Release characteristics of microspheres prepared by co-spray drying Actinobacillus pleuropneumoniae antigens and aqueous ethyl-cellulose dispersion

Using formalin inactivated Actinobacillus pleuropneumoniae antigens and aqueous ethylcellulose dispersions, microspheres of oral vaccines were developed by a co-spray drying process. The present study attempted to determine whether the dosage formulations of microspheres could form enteric matrices. To assess the enteric characteristics, an in vitro dissolution test was performed with the AQ6-AP microspheres; 95% of the A. pleuropneumoniae protein was released within 3 h at pH 7, but there was no release at pH 1.5. The scanning microscopy revealed that the surface structure of AQ6-AP microspheres became porous at neutral pH. The SDS-PAGE analysis showed that the release rate of proteins from the microspheres was pH dependent not only for the AQ6-AP formulation but also when antigens of A. pleuropneumoniae were replaced with porcine serum. The results suggest that the A. pleuropneumoniae antigens were entrapped in the AQ6 microspheres under the acidic conditions. In a mouse model, oral immunization with AQ6-AP microspheres containing A. pleuropneumoniae evoked systemic IgG and mucosal IgA responses against A. pleuropneumoniae antigens. Thus, the present method may further provide an opportunity to develop oral vaccines and mucosal immunity.