WASHINGTON, D.C.—Sometimes, it doesn’t pay to get the immune system all worked up against an infection. Since 1998, the chytrid fungus (Batrachochytrium dendrobatidis) has spread to half the world’s amphibians, eating away their skin, causing heart failure, and killing many of those infected. Last year, though, researchers suggested that one solution might be to “vaccinate” frogs against this killer. But that approach could backfire, Anna Savage, an evolutionary geneticist at the University of Central Florida, Orlando, reported this week at the Frontiers in Phylogenetics meeting here at the National Museum of Natural History. She and her colleagues study the lowland leopard frog, Lithobates yavapaiensis, native to the American Southwest to understand how this species persists despite periodical die-offs from fungal infection. They collected eggs from different locations, exposing some to the fungus. Then they counted the frogs’ white blood cells and looked at what genes were active in the skin and spleen, matching what they found with the animals’ survival over time. To their surprise, they found that the frogs that mounted the most vigorous specific or “acquired” immune response did the worst. The fungus kills off those white blood cells, so the frog making lots of them “is like throwing gas on the fire,” she reported. Thus a vaccine that stimulates this immune response “might not be a great idea,” and instead, a better treatment might be to suppress the immune system, she said. She intends to look at the disease in wild populations to see whether these results hold up there as well.