Effect of the novel DNA vaccine fusing inhibin α (1-32) and the RF-amide related peptide-3 genes on immune response, hormone levels and fertility in Tan sheep

• RFRP-3 gene was firstly constructed DNA vaccine for improving the fertility.
• The novel vaccine significantly increased the levels of reproductive hormones.
• The novel DNA vaccine had certain potency in improving fertility in Tan sheep.

The objective of the present study was to evaluate the effects of novel DNA vaccines fusing inhibin (INH) α (1-32) and RFamide-related peptide-3 (RFRP-3) genes on the immune response, reproductive hormone levels, and fertility of Tan sheep. Thirty-two female Tan sheep were divided into four groups (groups A, B, C, and D with 8 sheep per group) and respectively immunized (thrice, 20 d apart) with 0.6 mg of p-TPA-SINH/TPA-SRFRP (group A), p-SINH/SRFRP (group B), p-SINH (group C) or 0.4 ml saline (group D). Twenty days after primary immunization, all vaccines elicited significant immune responses, and the antibody levels of anti-INH and anti-RFRP-3 in the vaccinated groups were significantly higher (p < 0.05) than that of the control group. Immunization with p-TPA-SINH/TPA-SRFRP induced higher antibodies against INH and RFRP-3. Hormone levels of FSH and LH in group A immunized with p-TPA-SINH/TPA-SRFRP were significantly higher (p < 0.05) than those in group C, which are immunized with p-SINH and the control group 20 d after the third immunization. Additionally, the p-TPA-SINH/TPA-SRFRP, p-SINH/SRFRP, p-SINH and saline vaccine induced different twinning rate of ewes (37.5%, 37.5%, 12.5%, and 0, respectively), but no significant differences were found in improving twinning rate of ewes among four groups. These results suggested that neutralization of endogenous INH and RFRP-3 with novel DNA vaccine fusing INH α (1-32) and RFRP-3 genes successfully elicited a humoral immune response, increased reproductive hormone levels, but it did not significantly improve litter sizes and twinning rate of ewes in the present study.