Scientists from India and the US have found what they call an internal “switch” that controls mosquitoes’ immunity to malaria-causing Plasmodium parasites. If scientists can find a way to flip this switch, they could block the spread of malaria from mosquitoes to humans.
“We discovered a molecular switch. If the switch is on, then the mosquito has no immunity against parasites. If it is off then there is immunity,” said Sanjeev Kumar, lead author of the study and a researcher in the biological sciences group at the Birla Institute of Technology (BITS) in Pilani.
Kumar worked with a team at the US-based National Institutes of Health (NIH) to discover the switch. In mid-2008 he shifted from NIH to BITS. “India is a good place to do this work because we
have all types... of malaria,” he said.
A natural reaction inside the mosquito’s body after it sucks human blood might be responsible for protecting Plasmodium parasites from the natural germ-fighting agents in its stomach, found the scientists. Because of this reaction, the parasites can multiply and spread to humans.
As soon as a mosquito ingests a meal, the blood heads for the gut. Normally, a mosquito has strong anti-germ agents that hunt down and kill any invasive bacteria and parasites.
But, the scientists found that, this germ-fighting ability was blocked by a reaction in the mosquito’s body. Once blood reaches the gut, it triggers two proteins, an Immuno-Modulatory Peroxidase (IMPer) and dual oxidase (Duox). These proteins form a protective net-like bag around the blood meal.
The blood — and any parasites it contains — passes through the digestive system unscathed. The parasites multiply and move into the mo squito’s salivary glands, from where they pass into their next human victim.
When the scientists switched off the functioning of the two proteins, the bag didn’t form and all the Plasmodium parasites were killed.
The scientists knew about the bag, they didn’t know how it was formed.
The findings have implications for the study of human immunity. It has been long suspected that a similar reaction is what allows the good bacteria to survive in the stomach.
“We would like to investigate whether a similar network is present in human tissues, such as the colon,” said Carolina Barillas Mury, head of the Mosquito Immunity and Vector Competence Unit at NIH, another author.
The findings, which appeared Thursday in the Science Express, might one day help in developing a malaria vaccine, say the scientists.