Premier Presentation: Immune system responses to a drop in food supply: Not a global decline, but a shift in immune system strategy

Resource limitation (e.g. starvation) typically reduces all functions including immune responses.  However, after 2 days of starvation, 5th instar larval Manduca sexta caterpillars increase and/or maintain gene expression for important immune proteins such as lysozyme and attacin.  Corroborating the genomic results, enzymatic studies in starved caterpillars showed an increase in phenoloxidase activity and a maintenance of lysozyme-like activity.  However, despite the apparently positive effects of starvation on immune function, starved caterpillars were less resistant to Gram negative (Serratia marcescens) and Gram positive (Bacillus cereus) bacteria and fungi (Beauveria bassiana) than controls.   Moreover, starved caterpillars were unable to increase immune gene expression (e.g. attacin and lysozyme) after an immune challenge.  These results suggest that after a drop in food intake, there was a shift in the strategy of the caterpillar's immune system.    Constitutive immunity was enhanced, but inducible immunity was curtailed.  This shift is contrary to what would be predicted by standard ecoimmunological theory, that posits that constitutive immunity is expensive, and inducible immunity is cheap.  Starved organisms would not be expected to enhance constitutive immunity.