The introduction of flow cytometric bead-based technology has added a new approach for investigators to simultaneously measure multiple analytes in biological and environmental samples. This new technology allows for (1) evaluation of multiple analytes in a single sample; (2) utilization of minimal sample volumes to glean data; (3) reproducibility and results comparative with previous experiments; (4) direct comparison with existing assays; and (5) a more rapid evaluation of multiple samples in a single platform. The cytometric bead array (CBA) system enables simultaneous measurement of multiple analytes in sample volumes too small for traditional immunoassays. Results have been presented for the analysis of a variety of human cytokines. In addition, the technology allows for the design and creation of assays to measure a variety of analytes including inflammatory mediators, chemokines, immunoglobulin isotypes, intracellular signaling molecules, apoptotic mediators, adhesion molecules, and antibodies. New initiatives put forward by the Human Genome Project and the FDA require the development and use of assays for the rapid simultaneous quantitation of multiple analytes. The CBA technology provides the ability to quantify multiple proteins within a given sample, with precision and consistency.

To study human neutrophil (polymorphonuclear leukocyte (PMN)) migration and killing of bacteria in an environment similar to that found in inflamed tissues in vivo, we have used fibrin gels. Fibrin gels (1500 μm thick) containing Staphylococcus epidermidis were formed in Boyden-type chemotaxis chambers. PMN migrated <300 μm into these gels in 6 h and did not kill S. epidermidis when the gels contained heat-inactivated serum, C5-deficient serum, a streptococcal peptidase specific for a fragment of cleaved C5 (C5a), or anti-C5aR IgG. In contrast, in gels containing normal human serum, PMN migrated ∼1000 μm into the gels in 4 h and into the full thickness of the gels in 6 h, and killed 90% of S. epidermidis in 6 h. fMLP reduced PMN migration into fibrin gels and allowed S. epidermidis to increase by ∼300% in 4 h, whereas leukotriene B4 stimulated PMN to migrate the full thickness of the gels and to kill 80% of S. epidermidis in 4 h. We conclude that both complement opsonization and C5a-stimulated chemotaxis are required for PMN bacterial killing in fibrin gels, and that fMLP inhibits PMN bactericidal activity in fibrin gels. The latter finding is surprising and suggests that in the presence of fibrin fMLP promotes bacterial virulence.

1 The rabbit receptor for C5a was cloned from a genomic library and found to be 79.5% identical to the human homologue, the highest degree of similarity found so far in nonprimate laboratory animals. 2 The rabbit C5a receptor stably expressed in RBL cells binds human 125I-C5a (2 nM). Unlabelled C5a and the C-terminal analogue N-acetyl-Tyr-Ser-Phe-Lys-Pro-Met-Pro-Leu-D-Ala-Arg (Ac-YSFKPMPLaR) were found to be competitors of that binding, the peptide analogue retaining approximately 0.1% of the affinity of human C5a. 3 The order of potency human C5a>Ac-YSFKPMPLaR was conserved in bioassays based on rabbits (relaxation of the isolated portal vein and pulmonary artery; acute in vivo neutropenia), but with a decreasing potency gap between the two compounds, a likely consequence of the resistance to peptidases of the analogue. 4 The molecular definition of the rabbit C5a receptor evidenced a high preservation degree of sequence and pharmacologic properties relative to the human ortholog receptor, thus defining a set of molecular tools for the investigation of the role of C5a in physiologic and pathologic models based on the rabbit (e.g. atherosclerosis, inflammation).

The mouse anaphylatoxin C3a receptor (mC3aR) gene was isolated using a human C3aR cDNA probe. The genomic fragment contains an open reading frame of 1431 base pairs that encodes a peptide of 477 amino acids. A cDNA with identical sequence was subsequently obtained from the mouse pre-B cell line 70Z/3 by reverse transcriptase polymerase chain reaction based on sequence of the mC3aR gene. Northern blot analysis suggested expression of the mC3aR in lung and heart, and to a lesser extent, in brain, liver, muscle, kidney, and testis. The deduced amino acid sequence of the mouse C3aR is 65% identical to that of the human C3aR. Like the human receptor, mouse C3aR contains a predicted large extracellular loop of ∼165 amino acids (residues 161–325) between the fourth and fifth transmembrane domains. This loop, however, is the least conserved structure (45% identical sequence) of all the extracellular and intracellular domains between the mouse and human C3aRs. The mouse gene product bound 125I-labeled human C3a with a Kd of 2.54 nM when expressed in the stably transfected rat basophilic leukemic cell line RBL-2H3. Bound C3a could be effectively displaced by excess quantities of unlabeled C3a, but not by C4a or C5a. C3a induced dose-dependent calcium mobilization in the transfected cells, which could be blocked by pertussis toxin treatment. These results confirm that the cloned gene encodes a functional C3aR capable of coupling to a pertussis toxin-sensitive G protein. The sequence divergence of the large extracellular loop does not appear to affect C3a binding and transmembrane signaling.

