Encapsulation

Definition

A cellular immune response in which host hemocytes aggregate and deposit melanin around a foreign invader too large to be phagocytosed, forming a multilayered capsule that isolates and often kills the target through asphyxiation, starvation, or cytotoxic compounds. In insects and other arthropods, encapsulation is the primary defense against parasitoid eggs and larvae, nematodes, and other multicellular parasites that penetrate the hemocoel.

Etymology

Example

When a parasitoid wasp oviposits into a caterpillar, the host's granular cells and plasmatocytes may recognize the egg as foreign and initiate encapsulation, surrounding it with successive layers of hemocytes that melanize and harden into a dark, impenetrable sheath; some parasitoids evade this response by coating their eggs with host-like proteins or by injecting venom that suppresses hemocyte function.

Synonyms

• cellular encapsulation
• immune encapsulation

Related Terms

• hemocyte
• melanization
• Phagocytosis
• nodulation
• Parasitoid
• immune evasion
• humoral immunity
• granular cell
• Plasmatocyte

Usage Notes

Encapsulation is distinguished from nodulation (smaller, nodular aggregates around microbial clumps) and from humoral immunity (soluble antimicrobial peptides). The term is sometimes used more broadly in materials science or pharmacology, but in arthropod biology it refers specifically to this hemocyte-mediated process. Success rates of encapsulation vary with host age, nutritional state, temperature, and prior immune priming. Some specialists reserve 'encapsulation' for responses to metazoan parasites and 'nodulation' for microbial targets, though the cellular mechanisms overlap.