Functional and receptor binding characterization of recombinant murine macrophage inflammatory protein 2: sequence analysis and mutagenesis identify receptor binding epitopes

Arntl deficiency in myeloid cells reduces neutrophil recruitment and delays skeletal muscle repair

After a muscle injury, a process comprising inflammation, repair, and regeneration must occur in a time-sensitive manner for skeletal muscle to be adequately repaired and regenerated. This complex process is assumed to be controlled by various myeloid cell types, including monocytes and macrophages, though the mechanism is not fully understood. Aryl hydrocarbon receptor nuclear translocator-like (Arntl or Bmal1) is a transcription factor that controls the circadian rhythm and has been implicated in regulating myeloid cell functions. In the present study, we generated myeloid cell-specific Arntl conditional knockout (cKO) mice to assess the role of Arntl expressed in myeloid cell populations during the repair process after muscle injury. Myeloid cell-specific Arntl deletion impaired muscle regeneration after cardiotoxin injection. Flow cytometric analyses revealed that, in cKO mice, the numbers of infiltrating neutrophils and Ly6C^hi monocytes within the injured site were reduced on days 1 and 2, respectively, after muscle injury. Moreover, neutrophil migration and the numbers of circulating monocytes were significantly reduced in cKO mice, which suggests these effects may account, at least in part, for the impaired regeneration. These findings suggest that Arntl, expressed in the myeloid lineage regulates neutrophil and monocyte recruitment and is therefore required for skeletal muscle regeneration.

Commensal Staphylococcus aureus Provokes Immunity to Protect against Skin Infection of Methicillin-Resistant Staphylococcus aureus

Unlike USA300, a strain of community-acquired methicillin-resistant Staphylococcus aureus (MRSA), commensal Staphylococcus aureus (S. aureus) bacteria isolated from human skin demonstrated the ability to mediate the glycerol fermentation to produce short-chain fatty acids (SCFAs). Quantitative proteomic analysis of enzymes involved in glycerol fermentation demonstrated that the expression levels of six enzymes, including glycerol-3-phosphate dehydrogenase (GPDH) and phosphoglycerate mutase (PGM), in commensal S. aureus are more than three-fold higher than those in USA300. Western blotting validated the low expression levels of GPDH in USA300, MRSA252 (a strain of hospital-acquired MRSA), and invasive methicillin-susceptible S. aureus (MSSA). In the presence of glycerol, commensal S. aureus effectively suppressed the growth of USA300 in vitro and in vivo. Active immunization of mice with lysates or recombinant α-hemolysin of commensal S. aureus or passive immunization with neutralizing sera provided immune protection against the skin infection of USA300. Our data illustrate for the first time that commensal S. aureus elicits both innate and adaptive immunity via glycerol fermentation and systemic antibody production, respectively, to fight off the skin infection of pathogenic MRSA.

Bcl10 synergistically links CEACAM3 and TLR-dependent inflammatory signalling

The neutrophil-specific innate immune receptor CEACAM3 functions as a decoy to capture Gram-negative pathogens, such as Neisseria gonorrhoeae, that exploit CEACAM family members to adhere to the epithelium. Bacterial binding to CEACAM3 results in their efficient engulfment and triggers activation of an nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB)-dependent inflammatory response by human neutrophils. Herein, we report that CEACAM3 cross-linking is not sufficient for induction of cytokine production and show that the inflammatory response induced by Neisseria gonorrhoeae infection is elicited by an integration of signals from CEACAM3 and toll-like receptors. Using neutrophils from a human CEACAM-expressing mouse line (CEABAC), we use a genetic approach to reveal a molecular bifurcation of the CEACAM3-mediated antimicrobial and inflammatory responses. Ex vivo experiments with CEABAC-Rac2-/- , CEABAC-Bcl10-/- , and CEABAC-Malt1-/- neutrophils indicate that these effectors are not necessary for gonococcal engulfment, yet all 3 effectors contribute to CEACAM3-mediated cytokine production. Interestingly, although Bcl10 and Malt1 are often inextricably linked, Bcl10 enabled synergy between toll-like receptor 4 and CEACAM3, whereas Malt1 did not. Together, these findings reveal an integration of the specific innate immune receptor CEACAM3 into the network of more conventional pattern recognition receptors, providing a mechanism by which the innate immune system can unleash its response to a relentless pathogen.

