Inflammatory mediators released by complement-derived peptides

Complement C4a inhibits the secretion of hepatitis B virus screened by surface-enhanced laser desorption ionization time-flight mass spectrometry-based ProteinChip analysis

PURPOSE

Chronic hepatitis B (CHB) is a kind of chronic liver disease caused by persistent hepatitis B virus (HBV) infection. The study aims to seek the factors of host resistance to HBV and investigate their roles.

EXPERIMENTAL DESIGN

Protein profiles of 58 healthy controls and 121 CHB patients were obtained by SELDI-TOF/MS. Predicted protein was validated by ELISA. Protein expression was evaluated by Western blot in the persistently HBV expressing cell line HepG2.2.15 and non-HBV expressing cell line HepG2. The level of HBV DNA was subsequently detected by quantitative real-time PCR in HepG2.2.15 cells with complement C4a treatment.

RESULTS

Significantly altered protein peaks were found through statistical analysis, and m/z 4300 was predicted by databases and successfully matched with the fragment of complement C4a. According to ELISA, serum complement C4a was found to be significantly lower in CHB patients compared with healthy controls (p < 0.001) and the area under receiver operating characteristics curve is 0.78. Furthermore, complement C4a showed lower expression in HepG2.2.5 cells and the secretion of HBV DNA was inhibited by complement C4a.

CONCLUSIONS AND CLINICAL RELEVANCE

The present study implied the important role of complement C4a in inhibiting the HBV DNA secretion in CHB.

A low molecular weight proinflammatory factor from rat spleen lymphocytes. Isolation and partial characterization

A dialyzable low molecular weight proinflammatory factor (X (2)) from rat spleen lymphocytes was isolated through a combination of gel filtration and high voltage paper electrophoresis (HVE) and then partially characterized. It was able to potentiate the formation of carrageenin induced edema on the rat paw. Its amino acid analysis revealed Glu, Cys and Gly (1:1:1), but gammaGlu as N-terminal residue, initially suggesting oxidized glutathione (GSSG), since it showed exactly the same HV electrophoretic mobility as GSSG at pH 6.5. However, neither GSSG nor a synthetic homologue showed any proinflammatory activity. On basis of its infrared spectrum, HVE mobility and presence of a gamma-Glu-Cys-Gly (GSH) moiety, the hypothesis of identity of X (2) with leukotriene C(4) (LTC(4)) was raised. Once again it was not confirmed, since LTC(4) did not show any proinflammatory activity too, leading us to infer that, even excluding LTC(4), our data are consistent with a structure bearing a GSH moiety conjugated with a hydroxylated insaturated fatty acid chain which contributes a -COO(-) group, thus providing a final net charge of -2 at pH 6.5 and an Mr = 600-650.

Afferent pathways of pyrogen signaling

We and others recently showed that fever induced by intravenously or intraperitoneally injected lipopolysaccharide (LPS) may involve brain signaling via hepatic vagal afferents. This suggests that LPS fever may be initiated by mediators released mainly by cells in the liver, presumably macrophages (Kupffer cells, Kc). To verify this possibility, we disabled the Kc of conscious guinea pigs with gadolinium chloride and monitored their core temperature and associated preoptic prostaglandin E2 (PGE2) responses to i.v. LPS. Gadolinium chloride pretreatment significantly attenuated both the febrile and PGE2 rises, thus supporting the hypothesis. Additionally, fluorescein-labeled LPS was detected in Kc 15 minutes after its i.v. administration. Paradoxically, however, the label was also present in gadolinium chloride-pretreated guinea pigs. Thus, either Kc are not the primary source of pyrogenic mediators or LPS does not provide the stimulus for their production. Because the i.v. injection of LPS elicits virtually immediately the production of complement fragments, and Kc express their receptors and produce various mediators on their activation, we hypocomplemented guinea pigs with cobra venom factor. The core temperature rises produced by i.v. LPS were reduced by complement depletions > 60%. LPS i.v. per se decreased complement, that is, complement was consumed by 12% within 10 minutes. Thus, the onset of LPS fever may involve complement system and Kc activation, but their precise roles await clarification.

