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International journal of molecular sciences 22(14), 7332 (2021). doi:10.3390/ijms22147332 special issue: "Special Issue "Molecular Research in Cardiovascular Disease" / Special Issue Editors: Prof. Dr. Maria I. Dorobantu, Prof. Dr. Maya Simionescu", Published by Molecular Diversity Preservation International, Basel

Galectin-1 (gal-1) is a carbohydrate-binding lectin with important functions in angiogenesis, immune response, hemostasis and inflammation. Comparable functions are exerted by platelet factor 4 (CXCL4), a chemokine stored in the α-granules of platelets. Previously, gal-1 was found to activate platelets through integrin αIIbβ3. Both gal-1 and CXCL4 have high affinities for polysaccharides, and thus may mutually influence their functions. The aim of this study was to investigate a possible synergism of gal-1 and CXCL4 in platelet activation. Platelets were treated with increasing concentrations of gal-1, CXCL4 or both, and aggregation, integrin activation, P-selectin and phosphatidyl serine (PS) exposure were determined by light transmission aggregometry and by flow cytometry. To investigate the influence of cell surface sialic acid, platelets were treated with neuraminidase prior to stimulation. Gal-1 and CXCL4 were found to colocalize on the platelet surface. Stimulation with gal-1 led to integrin αIIbβ3 activation and to robust platelet aggregation, while CXCL4 weakly triggered aggregation and primarily induced P-selectin expression. Co-incubation of gal-1 and CXCL4 potentiated platelet aggregation compared with gal-1 alone. Whereas neither gal-1 and CXCL4 induced PS-exposure on platelets, prior removal of surface sialic acid strongly potentiated PS exposure. In addition, neuraminidase treatment increased the binding of gal-1 to platelets and lowered the activation threshold for gal-1. However, CXCL4 did not affect binding of gal-1 to platelets. Taken together, stimulation of platelets with gal-1 and CXCL4 led to distinct and complementary activation profiles, with additive rather than synergistic effects.

The innate immune response is the first line of defense against viruses, and type I interferon (IFN) is a critical component of this response. Similar to other viruses, the gammacoronavirus infectious bronchitis virus (IBV) has evolved under evolutionary pressure to evade and counteract the IFN response to enable its survival. Previously, we reported that IBV induces a delayed activation of the IFN response. In the present work, we describe the resistance of IBV to IFN and the potential role of accessory proteins herein. We show that IBV is fairly resistant to the antiviral state induced by IFN and identify that viral accessory protein 3a is involved in resistance to IFN, as its absence renders IBV less resistant to IFN treatment. In addition to this, we found that independently of its accessory proteins, IBV inhibits IFN-mediated phosphorylation and translocation of STAT1. In summary, we show that IBV uses multiple strategies to counteract the IFN response. IMPORTANCE In the present study, we show that infectious bronchitis virus (IBV) is resistant to IFN treatment and identify a role for accessory protein 3a in the resistance against the type I IFN response. We also demonstrate that, in a time-dependent manner, IBV effectively interferes with IFN signaling and that its accessory proteins are dispensable for this activity. This study demonstrates that the gammacoronavirus IBV, similar to its mammalian counterparts, has evolved multiple strategies to efficiently counteract the IFN response of its avian host, and it identifies accessory protein 3a as multifaceted antagonist of the avian IFN system.

The recruitment of leukocytes upon injury or inflammation to sites of injury or tissue damage has been investigated during recent decades and has resulted in the concept of the leukocyte adhesion cascade. However, the exact molecular mechanisms involved in leukocyte recruitment have not yet been fully identified. Since leukocyte recruitment remains an important subject in the field of infection, inflammation, and (auto-) immune research, we present a straightforward laminar flow-based assay to study underlying mechanisms of the adhesion, de-adhesion, and transmigration of leukocytes under venous and arterial flow regimes. The in vitro assay can be used to study the molecular mechanisms that underlie the interactions between leukocytes and their cellular partners in different models of vascular inflammation. This protocol describes a laminar flow-based assay using a parallel-flow chamber and an inverted phase contrast microscope connected to a camera to study the interactions of leukocytes and endothelial cells or platelets, which can be visualized and recorded then analyzed offline. Endothelial cells, platelets, or leukocytes can be pretreated with inhibitors or antibodies to determine the role of specific molecules during this process. Shear conditions, i.e. arterial or venous shear stress, can be easily adapted by the viscosity and flow rate of the perfused fluids and the height of the channel.