Adenovirus type 37 (Ad37) is a leading cause of epidemic keratoconjunctivitis (EKC), a severe and highly contagious ocular disease. Whereas most other adenoviruses infect cells by engaging CD46 or the coxsackie and adenovirus receptor (CAR), Ad37 binds previously unknown sialic acid-containing cell surface molecules. By glycan array screening, we show here that the receptor-recognizing knob domain of the Ad37 fiber protein specifically binds a branched hexasaccharide that is present in the GD1a ganglioside and that features two terminal sialic acids. Soluble GD1a glycan and GD1a-binding antibodies efficiently prevented Ad37 virions from binding and infecting corneal cells. Unexpectedly, the receptor is constituted by one or more glycoproteins containing the GD1a glycan motif rather than the ganglioside itself, as shown by binding, infection and flow cytometry experiments. Molecular modeling, nuclear magnetic resonance and X-ray crystallography reveal that the two terminal sialic acids dock into two of three previously established sialic acid-binding sites in the trimeric Ad37 knob. Surface plasmon resonance analysis shows that the knob-GD1a glycan interaction has high affinity. Our findings therefore form a basis for the design and development of sialic acid-containing antiviral drugs for topical treatment of EKC.

Salivary agglutinin is a high molecular mass component of human saliva that binds Streptococcus mutans, an oral bacterium implicated in dental caries. To study its protein sequence, we isolated the agglutinin from human parotid saliva. After trypsin digestion, a portion was analyzed by matrix-assisted laser/desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS), which gave the molecular mass of 14 unique peptides. The remainder of the digest was subjected to high performance liquid chromatography, and the separated peptides were analyzed by MALDI-TOF/post-source decay; the spectra gave the sequences of five peptides. The molecular mass and peptide sequence information showed that salivary agglutinin peptides were identical to sequences in lung (lavage) gp-340, a member of the scavenger receptor cysteine-rich protein family. Immunoblotting with antibodies that specifically recognized either lung gp-340 or the agglutinin confirmed that the salivary agglutinin was gp-340. Immunoblotting with an antibody specific to the sialyl Le x carbohydrate epitope detected expression on the salivary but not the lung glycoprotein, possible evidence of different glycoforms. The salivary agglutinin also interacted with Helicobacter pylori, implicated in gastritis and peptic ulcer disease, Streptococcus agalactiae, implicated in neonatal meningitis, and several oral commensal streptococci. These results identify the salivary agglutinin as gp-340 and suggest it binds bacteria that are important determinants of either the oral ecology or systemic diseases.

The local immune privilege of the fetus is created by the placenta. Fas ligand (FasL) expression in trophoblast has been implied as one of the mechanisms of fetal tolerance. However, the expression of membranal FasL by trophoblast has failed to explain this role of FasL. Two objections can be raised: (1) there have been contradictions considering which trophoblast cells, syncytiotrophoblast (ST) or cytotrophoblast, express FasL; (2) in vivo and in vitro studies have shown that the membranal form of FasL evokes inflammatory response and thus may promote fetal rejection. Using different assays and the FasL-specific antibody G247-4 we demonstrate beyond doubt that in vivo, (1) FasL is produced by and stored in the first trimester human ST only and (2) the human ST lacks surface membranal FasL. Instead, FasL, loaded in microvesicles, is stored in cytoplasmic granules. These results complement the recent in vitro studies of the microvesicular form of FasL secretion by cultured trophoblast cells, and suggest that placental FasL is synthesized by villous ST, stored in microvesicular form and secreted as exosomes. Secretion of the exosome-associated form of FasL may be one mechanism by which the placenta promotes a state of immune privilege. Additionally, FasL expression in Hofbauer cells is also demonstrated.

Most adenoviruses attach to host cells by means of the protruding fiber protein that binds to host cells via the coxsackievirus and adenovirus receptor (CAR) protein. Human adenovirus type 52 (HAdV-52) is one of only three gastroenteritis-causing HAdVs that are equipped with two different fiber proteins, one long and one short. Here we show, by means of virion-cell binding and infection experiments, that HAdV-52 can also attach to host cells via CAR, but most of the binding depends on sialylated glycoproteins. Glycan microarray, flow cytometry, surface plasmon resonance and ELISA analyses reveal that the terminal knob domain of the long fiber (52LFK) binds to CAR, and the knob domain of the short fiber (52SFK) binds to sialylated glycoproteins. X-ray crystallographic analysis of 52SFK in complex with 2-O-methylated sialic acid combined with functional studies of knob mutants revealed a new sialic acid binding site compared to other, known adenovirus:glycan interactions. Our findings shed light on adenovirus biology and may help to improve targeting of adenovirus-based vectors for gene therapy.

Adenovirus type 37 (Ad37) is one of the principal agents responsible for epidemic keratoconjunctivitis (EKC), a severe ocular infection that remains without any available treatment. Recently, a trivalent sialic acid derivative (ME0322, Angew. Chem. Int. Ed., 2011, 50, 6519) was shown to function as a highly potent inhibitor of Ad37, efficiently preventing the attachment of the virion to the host cells and subsequent infection. Here, new trivalent sialic acid derivatives were designed, synthesized and their inhibitory properties against Ad37 infection of the human corneal epithelial cells were investigated. In comparison to ME0322, the best compound (17a) was found to be over three orders of magnitude more potent in a cell-attachment assay (IC50 = 1.4 nM) and about 140 times more potent in a cell-infection assay (IC50 = 2.9 nM). X-ray crystallographic analysis demonstrated a trivalent binding mode of all compounds to the Ad37 fiber knob. For the most potent compound ophthalmic toxicity in rabbits was investigated and it was concluded that repeated eye administration did not cause any adverse effects.