There is more than one interleukin 1

In 1972, Gery and co-workers(1) detected a factor that promotes murine thymocyte proliferation in culture supernatants of human peripheral blood adherent leukocytes. This factor is active across species lines, does not support the growth of interleukin 2 (IL-2)-dependent lymphocyte lines, is produced by monocytic rather than lymphocytic leukocytes, and has subsequently been termed interleukin 1 (IL- 1)(2). More recently, it has become evident that IL-1 activities can be produced by virtually every nucleated cell type and, in addition, IL-1 has been reported to have stimulatory effects on the growth and differentiation of numerous cell types. In this review, Joost Oppenheim and his colleagues discuss the biochemical characteristics, gene cloning, cell sources, biological properties and actions of IL-1, and give reasons why this pleitotropic, nonspecific hormone-like cytokine is of considerable concern to immunologists.

Alarmins and antimicrobial immunity

Alarmins are endogenous mediators capable of enhancing innate and adaptive immune response through induction of concomitant recruitment and activation of antigen-presenting cells. Here we provide a brief overview of various alarmins, highlight their critical roles in innate and adaptive antimicrobial immunity, and speculate on potential usage of alarmins in combating aspergillosis.

Roles of antimicrobial peptides such as defensins in innate and adaptive immunity

A number of antimicrobial peptides such as defensins have multiple functions in host defence. Defensins are produced not only by phagocytic cells and lymphocytes, but also by the epithelial cell lining of the gastrointestinal and genitourinary tracts, the tracheobronchial tree, and keratinocytes. Some are produced constitutively, whereas others are induced by proinflammatory cytokines and exogenous microbial products. Defensins produced by cells in the course of innate host defence serve as signals which initiate, mobilise, and amplify adaptive immune host defences. Administration of defensins with antigens to mice enhances both cellular (Th1-dependent) and humoral (Th2-dependent) cytokine production and immune responses. Linkage of defensins to weak tumour antigens potentiates their immunoadjuvant effects. Defensins use multiple cellular receptors, which endows them with the capacity to marshall adaptive host defences against microbial invaders.

Effects of astragali radix on the growth of different cancer cell lines

AIM: To investigate the inhibitory effect of a Chinese herb medicine Astragali radix (AR) on growth of different cancer cell lines.

METHODS: To observe the in vitro effects of AR on tumor cell proliferation by trypan blue exclusion, MTS method and tritium thymidine incorporation assay. Apoptosis was detected by DNA ladder method.

RESULTS: The inhibition rates of AR on the cell respiration of AGS, KATOIII, HT29, MDA231, MEL7 and MEL14 were 68.25%, 62.36%, 22.8%, 27.69%, 2.85% and 5.14% respectively at the concentration of 100 ug/mL; it inhibited AGS DNA synthesis by 87.33% at the concentration of 50 ug/mL. The inhibitory effect on AGS was time-and dose-dependent. AR did not induce apoptosis in AGS cells.

CONCLUSION: AR specifically inhibits gastric cancer cells growth in vitro and the mechanism is mainly cytostatic but not cytotoxic or inducing apoptosis.

Mediators of innate immunity that target immature, but not mature, dendritic cells induce antitumor immunity when genetically fused with nonimmunogenic tumor antigens

Chemokine receptors are differentially expressed on immature and mature dendritic cells (DC). Herein, we demonstrate for the first time that murine antimicrobial peptides beta-defensins 2 and 3 bind murine CCR6, similarly to inflammatory chemokine macrophage-inflammatory protein 3alpha, and they chemoattract bone marrow-derived immature, but not mature DC. Using various chemokines or defensins fused with nonimmunogenic tumor Ags, we studied their capacity to delivery Ags to subsets of immune cells to elicit antitumor immunity. We demonstrate that DNA immunizations with fusion constructs with beta-defensin 2 or inflammatory chemokines that target immature DC, but not homeostatic chemokines secondary lymphoid tissue chemokine, CCL21, or stromal cell-derived factor 1, CXCL12, which chemoattract mature DC, elicit humoral, protective, and therapeutic immunity against two different syngeneic lymphomas.

Beta amyloid peptide (Abeta42) is internalized via the G-protein-coupled receptor FPRL1 and forms fibrillar aggregates in macrophages

The 42 amino acid form of beta amyloid (Abeta42) plays a pivotal role in neurotoxicity and the activation of mononuclear phagocytes in Alzheimer's disease (AD). Our recent study revealed that FPRL1, a G-protein-coupled receptor, mediates the chemotactic and activating effect of Abeta42 on mononuclear phagocytes (monocytes and microglia), suggesting that FPRL1 may be involved in the proinflammatory responses in AD. We investigated the role of FPRL1 in cellular uptake and the subsequent fibrillar formation of Abeta42 by using fluorescence confocal microscopy. We found that upon incubation with macrophages or HEK293 cells genetically engineered to express FPRL1, Abeta42 associated with FPRL1 and the Abeta42/FPRL1 complexes were rapidly internalized into the cytoplasmic compartment. The maximal internalization of Abeta42/FPRL1 complexes occurred by 30 min after incubation. Removal of free Abeta42 from culture supernatants at 30 min resulted in a progressive recycling of FPRL1 to the cell surface and degradation of the internalized Abeta42. However, persistent exposure of the cells to Abeta42 over 24 h resulted in retention of Abeta42/FPRL1 complexes in the cytoplasmic compartment and the formation of Congo red positive fibrils in macrophages but not in HEK 293 cell transfected with FPRL1. These results suggest that besides mediating the proinflammatory activity of Abeta42, FPRL1 is also involved in the internalization of Abeta42, which culminates in the formation of fibrils only in macrophages.

Cytokines: past, present, and future

This review provides an historical account of the discovery and development of cytokines. Cytokines are soluble extracellular proteins or glycoproteins that are crucial intercellular regulators and mobilizers of cells engaged in innate as well as adaptive inflammatory host defenses, cell growth, differentiation, cell death, angiogenesis, and development and repair processes aimed at the restoration of homeostasis. Although cytokines are occasionally produced constitutively, they are usually produced by virtually every nucleated cell type in response to injurious stimuli. Cytokines act on cells expressing complementary receptors. Cytokines have been assigned to various family groups based on the structural homologies of their receptors. This review shows how cytokine research evolved from phenomenological to molecular stages and from a focus on ligands to characterization of cytokine receptors. The advent of molecular biology, monoclonal antibodies, and microsequencing made it possible to obtain pure recombinant cytokine preparation for experimental and therapeutic applications. The development of targeted gene deletions revealed many cytokines to have unexpected pathophysiological functions. The identification of "virokines," homologues that mimic cytokine ligands and receptors, has provided impetus to the founding of biotechnology companies aimed at developing cytokine agonists and antagonists for therapeutic applications. The discipline of cytokinology is now endowed with several journals, multiple annual meetings, and many devoted investigators. The explosion in cytokine information over the past 40 years has been enormous and full of surprises. If past be prologue, with the advent of genomics and proteomics the future should witness even greater progress.

