Probing Immune Function During Aging in Adult Drosophila

Abstract

Virtually all multicellular organisms rely on a highly conserved innate immune system for defense against foreign microorganisms. Innate immunity consists primarily of a humeral response that culminates in the expression of antimicrobial peptides. In contrast to adaptive immunity seen in high order organisms, the innate immune response is not specific to the invader. In aging organisms, some of the most dramatic transcriptional changes take place within the innate immune system. In aging mammals, innate immune reorganization coincides with declining immune function, which often manifests itself as chronic inflammation. Similar to this state of chronic inflammation in mammals, Drosophila exhibit a marked upregulation of many innate immunity related genes. However, it remains unclear if this upregulation results in a similar decrease in immune function to that seen in mammals. If Drosophila is to be considered as a model organism in which to study the relationship between immunity and aging, it must first be determined whether it too undergoes declining immune function with age. By examining the response to quantifiable injections of bacteria, we were able to deduce that adult Drosophila do indeed undergo immune senescence. Elderly wildtype flies infected with various doses of bacteria showed a decreased ability to survive infection. Moreover, because the ability to clear the infection remains intact despite decreased survival following infection, it is believed that a bacterially produced factor is responsible for immune senescence in adult Drosophila.