The molecular basis of leukocytosis

Neutrophil gelatinase B potentiates interleukin-8 tenfold by aminoterminal processing, whereas it degrades CTAP-III, PF-4, and GRO-α and leaves RANTES and MCP-2 intact

Chemokines are mediators in inflammatory and autoimmune disorders. Aminoterminal truncation of chemokines results in altered specific activities and receptor recognition patterns. Truncated forms of the CXC chemokine interleukin (IL)-8 are more active than full-length IL-8 (1-77), provided the Glu-Leu-Arg (ELR) motif remains intact. Here, a positive feedback loop is demonstrated between gelatinase B, a major secreted matrix metalloproteinase (MMP-9) from neutrophils, and IL-8, the prototype chemokine active on neutrophils. Natural human neutrophil progelatinase B was purified to homogeneity and activated by stromelysin-1. Gelatinase B truncated IL-8(1-77) into IL-8(7-77), resulting in a 10- to 27-fold higher potency in neutrophil activation, as measured by the increase in intracellular Ca++concentration, secretion of gelatinase B, and neutrophil chemotaxis. This potentiation correlated with enhanced binding to neutrophils and increased signaling through CXC chemokine receptor-1 (CXCR1), but it was significantly less pronounced on a CXCR2-expressing cell line. Three other CXC chemokines—connective tissue-activating peptide-III (CTAP-III), platelet factor-4 (PF-4), and GRO-α—were degraded by gelatinase B. In contrast, the CC chemokines RANTES and monocyte chemotactic protein-2 (MCP-2) were not digested by this enzyme. The observation of differing effects of neutrophil gelatinase B on the proteolysis of IL-8 versus other CXC chemokines and on CXC receptor usage by processed IL-8 yielded insights into the relative activities of chemokines. This led to a better understanding of regulator (IL-8) and effector molecules (gelatinase B) of neutrophils and of mechanisms underlying leukocytosis, shock syndromes, and stem cell mobilization by IL-8.

Granulocyte colony-stimulating factor (G-CSF) downregulates its receptor (CD114) on neutrophils and induces gelatinase B release in humans

Despite the increasing use of granulocyte colony-stimulating factor (G-CSF) for the mobilization of stem cells and neutrophils, its pharmacodynamic actions are not fully understood. Because of the roles of G-CSF and gelatinase B in leucokinetics, we set out to characterize the interaction of G-CSF with its receptor in humans and its effects on gelatinase B release. G-CSF was infused at bolus doses of 1 microg/kg and 5 microg/kg, and compared to placebo and dexamethasone (1 mg/kg b.i.d), which enhances the plasma levels of endogenous G-CSF. The study was randomized, double-blind, four-way crossover, in eight healthy male volunteers. G-CSF dose-independently induced profound neutropenia (> 95%) within minutes and downregulated its own receptor (CD114) on neutrophils by 75%. The G-CSF/CD114 interaction dose-independently induced degranulation of neutrophils as evidenced by a 300-400% increase in CD11b expression. Degranulation induced up to a 10-fold increase in plasma levels of gelatinase B, an enzyme known to precipitate neutropenia and subsequent neutrophilia in animals. In this study, it was shown that G-CSF downmodulates CD114 expression on the surface of neutrophils in humans and the consequent degranulation enhances gelatinase B release into plasma, which may contribute to mobilization of neutrophils or stem cells.

Interference of antibacterial agents with phagocyte functions: immunomodulation or "immuno-fairy tales"?

Professional phagocytes (polymorphonuclear neutrophils and monocytes/macrophages) are a main component of the immune system. These cells are involved in both host defenses and various pathological settings characterized by excessive inflammation. Accordingly, they are key targets for immunomodulatory drugs, among which antibacterial agents are promising candidates. The basic and historical concepts of immunomodulation will first be briefly reviewed. Phagocyte complexity will then be unravelled (at least in terms of what we know about the origin, subsets, ambivalent roles, functional capacities, and transductional pathways of this cell and how to explore them). The core subject of this review will be the many possible interactions between antibacterial agents and phagocytes, classified according to demonstrated or potential clinical relevance (e.g., neutropenia, intracellular accumulation, and modulation of bacterial virulence). A detailed review of direct in vitro effects will be provided for the various antibacterial drug families, followed by a discussion of the clinical relevance of these effects in two particular settings: immune deficiency and inflammatory diseases. The prophylactic and therapeutic use of immunomodulatory antibiotics will be considered before conclusions are drawn about the emerging (optimistic) vision of future therapeutic prospects to deal with largely unknown new diseases and new pathogens by using new agents, new techniques, and a better understanding of the phagocyte in particular and the immune system in general.

