A new study has uncovered a previously unknown antiviral defense mechanism in sea anemones, revealing that animals may have evolved more than one way to fight viral infections. Researchers discovered that a protein resembling a key component of the human immune system actually plays the opposite role, yet remains essential for effective antiviral protection. The findings challenge assumptions about the evolution of immunity and suggest that fundamentally different antiviral strategies have emerged across the animal kingdom.
A new study led by PhD candidate Ton Sharoni and Prof. Yehu Moran of the Hebrew University of Jerusalem , in collaboration with researchers from the University of North Carolina at Charlotte, has uncovered a previously unknown antiviral defense mechanism in sea anemones. Published in Nature Ecology & Evolution , the findings challenge long-held assumptions about the evolution of immune systems and reveal that animals may have developed more than one molecular solution for combating viral infections.
Viruses are among the most persistent threats faced by living organisms. In humans and other vertebrates, antiviral defenses rely on a protein called MAVS, which activates immune responses when viral invaders are detected. Scientists have long sought to understand how deeply rooted this system is in animal evolution.
To investigate, the researchers turned to sea anemones, ancient marine animals that diverged from the lineage leading to humans more than 600 million years ago. As close relatives of corals and jellyfish, sea anemones offer a unique window into the early evolution of immunity.
The team identified a previously unknown protein, which they named CARDIB (CARD Inhibitor Binding protein). At first glance, CARDIB appeared remarkably similar to MAVS, suggesting it might represent an ancient version of the same antiviral machinery found in humans. But experiments revealed a surprising twist.
“Everything about CARDIB suggested it should function like MAVS,” said Prof. Yehu Moran, head of the Department of Ecology, Evolution and Behavior at the Hebrew University. “Instead, we discovered that it does the exact opposite. Rather than activating antiviral defenses, CARDIB normally suppresses them.”
The discovery raised an obvious question: why would an organism suppress its own immune system?
Using CRISPR gene editing, the researchers removed the CARDIB gene from sea anemones and exposed them to viral threats. Unexpectedly, animals lacking CARDIB became far more vulnerable to infection. Viruses multiplied more easily, antiviral defenses failed to activate properly, and the animals lost much of their ability to fight infection.
“The results were completely counterintuitive,” said Sharoni. “Although CARDIB acts as a brake on the immune system under normal conditions, that brake turns out to be essential for mounting an effective antiviral response.”
The findings reveal that sea anemones rely on an antiviral pathway fundamentally different from the one found in humans, despite using molecular components that appear strikingly similar.
The researchers also tested whether the newly discovered pathway matters outside laboratory conditions. Genetically modified sea anemones were transferred from laboratory aquaria to outdoor marine mesocosms supplied with natural estuarine water in South Carolina, exposing them to the diverse viruses and microorganisms present in their natural environment.
The results were striking. Within days, animals lacking CARDIB and related antiviral genes accumulated substantially more viruses than normal sea anemones. One immune gene that appeared only moderately important in laboratory experiments became clearly important in the natural environment.
“This demonstrated that the pathway we discovered is not simply a laboratory phenomenon,” said Moran. “It plays a crucial role in helping these animals cope with the viral challenges they face in nature.”
More broadly, the study suggests that evolution did not preserve a single antiviral strategy throughout animal history. Instead, different animal lineages may have evolved distinct molecular solutions to the same challenge: detecting and stopping viruses before they spread.
“Humans and sea anemones both need protection from viruses, but this work shows that evolution can organize those defenses in fundamentally different ways,” Moran added.
The discovery highlights the value of studying organisms beyond traditional biomedical models. Ancient animals such as sea anemones preserve evolutionary innovations that remain invisible when research focuses exclusively on humans, mice, and other familiar laboratory species.
As scientists continue exploring the diversity of life, they are uncovering unexpected solutions that evolution has devised for some of biology’s most fundamental problems.
Nature Ecology & Evolution
Experimental study
Animals
An ancient anthozoan protein reveals an alternative evolutionary path of antiviral signaling
26-Jun-2026