms of monocytic locomotion.

Differential mitogen-activated protein kinase stimulation by Fc gamma receptor IIa and Fc gamma receptor IIIb determines the activation phenotype of human neutrophils

Fc gamma Rs mediate immune complex-induced tissue injury. The hypothesis that Fc gamma RIIa and Fc gamma RIIIb control neutrophil responses by activating mitogen-activated protein kinases was examined. Homotypic and heterotypic cross-linking of Fc gamma RIIa and/or Fc gamma RIIIb resulted in a rapid, transient increase in ERK and p38 activity, with maximal stimulation between 1 and 3 min. Fc gamma RIIa and Fc gamma RIIIb stimulated distinct patterns of ERK and p38 activity, and heterotypic cross-linking failed to stimulate synergistic activation of either ERK or p38 activity. Both Fc gamma RIIa and Fc gamma RIIIb required activation of a nonreceptor tyrosine kinase and phosphatidylinositol 3-kinase for stimulation of ERK and p38. Inhibition of ERK activation with PD98059 enhanced H2O2 production stimulated by homotypic and heterotypic Fc gamma R cross-linking. Inhibition of p38 with SB203580 attenuated H2O2 production stimulated by Fc gamma RIIIb or heterotypic cross-linking, but had no effect on Fc gamma RIIa-stimulated H2O2 production. On the other hand, PD98059 inhibited actin polymerization stimulated by Fc gamma R cross-linking, while SB203580 had no effect. Inhibition of actin polymerization with cytochalasin D enhanced p38 activity stimulated by either Fc gamma RIIa or Fc gamma RIIIb, but cytochalasin D only enhanced H2O2 production stimulated by Fc gamma RIIIb. Our data indicate that Fc gamma RIIa and Fc gamma RIIIb independently activate ERK and p38. The two receptors demonstrate different efficacies for ERK and p38 activation, and they do not act cooperatively. ERK and p38 provide stimulatory and inhibitory signals for neutrophil responses to immune complexes. In addition, these data indicate that actin reorganization may play a role in mediating p38-dependent activation of respiratory burst upon stimulation of Fc gamma RIIIb in neutrophils.

Pleiotropic role of lyn kinase in leukotriene B4–induced eosinophil activation

The authors have examined the role of the src-family of protein tyrosine kinases in leukotriene B4(LTB4)–induced activation of guinea-pig eosinophils. Western blot analysis identified the src-like protein tyrosine kinases p53lyn, p56lyn, p56/59hck, p55fgr, and p56lck whereas p60src, p62yes, p55blk, and p59fyn were not detected. LTB4 promoted a rapid increase in p53/56lyn activity in eosinophils, which peaked at 5 seconds and remained elevated at 60 seconds; hck, fgr, and lck were not activated. A role for p53/56lyn in eosinophil activation was investigated with the use of the src-selective inhibitor PP1 (1 μmol/L to 10 μmol/L), which attenuated LTB4-stimulated p53/56lyn activity and the phosphorylation of extracellular signal-regulated kinase–2 in intact cells. At comparable concentrations, PP1 was also shown to attenuate LTB4-induced nicotinamide adenine dinucleotide phosphate (reduced form) (NADPH) oxidase activation, chemotaxis, and Ca++-dependent [3H]arachidonic acid (AA) release. Moreover, an inhibitor of mitogen-activated protein kinase kinase-1, PD 098059, significantly inhibited LTB4-induced chemotaxis but had no effect on oxidant production or [3H]AA release. Collectively, these results implicate lyn kinase in LTB4-induced eosinophil activation through the recruitment of divergent cell-signaling pathways.

