a decreasing trendp < 0.05
9 , TNF-α expression in the spleen, head kidney and intestine of the recombinant pPG-Aha1/Lc CC16 and pPG-Aha1-CTB/Lc CC16 groups was increased rapidly at the early stage of immunization, with a decreasing trend at day 28, and reached the highest level at the second booster immunization ( p < 0.05).