<p>Mosquitoes have potent innate defense mechanisms that protect them
from infection by diverse pathogens. Much remains unknown about how
different pathogens are sensed and specific responses triggered.
Leucine-Rich repeat IMmune proteins (LRIMs) are a mosquito-specific
family of putative innate receptors. Although some LRIMs have been
implicated in mosquito immune responses, the function of most family
members is largely unknown. We screened <i>Anopheles gambiae </i>LRIMs by RNAi for effects on mosquito infection by rodent malaria and found that LRIM9 is a <i>Plasmodium berghei </i>antagonist
with phenotypes distinct from family members LRIM1 and APL1C, which are
key components of the mosquito complement-like pathway. LRIM9
transcript and protein levels are significantly increased after blood
feeding but are unaffected by <i>Plasmodium </i>or midgut microbiota.
Interestingly, LRIM9 in the hemolymph is strongly upregulated by direct
injection of the ecdysteroid, 20-hydroxyecdysone. Our data suggest that
LRIM9 may define a novel anti-<i>Plasmodium </i>immune defense mechanism
triggered by blood feeding and that hormonal changes may alert the
mosquito to bolster its defenses in anticipation of exposure to
blood-borne pathogens.</p