Cytokines as adjuvants for avian vaccines.

The worldwide trend towards a reduced reliance on in-feed antibiotics has increased the pressure to develop alternative strategies to manage infectious diseases in poultry. With this in mind, there is a great emphasis on vaccine use and the enhancement of existing vaccines to provide long-term protection. Currently existing adjuvants for poultry can have deleterious side-effects, such as inflammation, resulting in the down-grading of meat quality and a subsequent reduction in profits. Therefore, to enhance the use of vaccination, alternative adjuvants must be developed. The use of recombinant cytokines as adjuvants in poultry is attracting considerable attention, and their potential role as such has been addressed by several studies. The recent identification of a number of chicken cytokine genes has provided the possibility to study their effectiveness in enhancing the immune response during infection and vaccination. This review focuses on the recent studies involving the assessment of cytokines as vaccine adjuvants.

Interleukin-2 directly induces activation and proliferation of chicken T cells in vivo.

Cytokines, as immune activators, have been investigated in mammalian systems as natural adjuvants and therapeutics. In particular, interleukin-2 (IL-2) has been studied widely as a vaccine adjuvant and immuno-enhancer because of its role in activating T cell proliferation. We show here that the first nonmammalian IL-2 gene cloned, chicken IL-2 (ChIL-2), exhibits similar biologic activities to those of mammalian IL-2. To assess the activities of ChIL-2 in vivo, we injected birds with recombinant ChIL-2 (rChIL-2) protein. rChIL-2 treatment induced peripheral blood lymphocytes to express cell surface IL-2 receptors (IL-2R) within 48 h and resulted in an increase in the proportion of peripheral blood CD4+ and CD8+ T cells. Using bromodeoxyuridine (BrdU) incorporation as a measurement of cell proliferation, we showed the increase in T cell populations to be due to cell proliferation. The ability of ChIL-2 to cause both activation and proliferation of T cells in vivo indicates that it has the potential to be used as an immune activator.

The emerging role of avian cytokines as immunotherapeutics and vaccine adjuvants.

The use of antibiotic feed additives and chemical antimicrobials in food production animals is a double-edged sword. On one hand, it helps to prevent the outbreak of disease and promotes the growth of animals, but on the other hand, concerns are mounting over the emergence of antibiotic-resistant bacteria. As a consequence, some countries have already banned the use of in-feed antibiotics which has resulted in meat producers urgently seeking environmentally friendly alternative methods to control disease. Cytokines are proteins that control the type and extent of an immune response following infection or vaccination. They therefore represent excellent naturally occurring therapeutics. The use of cytokines in poultry has become more feasible with the discovery of a number of avian cytokine genes. Since the immune system of chickens is similar to that of mammals, they offer an attractive model system to study the effectiveness of cytokine therapy in the control of disease in livestock. This review will focus on the recent advances made in avian cytokines, with a particular focus on their assessment as therapeutic agents and vaccine adjuvants.