The Hofbauer cells are of fetal origin, and can be detected as early as day 10 dpc in the human chorionic villous stroma. They are large (10-30µm) granulated cells, categorized as placental M2/alternatively activated macrophages.
The Hofbauer cells have features in common with macrophages, such as cytoplasmic processes, large vacuoles, many pinocytotic vesicles and intracytoplasmic granules, which enables micropinocytotic activity and phagocytosis. In addition, they have been shown to play a roles in early placental vasculogenesis, villous tree development and promotion of the placental mesenchyme.
The origin of these cells is proposed to be in monocyte progenitor cells of the hypoblast-derived yolk sac, that migrate to the mesenchymal core of the chorionic villi. However, alternative theories exist and since these cells precede the development of fetal circulation, it has been proposed that they originate in villous mesenchymal stem cells of the stroma, although later in development their origin could include fetal monocytes.