Enhancement of protective immune responses by oral vaccination with Saccharomyces cerevisiae expressing recombinant Actinobacillus pleuropneumoniae ApxIA or ApxIIA in mice
Sung Jae Shin1,†, Seung Won Shin1, Mi Lan Kang1, Deog Yong Lee1, Moon-Sik Yang2, Yong-Suk Jang2, Han Sang Yoo1,*
1Department of Infectious Diseases, College of Veterinary Medicine, BK21 for Veterinary Science and KRF Zoonotic Disease Priority Research Institute, Seoul National University, Seoul 151-742, Korea, 2Division of Biological Science, Institute for Molecular Biology and Genetics, Chonbuk National University, Jeonju 561-756, Korea
We previously induced protective immune response by oral immunization with yeast expressing the ApxIIA antigen. The ApxI antigen is also an important factor in the protection against Actinobacillus pleuropneumoniae serotype 5 infection; therefore, the protective immunity in mice following oral immunization with Saccharomyces cerevisiae expressing either ApxIA (group C) or ApxIIA (group D) alone or both (group E) was compared with that in two control groups (group A and B). The immunogenicity of the rApxIA antigen derived from the yeast was confirmed by a high survival rate and an ApxIA-specific IgG antibody response (p＜0.01). The highest systemic (IgG) and local (IgA) humoral immune responses to ApxIA and ApxIIA were detected in group E after the third immunization (p ＜ 0.05). The levels of IL-1■ and IL-6 after challenge with an A. pleuropneumoniae field isolate did not change significantly in the vaccinated groups. The level of TNF-■ increased in a time-dependent manner in group E but was not significantly different after the challenge. After the challenge, the mice in group E had a significantly lower infectious burden and a higher level of protection than the mice in the other groups (p＜0.05). The survival rate in each group was closely correlated to the immune response and histopathological observations in the lung following the challenge. These results suggested that immunity to the ApxIA antigen is required for optimal protection.