Hemocytes

Definition

Circulating cells in the hemolymph of invertebrates, primarily arthropods, that function analogously to vertebrate blood cells in immune defense, wound healing, and nutrient transport. Hemocytes include multiple morphological and functional classes—such as granulocytes, plasmatocytes, and spherulocytes in insects—that mediate phagocytosis, encapsulation of foreign bodies, nodule formation, and melanization responses.

Etymology

Greek haima (blood) + kytos (cell)

Example

In the tobacco hornworm (Manduca sexta), plasmatocytes are the most abundant hemocyte type and serve as the primary phagocytic responders to bacterial infection, while granulocytes release cytotoxic compounds during encapsulation of parasitoid wasp eggs.

Synonyms

• blood cells (invertebrate)
• coelomocytes (in some contexts)

Related Terms

• Hemolymph
• Phagocytosis
• Encapsulation
• melanization
• innate immunity
• Granulocyte
• Plasmatocyte

Usage Notes

Hemocytes are specific to invertebrate open circulatory systems and should not be conflated with vertebrate blood cells, though functional parallels exist. The term is most commonly applied to arthropods, particularly insects and crustaceans, but also appears in mollusk and echinoderm literature. Classifications of hemocyte types vary by taxon and researcher; 'granulocyte' and 'plasmatocyte' are standard for insects, while crustacean hemocyte typology uses partly overlapping terminology. Hemocyte counts and differential profiles are used as physiological indicators of stress, infection, or environmental quality in entomological and aquaculture research.