Adjuvant effects of chicken interleukin-18 in avian Newcastle disease vaccine

Interleukin-18 (IL-18) can induce interferon-γ (IFN-γ) production and promote Th1 immunity, and hence, it modulates immune functions. In the present study, the in vitro and in vivo immunomodulatory activities of full length or mature chicken IL-18 expressed in a prokaryotic expression system (pCHIL18-F and pCHIL18-M, respectively) and chicken IL-18 expressed in a eukaryotic expression system (euCHIL18) were examined. Results showed that pCHIL18-F, pCHIL18-M and euCHIL18 significantly enhanced IFN-γ mRNA expression in chicken splenocytes, which successfully increased IFN-γ-induced nitric oxide (NO) synthesis by macrophages. Vaccination with cell-cultured Newcastle disease vaccine (NDTC) co-administrated with pCHIL18-F, pCHIL18-M or euCHIL18 resulted in significant increments of hemagglutination inhibition (HI) titers, cell proliferation of peripheral blood mononuclear cells (PBMC), and ratios of CD8+ to CD4+ in chickens compared with inoculation of PBS or NDTC alone. Thus, full length and mature chicken IL-18 expressed using a prokaryotic system and using a eukaryotic system showed equivalent in vitro and in vivo biological activities, and all forms effectively enhanced cell-mediated and humoral immunity, suggesting possible future use as a potential adjuvant in chicken NDTC vaccine production.