Abstract
Background: Avian leukosis viruses (ALVs) are important contagious suppressive factors of chicken immunity and growth performance, resulted in enormous economic loss. Although virus eradication programs are applied in breeder flocks, ALVs are still widespread globally. Therefore, other valuable adjunct to reduce the negative effect of ALVs should be considered. Bursin-like peptide (BLP) showed remarkable immunomodulatory effects, whereas their influence on ALV-infected avian groups has not been reported. Here, a designed hybrid BLP was expressed in E. coli. The purified BLP was injected subcutaneously weekly in SPF chickens congenitally infected with a natural ALV strain. Then the influences of this BLP on the growth performance, immune response and virus titer of ALV-infected chickens were determined. Results: This BLP injection significantly improved the body weights of ALV-infected birds (P < 0.05). BLP injection significantly enhanced organ index in the BF in ALV-infected birds (P < 0.05). The weekly injection of BLP significantly lengthened the maintenance time of antibodies against Newcastle disease virus (NDV) attenuated vaccine of ALV-infected birds (P < 0.05) and boosted the antibody titer against avian influenza virus (AIV) H5 inactive vaccine of mock chicken (P < 0.05). BLP injection in mock chickens enhanced the levels of serum cytokines (IL-2, IL-4 and interferon-γ) (P < 0.05). Surprisingly, the novel BLP significantly inhibited expression of the ALV gp85 gene in the thymus (P < 0.05), kidney (P < 0.05) and bursa of Fabricius (BF) (P < 0.01) of ALV-infected chickens. Both viral RNA copy number and protein level decreased significantly with BLP (50 μg/mL) inoculation before ALV infection in DF1 cells (P < 0.05). Conclusions: This is the first report investigating the influence of BLP on the growth and immunity performance of chickens infected by ALV. It also is the first report about the antiviral effect of BLP in vivo and in vitro. This BLP expressed in E. coli showed potential as a vaccine adjuvant, growth regulator and antiretroviral drug in chickens to decrease the negative effects of ALV infection.