Oral administration of chicken NK-lysin or recombinant chicken IL-7 improves vaccine efficacy of Eimeria tenella Elongation Factor-1a (EF-1a) against coccidiosis in commercial broiler chickens

Authors: LEE, YOUNGSUB - US Department Of Agriculture (USDA); PARK, INKYUNG - US Department Of Agriculture (USDA); Lillehoj, Hyun

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/2023
Publication Date: 5/1/2023
Citation: Lee, Y., Park, I., Lillehoj, H.S. 2023. Oral administration of chicken NK-lysin or recombinant chicken IL-7 improves vaccine efficacy of Eimeria tenella Elongation Factor-1a (EF-1a) against coccidiosis in commercial broiler chickens. Poultry Science. 102:102611. https://doi.org/10.1016/j.psj.2023.102611.
DOI: https://doi.org/10.1016/j.psj.2023.102611

Interpretive Summary: Avian coccidiosis is a ubiquitous intestinal disease caused by several distinct species of Eimeria parasites with significant economic losses to global poultry industry, but there are no recombinant vaccines which are commercially available yet. In this study, ARS scientists describe a novel recombinant vaccine strategy using a subunit of Eimeria parasite antigen, 3-1E, which induces a broad cross-protective host immunity against several different species of Eimeria when chickens are immunized with 3-1E recombinant antigen mixed in the ISA78 commercial immunostimulatory adjuvant. The results of this study showed that the vaccine combination of recombinant 3-1E protein, chicken cytokine IL-7, a T-lymphocyte stimulating cytokine, emulsified in immune stimulating gel stimulated protective immune response with high serum antibodies and cellular immune response. Furthermore, incorporation of orally-delivered chicken antimicrobial peptide, NKlysin, into the vaccine strategy, also enhanced the protective efficacy of 3-1E recombinant vaccine. In summary, these results show the protective effects of the EF-1a recombinant vaccine, which can be further enhanced by co-injection with IL-7 or NK lysin against E. maxima infection. These results will facilitate the development of a novel immunostimulatory strategy against coccidiosis using recombinant antigen to reduce the use of antibiotics and save more than $13 billion economic losses due to coccidiosis.

Technical Abstract: Synergistic effects of orally-delivered chicken NK-lysin peptide 2 (cNK-2) or recombinant chicken IL-7 (rchIL-7) on vaccination with recombinant protein Eimeria elongation factor-1a (rEF-1a) against Eimeria maxima (E. maxima) infection was investigated in broiler chickens. Chickens were divided into six groups: control (CON, no Eimeria infection), non-immunized control (NC, PBS), Vaccination 1 (VAC 1, rEF-1a plus cNK-2), Vaccination 2 (VAC 2, rchIL-7 plus cNK-2), Vaccination 3 (VAC 3, rEF-1a/rchIL-7 plus cNK-2), and Vaccination 4 (VAC 4, rEF-1a/rchIL-7 in IMS plus cNK-2). All groups, except the CON and NC, were orally treated with cNK-2 plus MontanideTM IMS 1313 N VGPR for 5 days (from day 18 to day 22). The first immunization, except the VAC 4 group, was performed intramuscularly with MontanideTM ISA 78 VG on day 4, and the second immunization was given with the same concentration of components as the primary immunization one week later. The immunization of chickens in VAC 4 group was carried out by an oral inoculation emulsified in MontanideTM IMS on the same days. On day 19, all chickens except the CON group, were orally challenged with freshly sporulated oocysts of E. maxima (1.0 × 104 oocysts/chicken). The in vivo vaccination results showed that all chickens in VAC 1 and VAC 3 groups produced high (p < 0.05) levels of serum antibody titers to rEF-1a, and the VAC 3 chickens showed enhanced (p < 0.05) levels of serum IL-7. Furthermore, VAC 3 group showed significantly (p < 0.01) greater body weight gains at 6 and 9 days post-E. maxima infection (dpi) with a reduced fecal oocyst shedding at 6 dpi when the NC group showed maximum oocyst production. At 6 dpi, the average jejunal lesion score of NC group was 2.5 whereas chickens in the VAC 1 group showed a significantly (p < 0.05) lower jejunal lesion scores following E. maxima challenge infection. E. maxima challenge infection significantly (P < 0.05) up-regulated the expression levels of cytokines that are associated with inflammation (IL-6, IL-10, and IFN-gamma) in the jejunum at 4 dpi, but the cytokine gene expressions were down-regulated in VAC 1 or VAC 3 groups. Moreover, the gene expression levels of tight junction proteins, Jam 2 and Occludin, were significantly decreased (P < 0.05) following E. maxima challenge infection in jejunum at 4 dpi (NC), but their expressions were increased in VAC 3 group to the similar levels of CON group. The administration of chIL-7 and cNK-2, without rEF-1a, did not show any protective effects against E. maxima infection. Collectively, these results showed that the efficacy of rEF-1a vaccination was significantly enhanced when chickens were co-immunized with chIL-7 or oral cNK-2.