Molecular mechanisms of invasion by cancer cells, leukocytes and microorganisms

Invasion is a phenotype common to cancer cells, leukocytes, parasites, bacteria and viruses, involving cell-cell adhesion, cell-matrix adhesion, proteolysis and motility. These activities are regulated by the cross talk between invaders and host. We discuss the invasion-related molecular interactions of E-cadherin, integrins, matrix metalloproteinases and the chemokine receptor RANTES.

In vivo neutrophil recruitment by granulocyte chemotactic protein-2 is assisted by gelatinase B/MMP-9 in the mouse

Granulocyte chemotactic protein-2 (GCP-2) of the mouse is a potent neutrophil chemotactic and activating factor in vitro and in vivo. Gelatinase B/matrix metalloproteinase-9 is released from neutrophils within 1 h after stimulation with GCP-2. In vitro neutrophil chemotaxis by GCP-2 was not impaired by specific inhibitory monoclonal antibodies (mAb) against gelatinase B, indicating that gelatinase B is not involved in chemotaxis of neutrophils through polycarbonate filters. To investigate if gelatinase B degranulation is involved in in vivo cell migration toward GCP-2, experiments were performed with gelatinase B knockout mice. When mouse GCP-2 was injected intradermally in mice, a dose-dependent neutrophil chemotactic response was observed, and this cell migration was significantly impaired in young mice by genetic gelatinase B knockout. In adult vs. young gelatinase B-deficient mice, such compensatory mechanisms as higher basal neutrophil counts and less impairment of chemotaxis toward local GCP-2 injection were observed. These experiments prove the concept that gelatinase B release under pressure of GCP-2 is a relevant, but not exclusive, effector mechanism of neutrophil chemotaxis in vivo and that known mechanisms, other than the release of gelatinase B, allow for a full-blown chemotactic response and compensate for gelatinase B deficiency in adult life in the mouse.

Mobilization of stem/progenitor cells by sulfated polysaccharides does not require selectin presence

Employing carbohydrate ligands, which have been extensively used to block selectin function in vitro and in vivo, we have examined the involvement of such ligands in stem/progenitor cell mobilization in mice and monkeys. We found that sulfated fucans, branched and linear, are capable of increasing mature white cells in the periphery and mobilizing stem/progenitor cells of all classes (up to 32-fold) within a few hours posttreatment in a dose-dependent manner. To elicit the effect, the presence of sulfate groups was necessary, yet not sufficient, as certain sulfated hexosamines tested (chondroitin sulfates A or B) were ineffective. Significant mobilization of stem/progenitor cells and leukocytosis was elicited in selectin-deficient mice (L(-/-), PE(-/-), or LPE(-/-)) similar to that of wild-type controls, suggesting that the mode of action of sulfated fucans is not through blockade of known selectins. Other mechanisms have been entertained, in particular, the release of chemokines/cytokines, including some previously implicated in mobilization. Significant increases were documented in the levels of seven circulating chemokines/cytokines within a few hours after fucan sulfate treatment and support such a proposition. Additionally, an increase was noted in plasma metalloproteinase (MMP) 9, which might independently contribute to the mobilization process by enzymatically facilitating chemokine/cytokine release. Mobilization by sulfated polysaccharides provides a distinct paradigm in the mobilization process and uncovers an additional novel in vivo biological role for sulfated glycans. As similarly sulfated compounds were ineffective in vivo, the data also underscore the fact that polysaccharides with similar structures may elicit diverse in vivo effects.

Prevention of interleukin-8-induced mobilization of hematopoietic progenitor cells in rhesus monkeys by inhibitory antibodies against the metalloproteinase gelatinase B (MMP-9)

