the schlenke lab
@ emory university

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The cellular immune response against parasitic wasps
Innate immunity is often divided into two main components, the humoral response and
the cellular response.  The Drosophila humoral response has been intensely studied
for its role in combating bacterial and fungal infections, but the genes underlying the
cellular innate immune response of Drosophila (or of any other organism) are poorly
characterized.  Parasitic wasps are natural parasites of Drosophila that induce a
complex cellular immune response termed melanotic encapsulation.  A main focus of
our lab is to identify candidate D.  melanogaster cellular immunity genes using
transcriptomic and genetic screening approaches,
and then to functionally characterize
those candidate genes at the molecular level.

Parasitic wasp infection strategies
Like many other arthropods, Drosophila are infected by a diversity of parasitic wasps.
Fieldwork and laboratory studies undertaken by our lab have resulted in the collection

and lab rearing of 17 wasp species that attack D.  melanogaster in nature, and in
protocols for extracting and manipulating the venom (virulence) proteins wasps use to
suppress fly immunity.  Our goal is to identify and functionally characterize wasp venom
proteins, to understand the infection strategies parasites utilize to overcome host celluar
immune mechanisms.  Click here for one of our wasp attack videos.

Coevolution of host immune and pathogen virulence mechanisms
We are interested in long-term patterns of immune system and virulence protein evolution. 
For example, in previous work, we showed that it is Drosophila immune signaling proteins,
not recognition or attack proteins, that rapidly evolve (Schlenke and Begun 2003).  These
data identified “weak links” in the Drosophila immune system pathogens tend to exploit,
and suggested that the most common microbial infection strategies involve active
suppression of host immunity rather than passive evasion. Which fly immune proteins and
wasp virulence proteins mediate the evolutionary arms race between these particular
hosts and parasites?

Fly behavioral immune responses
Our lab has identified three kinds of behavioral immune mechanisms flies use to prevent
wasp infection or to cure themselves once infected, and we've started to characterize the
genetic basis for these behaviors. First, infected fly larvae therapeutically medicate
themselves by preferentially consuming plant and fungal secondary metabolites they are
resistant to. Second, adult flies prophylactically medicate their offspring by preferentially
laying their eggs in substrates with high secondary metabolite concentrations when they
sense wasp presence in their environments. Third, adult flies descrease egg production
in the presence of wasps, presumably because the eggs they produce are better-
provisioned for mounting anti-wasp immune responses later in life.

Evolutionary ecology of host-pathogen interactions
The fruitfly-wasp interaction can be exploited to answer general questions about the
evolution and ecology of host-pathogen interactions.  For example, we are using this
system to determine (1) whether different kinds of host immune mechanisms (cellular,
behavioral...) tend to tradeoff with one another over evolutionary time, (2) how within-host
competition favors different types of parasite life histories, and (3) whether generalist
parasites tend to be more immune suppressive and less immune evasive than specialist
parasites (Schlenke et al. 2007).