Immunomodulatory effects of Bacillus subtilis (natto) B4 spores on murine macrophages

To investigate the immunomodulatory effects of Bacillus subtilis (B. subtilis) (natto) B4 spores on murine macrophage, RAW 264.7 cells were cultured alone or with B subtilis (natto) B4 spores at 37°C for 12 hrs, then both cells and culture supernatants were collected for analyses. Exposure of RAW 264.7 cells to B. subtilis (natto) B4 spores had no significant effects on macrophage viability and amounts of extracellular lactate dehydrogenase (LDH). However, it remarkably increased the activities of acid phosphatase (ACP), lactate dehydrogenase (LDH) and inducible nitric oxide synthase (iNOS) in cells and the amounts of nitric oxide (NO) and cytokines (tumor necrosis factor-alpha, interferon-gamma, interleukin [IL]-1 beta, IL-6, IL-12, IL-10 and macrophage inflammatory protein-2) in culture supernatants. These results demonstrate that B. subtilis (natto) B4 spores are harmless to murine macrophages and can stimulate their activation through up-regulation of ACP and LDH activities and enhance their immune function by increasing iNOS activity and stimulating NO and cytokine production. The above findings suggest that B. subtilis (natto) B4 spores have immunomodulatory effects on macrophages.

Candida albicans-Staphylococcus aureus polymicrobial peritonitis modulates host innate immunity

Despite advances in medical device fabrication and antimicrobial treatment therapies, fungal-bacterial polymicrobial peritonitis remains a serious complication for surgery patients, those on peritoneal dialysis, and the critically ill. Using a murine model of peritonitis, we have demonstrated that monomicrobial infection with Candida albicans or Staphylococcus aureus is nonlethal. However, coinfection with these same doses leads to a 40% mortality rate and increased microbial burden in the spleen and kidney by day 1 postinfection. Using a multiplex enzyme-linked immunosorbent assay, we have also identified a unique subset of innate proinflammatory cytokines (interleukin-6, granulocyte colony-stimulating factor, keratinocyte chemoattractant, monocyte chemoattractant protein-1, and macrophage inflammatory protein-1α) that are significantly increased during polymicrobial versus monomicrobial peritonitis, leading to increased inflammatory infiltrate into the peritoneum and target organs. Treatment of coinfected mice with the cyclooxygenase (COX) inhibitor indomethacin reduces the infectious burden, proinflammatory cytokine production, and inflammatory infiltrate while simultaneously preventing any mortality. Further experiments demonstrated that the immunomodulatory eicosanoid prostaglandin E2 (PGE2) is synergistically increased during coinfection compared to monomicrobial infection; indomethacin treatment also decreased elevated PGE2 levels. Furthermore, addition of exogenous PGE2 into the peritoneal cavity during infection overrode the protection provided by indomethacin and restored the increased mortality and microbial burden. Importantly, these studies highlight the ability of fungal-bacterial coinfection to modulate innate inflammatory events with devastating consequences to the host.

A model of GAG/MIP-2/CXCR2 interfaces and its functional effects

MIP-2/CXCL2 is a murine chemokine related to human chemokines that possesses the Glu-Leu-Arg (ELR) activation motif and activates CXCR2 for neutrophil chemotaxis. We determined the structure of MIP-2 to 1.9 Å resolution and created a model with its murine receptor CXCR2 based on the coordinates of human CXCR4. Chemokine-induced migration of cells through specific G-protein coupled receptors is regulated by glycosaminoglycans (GAGs) that oligomerize chemokines. MIP-2 GAG-binding residues were identified that interact with heparin disaccharide I-S by NMR spectroscopy. A model GAG/MIP-2/CXCR2 complex that supports a 2:2 complex between chemokine and receptor was created. Mutants of these disaccharide-binding residues were made and tested for heparin binding, in vitro neutrophil chemotaxis, and in vivo neutrophil recruitment to the mouse peritoneum and lung. The mutants have a 10-fold decrease in neutrophil chemotaxis in vitro. There is no difference in neutrophil recruitment between wild-type MIP-2 and mutants in the peritoneum, but all activity of the mutants is lost in the lung, supporting the concept that GAG regulation of chemokines is tissue-dependent.

