Scientists Get Better Understanding of Frog's Failure to Fight off Deadly Fungus

Herpetologists now have a better understanding of the amphibian immune system and its inability to combat a deadly fungus that his killing frogs around the world.

The fungus, according to new research published in the journal Science, releases a toxic component that disables the amphibian's immune response system by inhibiting a wide range of cell types.

Interestingly, the toxin also disables cancer cells, a find that may lead to the development of new immuno-suppressive or anti-cancer agents.

The toxin is found in the fungus Batrachochytrium dendrobatidis, which has come to be recognized as one of the most prominent killers of amphibians worldwide.

Researchers are still puzzling over why frogs and other amphibians - which have immune systems nearly as sophisticated as humans - are unable to fight the fungus.

"Amphibians have excellent and complex immune systems -- nearly as complex as humans -- and they should be able to recognize and clear the fungus," said Louise Rollins-Smith, an associate professor of pathology, microbiology and immunology at Vanderbilt University.

Rollins-Smith and her colleagues tried to get a better understanding of how the frog's immune systems fail to respond effectively to the fungus. Previous studies suggested that as the fungus penetrated the first layer of defense on the frogs' skin, an immune cell response should have ignited. The fact that it did not suggests that the frogs' immune systems did not "see" the fungus.

But the new works suggests that the frogs' immune systems do indeed see the infiltrator, but that it is unable to respond to the fungus effectively.

We think it's not a block at the initial recognition stage," Rollins-Smith said. "The macrophages and neutrophils can see it as a pathogen, they can eat it up, they can do their thing."

But the fungus seems to inhibits the immune system's ability to take action against the invader and eventually overcomes the frogs.

"Fungal infection causes rapid behavioral changes -- frogs become lethargic and start to crawl out of the water -- suggesting that even though the fungus stays in the skin, the toxic material is having effects elsewhere."