LAUSR

Simple Summary 1. Oral inoculation with recombinant yeast co-expressing pig IL-2 and fused bovine cathelicidin (FBC) significantly enhanced systemic immunity in mice. 2. The inoculated mice displayed stronger resistance against E. coli or S. aureus infection. 3. Recombinant yeast co-expressing PIL-2 and FBC could facilitate the development of new immunopotentiator to prevent the infection of antibiotic-resistant bacteria. Abstract In order to develop an effective and safe immunomodulator to enhance the antimicrobial bioactivity and immunity of animals against infectious bacterial diseases, a recombinant plasmid pGAPZαA-IL2-B co-expressing pig interleukin-2 (PIL-2) and fused bovine cathelicidin (FBC) genes were constructed using the 2A self-cleavage technique. After being expressed in Pichia pastoris strain SMD1168, the recombinant yeast was administered orally to 5-week-old female ICR mice. The control mice were similarly dosed with P. pastoris with a blank plasmid or FBC recombinant plasmid alone. At 28 days post-treatment, the mice were challenged intraperitoneally with virulent strains of either E. coli or S. aureus. Compared with the control groups, the mice that received recombinant yeast co-expressing PIL-2/FBC manifested significant increases in the number of leukocytes, CD4+ and CD8+ T cells, IgG, and the gene expressions of TLRs(TLR1,4,6,9), antimicrobial peptides(CRP4 and CRAMP) and cytokines (IL-2, 4, 6, 7, 12, 15, 23, IFN-γ, and TNF-α) in the blood. Furthermore, the treated mice displayed significantly higher survival than the other two control groups after the challenge. These results suggest that the antimicrobial activity and immunity of animals can be effectively enhanced by the in vivo co-expression of IL-2 and the FBS gene, which can facilitate the development of new immunopotentiation molecules to overcome the infection of antibiotic-resistant bacteria.