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Enterococcus faecium is an emerging pathogen that causes infections in hospitalized patients with various co-morbid diseases. These underlying diseases are often associated with an acute-phase response that renders patients vulnerable to nosocomial infections. To study the influence of the acute-phase response induced by sterile tissue injury on host defence against E. faecium, mice were injected subcutaneously with either turpentine or casein 1 day before intraperitoneal infection with E. faecium. Control mice were subcutaneously injected with saline or sodium bicarbonate, respectively. Turpentine and casein induced an acute-phase response as reflected by increases in the plasma concentrations of interleukin-6, serum amyloid P and C3. A pre-existent acute-phase response in mice was associated with a strongly reduced capacity to clear E. faecium, resulting in prolonged bacteraemia for several days. The inflammatory response to E. faecium was impaired in mice with an acute-phase response, as shown by reduced capacity to mount a neutrophilic leucocytosis in peripheral blood and by decreased local cytokine concentrations. These data indicate that the acute-phase response impairs host defence against E. faecium, suggesting that this condition may contribute to the increased vulnerability of critically ill patients to enterococcal infections.

The binding of human serum amyloid P component (SAP) to blood cells and monocyte-derived dendritic cells was investigated by flow cytometry. Monocytes bound biotinylated SAP with avidity in a dose-dependent and saturable manner. By contrast, the binding of SAP to monocyte-derived dendritic cells was weak. No binding to erythrocytes, NK cells, T lymphocytes or B lymphocytes could be detected. The SAP-monocyte interaction was calcium-independent and readily inhibited by C1q. SAP was nonmitogenic for human mononuclear cells and had no apparent influence on lymphocyte proliferation induced by mitogenic lectins. We speculate that binding of SAP by monocytes could be of physiological relevance at extravascular sites by influencing complement regulation.

Serum amyloid P component (SAP) is a pentameric plasma protein associated with all known kinds of amyloid. The normal physiological function of the protein has not been fully elucidated but it may be involved in clearance of cellular debris and in innate immunity. An important clue to its normal function is the identity of ligands bound to SAP in the circulation. It has been reported that all SAP is complexed with C4-binding protein (C4bp) but other studies have not been able to confirm this. We here study this issue by a combination of crossed immunoelectrophoresis (CIE), size exclusion chromatography, and native polyacrylamide electrophoresis and we show that SAP in serum - analysed under native analysis conditions and free of immobilizing antibodies - does not have any major protein ligand. However, when the protein is aggregated by immobilized antibodies, C4bp and fibronectin clearly bind to SAP. If circulating SAP under normal circumstances bind any protein ligand in vivo, our results strongly suggest that this only occurs to a minor extent.

Limulus polyphemus C-reactive protein (CRP) (limulin) has approximately 30% amino acid sequence homology and shares at least one idiotypic determinant associated with ligand-binding activity with human CRP (hCRP); limulin also shares amino acid sequence homology and lectin activity with human serum amyloid P component (hSAP). In the present study panels of 14 anti-hCRP monoclonal antibodies (mAb) directed to distinct hCRP epitopes and 11 anti-hSAP mAb directed to distinct epitopes of hSAP were tested for reactivity with limulin and pentraxins of other species including rabbit CRP (raCRP), rat CRP and hamster female protein (FP) by ELISA and Western blot analyses. None of the anti-human pentraxin mAb showed strong cross-reactivity with limulin; only five mAb reacted with limulin at all, and cross-reactivities of these mAb with the other pentraxins, when present, also were weak. Cross-reactivity of limulin with hCRP and hSAP was similar, and in light of comparable amino acid sequence homology, suggests this molecule can be considered the limulus SAP as well as the limulus CRP. Several anti-hCRP mAb cross-reacted strongly with rabbit CRP and rat CRP; a few anti-hSAP cross-reacted strongly with FP; and weak cross-reactions were observed between hCRP and hSAP, but cross-reactivities between the pentraxins generally were limited and weak. A rabbit polyclonal antibody raised to highly conserved limulin peptide 141-156 and strongly reactive with limulin reacted weakly with hCRP and raCRP but failed to react with rat CRP, hSAP or FP. These studies emphasize a limited but distinct antigenic similarity between limulin, hCRP and other pentraxins, and identify mAb reactive with potential regions of shared structure and/or function between pentraxins of different species.

Monospecific antisera were raised by immunization with pentraxins, C-reactive protein (CRP) or serum amyloid P component (SAP), that had been isolated from man and a number of different vertebrate species. These antisera were used to test sera or serous fluids from a range of other vertebrate species and also some invertebrates. Cross-reactions between species were comparatively rare but were seen among primates and among ruminants. There was also cross-reactivity between these two groups. Antisera to plaice pentraxins did not react with sera from higher vertebrates but did recognize antigens in sera from other flat fish. No cross-reactivity was observed between CRP and SAP either within or between species despite the known homologies of amino acid sequence and similarities of structure within the family. Several reactions occurred with sera in which either CRP or SAP had previously not been sought or in which only preliminary investigations had been performed. The proteins detected were: CRP in goat, cow, sheep, cat and lemon sole; SAP in monkey and dab. These findings significantly extend the range of species in which pentraxins are known to be present.