Toll-like receptor 3 ligand polyinosinic:polycytidylic acid promotes wound healing in human and murine skin

Toll-like receptors (TLRs) are pattern-recognition receptors and have a critical role in both innate and adaptive responses to tissue injury. Our previous study showed that wound healing was impaired in TLR3-deficient mice. In this study, we investigated the capacity of the TLR3 agonist polyriboinosinic-polyribocytidylic acid (poly(I:C)) to promote the healing of skin wounds in humans and mice. We found that topical application with poly(I:C) accelerated the closure of wounds in patients with laser plastic surgery. In a mouse model, topical application of poly(I:C) markedly enhanced re-epithelialization, granulation, and neovascularization required for wound closure. Further studies revealed that poly(I:C) treatment resulted in enhanced recruitment of neutrophils and macrophages in association with upregulation of a chemokine, macrophage inflammatory protein-2 (MIP-2/CXCL2), in the wounds. The effect of poly(I:C) was abolished in TLR3-deficient mice or by treatment with MIP-2/CXCL2-neutralizing antibodies. These results suggest a potential therapeutic value of the TLR3 activator poly(I:C) for wound healing.

Chemokine CXCL1/KC and its receptor CXCR2 are responsible for neutrophil chemotaxis in adenoviral keratitis

Epidemic keratoconjunctivitis (EKC), caused by human adenovirus (HAdV), is one of the most common ocular infections and results in corneal inflammation and subepithelial infiltrates. Adenoviral keratitis causes significant morbidity to the patients, and is characterized by infiltration of leukocytes in the corneal stroma, and expression of chemokines. The exact role of these chemokines in adenoviral infection has not been studied due to lack of animal models. Here, we have characterized the role of chemokine CXCL1/KC and receptor CXCR2 in adenoviral keratitis using a novel mouse model. Analysis of chemokine expression, leukocyte infiltration, and development of keratitis was performed by ELISA, flow cytometry, and histopathology, respectively. Deficiency of CXCL1 and CXCR2 resulted in delayed infiltration of neutrophils, but not inflammatory monocytes in HAdV-37 corneal infection. CXCL1(-/-) mice showed decreased expression of CXCL2/MIP-2, but not CCL2/MCP-1. CXCR2(-/-) mice showed increased expression of CXCL1 and CXCL2, but not CCL2. Both CXCL1(-/-) and CXCR2(-/-) mice demonstrated keratitis similar to wild-type mice. In conclusion, both CXCL1 and CXCR2 play an important role in chemokine expression and neutrophil infiltration following adenoviral corneal infection, but have a redundant role in the development of keratitis.

Cytokine and Chemokine Expression Associated with Steatohepatitis and Hepatocyte Proliferation in Rats Fed Ethanol via Total Enteral Nutrition

To determine the temporal relationship between alcohol-induced changes in cytokines and chemokines, development of liver pathology and stimulation of hepatocyte proliferation, male Sprague-Dawley rats were intragastrically fed low carbohydrate-containing ethanol (EtOH) diets via total enteral nutrition (TEN) for up to 49 d. Induction of EtOH metabolism and appearance of steatosis preceded development of oxidative stress, inflammation, and cell death. A transitory peak of tumor necrosis factor (TNFα) and interferon gamma (IFNγ) was observed at 14 d followed by reduced expression of TNFα, IFNγ and another Th1 cytokine IL-12 accompanied by reduced expression of the Th1 regulators T-bet and STAT4. After 35–49 d of EtOH, at a time when hepatocyte proliferation was stimulated, IL-12 returned to control values and a second peak of TNFα occurred. The Th2 cytokine IL-4 remained suppressed throughout the study and was accompanied by reductions in the Th2 regulator GATA3. There was no temporal effect of EtOH on expression of IL-6 or TGFβ. IL-5 and IL-13 mRNA were undetectable. Chemokine CXCL-2 expression increased progressively up to 35 d and preceded the appearance of inflammatory infiltrates. These data suggest that steatosis, increased ethanol metabolism, a transient induction of the innate immune response and suppression of Th2 responses were acute consequences of ethanol treatment and were followed by suppression of Th1 responses. However, the majority of necrosis, apoptosis and a late peak of TNFα only occurred after 6–7 weeks of ethanol, coincided with the appearance of inflammatory infiltrates and were associated with stimulation of hepatocyte proliferation.