We have used high-resolution field emission scanning electron microscopy with backscatter electron imaging to detect immunogold-labeled C5a and interleukin-8 (IL-8) receptors on human blood neutrophils. The receptors were labeled with receptor-specific antibodies in combination with secondary antibody conjugated to immunogold. When neutrophils were isolated in a “nonactivated” state, both of these receptor populations were expressed primarily in clusters on nonprojecting domains of the cell membrane. When these cells were double labeled for C5a and IL-8 receptors, intermixing of these receptor species in a common cluster was not found. When neutrophils were isolated in an “activated” state, by mixing the blood with N-formylmethionyl-leucyl-phenylalanine, the cells were seen to be elongated and ruffled at their anterior pole, but the C5a receptors did not disperse or redistribute on the surface of the peptide-activated cells. Analysis of the distribution of human C5a receptors expressed by transfected mouse L-cell fibroblasts showed the C5a receptors to be clustered, but expressed on nonprojecting and projecting domains of the cell surface. These observations provide new information on the topographical expression of leukocyte receptors involved in directing cell migration. (J Histochem Cytochem 45:1461–1467, 1997)

The anaerobic bacteria P. gingivalis has been implicated as a primary causative agent in adult periodontitis. Several proteinases are produced by this bacteria and it is suggested that they contribute to virulence and to local tissue injury resulting from infection by P. gingivalis. Collagenases and cysteine proteinases (i.e., the gingipains) have been characterized as the predominant vesicular enzymes produced by this bacterium. It has been shown that an arginine-specific cysteine proteinase from P. gingivalis, called gingipain-1 or Arg-gingipain, can selectively cleave complement components C3 and C5. In the case of C5, cleavage by Arg-gingipain results in the generation of C5a, a potent chemotactic factor for PMNs. Since these bacterial proteinases are capable of generating pro-inflammatory factors at sites of infection, we examined the possibility that gingipains or other proteinases from this bacterium might attack or destroy cell surface proteins, such as receptor molecules. Using an affinity-purified rabbit antibody raised against residues 9-29 of the C5a receptor (i.e., C5aR; CD88), the signal transmitting element for the pro-inflammatory mediator C5a, we demonstrated that the mixture of proteinases in P. gingivalis vesicles cleaves the C5a receptor on human neutrophils. This vesicular proteinase activity did not require cysteine activation which indicates that proteinases other than the gingipains may be responsible for cleavage of the C5aR molecule. in addition, the purified Lys-gingipain, but not Arg-gingipain, also cleaved C5aR on the human neutrophils. The N-terminal region of CaR (residues 9-29, PDYGHYDDKDTLDLNTPVDKT) was readily cleaved by chymotrypsin, but not by trypsin, despite the presence of potential trypsin (i.e., lysyl-X) cleavage sites. The specific sites of C5aR 9-29 peptide cleavage were determined by mass spectroscopy for both chymotrypsin and Lys-gingipain. These studies suggest that the proteolytic activity in the bacterial vesicles that is responsible for cleaving C5aR is primarily a non-tryptic proteinase, distance from either Arg- or Lys-gingipain. Consequently, there appear to be additional proteinase(s) in the vesicles that attacks the cell surface molecule C5aR which are not the same (i.e., Arg- and Lys-gingipain) as were shown to generate pro-inflammatory activity from complement components C3 and C5. Evidence that the proteinases which attack the inflammatory precursor molecules (i.e., C3 and C5) exhibit different specificities than those that attack receptors to these bioactive complement products makes a particularly interesting story of how this bacteria avoids major host defense mechanisms. It is well known that generation of pro-inflammatory factors such as C3a and C5a at extra-vascular sites can promote edema, leukocyte recruitment and cellular activation responses that could lead to the release of toxic oxygen products and to phagocytosis of the bacteria. Destruction of receptors to these cellular activating factors generated by bacterial proteinases may eliminate the ability of these (i.e., complement-derived) and other mediators to carry out their anti-bacterial actions and thereby limit the host's defense mechanisms in responses to the infecting bacteria. The concept of anti-bacterial responses (i.e., oxygen radical generation and phagocytosis) being effectively eliminated at the injury site, by bacterial proteinases acting at the cellular receptor level, has not been studied in detail. In this case, the situation is particularly unusual because, once the bacterial gingipains generate potent plasma-derived inflammatory factors that can enhance edema and deliver essential nutrients to the bactgeria, other bacterial proteinases may destsroy their cellular receptors. These receptors transmit the signal activation mechanisms in the infiltrating cells that elicit bacterial killing.(ABSTRACT TRUNCATED)