Oral vaccination may be the most efficient way of inducing an immune response at the remote mucosal site through the common mucosal immune network. Antigen-specific secretory IgA (sIgA) is the major immunoglobulin type generally detected in the secretions of experimental animals following an effective oral immunization. Actinobacillus pleuropneumoniae causing disease in the lung of pig initially interacts, colonizes, and infects the host tissues at the mucosal surface of the respiratory tract. Also, importantly for A. pleuropneumoniae protection, the quantity of sIgA in the lung had merits associated with the mucosal immunity. However, there is no simple method to monitor the level of sIgA as an indicator for the induction of local immune responses by an oral vaccination in the target tissue. Therefore, the relationship between sIgA and IgG was analyzed to evaluate the induction of local immune responses by an oral immunization with Saccharomyces cerevisiae expressing the apxIA and apxIIA genes of A. pleuropneumoniae in this study. The correlation coefficient of determination (r2 × 100) for paired samples in both vaccinated and control groups showed a significant positive-relationship between IgG in sera and sIgA in the lung or intestine. These results indicated that IgG antibody titers in sera could be useful to indirectly predict local immune response, and sIgA, in the lung or intestine to evaluate the efficacy of an oral vaccination.
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