Hemagglutinating and fusogenic activities of Newcastle disease virus: studies on receptor binding specificity and pH-induced conformational changes

Vaccinal and wild strains of Newcastle Disease virus (NDV) were analyzed for cell receptor binding and fusogenic biological properties associated with their HN (hemagglutinin-neuraminidase) and F (fusion protein) surface structures respectively. The evaluation of the biological activities of HN and F was carried out respectively by determination of hemagglutinating titers and hemolysis percentages, using erythrocytes from various animal origins at different pH values. Significant differences in hemagglutination titers for some strains of NDV were detected, when interacting with goose, sheep, guinea-pip and human "O" group erythrocytes at neutral pH. Diversity of hemolysis percentagens was observed between different NDV strains at acid pH. These analysis were developed to evaluate particular aspects of the actual influence of the receptor specifity and pH on the receptor binding and fusogenic processes of Newcastle Disease viruses.

The role of antigenically different virus neuraminidases as structures implicated in receptor-binding processes

Influenza A viruses exhibit segmented nucleic acid coding for eight different proteins, two of them as glycoproteins exposed on their lipoprotein envelopes, hemagglutinin (HA) and neuraminidase (NA). Hemagglutinin exhibits recptor-binding activity while neuraminidase develps sialidase cleavage activity which acts on cell receptors. Influenza A strains responsible for human, avian, equine and porcine respiratory infections all over the world present antigenically different hemagglutinin (H1 to H14) and neutraminidase (N1 to N9) structures on their surface. The objective of the present investigation was study the role of N2, N8 and N9, anti-genically diverse neuraminidase structures of human (N2) and animal (N8 and N9) influenza viruses, in the receptor-binding process. REceptor-binding activity of N2 and N8 was anlyzed by crossed tests using H3N2 and H3N8 antisera and the hemagglutination inhibition test as a model. Hemangglutinating activity of antigenically different N2 and N8 structures was demonstrable and was inhibited by homologous antisera (N2-H3N2, N8-H3N8) but not by heterologous antisera (N2-H3-N8,N8-H3-N2). This previously demonstrated N9 hemagglutinating activity was analysed for receptor-binding specificity using hemagglutination test and NeuAc alpha2,3Gal and NeuAc alpha2,6Gal derivatized erythrocytes. This highly purified N9 strain was obtained from a virus strain isolated from terns by Dr. Peter Colman (CSIRO Division of Biomolecular Engineering, Parkville, Victoria, Australia)...

Comparative evaluation of a simple and sensitive assay for detection of orthomyxo and paramyxoviruses

Studies were done to evaluate comparatively the traditional HA assay and a more recently introduced lectin-neuraminidase (LN) methodologyin search of a simple and sensitive assay for virus detection during laboratorial diagnosis. The results proved the value of LN assay as a sensitive methodologyfor detection of virus particles, presenting results at least equal to those obtained by HA (hemagglutination) assay, with significant values of accumulated frequencies for LN/HA factors (ratios between LN and HA titers) higher than two. The accumulated values of frequencies for LN/HA factors as high as four were very significant, 72.7 (per cent) for influenzavirus and 60.7 (per cent) for Newcastle disease virus (NDV), moreover accumulated frequencies for LN/HA factors even as high as 32 were due to influenzavirus (45.4 per cent) and NDV (7.2 per cent) samples. After the storage period, most of those concentraded samples that even did not present HA titers could be detected through LN assay, demonstrating a lower threshold for virus detection

Hemagglutinating and sialidase activities of subpopulations of influenza A viruses

The present study was conducted to investigate the characteristics of two samples of influenza A/England/42/72 (H3N2) virus, one of them selected by an adsorption-elution technique, to determine the possible existence of virus variants or subpopulations. Based on specificity of virulence-related cell receptor-binding and sialidase activities, this selection technique using human O group erythrocytes revealed the presence of variants within a standard virus sample with diversity for their hemagglutinating and sialidase activities. The standard-like (E1) sample exhibited titers of 4 and 32 HAU (hemagglutinating units in 25 microliters) with human O group and chicken erythrocytes, respectively, while the sample obtained by the adsorption-elution process (E2) exhibited titers of 32 and 4 HAU, respectively, with these same types of erythrocytes. The E2 sample showed higher sialidase activity at pH values between 5.4 and 6.6 with human erythrocytes (128-256 HAU), but the E1 sample did not exhibit significant sialidase activity with either human or chicken erythrocytes. The different pH optima for hemolysis (5.2) and sialidase (5.4-6.6) activities and the higher hemolysis indexes present in samples with sialidase activity inhibited by heating (at 56 degrees C for 30 min) or by treatment with EDTA (dilution in buffer containing 2 mM EDTA, a chelating agent on calcium-dependent sialidase activity) demonstrate the independence of these activities in the selected sample: native E2 (absorbance = 0.18), EDTA-treated native E2 (absorbance = 0.28), heated E2 (absorbance = 0.26), EDTA-treated heated E2 (absorbance = 0.41).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of low pH on hemagglutinating and hemolytic activities of west equine encephalomyelitis virus

1. The hemagglutinating (HA) and hemolytic (HL) activities mediated by egg-propagated west equine encephalomyelitis (WEE) virus preparations were investigated. 2. The purified virus preparation exhibited the best HA and HL activity at pH 6.0 and 6.0-6.2, respectively, as observed in the HA and HL tests. 3. In the virus preparations, both HA and HL activities were completely lost upon pretreatment at low pH (6.0). 4. The present results suggest that the alphavirus-mediated HA and HL activities against chicken erythrocytes can be considered to be a fusion from without

Arbovirus: XVII - Acao experimental do virus Piry em camundongos desnutridos. / Arboviruses. XVII - Experimental effect of Piry virus in malnourished mice

Os autores descrevem lesoes predominantes em camundongos com desnutricao proteico-calorica e inoculados com virus Piry. Destas lesoes destacam-se a mielite centrifuga polioclasica e a vasculite de pequenos vasos, salientando a importancia do endotelio como sitio de replicagem viral