Antigen dependent adjuvant activity of a polydispersed β-(1,4)-linked acetylated mannan (acemannan)

Abstract

The adjuvant properties of a polydispersed β-(1,4)-linked acetylated mannan, acemannan (ACE-M), were evaluated. Day-old broiler chicks were randomly selected and allocated to four flocks (Vac 1–4). The Vac 1 flock was sham vaccinated with saline. The Vac 2 flock was vaccinated with an oil-based vaccine (Breedervac III; Newcastle disease virus (NDV), infectious bursal disease virus (IBDV) and infectious bronchitis virus). The Vac 3 flock was vaccinated with a vaccine—ACE-M mixture, and the Vac 4 flock was vaccinated with vaccine and ACE-M at separate anatomical sites. ELISA titres to NDV and IBDV were determined. The immune response to NDV at 21 days postvaccination (PV) was significantly enhanced (P ⩽ 0.05) by the addition of ACE-M to the vaccine, compared with vaccination without ACE-M. Subsequently, the vaccine—ACE-M mixture appeared to suppress the immune response to NDV. However, at day 35 PV, 95% of the Vac 3 chicks compared with 90% of the Vac 2 and 89% of the Vac 4 chicks exhibited protective titres. The response to IBDV differed from that to NDV. At day 21 PV the immune response to IBDV was essentially the same for all flocks that received vaccine, i.e. addition of ACE-M to the vaccine did not significantly enhance the immune response; however, it did significantly (P ⩽ 0.05) sustain the immune response at days 28 and 35. In addition to the observed effect on titres to NDV and IBDV, ACE-M also had an effect on flock immunity. ACE-M administration at a separate site resulted in higher protective titres and a narrower titre group distribution. Overall, this study clearly showed that ACE-M exhibits adjuvant properties and that the adjuvant effect is antigen dependent. It enhanced the immune response to both NDV and IBDV.