Novel insights into embryonic cardiac macrophages.

Macrophages are vital inhabitants of the developing heart. Nonetheless, their key role is not limited to prenatal processes, as embryo-derived macrophages govern the pool of cardiac macrophages also postnatally. Namely, embryonic cardiac macrophages are of yolk sac-, embryonic monocyte-, and heart-tissue origin. They persist, self-renew and/or are gradually replaced by blood monocytes and assume microenvironment-dependent macrophage phenotypes both in the pre- and postnatal heart. Still, it is during embryonic development that cardiac macrophages gain tissue-specific phenotypes and multifunctional diverse properties. Currently, with the emergence of newer research methods, novel facts about embryonic macrophage ontogeny, lifecycle, and repertoire of functions have been revealed. Meeting the high interest in cardiac macrophages, we present this up-to-date overview of embryonic cardiac macrophages, emphasizing the fundamental concepts and discrepancies related to macrophage characteristics, current research gaps, and potential future developments in this field.