Innate immune cells and antigen-presenting cells (APCs)

The term refers to the diverse population of leukocytes, including monocytes, macrophages, neutrophils, and dendritic cells, that are mobilized to the site of injection following the administration of the MF59C.1 adjuvant (Seubert et al., 2008). MF59C.1 is a squalene-based oil-in-water emulsion used primarily in influenza vaccines (e.g., Fluad) to enhance immunogenicity, particularly in older adults (Schultze et al., 2008). Instead of targeting a single receptor, MF59 acts as a "signal 0" that triggers a transient local inflammatory response, leading to the secretion of chemokines such as CCL2, CCL3, and CXCL8 (O'Hagan et al., 2013). These chemokines recruit innate immune cells from the blood, which then differentiate into mature antigen-presenting cells (APCs). These APCs are responsible for the efficient uptake of vaccine antigens and their subsequent transport to the draining lymph nodes, where they facilitate the activation of T and B lymphocytes (Calabro et al., 2011). This coordinated recruitment and activation are essential for the adjuvant's ability to increase the magnitude, persistence, and breadth of the vaccine-induced immune response.

Other names

Antigen-presenting cellsInnate immune cellsMonocytesMacrophagesDendritic cellsNeutrophilsMF59-activated cells

MF59 creates a local immunocompetent environment at the injection site, inducing the release of chemokines like CCL2 and CXCL8, which recruit monocytes and dendritic cells that then transport antigens to lymph nodes (O'Hagan et al., 2013; Seubert et al., 2008).