Functional Replacement of Murine CXCR2 by Its Human Homologue in the Development of Atherosclerosis in LDLR Knockout Mice

The CXC chemokine receptor CXCR2 has been implicated in the pathogenesis of several chronic diseases including atherosclerosis. To enable animal studies towards understanding the role of human CXCR2 (hCXCR2) in disease development, we previously generated hCXCR2 knockin (hCXCR2(+/+)) mice. We have demonstrated that the phenotype and the acute immune response of the hCXCR2(+/+) mice was identical to that of wild-type mice, indicating that hCXCR2 indeed takes over the function of endogenous mouse CXCR2 (mCXCR2). In the present paper, we extend these findings by studying whether hCXCR2 functionally replaces the role of mCXCR2 in a chronic disease model for atherosclerosis. We first defined which of two well-described atherosclerosis models (ApoE(-/-) or LDLR(-/-) mice) is most suited for this purpose. When expression of mCXCR2 and that of its ligands in atherosclerotic lesions were compared in these mice, increased expression levels were observed only in LDLR(-/-) mice. Further, cultured atherosclerotic aortas from LDLR(-/-) mice did secrete significantly higher levels of CXCR2 ligands compared to aortas from healthy controls. Since these results support the role of CXCR2 in the atherogenesis in the LDLR(-/-) mice, double mutant hCXCR2(+/+)/LDLR(-/-) mice were generated and diet-induced atherosclerosis in these mice was compared to that in LDLR(-/-) mice. Upon an atherogenic diet, the hCXCR2(+/+)/LDLR(-/-) mice developed plaque lesions in a similar manner to those in LDLR(-/-) mice, indicating successful functional replacement of mCXCR2 by hCXCR2 in this disease model. We conclude that hCXCR2(+/+)/LDLR(-/-) mice present an attractive model to study the role of hCXCR2 in atherosclerosis development and for future testing of novel pharmaceuticals designed to antagonize hCXCR2.

MCP-1 deficiency causes altered inflammation with impaired skeletal muscle regeneration

We examined the role of MCP-1, a potent chemotactic and activating factor for macrophages, in perfusion, inflammation, and skeletal muscle regeneration post-ischemic injury. MCP-1-/- or C57Bl/6J control mice [wild-type (WT)] underwent femoral artery excision (FAE). Muscles were collected for histology, assessment of tissue chemokines, and activity measurements of lactate dehydrogenase (LDH) and myeloperoxidase. In MCP-1-/- mice, restoration of perfusion was delayed, and LDH and fiber size, indicators of muscle regeneration, were decreased. Altered inflammation was observed with increased neutrophil accumulation in MCP-1-/- versus WT mice at Days 1 and 3 (P< or =0.003), whereas fewer macrophages were present in MCP-1-/- mice at Day 3. As necrotic tissue was removed in WT mice, macrophages decreased (Day 7). In contrast, macrophage accumulation in MCP-1-/- was increased in association with residual necrotic tissue and impaired muscle regeneration. Consistent with altered inflammation, neutrophil chemotactic factors (keratinocyte-derived chemokine and macrophage inflammatory protein-2) were increased at Day 1 post-FAE. The macrophage chemotactic factor MCP-5 was increased significantly in WT mice at Day 3 compared with MCP-1-/- mice. However, at post-FAE Day 7, MCP-5 was significantly elevated in MCP-1-/- mice versus WT mice. Addition of exogenous MCP-1 did not induce proliferation in murine myoblasts (C2C12 cells) in vitro. MCP-1 is essential for reperfusion and the successful completion of normal skeletal muscle regeneration after ischemic tissue injury. Impaired muscle regeneration in MCP-1-/- mice suggests an important role for macrophages and MCP-1 in tissue reparative processes.

Human CXCR2 (hCXCR2) takes over functionalities of its murine homolog in hCXCR2 knockin mice

