Suppression of immune responses is necessary to limit damage to host tissue during inflammation, but it can
Noninflamed skin venules support constitutive leukocyte rolling. P-selectin controls the rolling frequency, whereas E-selectin dictates rolling velocity (Vroll). Fucosylated selectin ligands are essential for all interactions, as rolling was absent in mice doubly deficient in alpha1,3-fucosyltransferase (FucT)-IV and FucT-VII. The rolling fraction was reduced in FucT-VII-/- animals but normal in FucT-IV-/- mice. However, Vroll was markedly increased in both strains. P-selectin ligands generated by FucT-VII are crucial for initial leukocyte tethering, whereas E-selectin ligands that permit maximum slowing of Vroll require simultaneous expression of FucT-IV and FucT-VII. These results demonstrate a role for FucT-IV in selectin-dependent adhesion and suggest that the endothelial selectins and FucTs have distinct but overlapping functions in the immunosurveillance of the skin.
Detachment of the rear of the cell from its substratum is an important aspect of locomotion. The signaling routes involved in this adhesive release are largely unknown. One of the few candidate proteins to play a role is RhoA, because activation of RhoA in many cell types leads to contraction, a mechanism probably involved in detachment. To study the role of RhoA in detachment regulation, we analyzed several subsets of expert migratory leukocytes by video microscopy. In contrast to fast-migrating neutrophils, eosinophils do not detach the rear of the cell unless stimulated with serum. When measuring the amount of active RhoA, with the use of a GSTRhotekin pulldown assay, we found that serum is an excellent activator of RhoA in granulocytes. Inhibition of RhoA or one of Rho's target proteins, the kinase ROCK, in neutrophils leads to the phenotype seen in eosinophils: the rear of the cell is firmly attached to the substratum, whereas the cell body is highly motile. ROCK-inhibition leads to impaired migration of granulocytes in filters, on glass, and through endothelial monolayers. Also, the ROCK signaling pathway is involved in changes of integrin-mediated adhesion. Eosinophil transduction by a tat-fusion construct containing active RhoA resulted in detachment stimulation in the presence of chemoattractant. From these results we conclude that activation of the RhoA-ROCK pathway is essential for detachment of migratory leukocytes.
IntroductionStaphylococcus aureus is a common human pathogen that induces both community-acquired and nosocomial infections. This Grampositive bacterium is well known for its suppurative diseases such as skin-limited abscesses and boils and more seriously endocarditis, sepsis, and toxic shock syndrome. 1,2 Its invasiveness is ascribed to the production of a wide repertoire of cell surface-expressed as well as secreted virulence factors that interfere with host defense. 2,3 Superantigens constitute a large portion of the secreted arsenal of staphylococci and modulate immune responses. They trigger nonspecific activation of T lymphocytes by binding to major histocompatibility complex (MHC) class II molecules on antigenpresenting cells outside the antigen-binding cleft and V  domains of T-cell receptors (TCRs). 4 We have described chemotaxis inhibitory protein of S aureus (CHIPS), an excreted virulence factor of S aureus. 5,6 CHIPS is known to inhibit formylated peptide-and complement factor C5a-induced responses in neutrophils through direct binding to the formyl peptide receptor and C5a receptor (C5aR), respectively. 7 Thereby, CHIPS inhibits the initial activation and migration of neutrophils to the site of infection; thus, it hampers clearance of S aureus by innate immune cells. Recently, the structure of CHIPS consisting of residues 31 to 121 (CHIPS ) was resolved. 8 CHIPS is composed of an ␣-helix packed onto a 4-stranded antiparallel -sheet, a domain also present in the C-terminal domain of superantigens. This protein also revealed to be homologous to the C-terminal domain of staphylococcal superantigen-like 5 (SSL5) and SSL7.SSLs are a family of secreted proteins identified through sequence homology to staphylococcal and streptococcal superantigens. 9 Eleven different SSLs exist that are encoded on staphylococcal pathogenicity island 2 in a conserved order. Staphylococci contain 7 to 11 different SSLs, and their homology varies between 36% and 67%. Allelic variants show 85% to 100% homology. 10,11 Determination of the crystal structures of SSL5 12 and SSL7 13 also revealed their high structural homology to superantigens; the N-terminal oligonucleotide/oligosaccharide-binding fold and the C-terminal -grasp domain characteristic for superantigens are also observed in SSLs. However, residues important for MHC class II and TCR binding of superantigens are not conserved in SSLs, which may explain their inability to display superantigenic activities. 9,10,12 Recently, Langley et al 14 described binding of complement component 5 and immunoglobulin A (IgA) by SSL7, suggesting a role for SSLs in staphylococcal defense against host immune responses. SSL7 was subsequently found to bind the C␣2/C␣3 interface of IgA Fc, which is the adhesion site for the Fc␣RI. 15 So far, no other functions have been linked to the SSLs.Neutrophil recruitment to sites of infection is a multistep process. 16 The initial tethering and rolling of neutrophils on the endothelium of vessel walls during inflammation are mediated by P-selec...
Recent studies suggest that chemotherapy, in addition to its cytotoxic effects on tumor cells, can induce a cascade of host events to support tumor growth and spread. Here, we used an experimental pulmonary metastasis model to investigate the role of this host response in metastasis formation. Mice were pretreated with chemotherapy and after clearance of the drugs from circulation, tumor cells were administered intravenously to study potential "protumorigenic" host effects of chemotherapy. Pretreatment with the commonly used chemotherapeutic agents cisplatin and paclitaxel significantly enhanced lung metastasis in this model. This corresponded to enhanced adhesion of tumor cells to an endothelial cell monolayer that had been pretreated with chemotherapy in vitro. Interestingly, chemotherapy exposure enhanced the expression of VEGF receptor 1 (VEGFR-1) on endothelial cells both in vitro and in vivo. Administration of antibodies targeting VEGFR-1 reversed the early retention of tumor cells in the lungs, thereby preventing the formation of chemotherapy-induced pulmonary metastases. The data indicate that chemotherapy-induced expression of VEGFR-1 on endothelial cells can create an environment favorable to tumor cell homing. Inhibition of VEGFR-1 function may therefore be used to counteract chemotherapy-induced retention of tumor cells within the metastatic niche, providing a novel level of tumor control in chemotherapy. Cancer Res; 71(22); 6976-85. Ó2011 AACR.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.