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J A Ember

Publications and source records attributed to J A Ember.

27 records · Page 2Linked to original sources
PubMed1995

C3a is a chemotaxin for human eosinophils but not for neutrophils. I. C3a stimulation of neutrophils is secondary to eosinophil activation.

Inflammatory action of the potent chemotaxin C5a has been well characterized on a variety of human cell types, including neutrophils, monocytes, basophils, and eosinophils. The cellular effects of C3a are less well defined. Contradictory reports have been published for C3a activation of neutrophils. Recent reports that C3a activates both basophils and eosinophils prompted us to reinvestigate the effects of C3a stimulation on eosinophils. We hypothesized that C3a activation of eosinophils, cells that are present in most neutrophil preparations, might lead to neutrophil activation. Using neutrophils of 98% purity, we observed no evidence of cellular activation after stimulation with either C3a, recombinant human C3a (rhC3a), or the synthetic C3a analogue C3a 57-77, Y57. Eosinophils purified to > 98% purity displayed concentration-dependent polarization, chemotaxis, and enzyme release by stimulation with C3a, rhC3a, and the synthetic C3a analogue. An inactive form of C3a, C3adesArg, failed to stimulate either eosinophils or neutrophils. Using neutrophil preparations containing 5-9% eosinophils, up to 20% of neutrophils became polarized after exposure to C3a. Likewise, we demonstrated that supernatant from C3a-stimulated eosinophils promotes neutrophil chemotaxis. Eosinophil polarization experiments were repeated in the presence of antibody to the C5a receptor (C5aR) to show that C3a and C5a interact with different receptors. C3a activates eosinophils in the presence of anti-C5aR antibody at concentrations that fully block C5a activation. We conclude that eosinophils are directly activated by either C3a or C5a, whereas C3a failed to activate neutrophils. C3a acts on eosinophils via a receptor that is distinct from C5aR. Since neutrophils are indirectly stimulated by C3a, eosinophils contaminating neutrophil preparations may explain earlier reports that C3a activates human neutrophils.

Amino Acid Sequence↗
PubMed1994

Decapeptide agonists of human C5a: the relationship between conformation and spasmogenic and platelet aggregatory activities.

A series of decapeptide analogues corresponding to the C-terminal region of human C5a anaphylatoxin (C5a65-74) was synthesized with residue substitutions to restrict conformational flexibility in the C-terminus. These conformationally constrained peptides behaved as agonists of C5a in spasmogenic assays (smooth muscle contraction in human fetal artery, guinea pig ileum, and guinea pig lung parenchyma) as well as guinea pig platelet aggregation. There were significant correlations in the potencies of these peptides between the various assays. A structure-function analysis led to the identification of a preferred backbone conformation that correlated with the expression of these biological responses. These backbone structural motifs were consistent with a helix-like conformation for residues 65-69, an elongated structure for residues 70-71, and a beta-turn of either type II or type V for residues (71)72-74. The most potent of these agonists expressed almost 5% of the potency of natural C5a.

Amino Acid Sequence↗
PubMed1994

Polymorphonuclear leukocyte behavior in a nonhuman primate focal ischemia model.

There is increasing interest in the role of polymorphonuclear (PMN) leukocytes in the evolution of focal cerebral infarction. Surgical preparation of focal cerebral ischemia models may alter leukocyte reactivity and thereby make interpretation of leukocyte function following ischemia/reperfusion difficult. The effects of surgical preparation and of experimental ischemia/reperfusion on granulocyte function have been examined prospectively in a baboon model. Twenty-six adolescent male baboons underwent surgical preparation, of which 21 underwent middle cerebral artery occlusion/reperfusion. Four additional animals served as nonsurgical controls. Peripheral venous blood specimens were taken for performing assays of leukocyte function at defined intervals before and after both the surgical preparation (i.e., the overall procedure for implantation of the middle cerebral artery occlusion device) and occlusion/reperfusion. A stress-related elevation in total leukocyte number was attributed mainly to an increase in the number of circulating PMN leukocytes. Values rose from 13.9 +/- 4.9 x 10(3) to 27.8 +/- 5.8 x 10(3)/microliters, (+/- SD; n = 21) for total leukocyte number, with p < 0.001, and from 4.3 +/- 2.1 x 10(3) to 15.9 +/- 4.7 x 10(3)/microliters (n = 21) for PMN leukocytes, with p < 0.001. Surgical preparation had no effect (p > or = 0.4) on the ability of PMN leukocytes, isolated 24 h after the implantation procedure, to display polarization, O2.- production, or beta-glucuronidase release when stimulated with human C5a. A moderate decrease in the chemotactic response to C5a resolved within the 7-day postsurgery (preocclusion) period. Three-hour middle cerebral artery occlusion and 1-h reperfusion resulted in a significant reduction in C5a-induced polarization.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Induction of interleukin-8 synthesis from monocytes by human C5a anaphylatoxin.