Pleiotropic role of lyn kinase in leukotriene B4–induced eosinophil activation

The authors have examined the role of the src-family of protein tyrosine kinases in leukotriene B4(LTB4)–induced activation of guinea-pig eosinophils. Western blot analysis identified the src-like protein tyrosine kinases p53lyn, p56lyn, p56/59hck, p55fgr, and p56lck whereas p60src, p62yes, p55blk, and p59fyn were not detected. LTB4 promoted a rapid increase in p53/56lyn activity in eosinophils, which peaked at 5 seconds and remained elevated at 60 seconds; hck, fgr, and lck were not activated. A role for p53/56lyn in eosinophil activation was investigated with the use of the src-selective inhibitor PP1 (1 μmol/L to 10 μmol/L), which attenuated LTB4-stimulated p53/56lyn activity and the phosphorylation of extracellular signal-regulated kinase–2 in intact cells. At comparable concentrations, PP1 was also shown to attenuate LTB4-induced nicotinamide adenine dinucleotide phosphate (reduced form) (NADPH) oxidase activation, chemotaxis, and Ca++-dependent [3H]arachidonic acid (AA) release. Moreover, an inhibitor of mitogen-activated protein kinase kinase-1, PD 098059, significantly inhibited LTB4-induced chemotaxis but had no effect on oxidant production or [3H]AA release. Collectively, these results implicate lyn kinase in LTB4-induced eosinophil activation through the recruitment of divergent cell-signaling pathways.

The requirement of both extracellular regulated kinase and p38 mitogen-activated protein kinase for stimulation of cytosolic phospholipase A(2) activity by either FcgammaRIIA or FcgammaRIIIB in human neutrophils. A possible role for Pyk2 but not for the Grb2-Sos-Shc complex

The signal transduction pathways initiated by opsonized zymosan (OZ) leading to activation of cytosolic phospholipase A(2) (cPLA(2)) in human neutrophils remain obscure. In a previous study, we showed that the activation of cPLA(2) by OZ is tyrosine kinase-dependent. The present study demonstrates that the signals initiated by OZ involve activation of tyrosine kinase Pyk2 but not the formation of the adhesion protein complex, Shc-Grb2-Sos. Stimulation of cPLA(2) activity by OZ is mediated by Fc gamma receptors (FcgammaRs) and not by complement receptors for the C3b protein. Cross-linking of FcgammaRIIA or FcgammaRIIIB induces p38 mitogen-activated protein (MAP) kinase and extracellular regulated kinase (ERK) phosphorylation. The kinetics of cPLA(2) activity stimulated by either of the FcgammaRs or by both is similar to that of p38 MAP kinase and was detected as early as 15 s after stimulation, maintained a plateau for 10 min, and decreased thereafter. ERK activation was detected also within 15 s but decreased significantly 5 min after stimulation. The MEK inhibitor, PD-098059, or the p38 MAP kinase inhibitor, SB-203580, caused a partial inhibition during the time course of cPLA(2) activity, whereas their combination caused a total inhibition. Thus, although ERK activation is significantly shorter than that of p38 MAP kinase, it is equally required for activation and maintenance of cPLA(2) activity by occupancy of a single receptor, FcgammaRIIA or FcgammaRIIIB.

Antineutrophil cytoplasmic antibodies (ANCA) and systemic vasculitis: update of assays, immunopathogenesis, controversies, and report of a novel de novo ANCA-associated vasculitis after kidney transplantation

OBJECTIVES

To characterize antineutrophil cytoplasmic antibodies (ANCA), their major autoantigens, disease associations, and pathophysiology in systemic vasculitides. To describe a patient with a novel de novo ANCA-associated vasculitis after kidney transplantation.

METHODS

We reviewed and compiled the literature on ANCA-related topics and systemic vasculitis. Laboratory and clinical data from a cadaveric kidney transplant patient who developed necrotizing vasculitis involving glomerular capillaries, with crescent formation associated with P-ANCA and myeloperoxidase, were analyzed.

RESULTS

Large-scale multi-center testing of patient and normal sera by the European ANCA Assay Standardization Project using immunofluorescence assays and enzyme immunoassays indicate the assays have good sensitivity and specificity, and diagnostic utility for ANCA-associated vasculitis. A few investigations covering basic and clinical research with ANCA remain controversial: whether endothelial cells do or do not express a 29-kd neutral serine protease termed proteinase-3 (PR-3), the target of ANCA in most individuals with Wegener's granulomatosis, and whether anti-myeloperoxidase (MPO) ANCAs recognize a restricted number of epitopes on MPO. This issue has relevance for using monoclonal antibodies to treat patients with vasculitis who have adverse effects from immunosuppressive drugs. The two allelic forms of FcgammaRIIa (H131/R131) and the two of FcgammaRIIlb (NA1/NA2) are discussed as possible inheritable genetic elements for vasculitic disorders and for signaling responses. Stimulatory and costimulatory molecules, and cytokine profiles of T lymphocytes are characterized to show that these cells are actively involved in the ANCA-associated vasculitides. The patient described had a de novo ANCA associated small vessel vasculitis which developed after renal transplantation.