Previously, we demonstrated that IL-8 induces rapid mobilization of hematopoietic progenitor cells (HPC) from the bone marrow of rhesus monkeys. Because activation of neutrophils by IL-8 induces the release of gelatinase B (MMP-9), which is involved in the degradation of extracellular matrix molecules, we hypothesized that MMP-9 release might induce stem cell mobilization by cleaving matrix molecules to which stem cells are attached. Rhesus monkeys were treated with a single i.v. injection of 0.1 mg/kg human IL-8, which resulted in a 10- to 100-fold increase in HPC within 30 min after injection. Zymographic analysis revealed a dramatic instantaneous increase in the plasma levels of MMP-9, followed by the increase in circulating HPC. Enzyme levels decreased at 2 h after injection of IL-8, simultaneously with the decrease in the numbers of circulating HPC. To test the hypothesis that MMP-9 induction was involved in HPC mobilization, rhesus monkeys were treated with a highly specific inhibitory monoclonal anti-gelatinase B antibody. Anti-gelatinase B at a dose of 1-2 mg/kg completely prevented the IL-8-induced mobilization of HPC, whereas a dose of 0.1 mg/kg had only a limited effect. Preinjection of inhibitory antibodies did not preclude the IL-8-induced production and secretion of MMP-9. Pretreatment with an irrelevant control antibody did not affect IL-8-induced mobilization, showing that the inhibition by the anti-gelatinase B antibody was specific. In summary, IL-8 induces the rapid systemic release of MMP-9 with concurrent mobilization of HPC that is prevented by pretreatment with an inhibitory anti-gelatinase B antibody, indicating that MMP-9 is involved as a mediator of the IL-8-induced mobilization of HPC.

Contribution of exertional hyperthermia to sympathoadrenal-mediated lymphocyte subset redistribution

The contribution of hyperthermia to the differential leukocytosis of exercise remains obscure. This study examined changes in circulating sympathoadrenal hormone concentrations and patterns of leukocyte and lymphocyte subset (CD3(+), CD4(+), CD8(+), CD19(+), CD3(-)16(+)/56(+)) redistribution during exercise, with and without a significant rise of rectal temperature (T(re)). Ten healthy men [age 26.9 +/- 5.7 (SD) yr, body mass 76.0 +/- 10.9 kg, body fat 13.9 +/- 4.6%, peak O(2) consumption: 48.0 +/- 12.4 ml x kg(-1) x min(-1)] exercised for 40 min (65% peak O(2) consumption) during water immersion at 39 or 18 degrees C. T(re) increased from 37.2 to 39.3 degrees C (P < 0.0001) after 40 min of exercise in 39 degrees C water but was held constant to an increment of 0.5 degrees C during exercise in 18 degrees C water. Application of this thermal clamp reduced exercise-associated increments of plasma epinephrine (Epi) and norepinephrine (NE) by >50% (P < 0.05) and abolished the postexercise increase in cortisol. Thermal clamping also reduced the exercise-induced leukocytosis and lymphocytosis. Multiple regression demonstrated that T(re) had no direct association with lymphocyte subset mobilization but was significantly (P < 0.0001) correlated with hormone levels. Epi was an important determinant of total leukocytes, lymphocytes, and CD3(+), CD4(+), CD8(+), and CD3(-)CD16(+)/56(+) subset redistribution. The relationship between NE and lymphocyte subsets was weaker than that with Epi, with the exception of CD3(-)CD16(+)/56(+) counts, which were positively (P < 0.0001) related to NE. Cortisol was negatively associated with leukocytes, CD14(+) monocytes, and CD19(+) B- and CD4(+) T-cell subsets but was positively related to granulocytes. We conclude that hyperthermia mediates exercise-induced immune cell redistribution to the extent that it causes sympathoadrenal activation, with alterations in circulating Epi, NE, and cortisol.

(R)evolutionary considerations in hematopoietic development

Evolutionary aspects of three characteristics of the mammalian hematopoietic system are considered in the context of both established and recent data. First, the lineage relationships among early members of the hematopoietic hierarchy are reconsidered in a tripartite model proposing lineage segregation based on vascular function, innate immunity, and acquired immunity on an evolutionary time scale. Second, the observation of two stem cell populations that differ in cell cycle status is considered as an evolved mechanism to enhance survival of the species in response to exposure to environmental toxins. Finally, the mobilization of hematopoietic stem cells into the peripheral circulation is proposed to be a mechanism for rapid dissemination of myeloid function during acute bacterial infections. These revolutionary hypotheses challenge some conventional concepts of stem cell biology, and provide an evolutionary context for considering mammalian hematopoiesis.

