Group A Streptococcus (GAS) is a human pathogen causing a wide range of mild to severe and life-threatening diseases. The GAS M1 protein is a major virulence factor promoting GAS invasiveness and resistance to host innate immune clearance. M1 displays an irregular coiled-coil structure, including the B-repeats that bind fibrinogen. Previously, we found that B-repeat stabilisation generates an idealised version of M1 (M1) characterised by decreased fibrinogen binding in vitro. To extend these findings based on a soluble truncated version of M1, we now studied the importance of the B-repeat coiled-coil irregularities in full length M1 and M1 expressed in live GAS and tested whether the modulation of M1-fibrinogen interactions would open up novel therapeutic approaches. We found that altering either the M1 structure on the GAS cell surface or removing its target host protein fibrinogen blunted GAS virulence. GAS expressing M1 showed an impaired ability to adhere to and to invade human endothelial cells, was more readily killed by whole blood or neutrophils and most importantly was less virulent in a murine necrotising fasciitis model. M1-mediated virulence of wild-type GAS was strictly dependent on the presence and concentration of fibrinogen complementing our finding that M1-fibrinogen interactions are crucial for GAS virulence. Consistently blocking M1-fibrinogen interactions by fragment D reduced GAS virulence in vitro and in vivo. This supports our conclusion that M1-fibrinogen interactions are crucial for GAS virulence and that interference may open up novel complementary treatment options for GAS infections caused by the leading invasive GAS strain M1.
Intravenous Immunoglobulin (IVIG) has been proposed as a potential therapeutic for Alzheimers disease (AD) and its efficacy is currently being tested in mild-to-moderate AD. Earlier studies reported the presence of anti-amyloid beta (A?) antibodies in IVIG. These observations led to clinical studies investigating the potential role of IVIG as a therapeutic agent in AD. Also, IVIG is known to mediate beneficial effects in chronic inflammatory and autoimmune conditions by interfering with various pathological processes. Therefore, we investigated the effects of IVIG and purified polyclonal A?-specific antibodies (pAbs-A?) on aggregation, toxicity and phagocytosis of A? in vitro, thus elucidating some of the potential mechanisms of action of IVIG in AD patients. We report that both IVIG and pAbs-A? specifically bound to A? and inhibited its aggregation in a dose-dependent manner as measured by Thioflavin T assay. Additionally, IVIG and the purified pAbs-A? inhibited A?-induced neurotoxicity in the SH-SY5Y human neuroblastoma cell line and prevented A? binding to rat primary cortical neurons. Interestingly, IVIG and pAbs-A? also increased the number of phagocytosing cells as well as the amount of phagocytosed fibrillar A? by BV-2 microglia. Phagocytosis of A? depended on receptor-mediated endocytosis and was accompanied by upregulation of CD11b expression. Importantly, we could also show that Privigen dose-dependently reversed A?-mediated LTP inhibition in mouse hippocampal slices. Therefore, our in vitro results suggest that IVIG may have an impact on different processes involved in AD pathogenesis, thereby promoting further understanding of the effects of IVIG observed in clinical studies.
The family of 4 related protease-activated receptors (PAR-1, 2, 3 & 4) expressed by mammalian cells allow to sense for and react to extracellular proteolytic activity. Since major human bacterial pathogens secret a wide array of protease(-s) we investigated whether they interfere with human PAR function.
Methicillin resistance in Staphylococcus aureus is conferred by the mecA-encoded penicillin-binding protein PBP2a. Additional genomic factors are also known to influence resistance levels in strain specific ways, although little is known about their contribution to resistance phenotypes in clinical isolates. Here we searched for novel proteins binding to the mec operator, in an attempt to identify new factor(s) controlling methicillin resistance phenotypes.
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