Introduction
Macrophages were first described as phagocytes in 1882 by Élie
Metchnikoff, this cell type has been found residing in almost every
tissue of the body as large, tissue-resident myeloid cells,
characterized as having pseudopodia and phagocytic granules and by
distinct functional profiles. As a central part of the innate immune
system, they serve a crucial host defense function, but also contribute
to the maintenance of tissue homeostasis by clearing apoptotic and
damaged cells. Macrophages also play an essential role during
organogenesis in embryonic development, where they are highly
concentrated at sites of high cell death, such as the developing limb
buds [1, 2]. These tissue re-modeling functions are maintained in
adults and support wound healing and tissue repair/remodeling processes
after infection and injury. Macrophages can also acquire tissue-specific
phenotypes and functions in different organs. Although they exert
tissue-specific functions, all such tissue-specific macrophages also
release common soluble mediators including enzymes, cytokines,
chemokines, and arachidonic acid derivatives, as well as glycoproteins
such as fibronectin, that help with the maintenance of homeostasis and
tissue repair [3, 4].