CONCLUSIONS

There have been significant advances in the development of sensitive and specific ANCA assays. The immunopathogenetic mechanism of ANCA involves the constitutive FcgammaRs, ligands, and signaling responses to activate cytokine-primed neutrophils. This may lead to the generation of reactive oxygen intermediates, degranulation, and secretion of intracellular granule contents, and ultimately inflammation and vasculitis.

Effect of allotype on activation of neutrophils by FcgammaRIIIB cross-linking

Human neutrophils constitutively synthesize two receptors for the constant region of IgG, FcgammaRII, and FcgammaRIIIB. Fluo-3-loaded neutrophils were treated with biotinylated Fab fragments of anti-FcgammaR antibodies and cross-linked with streptavidin, and intracellular calcium ([Ca2+](i)) was monitored by flow cytometry. Polymerization of filamentous actin was quantitated by NBD-phallacidin using flow cytometry. Cross-linking of FcgammaRII by monoclonal antibody (mAb) IV.3 induces an increase in [Ca2+](i), superoxide generation, and the polymerization of actin. [Ca2+](i) responses from cross-linking of FcgammaRIIIB by mAb 3G8 varied from minimal to no release. To determine whether discrepancies in 3G8-induced [Ca2+](i) release were due to allotype variation, we selected five donors who were homozygous for the NA1 allotype of FcgammaRIIIB and five who were either heterozygous or homozygous for the NA2 allotype and compared their [Ca2+](i) response and actin polymerization induced by FcgammaRIIIB cross-linking. Cross-linking of FcgammaRIIIB by 3G8 produced minimal [Ca2+](i) release and polymerization of actin irrespective of donor allotype.

Syk Activation Initiates Downstream Signaling Events During Human Polymorphonuclear Leukocyte Phagocytosis

We investigated the requirement for Syk activation to initiate downstream signaling events during polymorphonuclear leukocyte (PMN) phagocytosis of Ab-coated erythrocytes (EIgG). When PMN were challenged with EIgG, Syk phosphorylation increased in a time-dependent manner, paralleling the response of PMN phagocytosis. Pretreatment of PMN with piceatannol, a Syk-selective inhibitor, blocked EIgG phagocytosis and Syk phosphorylation. We found that piceatannol inhibited protein kinase Cδ (PKCδ) and Raf-1 translocation from cytosol to plasma membrane by &gt;90%. Extracellular signal-regulated protein kinase-1 and -2 (ERK1 and ERK2) phosphorylation was similarly blocked. We also investigated phosphatidylinositide 3-kinase (PI 3-kinase) activity and Syk phosphorylation using piceatannol, wortmannin, and LY294002, inhibitors of PI 3-kinase. The phosphorylation of Syk preceded the activation of PI 3-kinase. Both wortmannin and piceatannol inhibited PI 3-kinase, but only piceatannol inhibited Syk. In contrast to piceatannol, wortmannin did not inhibit PKCδ and Raf-1 translocation. To elucidate signaling downstream of Syk activation, we assessed whether the cell-permeable diacylglycerol analogue didecanoylglycerol could normalize PMN phagocytosis, PKCδ and Raf-1 translocation, and ERK1 and ERK2 phosphorylation inhibited by piceatannol. The addition of didecanoylglycerol to the Syk-inhibited phagocytosing PMN normalized all three without a concomitant effect on PI 3-kinase activity and Syk phosphorylation. We conclude that Syk activation following Fcγ receptor engagement initiates downstream signaling events leading to mitogen-activated protein kinase activation independent of PI 3-kinase activation.

CR3, FcgammaRIIA and FcgammaRIIIB induce activation of the respiratory burst in human neutrophils: the role of intracellular Ca(2+), phospholipase D and tyrosine phosphorylation