Human CXCR2 (hCXCR2) has been implicated in diverse inflammatory diseases. When roles of this receptor studied in animal models are extrapolated into men, large species differences in expression of the receptor and its ligands must be considered. These differences seriously weaken conclusions toward the role of hCXCR2 in the development of human diseases. It furthermore hampers straightforward testing of CXCR2 antagonists, especially when compounds discriminate between human and other species' receptors. Using gene targeting in embryonic stem cells, a hCXCR2 knockin mouse strain was generated in which endogenous murine CXCR2 (mCXCR2) sequences are replaced by the hCXCR2 gene. Correct targeting and expression on neutrophils were confirmed by Southern blot and immunohistochemical analyses. A phenotypic analysis of the hCXCR2 knockin mice, in comparison to wild-type and CXCR2 knockout mice, confirmed proper function of the hCXCR2 gene. In vivo migratory responses of neutrophils were intact in hCXCR2 knockin mice. Finally, an experiment with a CXCR2 antagonist demonstrated that the knockin model is indeed useful for in vivo evaluation of low-molecular weight compounds. In conclusion, our data unequivocally show that hCXCR2 can functionally replace mCXCR2, making this an attractive model to test novel pharmaceuticals designed to antagonize human CXCR2 in vivo.

Involvement of multiple signaling pathways in the post-bariatric induction of IL-6 and IL-8 mRNA and release in human visceral adipose tissue

The present studies were designed to determine the site of and the mechanism for the rapid increase in IL-6 and IL-8 mRNA observed in human visceral adipose tissue after removal during laparoscopic bariatric surgery. Upregulation of IL-6 and IL-8 mRNA as well as their release were seen within 3h whether one intact piece of tissue or minced pieces of adipose tissue were incubated in vitro. Most of the IL-6 and IL-8 mRNA content of visceral adipose tissue after 3h of incubation was in the non-fat cells. Actinomcyin D markedly reduced the upregulation of IL-6 and IL-8 mRNA. Incubation of adipose tissue explants with a soluble TNFalpha receptor (etanercept) plus a blocking antibody against IL-lbeta reduced by 55% the increase in IL-6 mRNA and by 42% that of IL-8 mRNA seen between 1 and 5h of incubation. The upregulation of IL-8 and IL-6 mRNA accumulation as well as their release over a 2 or 4h incubation was reduced by around 50% in the presence of an inhibitor of the p38 MAPK or an inhibitor of the NFkappaB pathway and by 85% in the presence of both inhibitors. The data suggest that the relative trauma and/or hypoxia that occurs when adipose tissue is removed results in the release of TNFalpha and IL-1beta. These cytokines, and probably other factors as well, enhance IL-6 and IL-8 mRNA accumulation in human adipose tissue explants through mechanisms involving the p38 MAPK and NFkappaB pathways.

Characterization of Nef-CXCR4 interactions important for apoptosis induction

The HIV-1 Nef protein was analyzed for apoptotic structural motifs that interact with the CXCR4 receptor and induce apoptosis in CD4(+) lymphocytes. Two apoptotic motifs were identified. One centered on Nef amino acids (aa) 50 to 60, with the overlapping 20-mer peptides retaining about 82% of the activity of the full Nef protein. The second centered on aa 170 to 180, with the overlapping 20-mer peptides retaining about 30% of the activity of the full protein. Significant apoptotic abilities were observed for 11-mer motif peptides spanning aa 50 to 60 and aa 170 to 180, with a scrambled version of the 11-mer motif peptide corresponding to aa 50 to 60 showing no apoptotic ability. Hallmarks of apoptosis, such as the formation of DNA ladders and caspase activation, that were observed with the full-length protein were equally evident upon exposure of cells to these motif peptides. A CXCR4 antibody and the endogenous ligand SDF-1alpha were effective in blocking Nef peptide-induced apoptosis as well as the physical binding of a fluorescently tagged Nef protein, while CCR5 antibodies were ineffective. The CXCR4-negative cell line MDA-MB-468 was resistant to the apoptotic peptides and became sensitive to the apoptotic peptides upon transfection with a CXCR4-expressing vector. A fluorescently tagged motif peptide and Nef protein displayed physical binding to CXCR4-transfected MDA-MB-468 cells, but not to CCR5-transfected cells. The removal of the apoptotic motif sequences from the full-length protein completely eliminated the ability of Nef to induce apoptosis. However, these modified Nef proteins still retained the ability to enhance viral infectivity. Thus, specific sequences in the Nef protein appear to be necessary for Nef protein-induced apoptosis as well as for physical interaction with CXCR4 receptors.

