Coronavirus disease 2019 (COVID-19) is a mild to moderate respiratory tract infection, however, a subset of patients progress to severe disease and respiratory failure. The mechanism of protective immunity in mild forms and the pathogenesis of severe COVID-19 associated with increased neutrophil counts and dysregulated immune responses remain unclear. In a dual-center, two-cohort study, we combined single-cell RNA-sequencing and single-cell proteomics of whole-blood and peripheral-blood mononuclear cells to determine changes in immune cell composition and activation in mild versus severe COVID-19 (242 samples from 109 individuals) over time. HLA-DR hi CD11c hi inflammatory monocytes with an interferon-stimulated gene signature were elevated in mild COVID-19. Severe COVID-19 was marked by occurrence of neutrophil precursors, as evidence of emergency myelopoiesis, dysfunctional mature neutrophils, and HLA-DR lo monocytes. Our study provides detailed insights into the systemic immune response to SARS-CoV-2 infection and reveals profound alterations in the myeloid cell compartment associated with severe COVID-19.
Adhesive interactions of leukocytes and endothelial cells initiate leukocyte migration to inflamed tissue and are important for immune surveillance. Acute and chronic inflammatory diseases show a dysregulated immune response and result in a massive efflux of leukocytes that contributes to further tissue damage. Therefore, targeting leukocyte trafficking may provide a potent form of antiinflammatory therapy. Leukocyte migration is initiated by interactions of the cell adhesion molecules E-, L-, and P-selectin and their corresponding carbohydrate ligands. Compounds that efficiently address these interactions are therefore of high therapeutic interest. Based on this rationale we investigated synthetic dendritic polyglycerol sulfates (dPGS) as macromolecular inhibitors that operate via a multivalent binding mechanism mimicking naturally occurring ligands. dPGS inhibited both leukocytic L-selectin and endothelial P-selectin with high efficacy. Size and degree of sulfation of the polymer core determined selectin binding affinity. Administration of dPGS in a contact dermatitis mouse model dampened leukocyte extravasation as effectively as glucocorticoids did and edema formation was significantly reduced. In addition, dPGS interacted with the complement factors C3 and C5 as was shown in vitro and reduced C5a levels in a mouse model of complement activation. Thus, dPGS represent an innovative class of a fully synthetic polymer therapeutics that may be used for the treatment of inflammatory diseases.anti-inflammatory drug | complement inhibition | multiple target binding | multivalent selectin inhibitor | synthetic polymer
Apoptotic cell death induces dramatic molecular changes in cells, becoming apparent on the structural level as membrane blebbing, condensation of the cytoplasm and nucleus, and loss of cell-cell contacts. The activation of caspases is one of the fundamental steps during programmed cell death. Here we report a detailed analysis of the fate of the Ca 2؉ -dependent cell adhesion molecule E-cadherin in apoptotic epithelial cells and show that during apoptosis fragments of Ecadherin with apparent molecular masses of 24, 29, and 84 kDa are generated by two distinct proteolytic activities. In addition to a caspase-3-mediated cleavage releasing the cytoplasmic domain of E-cadherin, a metalloproteinase sheds the extracellular domain from the cell surface during apoptosis. Immunofluorescence analysis confirmed that concomitant with the disappearance of E-cadherin staining at the cell surface, the E-cadherin cytoplasmic domain accumulates in the cytosol. In the presence of inhibitors of caspase-3 and/or metalloproteinases, cleavage of E-cadherin was almost completely blocked. The simultaneous cleavage of the intracellular and extracellular domains of E-cadherin may provide a highly efficient mechanism to disrupt cadherin-mediated cell-cell contacts in apoptotic cells, a prerequisite for cell rounding and exit from the epithelium.The crucial role of apoptosis during development and for tissue homeostasis of multicellular organisms is well established (1). Malfunctions of the death program and its control mechanisms often result in prenatal death during development and contribute to immune and neuronal diseases or cancer in the adult organism (2-4). The central mechanism of this cell death machinery is a proteolytic cascade mediated by the caspase family of cysteine proteinases (5, 6), which specifically cleave their substrates after aspartate residues. Caspases are synthesized as inactive proenzymes. After initiation of the apoptotic program these proenzymes are processed by two proteolytic events, generating a large subunit and a small subunit that form a heterodimer. The association of two heterodimers results in the formation of the active enzyme containing two catalytic sites (7,8). Depending on their position in the proteolytic cascade, caspase family members are divided into upstream initiator caspases and downstream effector caspases.The activation of this caspase cascade leads to the specific cleavage of substrate proteins and finally results in the morphological changes becoming apparent in apoptotic cells. The identification of an increasing number of caspase substrates has revealed different classes of cellular proteins that are cleaved during the effector phase of apoptosis. A set of substrate proteins is represented by proteins that protect living cells from apoptosis, e.g. ICAD/DFF45 (9, 10) and Bcl-2 (11, 12). Nuclear envelope proteins (e.g. lamin A and B (13-15) and LAP2 and Nup153 (16) (27)) and DNA repair (DNA-PK CS ) and of the splicing machinery (U1-70K) is assumed to support the disruption of structural...
