The highly pathogenic avian'influenza (HPAI) virus H5N1 causes death in poultry, resulting in significant economic loss in the poultry industry. HPAI H5N1 also poses a major public health threat as it can be transmitted directly nom infected poultry to humans with very high mortality rate level. The HA protein is the antigen of choice for the development of recombinant subunit vaccine to protect against HPAI H5N1. In this experiment, HA5.1 antigen nom avian influenza virus H5N1 was expressed in E. coli BL21 in the fusion form with thioredoxin. The fusion protein of Trx-HA5.1 of 57 .ilia was synthesized in insoluble inclusion body at 30°C under induction of 0.5 mM IPTG. Recombinant protein then was separated nom host soluble proteins by sonication combined with centrifugation. The recombinant protein solubHized in 2M Urea had antigenicity to bind with antibody against HA of virus H5Nl. Additionally Trx-HA5.1 had capable of triggering the production of neutralizing antibodies in chi,
ken when they were immunized with recombinant HA5.1 by subcutaneous injection or intranasal immunization. However, acquired HI titer of antibody raised by TrxHA5.1 was much lower than that evoked by commercial vaccines. Thus it is vital to increase the antigenic dose to gain HI titer of 7log2 that is stimulated by H5N1 vaccines to assess protective immunity of the recombinant antigen in chickens.