ELISA of complement C3a in bronchoalveolar lavage fluid

Activated complement factors within the lung may induce several local biological effects. In order to investigate local complement activation we have developed non-competitive two-site ELISAs of C3a and total C3 in bronchoalveolar lavage fluid (BALF). For the assay of C3a, both C3 and C3(H2O) were removed from the samples by precipitation with polyethylene glycol. It was necessary to add carrier proteins to BALF to remove C3 and C3(H2O) fully. The ELISA of C3a has the lowest limit of detection reported thus far, namely 0.045 nM (= 0.405 ng/ml). In BALF from healthy persons (n = 9) the C3a concentration was 0.20 nM (0.12-0.31 nM) (median, range). C3a was higher in BALF from patients with asthma or with sarcoidosis; asthma (n = 10), 0.45 nM (0.20-5.79 nM); sarcoidosis (n = 19), 1.31 nM (0.095-5.65 nM) (Mann-Whitney U test, p less than 0.005). In BALF from patients with Pneumocystis carinii pneumonitis (n = 10) the C3a concentration was 0.18 nM (0.07-0.57 nM). C3a concentrations in BALF may reflect local complement activation in the lung and/or diffusion into the lumen. This was studied by normalizing C3a concentrations in BALF into values for epithelial lining fluid (ELF), and calculating serum-to-ELF quotients of C3a, and C3a/total C3 quotients.

In vitro inhibition of the classical and alternate pathways of activation of human complement by N acetyl aspartyl glutamic acid (NAAGA)

A synthetic dipeptide, magnesium salt of N-acetyl-L-aspartyl-glutamic acid (NAAGA) identical to a natural dipeptide found as traces in cerebral tissues of mammalian brains, was shown to inhibit, in vitro, the hemolytic activity of both classical and alternate pathways complement; the required concentration of NAAGA was 2 to 10 mM. Cross immuno electrophoretic analysis demonstrated an inhibition of C3 cleavage by both classical and alternate pathway C3 convertases with 24 mM NAAGA. As expected, if C3 convertases were really the target of inhibition, the release of highly inflammatory C3a, C5a fragments scored by R.I.A. was impaired when complement was incubated with activators of classical and alternate pathways. Such a low molecular weight dipeptide, quite atoxic and inhibiting the complement dependent cytotoxicity and release of phlogistic by-products could be interesting for pharmacological manipulation of complement activation in inflammatory processes.

Preparation and characterization of monoclonal antibodies against the fifth component of rabbit complement (C5)

By immunizing mice genetically deficient in C5 we were able to obtain a group of monoclonal antibodies to rabbit C5 that cross-react with C5 from a wide variety of mammalian sera, including mouse. The specificity of the monoclonal antibodies was against native C5 and C5b but not C5a. The antibodies strongly inhibit the expression of C5 hemolytic activity. We suggest that these monoclonal antibodies will be useful for studying C5 as well as providing a way to selectively deplete C5 from plasma in vitro or in vivo.

The modulation of peritoneal macrophage chemiluminescence by acute pleural inflammation, prostanoids and cyclo/lipoxygenase inhibitors

The chemiluminescent (CL) response of peritoneal macrophages was suppressed by induction 4 h earlier of an inflammatory reaction in the pleural cavity which was negated by prior administration of indomethacin, ketoprofen and BW 755C. These changes were accompanied by a concomitant rise in peritoneal PGI2 levels which was abolished by drug pretreatment. In vitro treatment of normal peritoneal macrophages with PGI2 inhibited their subsequent CL response. Indomethacin and ketoprofen produced elevated CL of macrophages obtained from untreated controls in vitro which was blocked by the lipoxygenase inhibitor NDGA. BW 755C and NDGA in vitro strongly inhibited macrophage CL and partially inhibited CL in a cell-free system. Use of these drugs in vivo demonstrated that indomethacin and ketoprofen augmented the CL response of peritoneal macrophages while BW 755C had no effect. These results suggest the inflammatory process per se can modulate the functions of macrophages in parts of the body remote from the inflammatory site. Moreover this modulation may be under the control of the prostanoid system.

Formation of prostanoids during intravascular complement activation in the rabbit

Plasma concentrations of 6-oxo-prostaglandin F1 alpha (6-oxo-PGF1 alpha) and thromboxane B2 (TXB2) were measured by radioimmunoassay in arterial blood before and after injections of the complement activator, cobra venom factor (CVF). During the control period, the concentration of 6-oxo-PGF1 alpha, which gives the sum of prostacyclin plus 6-oxo-PGF1 alpha, and TXB2 were, respectively, less than 20 pg ml-1 and 70 +/- 15 pg ml-1. Intravenous injections of CVF induced dose-dependent, reversible elevations in the plasma levels of both prostanoids. The time courses for the increases of 6-oxo-PGF1 alpha and TXB2 paralleled the arterial hypotension and thrombocytopenia, suggesting the existence of a causal relationship between these parameters. The results further support our hypothesis that complement-dependent formation of arachidonic acid metabolites contributes to some of the haemodynamic and haematological changes occurring during endotoxin shock.

Inflammatory mediators and acute infections

In this paper some important mediation systems of inflammation are reviewed; special emphasis is laid on basic aspects of these systems, their interrelationships, and on clinically relevant effects with regard to the circulatory and pulmonary complications of sepsis. The references cited are selected on the basis of their review aspects.