Abstract.A novel member of the cadherin family of cell adhesion molecules has been characterized by cloning from rat liver, sequencing of the corresponding cDNA, and functional analysis after heterologous expression in nonadhesive $2 cells, cDNA clones were isolated using a polyclonal antibody inhibiting Ca2+-dependent intercellular adhesion of hepatoma cells. As inferred from the deduced amino acid sequence, the novel molecule has homologies with E-, P-, and N-cadherins, but differs from these classical cadherins in four characteristics. Its extracellular domain is composed of five homologous repeated domains instead of four characteristic for the classical cadherins. Four of the five domains are characterized by the sequence motifs DXNDN and DXD or modifications thereof representing putative Ca2+-binding sites of classical cadherins. In its NH2-terminal region, this cadherin lacks both the precursor segment and the endogenous protease cleavage site RXKR found in classical cadherins. In the extracellular EC1 domain, the novel cadherin contains an AAL sequence in place of the HAV sequence motif representing the common cell adhesion recognition sequence of E-, P-, and N-cadherin. In contrast to the conserved cytoplasmic domain of classical cadherins with a length of 150-160 amino acid residues, that of the novel cadherin has only 18 amino acids. Examination of transfected $2 cells showed that despite these structural differences, this cadherin mediates intercellular adhesion in a Ca2+-dependent manner. The novel cadherin is solely expressed in liver and intestine and was, hence, assigned the name LI-cadherin. In these tissues, LI-cadherin is localized to the basolateral domain of hepatocytes and enterocytes. These results suggest that LI-cadherin represents a new cadherin subtype and may have a role in the morphological organization of liver and intestine.C ELL-cell interactions are of fundamental importance for the development and the maintenance of tissues and organs in multicellular organisms. The basic morphogenetic processes involved in organogenesis, including cellular aggregation, segregation, and migration, are mediated and controlled by an increasingly large and complex number of cell adhesion molecules that exhibit a well-regulated spatiotemporal pattern of expression during development and regeneration (for review see Simons and Fuller, 1985;Ekblom et al
Abstract. In Trypanosoma brucei, the products of two genes, ESAG 6 and ESAG 7, located upstream of the variant surface glycoprotein gene in a polycistronic expression site form a glycosylphosphatidylinositolanchored transferrin-binding protein (TFBP) complex. It is shown by gel filtration and membrane-binding experiments that the TFBP complex is heterodimeric and binds one molecule of transferrin with high affinity (2,300 binding sites per cell; K D = 2.1 nM for the dominant expression site from T. brucei strain 427 and KD = 131 nM for ES1.3A of the EATRO 1125 stock). The ternary transferrin-TFBP complexes with iron-loaded or iron-flee ligand are stable between pH 5 and 8. Cellular transferrin uptake can be inhibited by 90% with Fab fragments from anti-TFBP antibodies. After uptake, the TFBP complex and its ligand are routed to lysosomes where transferrin is proteolytically degraded. While the degradation products are released from the cells, iron remains cell associated and the TFBP complex is probably recycled to the membrane of the flagellar pocket, the only site for exo-and endocytosis in this organism. It is concluded that the TFBP complex serves as the receptor for the uptake of transferrin in T. brucei by a mechanism distinct from that in mammalian cells.T RANSFERRIN (TF) 1 is the major serum glycoprotein that transports iron to most tissues in mammals. Diferric-TF (holo-TF) binds to a specific cell-surface receptor, the ligand-receptor complex is endocytosed and delivered to endosomes (for reviews see Crichton and Charloteaux-Wauters, 1987;Huebers and Finch, 1987). The low pH of endosomes triggers the release of iron from holo-TF but the resulting iron-free TF (apo-TF) remains bound to the receptor and is recycled back to the cell surface where, at neutral pH, apo-TF dissociates from the receptor. The human TF receptor is a transmembrane glycoprotein composed of two identical disulphide-linked subunits of 90 kD; each monomer can bind one molecule of TF. The intracellular domain of the receptor subunits contains specific signals for uptake in clathrin-coated vesicles (Trowbridge et al., 1993).African trypanosomes, the causative agents of sleeping sickness in humans and Nagana in cattle, are unicellular, flagellated protozoa that live extracellularly in the blood Address all correspondence to P. Overath,
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