Antibodies : who can save us and also may kill us

Insects don’t make the cells and antibodies characteristic of the vertebrate adaptive immune response. As a result, scientists assumed for years that insects rely on innate immune defenses that are neither heritable nor directed at any pathogen in particular. Over the last 20 years, though, evidence has emerged that invertebrates do inherit some types of immunity from their parents, but it’s still not clear how or how often it happens. In a study published December 15 in Cell Reports, researchers show that fruit flies (Drosophila melanogaster) and mosquitoes (Aedes aegypti) pass immunity to viruses to their progeny for multiple generations.

“The authors present a very thorough set of experiments that detail the existence of this transfer of some kind of immunological memory to the offspring from generation to generation,” says Barbara Milutinović, a postdoc at the Institute of Science and Technology Austria who did not participate in the work. Some scientists still discuss immunity in Drosophila as though it’s only innate and not tailored to certain pathogens, she adds, but “this study shows us . . . that there is something really specific going on.”

Maria Carla Saleh, an immunologist at Institut Pasteur in Paris, and her colleagues set out to understand immunity in insects because mosquitoes, while the vectors of so many viruses that make people sick, they themselves are unharmed by these infections. “The same virus will produce a fatal disease in humans, but the mosquito will be super happy,” she says. They focused on so-called persistent viral infections: those with high viral titers but no fitness costs for their insect hosts. Understanding the basis of persistent infections might make it possible to push the mosquito out of this persistent state—either toward succumbing to the pathogen or clearing it, she explains.

In Saleh’s lab, researchers often work with fruit flies because they have similar immune systems to mosquitoes and fruit flies are much easier to work with. In 2018, the team showed that D. melanogaster that were exposed to a virus as larvae successfully fought it off as adults whereas naïve adults didn’t. The next question was whether or not this sort of immune priming could be passed from parent to offspring, too.

In the new study, Saleh and colleagues injected female fruit flies with either recombinant Sindbis virus or a mock injection of the same volume containing no virus. Sindbis virus is carried by mosquitoes in Europe, Asia, Africa, and Australia. Infections are usually mild in people and may include arthritis, fever, and rash. In contrast, Sindbis in fruit flies produces high viral titers but doesn’t make them sick, nor does it pass from mother to offspring. After they received the injection, the females mated and laid eggs. Once the next generation reached adulthood, the researchers injected the new generation with the same recombinant Sindbis virus. The flies whose mothers had been infected with virus ended up with lower viral titers and lower activity of the reporter gene engineered into the virus than did the offspring of mothers that were mock infected before mating.

Regards
Sarah
Journal of Mucosal Immunology Research