From phagocyte diversity and activation to probiotics: back to Metchnikoff.

In this issue of the European Journal of Immunology, Siamon Gordon gives a detailed account of Metchnikoff's life and his achievements (Eur. J. Immunol. 2008. 38: 3257-3264). Looking back at the roots of innate immunity stimulates reflections on open issues in the field. Here, I give a personal view of some of these issues, including myeloid-derived suppressor cells, macrophage polarization and adaptive responses of mononuclear phagocytes.