Differential processing of stromal-derived factor-1alpha and stromal-derived factor-1beta explains functional diversity

The chemokine stromal-derived factor-1 (SDF-1), which is constitutively expressed in most tissues as SDF-1alpha and SDF-1beta resulting from alternative gene splicing, regulates hematopoiesis, lymphocyte homing, B-lineage cell growth, and angiogenesis. Because SDF-1alpha and SDF-1beta are constitutively and ubiquitously expressed, their degradation must serve an important regulatory role. Here we show that SDF-1alpha and SDF-1beta are secreted as full-length molecules. When exposed to human serum, full-length SDF-1alpha (1-68) undergoes processing first at the COOH terminus to produce SDF-1alpha 1-67 and then at the NH2 terminus to produce SDF-1alpha 3-67. By contrast, full-length SDF-1beta (1-72) is processed only at the NH2 terminus to produce SDF-1beta 3-72. CD26/dipeptidyl peptidase is responsible for serum cleavage of SDF-1alpha and SDF-1beta at the NH2 terminus. Serum processing of SDF-1alpha at the COOH terminus, which has not been previously reported, reduces the ability of the polypeptide to bind to heparin and to cells and to stimulate B-cell proliferation and chemotaxis. The additional processing at the NH2 terminus renders both forms of SDF-1 unable to bind to heparin and to activate cells. The differential processing of SDF-1alpha and SDF-1beta provides biologic significance to the existence of 2 splice forms of the chemokine and adds a tool to precisely regulate SDF-1's biologic activity by changes in specific activity.

Binding of ALX40-4C to APJ, a CNS-based receptor, inhibits its utilization as a co-receptor by HIV-1

APJ, a G protein-coupled seven-transmembrane receptor, has been shown to serve as a co-receptor for the entry of human immunodeficiency virus type 1 (HIV-1), and it is dramatically expressed in central nervous system (CNS)-based cells. ALX40-4C was identified as a small-molecule antagonist of the chemokine receptor CXCR4, which can specifically inhibit HIV-1 entry via this co-receptor. In this study, we demonstrated that ALX40-4C inhibited both APJ- and CXCR4/APJ-mediated cell membrane fusion in a dose-dependent manner. In competitive binding assays, (125)I-Apelin13 was replaced by ALX40-4C with an IC(50) of 2.9 microM, as compared with an IC(50) of 0.2 nM for Apelin13. Furthermore, ALX40-4C could block ligand-induced APJ internalization and signaling. ALX40-4C, as an antagonist to APJ, directly binds to and prevents use of APJ as a HIV-1 co-receptor. Thus, ALX-4C has potential utility for further elucidation of HIV-1 neuropathogenesis and therapy of HIV-1-induced encephalopathy.

Macrophage-dependent regulation of neutrophil mobilization and chemotaxis during development of sterile peritonitis in the rat

Pro-inflammatory cytokines attract leukocytes to inflamed tissues and activate them. Few attempts have been made to identify the sources of cytokines in vivo. We examined the importance of peritoneal macrophages in the mobilization and homing of neutrophils to a sterile peritonitis in the rat, with emphasis on their cytokine production. Macrophages, present in virtually all tissues, are known to be easily activated and to serve as an important source of cytokines. Flow cytometric analysis of cells stained intracellularly with tagged antibodies against various cytokines revealed that the peritoneal macrophages were stimulated to produce the following cytokines: interleukin (IL)-1beta, macrophage inflammatory protein-2 (MIP-2), and keratinocyte-derived cytokine (KC). High numbers of neutrophils, activated on arrival into the peritoneal cavity, also produced IL-1beta, whereas lower numbers contained interleukin-6, tumor necrosis factor-alpha, MIP-2, KC, and MIP-1alpha. This marked activation of peritoneal neutrophils was also reflected by increased surface expression of CD11b. On the other hand, peritoneal macrophages expressed high basal levels of CD11b, which were reduced 24 h after the onset of inflammation. In rats selectively depleted of macrophages by i.p. injection of liposome-containing clodronate, the massive influx of neutrophils to the peritoneal cavity was markedly reduced, as was the rapid mobilization of mature bone marrow neutrophils. Local macrophages are important both for the accumulation of neutrophils in the inflamed peritoneal cavity and for the early mobilization of neutrophils from the bone marrow. Macrophage-derived IL-1beta, MIP-2, and KC are possible mediators of neutrophil homing to inflamed tissues.

