Immunity

Definition

The capacity of an organism to resist or eliminate pathogens, parasites, or foreign substances through cellular and molecular defense mechanisms. In arthropods, immunity comprises innate (non-adaptive) responses including physical barriers, humoral factors such as antimicrobial peptides and phenoloxidase cascades, and cellular defenses like phagocytosis and encapsulation by hemocytes. Unlike vertebrate adaptive immunity, arthropod immunity lacks immunological memory and antibody-based recognition, though some insects show priming or trained immunity. Immunity in social insects additionally involves collective defenses such as hygienic behavior, social fever, and allo-grooming.

Etymology

From Latin immunitas, meaning exemption or freedom from obligation; adopted into biomedical usage to describe disease resistance.

Example

Mosquitoes deploy multiple immunity pathways to limit malaria parasite (Plasmodium) development: the complement-like protein TEP1 opsonizes ookinetes for melanotic encapsulation, while the IMD and Toll pathways trigger antimicrobial peptide production against invading stages.

Synonyms

• immune response
• immune defense

Related Terms

• innate immunity
• adaptive immunity
• hemocyte
• Encapsulation
• melanization
• antimicrobial peptide
• phenoloxidase cascade
• social immunity
• immune priming
• pathogen-associated molecular pattern
• PAMP

Usage Notes

Distinguish between systemic immunity (hemolymph-based defenses) and epithelial immunity (gut or cuticle barriers). 'Immunity' in arthropod literature typically refers to innate mechanisms; avoid implying vertebrate-style adaptive immunity unless discussing specific exceptions like immunological priming in some insects. The term is often used absolutely (resistance achieved) or relatively (degree of protection); specify which sense applies. Contrast with tolerance, where hosts limit damage without reducing pathogen loads.