Eotaxin (CCL11) induces in vivo angiogenic responses by human CCR3+ endothelial cells

Chemokines are attractants and regulators of cell activation. Several CXC family chemokine members induce angiogenesis and promote tumor growth. In contrast, the only CC chemokine, reported to play a direct role in angiogenesis is monocyte-chemotactic protein-1. Here we report that another CC chemokine, eotaxin (also known as CCL11), also induced chemotaxis of human microvascular endothelial cells. CCL11-induced chemotactic responses were comparable with those induced by monocyte-chemotactic protein-1 (CCL2), but lower than those induced by stroma-derived factor-1alpha (CXCL12) and IL-8 (CXCL8). The chemotactic activity was consistent with the expression of CCR3, the receptor for CCL11, on human microvascular endothelial cells and was inhibited by mAbs to either human CCL11 or human CCR3. CCL11 also induced the formation of blood vessels in vivo as assessed by the chick chorioallantoic membrane and Matrigel plug assays. The angiogenic response induced by CCL11 was about one-half of that induced by basic fibroblast factor, and it was accompanied by an inflammatory infiltrate, which consisted predominantly of eosinophils. Because the rat aortic sprouting assay, which is not infiltrated by eosinophils, yielded a positive response to CCL11, this angiogenic response appears to be direct and is not mediated by eosinophil products. This suggests that CCL11 may contribute to angiogenesis in conditions characterized by increased CCL11 production and eosinophil infiltration such as Hodgkin's lymphoma, nasal polyposis, endometriosis, and allergic diathesis.

The role of mammalian antimicrobial peptides and proteins in awakening of innate host defenses and adaptive immunity

Since we live in a dirty environment, we have developed many host defenses to contend with microorganisms. The epithelial lining of our skin, gastrointestinal tract and bronchial tree produces a number of antibacterial peptides, and our phagocytic neutrophils rapidly ingest and enzymatically degrade invading organisms, as well as produce peptides and enzymes with antimicrobial activities. Some of these antimicrobial moieties also appear to alert host cells involved in both innate host defense and adaptive immune responses. The epithelial cells are a source of constitutively produced beta defensin (HBD1) and proinflammatory cytokine-inducible beta defensins (HBD2 and -3) and cathelicidin (LL37). The neutrophils-derived antimicrobial peptides are released on demand from their cytoplasmic granules. They include the enzymes cathepsin G and chymase, azurocidin, a defensins and cathelicidin. In contrast, C5a and C3b are produced by activation of the serum complement cascade. The antimicrobial moieties direct the migration and activate target cells by interacting with selected G-protein-coupled seven-transmembrane receptors (GPCRs) on cell surfaces. The beta defensins interact with the CCR6 chemokine GPCRs, whereas cathelicidins interact with the low-affinity FPRL-1 receptors. The neutrophil-derived cathepsin G acts on the high-affinity FMLP receptor (GPCR) known as FPR, while the receptors for chymase and azurocidin have not been identified as yet. The serum-derived C5a uses a GPCR known as C5aR to mediate its chemotactic and cell-activating effects. Consequently, all these ligand-receptor interactions in addition to mediating chemotaxis also activate receptor-expressing cells to produce other mediators of inflammation.

Participation of mammalian defensins and cathelicidins in anti-microbial immunity: receptors and activities of human defensins and cathelicidin (LL-37)

Defensins and cathelicidins are the two major families of mammalian anti-microbial proteins. They contribute to host, innate, anti-microbial defense by disrupting the integrity of the bacterial cell membrane. However, several members of the mammalian anti-microbial proteins including defensins and cathelicidins have been shown recently to have chemotactic effects on host cells. Human neutrophil alpha-defensins are chemotactic for resting, naïve CD45RA/CD4 T cells, CD8 T cells, and immature dendritic cells. Human beta-defensins are also chemotactic for immature dendritic cells but induce the migration of memory CD45RO/CD4 T cells. In contrast, cathelicidin/LL-37 is chemotactic for neutrophils, monocytes, and T cells but not for dendritic cells. Thus, these anti-microbial peptides have distinct, host-target cell spectra. The chemotactic activities of human beta-defensins and cathelicidin/LL-37 are mediated by human CC chemokine receptor 6 and formyl peptide receptor-like 1, respectively. The capacities of defensins and cathelicidins to mobilize various types of phagocytic leukocytes, immature dendritic cells, and lymphocytes, together with their other effects such as stimulating IL-8 production and mast cell degranulation, provide evidence for their participation in alerting, mobilizing, and amplifying innate and adaptive anti-microbial immunity of the host.

Bidirectional heterologous desensitization of opioid and chemokine receptors

Opioids are known to suppress a number of elements of the immune response, including antimicrobial resistance, antibody production, and delayed-type hypersensitivity. Phagocytic cells may be particularly susceptible to opioid administration, since reduced production of the cytokines IL-1, IL-6 and TNF-alpha, monocyte-mediated phagocytosis, and both neutrophil and monocyte chemotaxis have all been well established. Earlier studies have shown that both mu- and delta-opioid agonists induce a chemotactic response in monocytes and neutrophils. In addition, mu- and delta-opioid administration inhibited the chemotactic response of these cell populations to a number of chemokines through a process of heterologous desensitization. We report here that mu-, delta-, and kappa-opioid agonists also induce a chemotactic response in T lymphocytes. Using the human T-cell line Jurkat, we have confirmed previous observations that pre-incubation with met-enkephalin (MetEnk), an endogenous opioid agonist, prevents the subsequent chemotactic response to the chemokine RANTES. On the other hand, treatment with MetEnk does not alter the response to the chemokine SDF-1 alpha. Moreover, we found that pre-treatment with RANTES prevented a subsequent response of monocytes to the mu-opioid agonist DAMGO. These results suggest that activation of members of the opioid and chemokine receptor families leads to downregulation of each other's leukocyte migratory activities.

The Neutrophil Granule Protein Cathepsin G Activates Murine T Lymphocytes and Upregulates Antigen-Specific Ig Production in Mice

Cathepsin G is a neutrophil granule derived antimicrobial chymotrypsin-like enzyme. Our previous study showed that cathepsin G induces chemotactic migration of human phagocytic leukocytes and increases random migration of T lymphocytes. In this study, we investigated the capacity of cathepsin G to activate T lymphocytes and to modulate antigen-specific humoral responses in mice. We found that cathepsin G is mitogenic for and induces production of IFN-gamma by murine T cells in vitro. Injection of cathepsin G in BALB/c mice immunized with keyhole limpet hemocyanin (KLH) adsorbed to aluminum hydroxide resulted in a significantly increased production of KLH-specific IgG1 and IgG2a antibodies. There was a dose-dependent increase in KLH-specific proliferation of lymphocytes from draining lymph nodes from mice treated with KLH and cathepsin G when compared with those treated with KLH alone. Subsequent analysis of IFN-gamma and IL-4 release following in vitro re-stimulation of draining lymph node lymphocytes obtained from KLH-immunized mice suggested that cathepsin G augments KLH-specific Ig antibody production via activation of T cells, presumably involving both Th1 and Th2 pathways. Thus, neutrophil granule cathepsin G, in addition to its capacity to kill microbes and to enhance leukocyte motility, activates T lymphocytes and modulates humoral immunity.

