Potentiation of humoral immune responses to vaccine antigens by recombinant chicken IL-18 (rChIL-18)

Mammalian interleukin-18 (IL-18) is one of the pro-inflammatory cytokines involved in innate immune responses to microbial infection preceding the induction of both cellular and humoral immune responses. We assessed the potential of Escherichia coli-expressed His-tag purified recombinant chicken IL-18 (rHis-ChIL-18) as a potentiator of vaccine-induced immune responses in 3 week-old SPF chickens and compared it with several commonly used traditional immunostimulating adjuvants. We found that rHis-ChIL-18 significantly enhanced antibody responses to Clostridium perfringens α-toxoid and Newcastle disease virus (NDV) antigens, comparable to the Al(OH)3–gel, Miglyol and chitosan adjuvant. However, antibody responses were lower than water-in-oil (w/o) emulsions and combinations of rHis-ChIL-18 with Al(OH)3–gel, Miglyol or chitosan. Improved HI-titers for infectious bronchitis virus (IBV) were not noted. We conclude that rHis-ChIL-18, when delivered in the proper context, is a novel and safe immunostimulator in chickens.