Histiocyte

Definition
noun, plural: histiocytes
A reticular connective tissue macrophage or a dendritic cell, derived from the bone marrow precursor cells
Supplement
Histiocytes are differentiated cells of the mononuclear phagocyte system, i.e. a part of the immune system comprised of the phagocytic cells found in reticular connective tissue. They may be the tissue macrophages (cells capable of phagocytosis) or the dendritic cells (cells involved in processing and presenting antigens).¹ Thus, the histiocytes are primarily involved in phagocytosis and antigen presentation.
Histiocytes came from the stem cells of the bone marrow. They, then, migrate into the bloodstream as monocytes. When they reach and enter a certain organ they undergo differentiation to become histiocytes as influenced by growth factors, GM-CSF, TNF, and IL-4.²
A monocyte that became a histiocyte can be identified histologically through their morphological characteristics and their function.¹ Cytologically, histiocytes would be larger, their cytoplasm, abundant and eosinophilic. As a macrophage, they would express CD68 and their cytoplasm rich with acid phosphatase laden lysosomes. Dendritic histiocytes have bean-shaped nucleus and thin cytoplasmic processes. They express Factor XIIIa, CD1c, and Class II Human leukocyte antigens.²
Word origin: histo– ‎(“tissue”) +‎ –cyte ‎(“cell”)
See also:

• macrophage
• mononuclear phagocyte system

Reference(s):

¹ Mutasim, D. F. (2015). Practical Skin Pathology. Springer. p.33.

² Histiocyte. Retrieved from https://en.wikipedia.org/wiki/Histiocyte.