Differential regulation of formyl peptide receptor-like 1 expression during the differentiation of monocytes to dendritic cells and macrophages

Monocytes are the common precursors for myeloid dendritic cells (DC) and macrophages. Identification of chemotactic receptors expressed by myeloid DC, macrophages, and their precursors in the course of differentiation and maturation is important not only for elucidation of their in vivo trafficking, but also for understanding of the functional distinction between DC and macrophages. We chose to study formyl peptide receptor like-1 (FPRL1), a chemotactic receptor known to interact with several endogenous agonists that are involved in inflammatory and host defense responses. Here we show that FPRL1 is down-regulated as monocytes differentiate into DC. This down-regulation occurs at both mRNA and functional levels. Therefore, the interaction of FPRL1 with its agonists is more likely to regulate the in vivo trafficking of DC precursors than DC. In contrast, FPRL1 expression is maintained at both mRNA and functional levels as monocytes differentiate into macrophages. Thus, our results demonstrate further distinctions between myeloid DC and macrophages, albeit they share a common precursor. The fact that macrophages rather than myeloid DC express functional FPRL1 suggests that this chemotactic receptor may be more involved in inflammatory reactions and innate host defense than in adaptive immune responses.

Pleiotropic roles of formyl peptide receptors

FPR and FPRL1 belong to the seven-transmembrane, G protein-coupled chemoattractant receptor superfamily. Because of their capacity to interact with bacterial chemotactic formylated peptides, these receptors are thought to play a role in host defense against microbial infection. Recently, a variety of novel agonists have been identified for these receptors, including several host-derived endogenous molecules that are involved in proinflammatory responses. Most notably is the use of FPRL1 by at least three amyloidogenic protein and peptide ligands, the serum amyloid A (SAA), the 42 amino acid form of beta amyloid (Abeta(42)), and the prion peptide PrP106-126, to chemoattract and activate human phagocytic leukocytes. These new findings have greatly expanded the functional scope of the formyl peptide receptors and call for more in-depth investigation of the role of these receptors in pathophysiological conditions.

Amyloid (beta)42 activates a G-protein-coupled chemoattractant receptor, FPR-like-1

Amyloid beta (Abeta) is a major contributor to the pathogenesis of Alzheimer's disease (AD). Although Abeta has been reported to be directly neurotoxic, it also causes indirect neuronal damage by activating mononuclear phagocytes (microglia) that accumulate in and around senile plaques. In this study, we show that the 42 amino acid form of beta amyloid peptide, Abeta(42), is a chemotactic agonist for a seven-transmembrane, G-protein-coupled receptor named FPR-Like-1 (FPRL1), which is expressed on human mononuclear phagocytes. Moreover, FPRL1 is expressed at high levels by inflammatory cells infiltrating senile plaques in brain tissues from AD patients. Thus, FPRL1 may mediate inflammation seen in AD and is a potential target for developing therapeutic agents.

Inhibition of RANTES/CCR1-mediated chemotaxis by cosalane and related compounds

The anti-HIV agent cosalane and several of its analogues inhibited RANTES-induced migration of human monocytes, but they did not inhibit migration induced by MIP1alpha or MIP1beta. RANTES-induced migration of single receptor CCRI-HEK transfectants was also inhibited by the cosalanes. Acetylation of the reactive amino groups of RANTES abrogated the inhibitory activity of cosalane. The data suggest that cosalane and its structural analogues may interfere with the RANTES/CCR1 interaction by binding to RANTES.

Characterization of chenodeoxycholic acid as an endogenous antagonist of the G-coupled formyl peptide receptors

OBJECTIVE AND DESIGN

To demonstrate the role of bile acids in immune modulation we examined the ability of select bile acids to inhibit leukocyte migration and chemoattractant receptor function.

MATERIALS

To elucidate this mechanism, we employed primary human monocytes, neutrophils and cell lines transfected to express either the high affinity fMLP receptor (FPR) or the low affinity fMLP receptor like 1 (FPRL1).

TREATMENT

Cells were treated with chenodeoxycholic acid (CDCA) and related bile acids in a 0-400 micromolar range.

METHOD

Cell viability, chemotaxis and calcium flux analysis were preformed.

RESULTS

We observed that pathophysiological levels (< or = 150 micromolar) of CDCA competitively inhibited 3H-fMLP binding to human monocytes, FPR and FPRL1 transfected cells. Additionally, CDCA reduced both the chemotactic and calcium flux responses induced by fMLP or "W" peptide. Further, CDCA inhibited anti-FPR antibody binding to monocytes.

CONCLUSIONS

CDCA selectively inhibited human leukocyte chemotaxis and calcium flux induced by fMLP, but not other chemoattractants, suggesting a mechanism for inhibition of inflammation and suppression of innate immune response.

The structure of human beta-defensin-2 shows evidence of higher order oligomerization

Defensins are small cationic peptides that are crucial components of innate immunity, serving as both antimicrobial agents and chemoattractant molecules. The specific mechanism of antimicrobial activity involves permeabilization of bacterial membranes. It has been postulated that individual monomers oligomerize to form a pore through anionic membranes, although the evidence is only indirect. Here, we report two high resolution x-ray structures of human beta-defensin-2 (hBD2). The phases were experimentally determined by the multiwavelength anomalous diffraction method, utilizing a novel, rapid method of derivatization with halide ions. Although the shape and charge distribution of the monomer are similar to those of other defensins, an additional alpha-helical region makes this protein topologically distinct from the mammalian alpha- and beta-defensin structures reported previously. hBD2 forms dimers topologically distinct from that of human neutrophil peptide-3. The quaternary octameric arrangement of hBD2 is conserved in two crystal forms. These structures provide the first detailed description of dimerization of beta-defensins, and we postulate that the mode of dimerization of hBD2 is representative of other beta-defensins. The structural and electrostatic properties of the hBD2 octamer support an electrostatic charge-based mechanism of membrane permeabilization by beta-defensins, rather than a mechanism based on formation of bilayer-spanning pores.

