cerevisiae or those not immunized. Furthermore, oral immunization induced T helper 1-type immune responses mediated via increased serum concentrations of IgG2a and an increase predominantly of IFN-γ-producing cells in their spleens and lamina propria. Our findings suggest that surface-displayed ApxIIA#5-expressed on S. cerevisiae may be a promising candidate for an oral vaccine delivery system for eliciting systemic and mucosal immunity. Saccharomyces cerevisiae, which is typically used in oral vaccines and drugs, is classified as a GRAS organism [1, 2]. Currently, there is great interest in developing mucosal, particularly oral, vaccines, because such vaccines would not only induce locally and

systemically protective immune responses learn more against infectious disease, but would also be safe and convenient to administer. Several oral delivery systems Metformin using live oral vaccines such as a Salmonella typhimurium mutant, Lactobacillus spp., or S. cerevisiae [3-5] have been attempted. Among these delivery systems, the S. cerevisiae yeast expression system has several advantages: high expression levels, ease of scale-up, low cost and the adjuvant potential of yeast cell-wall components such as β-1,3-D-glucan and mannan [6]. Yeast-based expression systems have been developed and successfully used to produce

recombinant proteins [2, 6]. These systems have been employed in pharmaceutical, livestock feed and food industry applications [7]. Recently, the genetic engineering technique of yeast cell-surface Florfenicol display has been used to display heterologous proteins on the surfaces of yeast cells [2, 7-9]. This system could be a good candidate for a live oral vaccine carrier because it stably maintains surface-expressed epitopes with a high density of proteins [8]. Actinobacillus pleuropneumoniae is the causative agent of porcine pleuropneumonia, a highly contagious endemic disease of pigs that results in significant economic losses worldwide [10, 11]. A. pleuropneumoniae can result in various clinical signs ranging from peracute to chronic, infected pigs typically having hemorrhagic, necrotizing pneumonia,

often associated with fibrinous pleuritis [10]. The ApxII toxin, which is believed to be involved in the virulence of A. pleuropneumoniae, has been used as a vaccine protein [12]. The antigenic determinant of ApxIIA (ApxIIA#5) has been shown to induce a strong protective immune response against A. pleuropneumoniae [13]. ApxIIA, expressed in either S. cerevisiae or Nicotiana tabacum, has previously been reported to be capable of inducing protective immune responses against A. pleuropneumoniae in mice [3, 12, 14]. Moreover, surface-displayed expression of ApxIIA#5 on S. cerevisiae has been studied and induction of antigen-specific immune responses and protection against A. pleuropneumoniae in mice assessed [9]. In the present study, we demonstrated that surface-displayed expression of ApxIIA#5 on S.