Staphylococcus aureus Staphopain A inhibits CXCR2-dependent neutrophil activation and chemotaxis

Neutrophil activation and recruitment to the site of infection are critical for host immunity. In humans, the cysteine protease Staphopain A of the pathogen S. aureus blocks this process by cleaving the chemokine receptor CXCR2.

The CXC chemokine receptor 2 (CXCR2) on neutrophils, which recognizes chemokines produced at the site of infection, plays an important role in antimicrobial host defenses such as neutrophil activation and chemotaxis. Staphylococcus aureus is a successful human pathogen secreting a number of proteolytic enzymes, but their influence on the host immune system is not well understood. Here, we identify the cysteine protease Staphopain A as a chemokine receptor blocker. Neutrophils treated with Staphopain A are unresponsive to activation by all unique CXCR2 chemokines due to cleavage of the N-terminal domain, which can be neutralized by specific protease inhibitors. Moreover, Staphopain A inhibits neutrophil migration towards CXCR2 chemokines. By comparing a methicillin-resistant S. aureus (MRSA) strain with an isogenic Staphopain A mutant, we demonstrate that Staphopain A is the only secreted protease with activity towards CXCR2. Although the inability to cleave murine CXCR2 limits in-vivo studies, our data indicate that Staphopain A is an important immunomodulatory protein that blocks neutrophil recruitment by specific cleavage of the N-terminal domain of human CXCR2.

Biocompatibility of a glucose-polymer-containing peritoneal dialysis fluid

The currently available glucose-containing peritoneal dialysis fluids (PDF), which are all hyperosmolar, are toxic to the cells present in the peritoneal cavity. However, glucose-polymer solutions, being isosmolar, may have improved biocompatibility in this respect. We therefore compared in vitro the effects of PDF containing glucose-polymers with that of glucose solutions on the function of donor granulocytes and monocytes (MN), and on the viability of mesothelial cells. In addition, the function of peritoneal macrophages (PMO) of eight patients was studied in a randomized cross-over setting following intraperitoneal exposure to glucose-polymer-versus glucose-monomer-containing fluid of comparable ultrafiltration capacity. Donor granulocytes, as well as MN, showed significantly better phagocytosis of both Staphylococcus epidermidis and Escherichia coli after incubation in the glucose-polymer solution as compared with the 3.86% glucose-containing fluid. Their oxidative metabolism, as measured by chemiluminescence, also showed that the glucose-polymer solution was less inhibitory than fluids containing 2.27 or 3.86% glucose. Patient-derived PMO showed a significantly better phagocytic capacity for S epidermidis and E coli, a significantly higher killing of E coli, and a significantly higher chemiluminescence response after intraperitoneal exposure to the glucose-polymer solution as compared with the glucose-monomer-based fluid. Increasing the osmolality of the glucose-polymer solution to that of the respective glucose solutions blunted the favorable effect on phagocyte function, suggesting the beneficial effect to be osmolality-mediated. However, no major difference was observed between the glucose-polymer solution and the glucose-based fluid in their effects on mesothelial viability.(ABSTRACT TRUNCATED AT 250 WORDS)

Llama single-chain antibody that blocks lipopolysaccharide binding and signaling: prospects for therapeutic applications

Sepsis is a considerable health problem and a burden on the health care system. Endotoxin, or lipopolysaccharide (LPS), present in the outer membrane of gram-negative bacteria, is responsible for more than 50% of the sepsis cases and is, therefore, a legitimate target for therapeutic approaches against sepsis. In this study, we selected and characterized a llama single-chain antibody fragment (VHH) directed to Neisseria meningitidis LPS. The VHH, designated VHH 5G, showed affinity to purified LPS as well as to LPS on the surfaces of the bacteria. Epitope mapping using a panel of N. meningitidis mutants revealed that VHH 5G recognizes an epitope in the inner core of LPS, and as expected, the VHH proved to have broad specificity for LPS from different bacteria. Furthermore, this VHH blocked binding of LPS to target cells of the immune system, resulting in the inhibition of LPS signaling in whole blood. Moreover, it was found to remove LPS efficiently from aqueous solutions, including serum. The selected anti-LPS VHH is a leading candidate for therapies against LPS-mediated sepsis.

Complement activity is associated with disease severity in multifocal motor neuropathy

Objective:

To investigate whether high innate activity of the classical and lectin pathways of complement is associated with multifocal motor neuropathy (MMN) and whether levels of innate complement activity or the potential of anti-GM1 antibodies to activate the complement system correlate with disease severity.

