[Differentiation of equine influenza viruses subtype 2 with monoclonal antibodies].

Infections and clinical diseases caused by equine 2 influenza A viruses are observed worldwide. The frequency of these outbreaks supports the hypothesis that antigenic variation of the surface proteins may play an important role. For the demonstration of these variations, monoclonal antibodies (Mabs) were prepared. They are directed against the hemagglutinin or the neuraminidase of the prototype strain a/eq/Miami/1/63. In hemagglutination-inhibition assays with Mabs two reaction patterns were observed: four Mabs inhibited 14 out of 17 strains tested. Another Mab recognized the hemagglutinin of only 4 strains. One strain was not inhibited by any of the Mabs. This reaction pattern was not changed by purification of the Mabs using different techniques. Following tween 80/ether treatment of some strains, the Mab reacting more strain-specific had higher titers against the four closely related strains. Tween 80/ether treatment did not affect the titers of the Mabs reacting more subtype-specific. Analysis of the neuraminidase of 17 strains revealed a marked variation in two strains. Different purification procedures had some influence on the titers of the Mabs but did not alter the pattern of the reaction. The antigenic variation of surface proteins detected by Mabs are not seen so clearly when conventional antisera are used. Therefore, antigenic variations are probably not responsible for outbreaks of equine influenza in vaccinated animals.