Down-regulation of the chemokine receptor CCR5 by activation of chemotactic formyl peptide receptor in human monocytes

Interactions between cell surface receptors are important regulatory elements in the complex host responses to infections. In this study, it is shown that a classic chemotactic factor, the bacterial chemotactic peptide N-formyl-methionyl-leucylphenyl-alanine (fMLF), rapidly induced a protein-kinase-C-mediated serine phosphorylation and down-regulation of the chemokine receptor CCR5, which serves as a major human immunodeficiency virus (HIV)-1 coreceptor. The fMLF binding to its receptor, formyl peptide receptor (FPR), resulted in significant attenuation of cell responses to CCR5 ligands and in inhibition of HIV-1-envelope-glycoprotein-mediated fusion and infection of cells expressing CD4, CCR5, and FPR. The finding that the expression and function of CCR5 can be regulated by peptides that use an unrelated receptor may provide a novel approach to the design of anti-inflamatory and antiretroviral agents. (Blood. 2000;96:2887-2894)

LL-37, the neutrophil granule- and epithelial cell-derived cathelicidin, utilizes formyl peptide receptor-like 1 (FPRL1) as a receptor to chemoattract human peripheral blood neutrophils, monocytes, and T cells

We have previously shown that antimicrobial peptides like defensins have the capacity to mobilize leukocytes in host defense. LL-37 is the cleaved antimicrobial 37-residue, COOH-terminal peptide of hCAP18 (human cationic antimicrobial protein with a molecular size of 18 kD), the only identified member in humans of a family of proteins called cathelicidins. LL-37/hCAP18 is produced by neutrophils and various epithelial cells. Here we report that LL-37 is chemotactic for, and can induce Ca(2+) mobilization in, human monocytes and formyl peptide receptor-like 1 (FPRL1)-transfected human embryonic kidney 293 cells. LL-37-induced Ca(2+) mobilization in monocytes can also be cross-desensitized by an FPRL1-specific agonist. Furthermore, LL-37 is also chemotactic for human neutrophils and T lymphocytes that are known to express FPRL1. Our results suggest that, in addition to its microbicidal activity, LL-37 may contribute to innate and adaptive immunity by recruiting neutrophils, monocytes, and T cells to sites of microbial invasion by interacting with FPRL1.

Leukocyte granule proteins mobilize innate host defenses and adaptive immune responses

"... It is likely that the leukocyte granulations are in fact secretory products, which the cell dissolves and spreads to the environment as needed", Paul Ehrlich, 1900. Neutrophil granules have long been recognized as mediators of innate host defense. Newly discovered functions for individual granule proteins suggest that granule constituents may also participate in adaptive immune responses. Neutrophil granule-derived cathepsin G, azurocidin/CAP37 and alpha-defensins have been shown to be chemotactic for mononuclear cells and neutrophils. Analysis of the chemotactic activity of alpha-defensins shows that they induce CD45RA+ and CD8 T-lymphocyte cell migration at concentrations 10 to 100-fold below that required for direct bactericidal activity. Additionally, alpha and beta defensins form chemotactic gradients for immature dendritic cells. Recruiting immature dendritic cells to sites of infection is one way for neutrophil granule proteins to initiate adaptive immune responses. Granules found in other leukocytes such as mast cells also contain serine proteases, such as chymase, that are known to chemoattract neutrophils and mononuclear cells. Preliminary evidence suggests that exocytosis of granule-derived products from a variety of leukocytes can mobilize inflammatory cells and immunocytes. Thus, leukocyte granule-derived proteins, more rapidly than chemokines, can mobilize cells that mediate innate host defense and adaptive immunity.

Differential expression and responsiveness of chemokine receptors (CXCR1-3) by human microvascular endothelial cells and umbilical vein endothelial cells

The basis for the angiogenic effects of CXC chemokines such as interleukin 8 (IL-8) and for angiostatic chemokines such as interferon-inducible protein 10 (IP-10) has been difficult to assess. We recently reported, based on an RNase protection assay, that human umbilical vein endothelial cells (HUVECs) did not express detectable mRNA for the IL-8 receptors CXCR1 and CXCR2. This raised the possibility of heterogeneity of receptor expression by different endothelial cell (ECs) types. Since systemic angiogenesis induced by IL-8 would more likely involve microvessel ECs, we investigated CXC receptor expression on human microvascular dermal endothelial cells (HMECs). By confocal microscopy and immunofluorescence we observed that HMECs consistently expressed high levels of CXCR1 and CXCR4 (mean fluorescence intensity of 261+/-22.1 and 306.2+/-19, respectively) and intermediate levels of CXCR3 and CXCR2 (173.9+/-30. 2 and 156+/-30.9, respectively). In contrast, only a small proportion of HUVEC preparations expressed low levels of CXCR1, -2, and -3 (66+/-19.9; 49+/-15, and 81.4+/-17.9, respectively). However, both HMECs and HUVECs expressed equal levels of CXCR4. As expected, HMECs had more potent chemotactic responses to IL-8 than HUVECs, and this was correlated with the levels of IL-8 receptors on the ECs. Antibodies to CXCR1 and CXCR2 each had inhibitory effects on chemotaxis of HMECs to IL-8, indicating that both IL-8 receptors contributed to the migratory response of these cells toward IL-8. Assessment of the functional capacity of CXCR3 unexpectedly revealed that HMECs migrated in response to relatively higher concentrations (100-500 ng/ml) of each of the 'angiostatic' chemokines IP-10, ITAC, and MIG. Despite this, the 'angiostatic' chemokines inhibited the chemotactic response of HMECs to IL-8. IL-8 and SDF-1alpha but not IP-10 induced calcium mobilization in adherent ECs, suggesting that signaling events associated with calcium mobilization are separable from those required for chemotaxis. Taken together, our data indicated that functional differences among EC types is dependent on the level of the expression of CXC chemokine receptors. Whether this heterogeneity in receptor expression by ECs reflects distinct differentiation pathways remains to be established.

Novel pathophysiological role of classical chemotactic peptide receptors and their communications with chemokine receptors

The bacterial N-formylpeptides, such as N-formyl-Met-Leu-Phe (fMLF), are some of the first identified and most potent chemoattractants for phagocytic leukocytes. Two fMLF receptors, the high affinity formyl peptide receptor (FPR) and its low affinity variant FPR-like 1 (FPRL1), belong to the seven-transmembrane, Gi protein-coupled receptor superfamily which also includes chemokine receptors. Despite their reaction with bacterial chemotactic peptides, the physiological role of these receptors in humans remains unclear. Our recent studies have identified novel exogenous as well as host-derived agonists for FPR and FPRL1. Furthermore, activation of these receptors by their agonists results in desensitization of the receptors for other chemoattractants, including two chemokine receptors, CCR5 and CXCR4, which serve as major co-receptors for HIV-1. These results suggest that FPR and FPRL1 may play important roles not only in host defense and immunological responses but also in the fine tuning of cell activation in the presence of multiple stimuli.