CCR2 and CCR5 receptor-binding properties of herpesvirus-8 vMIP-II based on sequence analysis and its solution structure

Human herpesvirus-8 (HHV-8) is the infectious agent responsible for Kaposi's sarcoma and encodes a protein, macrophage inflammatory protein-II (vMIP-II), which shows sequence similarity to the human CC chemokines. vMIP-II has broad receptor specificity that crosses chemokine receptor subfamilies, and inhibits HIV-1 viral entry mediated by numerous chemokine receptors. In this study, the solution structure of chemically synthesized vMIP-II was determined by nuclear magnetic resonance. The protein is a monomer and possesses the chemokine fold consisting of a flexible N-terminus, three antiparallel beta strands, and a C-terminal alpha helix. Except for the N-terminal residues (residues 1-13) and the last two C-terminal residues (residues 73-74), the structure of vMIP-II is well-defined, exhibiting average rmsd of 0.35 and 0.90 A for the backbone heavy atoms and all heavy atoms of residues 14-72, respectively. Taking into account the sequence differences between the various CC chemokines and comparing their three-dimensional structures allows us to implicate residues that influence the quaternary structure and receptor binding and activation of these proteins in solution. The analysis of the sequence and three-dimensional structure of vMIP-II indicates the presence of epitopes involved in binding two receptors CCR2 and CCR5. We propose that vMIP-II was initially specific for CCR5 and acquired receptor-binding properties to CCR2 and other chemokine receptors.

Ratio of local to systemic chemokine concentrations regulates neutrophil recruitment

CXC chemokines are important regulators of local neutrophil recruitment. In this study, we examined the role of the ratio of local to systemic chemokine concentrations as a significant factor determining local neutrophil recruitment. Thioglycollate was injected intraperitoneally into BALB/c mice resulting in a dose-dependent increase in neutrophil recruitment and local inflammation, as measured by peritoneal levels of interleukin 6. At the high dose of 3% thioglycollate, antibody inhibition of the murine chemokines KC and macrophage inflammatory protein-2 caused a reduction in peritoneal neutrophil recruitment by as much as 93%. A paradoxical effect was observed with a 0.3% thioglycollate intraperitoneal challenge. In this situation, inhibition of KC resulted in a significant increase in peritoneal neutrophils, and inhibition of macrophage inflammatory protein-2 also resulted in increased peritoneal neutrophils. These results were consistent with a reverse chemotactic gradient as described by the ratio of peritoneal to plasma KC levels. A higher ratio (ie, increased peritoneal chemokines compared to plasma) resulted in increased neutrophil recruitment after either the 3% or 0.3% thioglycollate challenge. Our results demonstrate that whereas sufficient local concentrations of chemokines are necessary, a critical factor dictating local neutrophil recruitment is the ratio of the local to the systemic chemokine concentrations.

Recombinant protein expression in Pichia pastoris

The methylotrophic yeast Pichia pastoris is now one of the standard tools used in molecular biology for the generation of recombinant protein. P. pastoris has demonstrated its most powerful success as a large-scale (fermentation) recombinant protein production tool. What began more than 20 years ago as a program to convert abundant methanol to a protein source for animal feed has been developed into what is today two important biological tools: a model eukaryote used in cell biology research and a recombinant protein production system. To date well over 200 heterologous proteins have been expressed in P. pastoris. Significant advances in the development of new strains and vectors, improved techniques, and the commercial availability of these tools coupled with a better understanding of the biology of Pichia species have led to this microbe's value and power in commercial and research labs alike.

Leukocyte arrest during cytokine-dependent inflammation in vivo

Leukocyte rolling along the walls of inflamed venules precedes their adhesion during inflammation. Rolling leukocytes are thought to arrest by engaging beta2 integrins following cellular activation. In vitro studies suggest that chemoattractants may instantaneously activate and arrest rolling leukocytes. However, how leukocytes stop rolling and become adherent in inflamed venules in vivo has remained rather mysterious. In this paper we use a novel method of tracking individual leukocytes through the microcirculation to show that rolling neutrophils become progressively activated while rolling down the venular tree. On average, leukocytes in wild-type mice roll for 86 s (and cover 270 microm) before becoming adherent with an efficiency around 90%. These rolling leukocytes exhibit a gradual beta2 integrin-dependent decrease in rolling velocity that correlates with an increase in intracellular free calcium concentration before arrest. Similar tracking analyses in gene-targeted mice demonstrate that the arrest of rolling leukocytes is very rare when beta2 integrins are absent or blocked by a mAb. Arrest is approximately 50% less efficient in the absence of E-selectin. These data suggest a model of leukocyte recruitment in which beta2 integrins play a critical role in stabilizing leukocyte rolling during a protracted cellular activation period before arrest and firm adhesion.

