Potentiating effect of pidotimod on immune responses of chickens to live attenuated Newcastle disease vaccines

Abstract

Pidotimod is a synthetic dipeptide with immunomodulatory activity, but the capacity of pidotimod as an immunologic adjuvant to improve vaccine immunogenicity remains unclear. This study evaluated the effectiveness of pidotimod on immune responses of chickens to Newcastle disease (ND) vaccine, and its efficiency to improve protection against highly virulent ND virus (NDV). A total of 300 one-day-old broilers were divided into five groups (numbered I to V). Group I were unvaccinated and served as blank control group. Chickens in Group II to V were immunised with ND vaccine and supplemented with 0, 0.5, 1, 2 g/L of pidotimod in drinking water. The results showed that treatment with pidotimod (1 g/L) remarkably improved (p < .05) the potency of ND vaccine in chickens, as demonstrated by increased immune organ index (organ weight/body weight) and elevated antibody production. Meanwhile, no adverse effect on growth performance was observed. Moreover, as an adjuvant to ND vaccine, pidotimod (1 g/L) also dramatically promoted (p < .05) cell-mediated immunity, as characterised by increased lymphocytes proliferation and elevated ratio of CD4+ to CD8+ cells following NDV stimulation. Furthermore, administration of pidotimod (1 g/L) was efficient in inducing effective protection against lethal NDV challenge. Collectively, these data indicate that pidotimod may have the potential to be used as an effective vaccine adjuvant and the immunopotentiating effects deserve further study.