Differential regulation of responsiveness to fMLP and C5a upon dendritic cell maturation: correlation with receptor expression

The trafficking of immature and mature dendritic cells (DCs) to different anatomical sites in vivo is critical for fulfilling their roles in the induction of Ag-specific immune responses. Although this process is complex and regulated by many mediators, the capacity of DCs to migrate is predominantly dependent on the expression of particular chemotactic receptors on the surface of DCs that enable them to move along chemotactic gradients formed by the corresponding chemokines and/or classical chemoattractants. Here we show that immature DCs (iDCs) respond to both fMLP and C5a as determined by chemotaxis and Ca2+ mobilization, whereas mature DCs (mDCs) respond to C5a, but not fMLP. Additionally, iDCs express the receptors for both fMLP and C5a at mRNA and protein levels. Upon maturation of DCs, fMLP receptor expression is almost completely absent, whereas C5a receptor mRNA and protein expression is maintained. Concomitantly, mDCs migrate chemotactically and mobilize intracellular Ca2+ in response to C5a, but not fMLP. Thus the interaction between C5a and its receptor is likely involved in the regulation of trafficking of both iDCs and mDCs, whereas fMLP mobilizes only iDCs. The differential responsiveness to fMLP and C5a of iDCs and mDCs suggests that they play different roles in the initiation of immune responses.

LEC induces chemotaxis and adhesion by interacting with CCR1 and CCR8

Liver-expressed chemokine (LEC) is an unusually large CC chemokine, which is also known as LMC, HCC-4, NCC-4, and CCL16. Previously, LEC was shown to induce leukocyte migration but the responsible signaling receptors were not characterized. We report chemotaxis and competitive binding studies that show LEC binds to and activates CCR1 and CCR8 transfected HEK-293 cells. LEC induced maximal migration of CCR1 and CCR8 transfected cells at 89.3 nmol/L and cell adhesion at 5.6 nmol/L. The molar concentration of LEC required to induce maximum cell migration is 20- to 200-fold greater than that required for RANTES or I309, respectively. All 3 chemokines induced maximal static adhesion at 5 to 7 nmol/L. A neutralizing polyclonal antibody to LEC was developed to demonstrate that the unusually high concentration of LEC required to induce chemotaxis was a property of LEC and not as a result of an irrelevant protein contamination. This study suggests that LEC may be a more effective inducer of cell adhesion than cell migration.

Human endothelial cells express CCR2 and respond to MCP-1: direct role of MCP-1 in angiogenesis and tumor progression

Although several CXC chemokines have been shown to induce angiogenesis and play roles in tumor growth, to date, no member of the CC chemokine family has been reported to play a direct role in angiogenesis. Here we report that the CC chemokine, monocyte chemotactic protein 1 (MCP-1), induced chemotaxis of human endothelial cells at nanomolar concentrations. This chemotactic response was inhibited by a monoclonal antibody to MCP-1. MCP-1 also induced the formation of blood vessels in vivo as assessed by the chick chorioallantoic membrane and the matrigel plug assays. As expected, the angiogenic response induced by MCP-1 was accompanied by an inflammatory response. With the use of a rat aortic sprouting assay in the absence of leukocytic infiltrates, we ruled out the possibility that the angiogenic effect of MCP-1 depended on leukocyte products. Moreover, the direct effect of MCP-1 on angiogenesis was consistent with the expression of CCR2, the receptor for MCP-1, on endothelial cells. Assessment of supernatant from a human breast carcinoma cell line demonstrated the production of MCP-1. Treatment of immunodeficient mice bearing human breast carcinoma cells with a neutralizing antibody to MCP-1 resulted in significant increases in survival and inhibition of the growth of lung micrometastases. Taken together, our data indicate that MCP-1 can act as a direct mediator of angiogenesis. As a chemokine that is abundantly produced by some tumors, it can also directly contribute to tumor progression. Therefore, therapy employing antagonists of MCP-1 in combination with other inhibitors of angiogenesis may achieve more comprehensive inhibition of tumor growth.

Human neutrophil defensins selectively chemoattract naive T and immature dendritic cells

Defensins, a family of cationic, structurally related, antimicrobial peptides, contribute to host defense by disrupting the cytoplasmic membrane of microbes. Here we show that human neutrophil defensins selectively induce the migration of human CD4+/CD45RA+ naive and CD8+, but not CD4+/CD45RO+ memory, T cells. Moreover, human neutrophil defensins are chemotactic for immature human dendritic cells derived from either CD34+ progenitors or peripheral blood monocytes. Upon maturation induced by treatment with tumor necrosis factor alpha (TNF-alpha), dendritic cells lose their responsiveness to human neutrophil defensins. The chemotactic effect of human neutrophil defensins on both T and dendritic cells is pertussis toxin-sensitive, suggesting that a G(ialpha) protein-coupled receptor is responsible. Human neutrophil defensins are also chemotactic for immature murine dendritic cells. These data suggest that, in addition to their antimicrobial role, human neutrophil defensins also contribute to adaptive immunity by mobilizing T cells and dendritic cells.

Are chemokines essential or secondary participants in allergic responses?

OBJECTIVES

This review will provide a concise and critical overview of the rapidly evolving concepts in chemokine biology with a special relevance to allergic responses. The article is intended for clinicians with little or no expertise in chemokine biology.

DATA SOURCES

A detailed literature search was performed through MEDLINE (PubMed). Those reports considered important and relevant to the topic were critically reviewed and their conclusions included.

RESULTS

Chemokines are a group of structurally related small proteins with a common biological activity of inducing directional migration (chemotaxis) of various cell types. Chemokines such as eotaxins and MCP-4 play a key role in selective eosinophil recruitment to sites of inflammation in allergies and asthma. Several other chemokine activities relevant to allergic responses are: activation of basophils and eosinophils to release inflammatory mediators, regulation of IgE responses, and Th1/Th2-type cytokine balance. A number of therapeutic strategies aimed at inhibiting chemokine function are being tested in animal models of allergies and asthma.

CONCLUSIONS

Chemokines have been widely viewed as pathogenic mediators of acute and chronic inflammation and tissue damage in allergies and asthma. On the other hand, recent evidence suggests that endogenous production of certain chemokines might be beneficial to the host in preventing allergic response. Met-RANTES, a modified antagonist of RANTES, and eotaxin receptor (CCR3) antagonists, represent promising novel therapeutic agents potentially useful in atopic disorders. Thus, suppression of chemokines may interrupt the sequence of signals culminating in an allergic response. Whether chemokines are actually essential for an allergic response awaits confirmation with gene knockout animal experiments.

