Histiocytes

Histiocytes are cells within the mononuclear phagocyte system that reside in tissues as part of innate immunity. They are tissue macrophages and dendritic cells that originate from circulating monocytes, which migrate into tissues and differentiate in response to local signals.

In normal physiology, histiocytes perform phagocytosis of debris, dead cells, and pathogens; they also secrete cytokines and present antigens to T cells, contributing to both innate and adaptive immunity. They are involved in wound healing, remodeling, and clearance of immune complexes. In various tissues they have specialized forms, such as alveolar macrophages in the lungs, Kupffer cells in the liver, microglia in the brain, and Langerhans cells in the epidermis.

The term histiocyte historically encompassed a broad group of tissue-resident macrophages and dendritic cells. In pathology, histiocytes may be identified with immunohistochemical markers such as CD68 for macrophages and CD1a or langerin for Langerhans cells.

Disorders related to histiocytes include histiocytoses, a spectrum of diseases with abnormal proliferation of histiocytes, such as Langerhans cell histiocytosis. Hyperinflammatory conditions like hemophagocytic lymphohistiocytosis involve excessive activation of histiocytes/macrophages, leading to systemic inflammation. Treatment depends on the specific disorder.

This article uses the term histiocytes to refer to tissue-resident immune cells of the mononuclear phagocyte system.