Mosquitoes ramp up their immune system after drinking blood to help fight off the parasites that blood might contain, a new study has found.
"This appears to be a new mechanism by which the mosquito is anticipating a parasite infection," said Michael Povelones, an assistant professor in University of Pennsylvania's School of Veterinary Medicine, who co-authored the study.
"With malaria and other vector-borne diseases, we're faced with problems of not having effective vaccines, drug-resistant parasites and insecticide-resistant vectors," said Povelones.
"But as it turns out, mosquitoes do a great job of controlling infection in their own bodies," said Povelones.
"If we can use that information to our advantage, we might be able to find new avenues of preventing mosquitoes from transmitting disease," he said.
Researchers already knew that a group of molecules called leucine-rich repeat immune proteins, or LRIMs, were important players in mosquitoes' immune defence.
In a paper published in 2009 in Science, Povelones and colleagues reported that two of these LRIMs, LRIM1 and APL1C, are part of a signalling pathway akin to the human complement system, which coordinates immune response through a cascade of signalling interactions.
In mosquitoes, LRIM1 and APL1C helped target malarial parasites for destruction.
In the current study, the researchers wanted to gain a deeper understanding of what the other identified LRIM proteins - there are at least two dozen - did for mosquito immunity.
Using RNA inhibitors, which block production of particular RNA transcripts, they "turned off" one LRIM at a time in live Anopheles gambiae mosquitoes.
Then, they exposed the insects to Plasmodium berghei, a parasite that is related to Plasmodium falciparum, which causes malaria in humans.
When one protein, LRIM9, was blocked, parasite levels in the mosquitoes increased three-fold. Researchers found that adult females had the highest expression levels of LRIM9, with more than 20 times the amount of LRIM9 as adult males.
Adult females are the only mosquitoes that drink blood, leading the researchers to consider whether it was something about this meal that triggered activation of LRIM9.
The team fed mosquitoes blood from mice that were either infected with P berghei parasite or were uninfected. No matter whether the insects drank the infected or uninfected blood, LRIM9 levels surged 48 hours after their meal.
Povelones and colleagues believe that LRIM9 may help the mosquito immune system recognise pathogens and may also recruit or interact with other immune system components.
The study is published in the Journal of Innate Immunity.
