Specific antibody responses and generation of antigenic variants in chickens immunized against a virulent avian influenza virus

To examine the specificity of the antibody response to the influenza hemagglutinin and the generation of antigenic variants, chickens were immunized against the highly virulent H5 virus A/Ty/Ont/7732/66 (H5N9) and then challenged with a lethal dose of the virus. The antibody responses of these chickens to the hemagglutinin (HA) were examined with an enzyme-linked immunosorbent assay (ELISA) in which their sera were titrated for the ability to block the binding of monoclonal antibodies (MAbs) to five distinct neutralizing epitopes on the viral HA. Based on the ELISA results, a majority (5/6) of the chickens produced antibodies to three of the five neutralizing epitopes on the viral HA. After challenge, two of six immunized chickens shed virus and died; antigenic comparisons of isolates from these two chickens indicated the presence of an antigenic variant; i.e., there was a change in one neutralizing epitope on the HA of virus shed by one chicken. None of the chickens had produced antibodies to this particular epitope on the viral HA. Inoculation of chickens with this variant resulted in 100% mortality, demonstrating that a change in this particular epitope did not alter the virulence of the virus. These studies indicate that chickens immunized against highly virulent influenza viruses may excrete virulent variants following challenge with live virus. /// Para examinar la especificidad de la respuesta de anticuerpos a la hemoaglutinina de influenza y la generación de variantes antigénicas, se inmunizaron pollos contra la cepa altamente virulenta de influenza aviar A/Ty/Ont/7732/66 (H5N9) y luego fueron desafiados con una dosis letal del virus. Se examinaron las respuestas de anticuerpos de estos pollos a la hemoaglutinina (HA) usando una prueba de bloqueo al inmunoensayo con enzimas asociadas (ELISA). En esta prueba, el suero se titula por su capacidad de bloquear la unión de los anticuerpos monoclonales a 5 epítopes neutralizantes diferentes de la hemoaglutinina viral. Basado en los resultados obtenidos en la prueba ELISA, la mayoría de los pollos (5/6) produjeron anticuerpos contra 3 de los 5 epítopes neutralizantes de la hemoaglutinina viral. Después del desafío, se tomaron hisopos traqueales y cloacales para el aislamiento de virus que fueron luego examinados con varios anticuerpos monoclonales preparados contra la hemoaglutinina H5. Dos de los 6 pollos inmunizados eliminaron virus y murieron; la comparación antigénica de los virus aislados de estos 2 p