Insect immunity shows specificity in protection upon secondary pathogen exposure

Area of Science:

• Immunology
• Invertebrate biology
• Evolutionary biology

Background:

• Vertebrate immunological memory confers specific, long-term protection against pathogens.
• The existence of specific immune priming in invertebrates is debated.
• Specific immune priming is defined as functional, mechanism-independent protection specificity.

Purpose of the Study:

• To investigate the presence and specificity of immune priming in the social insect Bombus terrestris.
• To determine if prior exposure to a bacterial pathogen confers long-term, specific protection against a secondary challenge.

Main Methods:

• Workers of Bombus terrestris were exposed to one of three bacterial pathogens.
• After a period, insects were challenged with either the homologous or a heterologous bacterium.
• A reciprocal design ensured all combinations of initial and secondary exposures were tested.

Main Results:

• Bombus terrestris workers showed significantly increased protection several weeks after initial exposure.
• This enhanced protection was specific to the primary pathogen, demonstrating narrow specificity.
• Protection against a heterologous pathogen was not significantly improved, confirming specificity.

Conclusions:

• The invertebrate immune system is capable of specific and durable induced protection, termed immune priming.
• Specific immune priming in invertebrates suggests convergent evolution of immune defenses facing similar selective pressures.
• This finding challenges previous assumptions about the limitations of invertebrate immune responses.