SUMMARY An investigation was made of 3 serological tests (virus neutralization, complement fixation and indirect immunofluorescence), which are applicable to epidemiological studies of infections by Equid herpesvirus 1 (EHV‐1). Sera from gnotobiotic foals inoculated intranasally with various strains of EHV‐1 were unable in some cases to neutralize heterologous strains and these results were not consistent with the existence of clearly‐defined subtypes of EHV‐1, as previously proposed. The cross‐reactions in complement‐fixation tests paralleled those with neutralization but immunofluorescence tests were found to be both more sensitive and more broadly reactive than the other two. Complement‐fixing antibodies declined more rapidly following experimental infection than did those measured by neutralization or immunofluorescence. The results are discussed in relation to the diagnosis of EHV‐1 infection and the significance they may have for the epidemiology of this disease. RÉSUMÉ En utilisant 3 tests sérologiques (Fixation du complément, Neutralisation du virus, Immuno‐fluorescence indirecte), on a procédéà des recherches épidémiologiques des infections équines par les Herpesvirus 1 (EHV‐1). Des sérums provenant de foals gnotobiotiques inoculés par voie transnasale avec diverses souches de EHV‐1 n'ont pu, dans certains cas, neutraliser des souches hétérologues; ces résultats ne concordaient pas avec l'hypothèse antérieurement formulée qui supposait l'existence de sous‐types EHV‐1 bien définis. Les réactions croisées obtenues par la Fixation du Complément donnèrent des résultats similaires à ceux obtenus par neutralisation. Au contraire, les épreuves par immunofluorescence furent à la fois plus sensibles et plus intenses. Les anticorps fixant le complément à la suite d'une infection expérimentale diminuèrent plus rapidement que les anticorps mesurés par neutralisation ou par immuno‐fluorescence. Ces résultats sont discutés quant à la valeur diagnostique et quant à la signification qu'ils peuvent avoir pour étudier l'épidémiologie de la maladie. ZUSAMMENFASSUNG 3 serologische Nachweismethoden (Virus‐Neutralisation; Komplementbindung und indirekte Immunofluoreszenz) wurden überprüft, die für epidemiologische Studien von EHV‐1‐Infektionen in Frage kommen. Serumproben von gnotobiotischen Fohlen, die intranasal mit verschiedenen EHV‐1 Stämmen inokuliert worden waren, zeigten sich in gewissen Fällen nicht fähig heterologe Stämme zu neutralisieren. Diese Resultate stimmen nicht überein mit der Existenz klar definierter Subtypen von EHV‐1, die früher vorgeschlagen wurden. Die Kreuzreaktionen im Komplementbindungstester‐gaben dieselben Resultate wie die Virusneutralisation, aber die Immunofluoreszenz erwies sich als empfindlicher und reagierte breiter als die beiden anderen Tests. Komplementbindende Antikörper fielen nach experimenteller Infektion schneller ab als die mit Neutralisation und Immunofluoreszenz nachgewiesenen. Diese Befunde werden besprochen unter Berücksichtigung ihrer Bedeutung für die Diagnose von EHV‐1 Infekt...
Four major neutralizing regions of the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein were identified and characterized with a panel of 80 HIV-1 antibody-positive human sera. Levels of neutralizing antibodies against the HIV-1 strains IIIB, SF2, and RF were compared with reactivity in ELISAs against peptides that correspond to certain regions of the HIV-1 envelope. A correlation between high neutralizing activity and strong seroreactivity against specific peptides suggested that the corresponding regions might be involved in neutralization. This was further substantiated by using peptides to inhibit neutralization by a panel of 10 HIV-1 antibody-positive sera. The positions of three neutralizing sites, defined earlier mostly by antisera from animals, were confirmed in the present study. Human sera thus recognize the strain-specific third variable region of gp120 (amino acids 304-318), the C-terminal end of gp120 (amino acids 489-508), and the conserved region in the intracellular part of gp41 (amino acids 732-746). It is likely that these different regions mediate help rather than self-sufficient neutralization. Furthermore, a human neutralizing region was detected in a conserved part of gp41 (amino acids 647-671). Accordingly, neutralizing antibodies directed to this region were found to be cross-reactive between HIV-1 strains. Peptides corresponding to these four regions were able to inhibit neutralization mediated by serum from HIV-1 antibody-positive individuals. These results indicate that this conserved B-cell epitope of the HIV-1 envelope elicits a virus-neutralizing antibody response during natural infection in humans and may therefore be considered for inclusion in a vaccine against HIV-1.
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