Pre-exposure of Galleria mellonella larvae
to different doses of Aspergillus fumigatus
conidia causes differential activation of cellular
and humoral immune responses
Larvae of Galleria mellonella are useful models for studying the virulence of microbial pathogens or for evaluating
the potency of antimicrobial agents. In this work we demonstrated that prior exposure of larvae to non-lethal doses
of Aspergillus fumigatus conidia increases the resistance of larvae to a lethal dose (1 x 107 20 μl-1) 24 h later. Exposure
of larvae to a conidia concentration of 1 x 104 20 μl-1 leads to an increase in hemocyte density but an inoculum of
1 x 105 conidia leads to enhanced expression of antimicrobial peptides, increased binding of proteins (e.g., arylophorin,
prophenoloxidase, apolipophorin) to conidia and elevated hemocyte density. These results suggest that a low dose of
conidia (1 x 104) predominantly activates the cellular immune response but that a higher dose (1 x 105) that is still not
lethal activates a humoral immune response to the greatest extent. While insects have an immune system analogous to
the innate immune response of mammals these results suggest that it is capable of assessing the extent of the microbial
challenge and mounting a ‘proportionate’ immune response which may have important survival advantages