Defensins act as potent adjuvants that promote cellular and humoral immune responses in mice to a lymphoma idiotype and carrier antigens

Defensins released by neutrophils are able to kill a broad spectrum of microbes. They also induce leukocyte migration in vitro and elicit inflammatory leukocyte responses at s.c. injection sites in mice. In vitro experiments showed that human defensins enhanced concanavalin A-stimulated murine spleen cell proliferation and IFN-gamma production. This led us to examine the effects of human defensins on specific immune responses in vivo. BALB/c mice were immunized with 50 microg of keyhole limpet hemocyanin (KLH) adsorbed to aluminum hydroxide and administered with defensins in aqueous solution. Intraperitoneal administration of defensins significantly increased the production of KLH-specific IgG1, IgG2a and IgG2b antibodies 14 days after immunization. In vitro splenic KLH-specific proliferative responses were higher in mice treated with KLH and defensins than in those treated with KLH alone. Increased IFN-gamma and, to a lesser extent, IL-4 production were also detected in the supernatants of ex vivoKLH-activated spleen cells from mice treated with defensins. Finally, defensins significantly enhanced the antibody response to a syngeneic tumor antigen, lymphoma Ig idiotype and also augmented resistance to tumor challenge. These results indicate that defensins act as potent immune adjuvants by inducing the production of lymphokines, which promote T cell-dependent cellular immunity and antigen-specific Ig production. Thus, defensins appear to function as neutrophil-derived signals that promote adaptive immune responses.

International union of pharmacology. XXII. Nomenclature for chemokine receptors

Chemokine receptors comprise a large family of seven transmembrane domain G protein-coupled receptors differentially expressed in diverse cell types. Biological activities have been most clearly defined in leukocytes, where chemokines coordinate development, differentiation, anatomic distribution, trafficking, and effector functions and thereby regulate innate and adaptive immune responses. Pharmacological analysis of chemokine receptors is at an early stage of development. Disease indications have been established in human immunodeficiency virus/acquired immune deficiency syndrome and in Plasmodium vivax malaria, due to exploitation of CCR5 and Duffy, respectively, by the pathogen for cell entry. Additional indications are emerging among inflammatory and immunologically mediated diseases, but selection of targets in this area still remains somewhat speculative. Small molecule antagonists with nanomolar affinity have been reported for 7 of the 18 known chemokine receptors but have not yet been studied in clinical trials. Virally encoded chemokine receptors, as well as chemokine agonists and antagonists, and chemokine scavengers have been identified in medically important poxviruses and herpesviruses, again underscoring the importance of the chemokine system in microbial pathogenesis and possibly identifying specific strategies for modulating chemokine action therapeutically. The purpose of this review is to update current concepts of the biology and pharmacology of the chemokine system, to summarize key information about each chemokine receptor, and to describe a widely accepted receptor nomenclature system, ratified by the International Union of Pharmacology, that is facilitating clear communication in this area.

Beta-defensins: linking innate and adaptive immunity through dendritic and T cell CCR6

Defensins contribute to host defense by disrupting the cytoplasmic membrane of microorganisms. This report shows that human beta-defensins are also chemotactic for immature dendritic cells and memory T cells. Human beta-defensin was selectively chemotactic for cells stably transfected to express human CCR6, a chemokine receptor preferentially expressed by immature dendritic cells and memory T cells. The beta-defensin-induced chemotaxis was sensitive to pertussis toxin and inhibited by antibodies to CCR6. The binding of iodinated LARC, the chemokine ligand for CCR6, to CCR6-transfected cells was competitively displaced by beta-defensin. Thus, beta-defensins may promote adaptive immune responses by recruiting dendritic and T cells to the site of microbial invasion through interaction with CCR6.

Chemokines as molecular targets for therapeutic intervention

Despite the youth of the chemokine field, many antagonists of chemokine function have already been identified and tested at the preclinical level. These include neutralizing antibodies, peptidyl and non-peptidyl antagonists and non-specific immunosuppressive agents. These early studies suggest that chemokine agonists have the potential to regulate many diseases, ranging from HIV-1 infection and tumor growth to acute and chronic inflammation. Clinical application will depend on pharmaceutical development. Great strides have been made in defining structural domains of the chemokines involved in receptor binding and activation. The identification of receptors is rapidly progressing, but with 50 potential ligands and 15 characterized receptors, it is obvious that additional molecular studies are needed. The intriguing observation that several pathogens either use chemokine receptors as entry portals or produce chemokine decoys to subvert the immune system suggests that there is much to be learned about the immune system from studies of "virokines." Future studies should lead to the discovery and design of more effective inhibitors and antagonists with therapeutic benefit.

Cutting edge: immature dendritic cells generated from monocytes in the presence of TGF-beta 1 express functional C-C chemokine receptor 6

Although CD34+ progenitor-derived immature dendritic cells (DCs) express CCR6, several recent studies reported that monocyte-derived immature DCs do not do so. We observed that DCs generated from monocytes in the presence of GM-CSF, IL-4, and TGF-beta 1 consistently responded to liver and activation-regulated chemokine (LARC, also known as macrophage inflammatory protein-3 alpha). These immature DCs expressed one class of high-affinity binding sites for LARC, and expressed both CCR6 mRNA and protein. Therefore, LARC-CCR6 interaction presumably also contributes to the regulation of trafficking of monocyte-derived DCs, and utilization of TGF-beta can potentially provide a ready source of CCR6+ monocyte-derived DCs for therapeutic purposes.

Reduced risk of AIDS lymphoma in individuals heterozygous for the CCR5-delta32 mutation

Non-Hodgkin's lymphoma (NHL) has been increasing in frequency in the industrialized world, but the environmental and genetic factors that contribute to susceptibility are not known. B-cell lymphomas represent a major cause of morbidity and mortality in HIV-infected individuals. The identification of a deletion in the CCR5 chemokine receptor gene that alters the risk for infection and progression to AIDS led us to examine a potential role of this gene in AIDS lymphoma. A matched case-control analysis was performed using all eligible NHL cases in the Multicenter AIDS Cohort Study. Patients were matched for age, study center, time AIDS-free, and slope of the CD4+ T-cell decline. The CCR5-delta32 allele was found to be associated with a 3-fold lower risk of NHL among individuals after controlling for time of infection and progression toward AIDS. The CCR5 gene was not associated with a difference in risk for Kaposi's sarcoma, another common malignancy in AIDS patients, or opportunistic infections. Costimulation of normal phorbol 12-myristate 13-acetate-treated B cells with the CCR5 ligand RANTES induced a proliferative response, indicating that RANTES is a mitogen for B cells. Taken together, these findings suggest that the CCR5 gene plays a role in the risk of NHL in HIV-infected patients, perhaps through a mechanism involving a decreased response of B cells to the mitogenic activity of RANTES.