Heterologous protein expression in the methylotrophic yeast Pichia pastoris

During the past 15 years, the methylotrophic yeast Pichia pastoris has developed into a highly successful system for the production of a variety of heterologous proteins. The increasing popularity of this particular expression system can be attributed to several factors, most importantly: (1) the simplicity of techniques needed for the molecular genetic manipulation of P. pastoris and their similarity to those of Saccharomyces cerevisiae, one of the most well-characterized experimental systems in modern biology; (2) the ability of P. pastoris to produce foreign proteins at high levels, either intracellularly or extracellularly; (3) the capability of performing many eukaryotic post-translational modifications, such as glycosylation, disulfide bond formation and proteolytic processing; and (4) the availability of the expression system as a commercially available kit. In this paper, we review the P. pastoris expression system: how it was developed, how it works, and what proteins have been produced. We also describe new promoters and auxotrophic marker/host strain combinations which extend the usefulness of the system.

NH2- and COOH-Terminal Truncations of Murine Granulocyte Chemotactic Protein-2 Augment the In Vitro and In Vivo Neutrophil Chemotactic Potency

Chemokines are important mediators of leukocyte migration during the inflammatory response. Post-translational modifications affect the biological potency of chemokines. In addition to previously identified NH2-terminally truncated forms, COOH-terminally truncated forms of the CXC chemokine murine granulocyte chemotactic protein-2 (GCP-2) were purified from conditioned medium of stimulated fibroblasts. The truncations generated 28 natural murine GCP-2 isoforms containing 69–92 residues, including most intermediate forms. Both NH2- and COOH-terminal truncations of GCP-2 resulted in enhanced chemotactic potency for human and murine neutrophils in vitro. The truncated isoform GCP-2(9–78) was 30-fold more potent than intact GCP-2(1–92)/LPS-induced CXC chemokine (LIX) at inducing an intracellular calcium increase in human neutrophils. After intradermal injection in mice, GCP-2(9–78) was also more effective than GCP-2(1–92)/LIX at inducing neutrophil infiltration. Similar to human IL-8 and GCP-2, murine GCP-2(9–78) and macrophage inflammatory protein-2 (MIP-2) induced calcium increases in both CXCR1 and CXCR2 transfectants. Murine GCP-2(9–78) could desensitize the calcium response induced by MIP-2 in human neutrophils and vice versa. Furthermore, MIP-2 and truncated GCP-2(9–78), but not intact GCP-2(1–92)/LIX, partially desensitized the calcium response to human IL-8 in human neutrophils. Taken together, these findings point to an important role of post-translationally modified GCP-2 to replace IL-8 in the mouse.

Crystal structure of chemically synthesized [N33A] stromal cell-derived factor 1alpha, a potent ligand for the HIV-1 "fusin" coreceptor

Stromal cell-derived factor-1alpha (SDF-1alpha ) is a member of the chemokine superfamily and functions as a growth factor and chemoattractant through activation of CXCR4/LESTR/Fusin, a G protein-coupled receptor. This receptor also functions as a coreceptor for T-tropic syncytium-inducing strains of HIV-1. SDF-1alpha antagonizes infectivity of these strains by competing with gp120 for binding to the receptor. The crystal structure of a variant SDF-1alpha ([N33A]SDF-1alpha ) prepared by total chemical synthesis has been refined to 2.2-A resolution. Although SDF-1alpha adopts a typical chemokine beta-beta-beta-alpha topology, the packing of the alpha-helix against the beta-sheet is strikingly different. Comparison of SDF-1alpha with other chemokine structures confirms the hypothesis that SDF-1alpha may be either an ancestral protein from which all other chemokines evolved or the chemokine that is the least divergent from a primordial chemokine. The structure of SDF-1alpha reveals a positively charged surface ideal for binding to the negatively charged extracellular loops of the CXCR4 HIV-1 coreceptor. This ionic complementarity is likely to promote the interaction of the mobile N-terminal segment of SDF-1alpha with interhelical sites of the receptor, resulting in a biological response.