Interleukin-8 (IL-8) is an important mediator of inflammation and has been shown to be a potent chemotactic/cell activator for polymorphonuclear neutrophils (PMNs). T lymphocytes, and basophils. Cellular sources of IL-8 include monocytes, PMNs, endothelial cells, epithelial cells, and keratinocytes when stimulated by factors such as lipopolysaccharide, IL-1, and tumor necrosis factor-alpha. This report demonstrates that C5a, in addition to being a direct mediator of inflammation, can induce both IL-8 synthesis and high levels of release from monocytes. Natural human C5a and a synthetic C-terminal analogue peptide of C5a each induced IL-8 synthesis and release from CD14+ human peripheral blood mononuclear cells. Antigenic reactivity based on enzyme-linked immunosorbent assay gave evidence that IL-8 was present in the culture supernatants of stimulated peripheral blood mononuclear cells. Proof that supernatant levels of IL-8 attain biologically significant quantities was provided by human PMN chemotaxis assays. The quantity of IL-8 recovered from C5a-activated monocytes in peripheral blood mononuclear cells is up to 1,000-fold greater than that released from comparable numbers of PMNs under similar conditions. Therefore, IL-8 released from C5a-activated monocytes may play a significant role in expanding and prolonging cellular infiltration and activation at sites of infection, inflammation, or tissue injury. This observation suggests an important humoral amplification loop for inflammatory events involving both complement activation and cytokine release.

Antigens, CD↗
PubMed1993

Anti-C5a receptor antibodies. Characterization of neutralizing antibodies specific for a peptide, C5aR-(9-29), derived from the predicted amino-terminal sequence of the human C5a receptor.

Results obtained indicate that a site-directed polyclonal antibody specific for a synthetic peptide based on the predicted amino-terminal sequence of human C5aR (anti-C5aR(9-29)) is capable of binding to both normal human and transfected cells bearing C5aR. Flow cytometric analysis of stable murine L cell transfectants (C5aR-neo), human neutrophils, and human monocytes indicated that these cells bound anti-C5aR(9-29) in a specific manner. Moreover, F(ab')2 fragments of anti-C5aR(9-29) specifically neutralized proinflammatory and immunoregulatory activities induced by natural human C5a. This antiserum was found to block, in a dose-dependent manner, 1) zymosan-induced neutrophil chemotaxis, 2) C5a-induced enzyme release from neutrophils, and 3) C5a-induced cytokine production (IL-6 and IL-8) from human monocytes in vitro. These results suggest that this site-directed polyclonal antiserum specifically interacts with the human C5aR molecule. To the best of our knowledge, none of the existing reports in the literature provided evidence for a site-directed antiserum to C5aR that was capable of specifically blocking C5a-mediated inflammatory/immunoregulatory activities in vitro. Studies conducted with anti-C5aR(9-29) indicated that this antiserum effectively blocked C5a-mediated cell activation but by itself did not activate either neutrophils or monocytes. Combined, these data suggest that this antiserum does not interact with the C5a "effector" site but sterically interferes with C5a binding to its receptor by interacting with the extracellular amino-terminal region of the receptor.

Amino Acid Sequence↗
PubMed1992

Biologic activity of synthetic analogues of C5a anaphylatoxin.

