Cytocrine

Cytocrine is a term used in cell biology to describe a mode of intercellular communication in which secretory products are delivered directly from a donor cell into a neighboring recipient cell, rather than being released into extracellular spaces or the bloodstream. The word derives from cyt- meaning cell and -crine from krinein, related to secretion; it is analogous to endocrine, exocrine, and paracrine signaling, but emphasizes direct intercellular transfer.

In epidermal biology, cytocrine transfer is best known for pigment distribution. Melanocytes generate melanosomes and extend dendritic processes into surrounding keratinocytes; pigment can be transferred along these processes, with keratinocytes phagocytosing pigment-containing tips. This cytocrine transfer contributes to the spread of melanin across the epidermal layer and helps determine skin, hair, and eye color. The mechanism has been described as involving direct cytoplasmic exchange or transfer of pigment-containing organelles, rather than secretion into the surrounding fluid.

Beyond pigmentation, the term cytocrine has appeared in broader cell biology to describe direct cytoplasmic exchange between neighboring cells in some systems, though the evidence and terminology vary. In contemporary literature, cytocrine is less commonly used than more specific terms such as melanosome transfer or pigment transfer, and may be encountered as a historical or descriptive label rather than a distinct signaling pathway.

See also: Melanosome transfer, Melanocyte, Keratinocyte, Melanin.