Methods:

We performed a case-control study including 79 patients with MMN and 79 matched healthy controls. Muscle weakness was documented with Medical Research Council scale sum score and axonal loss with nerve conduction studies. Activity of the classical and lectin pathways of complement was assessed by ELISA. We also determined serum mannose-binding lectin (MBL) concentrations and polymorphisms in the MBL gene (MBL2) and quantified complement-activating properties of anti-GM1 IgM antibodies by ELISA.

Results:

Activity of the classical and lectin pathways, MBL2 genotypes, and serum MBL concentrations did not differ between patients and controls. Complement activation by anti-GM1 IgM antibodies was exclusively mediated through the classical pathway and correlated with antibody titers (p < 0.001). Logistic regression analysis showed that both high innate activity of the classical pathway of complement and high complement-activating capacity of anti-GM1 IgM antibodies were significantly associated with more severe muscle weakness and axonal loss.

Conclusion:

High innate activity of the classical pathway of complement and efficient complement-activating properties of anti-GM1 IgM antibodies are determinants of disease severity in patients with MMN. These findings underline the importance of anti-GM1 antibody–mediated complement activation in the pathogenesis and clinical course of MMN.

Effects of granulocyte colony-stimulating factor (G-CSF) treatment on granulocyte function and receptor expression in patients with ventilator-dependent pneumonia

Considerable experimental evidence in animals suggests that treatment with G-CSF may have a beneficial effect in the management of severe infections in non-neutropenic hosts. This beneficial effect is attributed to an enhancement of granulopoiesis and neutrophil function, the latter possibly involving up-regulation of receptors on neutrophils that are involved in antibody-mediated cytotoxicity and killing of microorganisms. We compared neutrophil function and phenotype in blood and bronchoalveolar lavage fluid (BALF) of 10 patients with severe ventilator-dependent pneumonia, at baseline and following initiation of G-CSF treatment as adjunct to standard therapy. G-CSF treatment was associated with three-fold increased blood neutrophil counts at day 3 of treatment compared with baseline counts. Mean serum G-CSF concentration increased from 313 to 2007 pg/ml. After correction for lavage dilution effects, BALF G-CSF levels did not differ significantly from baseline, nor did neutrophil receptor expression (FcgammaRI, FcgammaRII, FcgammaRIII, CR3, and L-selectin) or indicators of neutrophil function such as respiratory burst activity, phagocytosis and killing of Candida albicans in BALF or blood. The mortality in this group of patients was 30% and compared favourably to the APACHE II-derived predicted mortality of 60%. We conclude that the possible therapeutic benefit of G-CSF administration in the early phase of severe bacterial pneumonia is not readily explained by its effect on baseline indicators of neutrophil function or receptor expression.

Versatile vector suite for the extracytoplasmic production and purification of heterologous His-tagged proteins in Lactococcus lactis

Recent studies have shown that the Gram-positive bacterium Lactococcus lactis can be exploited for the expression of heterologous proteins; however, a versatile set of vectors suitable for inducible extracellular protein production and subsequent purification of the expressed proteins by immobilized metal affinity chromatography was so far lacking. Here we describe three novel vectors that, respectively, facilitate the nisin-inducible production of N- or C-terminally hexa-histidine (His6)-tagged proteins in L. lactis. One of these vectors also encodes a tobacco etch virus (TEV) protease cleavage site allowing removal of the N-terminal His6-tag from expressed proteins. Successful application of the developed vectors for protein expression, purification and/or functional studies is exemplified with six different cell wall-bound or secreted proteins from Staphylococcus aureus. The results show that secretory production of S. aureus proteins is affected by the position, N- or C-terminal, of the His6-tag. This seems to be due to an influence of the His6-tag on protein stability. Intriguingly, the S. aureus IsdB protein, which is phosphorylated in S. aureus, was also found to be phosphorylated when heterologously produced in L. lactis, albeit not on the same Tyr residue. This implies that this particular post-translational protein modification is to some extent conserved in S. aureus and L. lactis. Altogether, we are confident that the present vector set combined with the L. lactis expression host has the potential to become a very useful tool in optimization of the expression, purification and functional analysis of extracytoplasmic bacterial proteins.