New insights into the biology of the acute phase response

Innate or natural immunity is a highly conserved defense mechanism against infection found in all multicellular organisms. The acute phase response is the set of immediate inflammatory responses initiated by pattern recognition molecules. These germ cell-encoded proteins recognize microbial pathogens based on shared molecular structures and induce host responses that localize the spread of infection and enhance systemic resistance to infection. Innate immunity also influences the initiation and type of adaptive immune response by regulating T cell costimulatory activity and antigen presentation by antigen presenting cells and by influencing mediator production, which affects lymphocyte function and trafficking. Acute phase protein concentrations rapidly increase after infection, and their production is controlled primarily by IL-6- and IL-1-type cytokines. The acute phase proteins provide enhanced protection against microorganisms and modify inflammatory responses by effects on cell trafficking and mediator release. For example, serum amyloid A has potent leukocyte activating functions including induction of chemotaxis, enhancement of leukocyte adhesion to endothelial cells, and increased phagocytosis. The constellation of inflammatory responses seen after endotoxin administration to humans represents an in vivo model of the acute phase response. Studies with inflammatory modifying agents, such as soluble dimeric TNF receptor and IL-10, show that these responses are not dependent on a single mediator but result from multiple overlapping inflammatory pathways. Understanding the factors that initiate and alter the magnitude and duration of the acute phase response represents an important step in the development of new therapies for infectious and inflammatory diseases.

Inhibition of tyrosine kinase activation blocks the down-regulation of CXC chemokine receptor 4 by HIV-1 gp120 in CD4+ T cells

Because the binding of HIV-1 envelope to CD4 initiates a configurational change in glycoprotein 120 (gp120), enabling it to interact with fusion coreceptors, we investigated how this process interferes with the expression and function of CXC chemokine receptor 4 (CXCR4) in CD4+ T lymphocytes. A recombinant gp120 (MN), after preincubation with CD4+ T lymphocytes, significantly inhibited the binding and chemotaxis of the cells in response to the CXCR4 ligand stromal cell-derived factor-1alpha (SDF-1alpha), accompanied by a markedly reduced surface expression of CXCR4. gp120, but not SDF-1alpha, induced rapid tyrosine phosphorylation of src-like kinase p56lck in CD4+ T cells, whereas both gp120 and SDF-1alpha caused phosphorylation of the CXCR4. The tyrosine kinase inhibitor herbimycin A abolished the phosphorylation of p56lck and CXCR4 induced by gp120 in association with maintenance of normal expression of cell surface CXCR4 and a migratory response to SDF-1alpha. Thus, a CD4-associated signaling molecule(s) including p56lck is activated by gp120 and is required for the down-regulation of CXCR4.

Thioredoxin, a redox enzyme released in infection and inflammation, is a unique chemoattractant for neutrophils, monocytes, and T cells

Thioredoxin (Trx) is a ubiquitous intracellular protein disulfide oxidoreductase with a CXXC active site that can be released by various cell types upon activation. We show here that Trx is chemotactic for monocytes, polymorphonuclear leukocytes, and T lymphocytes, both in vitro in the standard micro Boyden chamber migration assay and in vivo in the mouse air pouch model. The potency of the chemotactic action of Trx for all leukocyte populations is in the nanomolar range, comparable with that of known chemokines. However, Trx does not increase intracellular Ca2+ and its activity is not inhibited by pertussis toxin. Thus, the chemotactic action of Trx differs from that of known chemokines in that it is G protein independent. Mutation of the active site cysteines resulted in loss of chemotactic activity, suggesting that the latter is mediated by the enzyme activity of Trx. Trx also accounted for part of the chemotactic activity released by human T lymphotropic virus (HTLV)-1-infected cells, which was inhibited by incubation with anti-Trx antibody. Since Trx production is induced by oxidants, it represents a link between oxidative stress and inflammation that is of particular interest because circulating Trx levels are elevated in inflammatory diseases and HIV infection.

Naturally occurring CCR5 extracellular and transmembrane domain variants affect HIV-1 Co-receptor and ligand binding function

Analysis of CCR5 variants in human immunodeficiency virus, type 1 (HIV-1), high risk cohorts led to the identification of multiple single amino acid substitutions in the amino-terminal third of the HIV-1 co-receptor CCR5 suggesting the possibility of protective and permissive genotypes; unfortunately, the low frequency of these mutations did not led to correlation with function. Therefore, we used analytical methods to assess the functional and structural significance of six of these variant receptors in vitro. These studies showed three categories of effects on CCR5 function. 1) Mutations in the first extracellular domain of CCR5 severely reduce specific ligand binding and chemokine-induced chemotaxis. 2) An extracellular domain variant, A29S, when co-expressed with CD4, supported HIV-1 infection whereas the others do not. 3) The transmembrane region variants of CCR5 support monotropic HIV-1 infection that is blocked by addition of some receptor agonists. Mutations in the first and second transmembrane domains increase RANTES (regulated on activation normal T-cell expressed) binding affinity but did not affect MIP1beta binding affinity presumably based on differences in ligand-receptor interaction sites. Furthermore, the CCR5 transmembrane mutants do not respond to RANTES with the classical bell-shaped chemotactic response curve, suggesting that they are resistant to RANTES-induced desensitization. These data demonstrate that single amino acid changes in the extracellular domains of CCR5 can have profound effects on both HIV-1 co-receptor and specific ligand-induced functions, whereas mutations in the transmembrane domain only affect the response to chemokine ligands.

T20/DP178, an ectodomain peptide of human immunodeficiency virus type 1 gp41, is an activator of human phagocyte N-formyl peptide receptor

Human immunodeficiency virus type 1 (HIV-1) envelope protein gp41 mediates viral fusion with human host cells. The peptide segment T20/DP178, located in the C-terminus of the ectodomain of gp41, interacts with the N-terminal leucine zipper-like domain on gp41 to establish the fusogenic conformation of the virus. Synthetic T20/DP178 peptide is highly efficacious in inhibiting HIV-1 infection in vitro by disrupting the transformation of fusogenic status of viral gp41; thus, it has been proposed for clinical trial. We report that synthetic T20/DP178 is a chemoattractant and activator of human peripheral blood phagocytes but not of T lymphocytes. We further demonstrate that T20/DP178 specifically activates a seven-transmembrane, G-protein-coupled phagocyte receptor for N-formylated chemotactic peptides, formyl peptide receptor (FPR). Moreover, synthetic T20/DP178 analogs lacking N-terminal amino acids acted as FPR antagonists. Our results suggest that gp41 peptides regulate phagocyte function via FPR and identify a novel mechanism by which HIV-1 may modulate innate immunity.

