Substituted Sialic Acid Prosthetic Groups as Determinants of Viral Hemagglutination

Abstract

Inhibitors of hemagglutination by type A2 influenza virus and a recently isolated strain of type B influenza virus were separated by sucrose density gradient centrifugation and agarose gel filtration from horse serum. Using selected reagents, it was demonstrated that the active substituent on the horse serum inhibitor of A2 influenza virus was 4- O -acetyl- N -acetylneuraminic acid; however, the active substituent on the inhibitor of the influenza B virus was shown to be N -acetylneuraminic acid (NANA). Sodium metaperiodate treatment of a component of horse serum resulted in a 10 to 15-fold enhancement of inhibitory activity against the type B virus, whereas the A2 inhibitor was completely destroyed. Since this enhancement did not occur with influenza B viruses isolated prior to 1965, it was considered that this sensitivity to an oxidized NANA glycoside may have been a reflection of an antigenic change which occurred at that time. The use of different virus strains and selected chemical reagents to define the important sialic acid prosthetic groups active in inhibition was described.

Molecular Mechanisms of Serum Resistance of Human Influenza H3N2 Virus and Their Involvement in Virus Adaptation in a New Host

“…In marked contrast to pig and rabbit sera, horse serum retained up to 30% inhibitory activity against the LA/87 virus after NA treatment, indicating that substantial amounts of NA-resistant inhibitors are present in horse, but not in pig or rabbit, serum. Previous studies have shown that ␣ 2 -macroglobulin is the principal inhibitor in horse serum for H2N2 and H3N2 viruses and that 4-O-acetylated sialic acid, which represents about 30% of the total sialic acids in EM (16), confers this inhibitor's resistance to bacterial and viral NA (16,24,25,31). Our results are consistent with these previous findings in that LA/87 NA is unable to cleave 4-O-acetylated sialic acid residues from ␣ 2 -macroglobulin and in that LA/87 HA does bind this type of sialic acid.…”

“…A potent ␥ inhibitor of H2 and H3 human influenza viruses, equine ␣ 2 -macroglobulin (EM), contains a Neu4,5Ac 2 2-6Gal moiety that is insensitive to viral NA and thus resists inactivation by this enzyme (16,24,31). Cultivation of human H3 influenza viruses in the presence of horse serum results in the selection of variants that have a decreased affinity for the Neu5Ac2-6Gal-specific receptors due to a single amino acid substitution (226L3Q) in their HA (32,33).…”

Distribution of O-Acetylated Sialic Acids among Target Host Tissues for Influenza Virus

“…The guinea pig tissues examined here did not display the 4-O-Ac Sia on airway-exposed tissues in the upper respiratory tract (trachea), so its role in laboratory infections performed with human viruses is unknown. Horse and guinea pig sera have long been known to be potent inhibitors of several H2 and H3 human influenza strains ( 35 , 36 , 65 ), and resistance to those sera could be selected through mutations in the HA at residue 145 (H3) that ablate 4-O-Ac binding ( 61 ). The presence of various amounts of sialidase-resistant Sias may therefore contribute to selection of influenza virus populations with HA variants, while its display on some horse and guinea pig cells in culture may provide an in vitro system suitable for the study of this modified Sia and its interactions with influenza and other viruses.…”

“…One reported effect of O-acetylation is a general reduction in susceptibility to cleavage by sialidases, including influenza virus NA ( 34 ). A number of inhibitors of influenza viruses were identified historically, including the γ-inhibitors, which are defined as sugar molecules that interact with influenza viruses to inhibit infection by acting as “decoy” receptors ( 35 – 38 ). The 9-O-Ac Sias were also reported to reduce the sialidase activity of NA by almost 3-fold ( 39 ).…”

Glycan microarray technologies: tools to survey host specificity of influenza viruses

“…For many years, techniques to study the interactions of the influenza virus with host cell receptors have used whole viruses. This includes haemagglutination assays, which measure the ability of intact influenza virus and other viruses to agglutinate red blood cells (RBCs), and haemagglutination inhibition assays, which detect and quantify antibodies and soluble receptor analogues that inhibit RBC agglutination by intact viruses [20][21][22][23][24] . With the identification and isolation of specific α2-3-sialidases and α2-6-sialidases, and advances in technologies for genetic manipulation of the influenza genome, a haemadsorption assay based on desialylation of endogenous sialic acid from RBCs, followed by selective linkage-specific resialylation of RBCs, and subsequent analysis of their binding to viruses or cells transfected with influenza HA, has become routine in many laboratories 21,24 .…”