The MCP/eotaxin subfamily of CC chemokines

Migration of leukocytes from the bone marrow to the circulation, the primary lymphoid organs and inflammatory sites is directed by chemokines and specific receptor interactions. Besides the role of this group of low molecular weight cytokines in leukocyte attraction and activation, anti-HIV and hematopoietic activities were also attributed to chemokines. On the basis of the number and arrangement of the conserved cysteines, chemokines are subdivided in two multi-member families, namely the CXC and CC chemokines, whereas fractalkine (CX3C) and lymphotactin (C) are unique relatives. The CC chemokines possess four cysteines of which the first two are adjacent. Functionally, they form a rather heterogeneous family. Here, the focus is on the monocyte chemotactic proteins and eotaxin which, on a structural basis, can be considered as a CC chemokine subfamily. Not only the protein sequences, but also the gene structures, chromosomal location, biological activities and receptor usage exhibit considerable similarities. The review is complemented with a comparison of the biological functions of the MCP/eotaxin-subfamily in physiology and pathology.

Plasminogen activators and matrix metalloproteases, mediators of extracellular proteolysis in inflammatory demyelination of the central nervous system

The role of extracellular proteolysis in inflammatory demyelination, originally hypothesized as a mechanism for myelin degradation, is increasingly recognized as a pathogenetic step and as a target for therapy in human demyelinating disease. The activation of ubiquitous plasminogen by urokinase (u-PA) and tissue-type plasminogen activator (t-PA), which is associated with various neuropathologies, including multiple sclerosis (MS), is the key initiator of the activation cascade of the four classes of matrix metalloproteinases (MMPs): collagenases, stromelysins, membrane-type metalloproteinases and gelatinases. Spatiotemporal protein and mRNA expression of gelatinase B (MMP-9) and matrilysin (MMP-7) have been documented respectively in MS lesions and in the central nervous system (CNS) of animals developing experimental autoimmune encephalomyelitis (EAE). A close interaction between disease-promoting cytokines and extracellularly acting proteases is deduced from in vitro experiments. Cytokines regulate the balance between the proteases and their respective specific inhibitors at the transcriptional level, while proteolysis is a reciprocal mechanism to enhance (by activation) or downmodulate (by degradation) the specific activities of cytokines. In acute inflammation the contribution of chemokines is hierarchically organised, interleukin-8 (IL-8) and related CXC-chemokines inducing a rapid influx of neutrophils in the acute lesions and an instantaneous exocytosis of gelatinase B granules. This results in sudden and extensive damage to the CNS. In chronic disease involving autoimmune processes CC-chemokines that act mainly on mononuclear cell types appear to be more strictly regulated. As MMPs modify matrix components, promoting extravasation of lymphocytes and monocytes/macrophages and have the potential to generate encephalitogenic peptides from myelin basic protein, novel treatments for demyelinating diseases may be predicted by specific inhibition of these enzymes. Here we review plasminogen activators and the MMP family, in the context of their role in CNS inflammation and demyelination and highlight studies in which intervention in these protease cascades are and may be used to treat demyelinating diseases.

Concepts and principles of O-linked glycosylation

The biosynthesis, structures, and functions of O-glycosylation, as a complex posttranslational event, is reviewed and compared for the various types of O-glycans. Mucin-type O-glycosylation is initiated by tissue-specific addition of a GalNAc-residue to a serine or a threonine of the fully folded protein. This event is dependent on the primary, secondary, and tertiary structure of the glycoprotein. Further elongation and termination by specific transferases is highly regulated. We also describe some of the physical and biological properties that O-glycosylation confers on the protein to which the sugars are attached. These include providing the basis for rigid conformations and for protein stability. Clustering of O-glycans in Ser/Thr(/Pro)-rich domains allows glycan determinants such as sialyl Lewis X to be presented as multivalent ligands, essential for functional recognition. An additional level of regulation, imposed by exon shuffling and alternative splicing of mRNA, results in the expression of proteins that differ only by the presence or absence of Ser/Thr(/Pro)-rich domains. These domains may serve as protease-resistant spacers in cell surface glycoproteins. Further biological roles for O-glycosylation discussed include the role of isolated mucin-type O-glycans in recognition events (e.g., during fertilization and in the immune response) and in the modulation of the activity of enzymes and signaling molecules. In some cases, the O-linked oligosaccharides are necessary for glycoprotein expression and processing. In contrast to the more common mucin-type O-glycosylation, some specific types of O-glycosylation, such as the O-linked attachment of fucose and glucose, are sequon dependent. The reversible attachment of O-linked GlcNAc to cytoplasmic and nuclear proteins is thought to play a regulatory role in protein function. The recent development of novel technologies for glycan analysis promises to yield new insights in the factors that determine site occupancy, structure-function relationship, and the contribution of O-linked sugars to physiological and pathological processes. These include diseases where one or more of the O-glycan processing enzymes are aberrantly regulated or deficient, such as HEMPAS and cancer.