T21/DP107, A synthetic leucine zipper-like domain of the HIV-1 envelope gp41, attracts and activates human phagocytes by using G-protein-coupled formyl peptide receptors

A leucine zipper-like domain, T21/DP107, located in the amino terminus of the ectodomain of gp41, is crucial to the formation of fusogenic configuration of the HIV-1 envelope protein gp41. We report that the synthetic T21/DP107 segment is a potent stimulant of migration and calcium mobilization in human monocytes and neutrophils. The activity of T21/DP107 on phagocytes was pertussis toxin-sensitive, suggesting this peptide uses Gi-coupled seven-transmembrane receptor(s). Since the bacterial chemotactic peptide fMLP partially desensitized the calcium-mobilizing activity of T21/DP107 in phagocytes, we postulated that T21/DP107 might preferentially use a lower affinity fMLP receptor. By using cells transfected to express cloned prototype chemotactic N-formyl peptide receptor (FPR) or its variant, FPR-like 1 (FPRL1), we demonstrate that T21/DP107 activates both receptors but has a much higher efficacy for FPRL1. In addition, T21/DP107 at nM concentrations induced migration of FPRL1-transfected human embryonic kidney 293 cells. In contrast, fMLP did not induce significant chemotaxis of the same cells at a concentration as high as 50 microM. Although a lipid metabolite, lipoxin A4, was a high-affinity ligand for FPRL1, it was not reported to induce Ca2+ mobilization or chemotaxis in FPRL1-transfected cells. Therefore, T21/DP107 is a first chemotactic peptide agonist identified thus far for FPRL1. Our results suggest that this peptide domain of the HIV-1 gp41 may have the potential to activate host innate immune response by interacting with FPR and FPRL1 on phagocytes.

Symposium overview: alterations in cytokine receptors by xenobiotics

A symposium entitled Alterations in Cytokine Receptors by Xenobiotics was held at the 37th Annual Meeting of the Society of Toxicology (SOT) in Seattle, Washington. The symposium was sponsored by the Immunotoxicology Specialty Section of SOT and was designed to present information on the effect of several different classes of xenobiotics on various aspects of receptor function (i.e., post-receptor signal transduction of receptor expression), or the involvement of cytokine receptors in the action of the toxicant under consideration. This symposium brought together scientists in the area of receptor immunobiology whose expertise in receptor modulation encompassed those major signaling agents involved in the normal immune response, i.e., proinflammatory cytokines, chemokines, interleukins, and interferons. The following is a summary of each of the individual presentations.

Vascular endothelial growth factor and basic fibroblast growth factor induce expression of CXCR4 on human endothelial cells: In vivo neovascularization induced by stromal-derived factor-1alpha

The contribution of chemokines toward angiogenesis is currently a focus of intensive investigation. Certain members of the CXC chemokine family can induce bovine capillary endothelial cell migration in vitro and corneal angiogenesis in vivo, and apparently act via binding to their receptors CXCR1 and CXCR2. We used an RNAse protection assay that permitted the simultaneous detection of mRNA for various CXC chemokine receptors in resting human umbilical vein endothelial cells (HUVECs) and detected low levels of only CXCR4 mRNA. Stimulation of HUVECs with vascular endothelial growth factor (VEGF) or basic fibroblast growth factor (bFGF) up-regulated levels of only CXCR4 mRNA. CXCR4 specifically binds the chemokine stromal-derived factor-1alpha (SDF-1alpha). Competitive binding studies using 125I-labeled SDF-1alpha with Scatchard analysis indicated that VEGF or bFGF induced an average number of approximately 16,600 CXCR4 molecules per endothelial cell, with a Kd = 1.23 x 10(-9) mol/L. These receptors were functional as HUVECs and human aorta endothelial cells (HAECs) migrated toward SDF-1alpha. Although SDF-1alpha-induced chemotaxis was inhibited by the addition of a neutralizing monoclonal CXCR4 antibody, endothelial chemotaxis toward VEGF was not altered; therefore, the angiogenic effect of VEGF is independent of SDF-1alpha. Furthermore, subcutaneous SDF-1alpha injections into mice induced formation of local small blood vessels that was accompanied by leukocytic infiltrates. To test whether these effects were dependent on circulating leukocytes, we successfully obtained SDF-1alpha-induced neovascularization from cross sections of leukocyte-free rat aorta. Taken together, our data indicate that SDF-1alpha acts as a potent chemoattractant for endothelial cells of different origins bearing CXCR4 and is a participant in angiogenesis that is regulated at the receptor level by VEGF and bFGF.

Mechanisms for induction of acquired host immunity by neutrophil peptide defensins

Human neutrophil peptide (HNP) defensins were studied to determine their potential effects on adaptive mucosal immunity. Intranasal delivery of HNPs plus ovalbumin (OVA) enhanced OVA-specific serum IgG antibody (Ab) responses. However, OVA-specific IgA Abs were not induced in mucosal secretions or in serum. CD4(+) T cells of intranasally immunized mice displayed higher OVA-specific proliferative responses and elevated production of interferon gamma, interleukin (IL) 5, IL-6, and IL-10 when compared with control groups receiving OVA alone. In vitro, HNPs also enhanced both proliferative responses and T helper (Th) cytokine secretion profiles of CD3epsilon-stimulated spleen- and Peyer's patch-derived naive CD4(+) T cells. HNPs modulated the expression of costimulatory molecules by lipopolysaccharide- or CD3epsilon-stimulated splenic and Peyer's patch B or T cell populations, respectively. These studies show that defensins enhance systemic IgG, but not IgA, Ab responses through help provided by CD4(+) Th1- and Th2-type cytokines and foster B and T cell interactions to link innate immunity with the adaptive immune system.

A seven-transmembrane, G protein-coupled receptor, FPRL1, mediates the chemotactic activity of serum amyloid A for human phagocytic cells

We have previously reported (Badolato, R., J.M. Wang, W.J. Murphy, A. R. Lloyd, D.F. Michiel, L.L. Bausserman, D.J. Kelvin, and J.J. Oppenheim. 1994. J. Exp. Med. 180:203; Xu, L., R. Badolato, W.J. Murphy, D.L. Longo, M. Anver, S. Hale, J.J. Oppenheim, and J.M. Wang. 1995. J. Immunol. 155:1184.) that the acute phase protein serum amyloid A (SAA) is a potent chemoattractant for human leukocytes in vitro and mouse phagocytes in vivo. To identify the signaling mechanisms, we evaluated patterns of cross-desensitization between SAA and other leukocyte chemoattractants. We found that the chemotactic bacterial peptide, N-formyl- methionyl-leucyl-phenylalanine (fMLP), was able to specifically attenuate Ca2+ mobilization in human phagocytes induced by SAA, but only at very high concentrations, suggesting that SAA uses a low affinity fMLP receptor. Here we demonstrate that SAA selectively induced Ca2+ mobilization and migration of HEK cells expressing FPRL1, a human seven-transmembrane domain phagocyte receptor with low affinity for fMLP, and high affinity for lipoxin A4. Furthermore, radiolabeled SAA specifically bound to human phagocytes and FPRL1-transfected 293 cells. In contrast, SAA was not a ligand or agonist for FPR, the high affinity fMLP receptor. Thus, SAA is the first chemotactic ligand identified for FPRL1. Our results suggest that FPRL1 mediates phagocyte migration in response to SAA.