ADAMO, Shelley A*; PARSONS, N; Dalhousie University; Dalhousie University: Why does stress suppress immunity? A possible answer from insects.

Both vertebrates and mollusks (e.g. oysters) become more susceptible to disease after exposure to a stressor, suggesting that stress-induced immunosuppression is an old and wide spread phenomenon. We found that insects are also immunosuppressed by stress. Physical exercise, restraint, flight, heat, agonistic behaviour and elevated levels of the fight-or-flight neurohormone octopamine reduced immune function (lysozyme-like activity) and disease resistance (resistance to the bacterium Serratia marcescens) in the cricket Gryllus texensis. However, a brief escape run, exposure to cold and a minor cut to the wing did not induce an increase in hemolymph octopamine titres nor did they reduce resistance to S. marcescens. These results suggest that a prolonged period of elevated metabolism coupled with neurohormonal octopamine release are required for immunosuppression. We found no evidence that immune resources are undergoing redistribution after stress. Wound infection was more likely after restraint stress than in controls. Preliminary evidence suggests that the decline in immune function after stress is due to a physiological constraint involving carrier molecules (lipophorins) that are required both for ferrying lipid energy compounds from fat body to muscle as well as for normal immune function.