Human neutrophils express two different types of phagocytic receptors, complement receptors (CR) and Fc receptors. In order to characterize the different signaling properties of each receptor we have used non-adherent human neutrophils and investigated CR3, FcgammaRIIA and FcgammaRIIIB for their signaling capacity. Selective activation of each receptor was achieved by coupling specific antibodies to heat-killed Staphylococcus aureus particles, Pansorbins, through their Fc moiety. Despite the fact that these particles are not phagocytosed, we show that addition of Pansorbins with anti-CD18 antibodies recognizing CR3 induced prominent signals leading to a respiratory burst. Stimulation with anti-FcgammaRIIIB Pansorbins induced about half of the response induced by anti-CR3 Pansorbins, whereas anti-FcgammaRIIA Pansorbins induced an even weaker signal. However, FcgammaRIIA induced strong phosphorylation of p72(syk) whereas FcgammaRIIIB induced only a very weak p72(syk) phosphorylation. During CR3 stimulation no tyrosine phosphorylation of p72(syk) was seen. Both phospholipase D and NADPH oxidase activities were dependent on intracellular calcium. This is in contrast to tyrosine phosphorylation of p72(syk) that occurred even in calcium-depleted cells, indicating that oxygen metabolism does not affect p72(syk) phosphorylation. Inhibitors of tyrosine phosphorylation blocked the respiratory burst induced by both FcgammaRIIA and FcgammaRIIIB as well as CR3. This shows that tyrosine phosphorylation of p72(syk) is an early signal in the cascade induced by FcgammaRIIA but not by CR3.

A molecular mechanism of integrin crosstalk: alphavbeta3 suppression of calcium/calmodulin-dependent protein kinase II regulates alpha5beta1 function

Many cells express more than one integrin receptor for extracellular matrix, and in vivo these receptors may be simultaneously engaged. Ligation of one integrin may influence the behavior of others on the cell, a phenomenon we have called integrin crosstalk. Ligation of the integrin alphavbeta3 inhibits both phagocytosis and migration mediated by alpha5beta1 on the same cell, and the beta3 cytoplasmic tail is necessary and sufficient for this regulation of alpha5beta1. Ligation of alpha5beta1 activates the calcium- and calmodulin-dependent protein kinase II (CamKII). This activation is required for alpha5beta1-mediated phagocytosis and migration. Simultaneous ligation of alphavbeta3 or expression of a chimeric molecule with a free beta3 cytoplasmic tail prevents alpha5beta1-mediated activation of CamKII. Expression of a constitutively active CamKII restores alpha5beta1 functions blocked by alphavbeta3-initiated integrin crosstalk. Thus, alphavbeta3 inhibition of alpha5beta1 activation of CamKII is required for its role in integrin crosstalk. Structure-function analysis of the beta3 cytoplasmic tail demonstrates a requirement for Ser752 in beta3-mediated suppression of CamKII activation, while crosstalk is independent of Tyr747 and Tyr759, implicating Ser752, but not beta3 tyrosine phosphorylation in initiation of the alphavbeta3 signal for integrin crosstalk.

FMLP- and TNF-stimulated monoclonal Lym-1 antibody-dependent lysis of B lymphoblastoid tumour targets by neutrophils

Human neutrophils, incubated with Cr51-labelled B lymphoblastoid Raji cells in the presence of the anti-target monoclonal antibody (mAb) Lym-1 plus formyl-methionyl-leucyl-phenylalanine (FMLP) or tumour necrosis factor alpha (TNF-alpha), were found to induce significant C51 release, i.e. significant cytolysis. The lytic process was inhibited by mAb IV.3, specific for the Fcgamma receptor (FcgammaR) type II. The mAb 3G8, which reacts with FcgammaR type III, was ineffective. Moreover, the lysis was inhibited by the anti-CD18 mAb MEM-48. These data suggest that FMLP/Lym-1 as well as TNF-alpha/Lym-1 cytolytic systems strictly require FcgammaRII and CD18 integrins. As the lysis induced by TNF-alpha/Lym-1 was prevented by pertussis toxin (PT), PT-sensitive G-proteins are likely to intervene in post-FcgammaRII signal transduction. Both the FMLP- and the TNF-alpha-dependent systems were also found to be equally susceptible to inhibition by various inhibitors of kinases (genistein, staurosporin, 1-(5-isoquinolinnylsulphonyl)-2-methylpiperazine and wortmannin). On the contrary, an inhibitor of protein kinase C (bis-indolyl-maleimide, BIM) was effective only in the FMLP/Lym-1 cytolytic system. Therefore, it appears that signals delivered by FMLP or TNF-alpha, BIM-sensitive and insensitive respectively, converge and synergize with those from G-protein-coupled FcgammaRII and, probably, CD18-integrins to promote the expression of the neutrophil cytolytic potential.