A study of the sensitivity of erythrocytes to lysis by heterologous sera via the alternative complement pathway

In order to get insight in the distribution of alternative complement pathway activities as detected by lysis of xenogeneic erythrocytes in the presence of magnesium and ethyleneglycol-bis-(2-aminoethyl)-tetra-acetic acid (EGTA) over the species, the 156 heterologous combinations of erythrocytes and sera out of thirteen animal species were tested. An order could be noticed in the species with respect to serum complement activity tending to negative correlation with the sensitivity of the corresponding erythrocytes to lysis by heterologous sera. So far, the most sensitive erythrocyte for each individual serum must be considered to be the target cell of choice for developing assays for alternative complement pathway activity in the serum involved. In this series of animals only for rabbit serum no sensitive target cell was found. The order observed, in connection with the failing lysis of erythrocytes by homologous sera, suggests further that in restriction of heterologous hemolysis in general one erythrocyte-associated, species-nonspecific regulatory principle may be involved, whereas in homologous restriction, most probably, also species-specific factors play a role.

Low-calcium peritoneal dialysis fluid should not impact peritonitis rates in continuous ambulatory peritoneal dialysis

It has been suggested that reducing the calcium content of peritoneal dialysis fluid (PDF) to 2.5 mEq/L decreases peritoneal macrophage (PMO) function and increases the incidence of peritonitis (especially Staphylococcus epidermidis peritonitis) in continuous ambulatory peritoneal dialysis patients. We studied the uptake and killing of S epidermidis and Escherichia coli by PMOs and peripheral blood leukocytes incubated in control buffer (Hank's balanced salt solution containing 0.1% gelatin [GHBSS]) and PDF containing varying concentrations of calcium (O to 3.5 mEq/L) and magnesium (O to 1.5 mEq/L) using ether diamine tetraacetic acid and ethylenediaminetetraacetic acid chelation, respectively. In addition, interleukin-1-beta-induced interleukin-6 production by human mesothelial cells was measured in the presence of concentrations of calcium increasing from 0 to 3.0 mmol/L. Fc receptor- mediated uptake of S epidermidis by PMO in the complete absence of Ca++ was comparable to that by PMO incubated in GHBSS with calcium. In contrast, the complement-dependent uptake of E coli was significantly lower in GHBSS devoid of Ca++ (46% +/- 5% v 24% +/- 3%; 0.05 < P < 0.02). No effect on intracellular killing of either microorganism by PMO was observed. The same held true for the phagocytic and killing capacity of polymorphonuclear granulocytes and monocytes obtained from healthy donors. Using Ca++ (2 to 3.5 mEq/L) and Mg++ (0.5 to 1.5 mEq/L) concentrations as applied in commercial PDFs, however, phagocytes performed as well as in control buffer. Interleukin-6 production by stimulated human mesothelial cells also required a small amount of Ca++ only, being normal above the 0.1 to 3 mmol/L Ca+ + range tested. Thus, complement- dependent uptake of bacteria by phagocytes is calcium dependent, whereas antibody-dependent uptake of S epidermidis is not. The concentrations of calcium in the current PDFs, however, will not compromise human mesothelial cells and leukocyte functions, and therefore should not impact the peritonitis rate.

In vitro compatibility of a 1.1% amino acid containing peritoneal dialysis fluid with phagocyte function

The effects of a recently introduced peritoneal dialysis fluid (PDF) containing amino acids (AA) were compared with those of a glucose-based PDF (G-PDF) on viability and function of donor granulocytes (PMNs) in vitro. After 30 min incubation in the PDF, viability, assessed by trypan blue exclusion, and phagocytosis capacity (PC), tested in two assays using a fluorescein and a 3H-labeled Staphylococcus epidermidis strain, were significantly better in AA-PDF than in G-PDF (p < 0.002 in the 3H-assay). Bactericidal activity was not different in the PDFs. If pH of G-PDF was adjusted from 5.2 to neutral, differences in PC disappeared. In AA-PDF, PMN chemiluminescence (CL) response was significantly higher than in G-PDF (p < 0.003). At neutral pH, however, PMNs showed a significant stronger CL-response in 1.36% G-PDF than in AA-PDF (p < 0.05). These data suggest that this AA-PDF has little detrimental effect on phagocyte viability and function. The improved compatibility over G-PDF in in vitro tests seems to be pH dependent. The reduced chemiluminescence response compared to 1.36% G-PDF with neutral pH is possibly due to quenching by (one of the) amino acids and osmolarity.