The C activation fragment C5a is the most potent plasma-derived chemotactic factor known. This humoral factor induces both neutrophil and macrophage activation at low nanomolar concentrations. We have synthesized a series of C-terminal C5a analogues that exhibit all of the characteristic biologic activities of C5a. These peptides apparently contain the effector site for C5a receptor-mediated cellular activation, but express only a fraction of the potency of intact C5a. We have demonstrated the following in vitro activities for these C5a peptides: 1) ileal (guinea pig) contraction; 2) platelet (guinea pig) activation; and 3) neutrophil (human) polarization and chemotaxis. The effect of C5a peptides in vivo was evaluated by measuring enhancement in vascular permeability. Although potencies of the most effective synthetic C5a analogues were on the order of 0.01 to 0.1% that of the natural factor, our biologic data confirm that the C5a peptides are full agonists of the intact factor and may be useful substitutes for intact C5a. Furthermore, our results indicate that elongation of the C5a analogues from 10 to 19 residues in length contributes little toward enhancing or decreasing potency of the synthetic C5a analogues. Replacement of residues in the effector region by D-amino acids or by introduction of a cyclic group to reduce flexibility of the backbone decreased potency of the analogues. Substitution of His 67 by Phe in the decapeptide C5a 65-74 resulted in a significant increase in potency of the C5a analogue. The marked enhancement in potency from replacing His 67 by Phe in analogue C5a peptides identifies an important hydrophobic subsite. We conclude that site-specific amino acid modifications in or near the C-terminal effector site sequence can diminish or optimize potency of the model C5a peptides. However, there apparently are subsites on folded C5a, from regions other than the C-terminal portion of the molecule, that contribute significant receptor interactions. These subsites must be identified and incorporated into C5a model peptide designs before expression of full potency by synthetic analogues of this factor will be realized.

Amino Acid Sequence↗
PubMed1991

Designing synthetic superagonists of C3a anaphylatoxin.

An extensive structure-activity study of synthetic analogues of the C3a anaphylatoxin was conducted. Our goal was to map C3a-C3a receptor interactions by designing synthetic analogue molecules having maximal biologic potency. Nonspecific binding of the polycationic C3a to polyanionic molecules on cellular surfaces often obscures specific binding to the receptor. Less cationic synthetic C3a analogues would be useful tools in identifying and characterizing the various cell types having C3a receptors. These factors should also be useful as pharmacologic probes for mechanism studies, as high-affinity ligands for target cell identification, and for receptor isolation. Attachment of amino-terminal hydrophobic groups such as Fmoc to C3a analogues [as orginally introduced by Gerardy-Schahn et al. (1988) Biochem. J. 255, 209] markedly enhanced the potency of synthetic C3a peptides. The enhancement effect on potency from introducing hydrophobic groups to C3a analogues was interpreted as possibly being nonspecific. Our systematic search for an optimal peptide length, composition, and N-terminal hydrophobic unit resulted in several superpotent C3a analogues having 200-1500% the potency of natural C3a. One particularly potent C3a peptide was designed by incorporating two tryptophanyl residues at the N-terminal end of a 15-residue C3a analogue. The superpotent peptide W-W-G-K-K-Y-R-A-S-K-L-G-L-A-R has several residues differing (underlined) from the sequence corresponding to positions 63-77 in human C3a, a region that contains the essential functional site of the molecule. This 15-residue model peptide exhibited the greatest biological potency of all peptides tested, being 12-15 times more active than natural C3a. Since an optimal distance was found to exist between the N-terminal hydrophobic unit (W-W) and the C-terminal primary binding site (LGLAR), we concluded that the hydrophobic unit interacts specifically with a secondary binding site on the C3a receptor. The presence of both a primary (effector) and secondary (hydrophobic) binding site on these linear synthetic ligands, which can interact cooperatively with the C3a receptor, presumably accounts for the high relative potency of the analogues. Our design of superpotent analogues of C3a demonstrates the feasibility for constructing small synthetic peptides to mimic natural biologic factors that depend on secondary or tertiary structure for their activity. These synthetic peptide studies demonstrate that a linear array of amino acids (e.g., W-W) can successfully substitute for a conformation-dependent binding site on a bioactive factor.

Amino Acid Sequence↗
PubMed1989

Characterization of the human neutrophil response to sex pheromones from Streptococcus faecalis.

Synthetic analogs of sex pheromones from Streptococcus faecalis and related pheromone inhibitors have been assayed for their possible effects on human neutrophil leukocyte activation. These sex pheromones are hydrophobic peptides that have regulatory roles in bacterial mating behavior leading to intercellular plasmid transfer. Five of the seven peptides tested were chemotactic for neutrophils in the 10(-5) to 10(-6) M concentration range. Exposure of neutrophils to these same peptides induced polarization of the cells and triggered superoxide production. Cross-desensitization experiments suggest that S. faecalis bacterial peptides act via the fMLF-receptor on neutrophils. This conclusion is supported by the results that leukocyte polarization responses induced by synthetic analogs of S. faecalis sex pheromones can be blocked by t-Boc-FLFLF, a known antagonist of fMLF. It is concluded that inflammatory properties of bacterial supernatants, particularly in the case of S. faecalis strains and perhaps in other bacterial genuses, are contributed in part by nonformylated hydrophobic oligopeptides that recognize and act through the fMLF receptor to activate neutrophils.

Cell Movement↗