Does adjuvanticity depend on the ability to recruit specific immune cells?

Evaluation of: Calabro SM, Tortoli BC, Baudner A et al. Vaccine adjuvants alum and MF59 induce rapid recruitment of neutrophils and monocytes that participate in antigen transport to draining lymph nodes. Vaccine 29(9), 1812-1823 (2011). Adjuvants are used to enhance the delivery and immunogenicity of vaccines. An important function of adjuvants is the recruitment of immune cells to the site of injection. Little is known, however, about the mechanisms involved in such cell recruitment. In a recent paper published in Vaccine, Calabro et al. demonstrate that following intramuscular administration of either alum or MF59, various cell populations, including neutrophils, monocytes, eosinophils, macrophages and dendritic cells, are being recruited to the site of immunization. Interestingly, the number of neutrophils increases by approximately 2000-fold within 16 h and antigen-positive neutrophils were subsequently found in the draining lymph nodes, suggesting an important function of these cells in the induction of adaptive immunity. However, antibody-mediated ablation of neutrophils had no impact on the induction of specific immune responses in these mice, raising the question of whether the function of neutrophils can be substituted by other immune cells.