Insects are able to develop enhanced resistance in response to repeated infection.
This phenomenon is called immune priming. In this work, so-called "primed" Galleria
mellonella larvae were re-infected with a lethal dose of Candida albicans 48 h after
injection of a non-lethal dose, while "non-primed" larvae were infected only with
a lethal dose. The increased resistance of the primed larvae correlated with a slower
rate of body colonisation by the fungus. Changes in the protein profiles were detected
in the whole hemolymph of the primed insects. The analysis of low-molecular weight
proteins and peptides obtained with the use of three different organic solvents and
comparative quantitative HPLC analysis thereof showed that the primed larvae did not
have higher amounts of any infection-inducible polypeptides than the non-primed larvae.
Moreover, electrophoresis of low-molecular weight polypeptides revealed an even lower
level of immune-induced peptides in the primed larvae than in the non-primed ones.Furthermore,
the defence activity of larval hemolymph, i.e. the antifungal, antibacterial, and
lysozyme-type activity, was up-regulated in the primed larvae at the time of re-infection
and, consequently, at the early time points after the infection with the lethal dose.
Twenty four hours after the infection, these parameters were equally high in the non-primed
and primed larvae. Accordingly, at the time of the injection of the lethal dose, certain
immune-inducible genes were up-regulated. However, 24 h after the infection with the
lethal dose, their expression in both groups was incomparably higher than at the time
of the infection and, in most cases, it was as high in the primed larvae as in the
non-primed ones. We found that only anti yeast-like activity was enhanced 24 h after
the re-infection. This correlated with results obtained by testing the priming effect
in heterologous systems: the primed animals did not exhibit higher resistance to the
other pathogens tested.