Scientists have discovered a previously unknown way sea anemones protect themselves from viruses, revealing that the evolution of animal immune systems may be much more diverse than previously thought. The newly identified defense relies on a protein that is very similar to one of humans’ most important antiviral proteins, but is essential for protecting animals from infection, yet performs the opposite function. This finding suggests that evolution has produced multiple successful strategies to combat viruses across the animal kingdom.
The research was led by Ton Sciaroni, a doctoral candidate at the Hebrew University of Jerusalem, and Professor Yev Moran, in collaboration with scientists at the University of North Carolina at Charlotte. natural ecology and evolution. This challenges the long-held idea that animals have inherited a single core antiviral system from a common ancestor, and instead points to multiple evolutionary solutions to resist viral infections.
Ancient animals offer new clues about immunity
Viruses have threatened living things throughout evolutionary history. In humans and other vertebrates, one of the body’s key antiviral defenses relies on a protein called MAVS. When a virus is detected, MAVS helps kickstart the immune system so it can respond to the infection.
To find out how old this defense system is, researchers studied sea anemones. These ancient marine animals diverged from the evolutionary lineage that would eventually lead to humans more than 600 million years ago. Sea anemones are related to corals and jellyfish, giving scientists a glimpse into the early evolution of animal immunity.
During the study, the research team discovered a previously unknown protein they named CARDIB (CARD Inhibitor Binding Protein). Initially, CARDIB was so similar to MAVS that researchers wondered if CARDIB might play the same antiviral role seen in humans.
That assumption quickly crumbled.
“Everything about CARDIB suggested that it should function like MAVS,” said Professor Yev Moran, head of the Department of Ecology, Evolution and Behavior at Hebrew University. “Instead, we found that it does exactly the opposite. Rather than activating antiviral defenses, CARDIB typically suppresses them.”
Amazing proteins that slow and protect your immune system
This discovery immediately raised important questions. Why do animals deliberately suppress their own immune responses?
To test this, the researchers used CRISPR gene editing to remove the CARDIB gene from sea anemones before exposing them to the virus.
The results were unexpected. Sea anemones without CARDIB were more susceptible to infection. The virus multiplied more rapidly, the animals were no longer able to properly activate their antiviral defenses, and their ability to fight infection was dramatically reduced.
“The results were completely counterintuitive,” Sciaroni said. “CARDIB acts as a brake on the immune system under normal conditions, and we found that that brake is essential for mounting an effective antiviral response.”
Overall, the experiments showed that sea anemones rely on fundamentally different antiviral pathways than those used by humans, even though both systems contain surprisingly similar molecular components.
The natural environment confirms the discovery
The researchers also wanted to determine whether this newly identified immune pathway was important outside of carefully controlled laboratory conditions.
To answer that question, researchers moved genetically modified sea anemones from a laboratory aquarium to an outdoor marine mesocosm fed by natural estuarine water in South Carolina. This exposed animals to a wide variety of viruses and microorganisms that are present in their normal environment.
The difference was obvious within a few days. Sea anemones lacking CARDIB and related antiviral genes accumulated significantly more virus than unmodified animals. The researchers also discovered that certain immune genes that appeared to be only moderately important in clinical tests became clearly important under natural environmental conditions.
“This proves that the pathway we discovered is not just a laboratory phenomenon,” Moran said. “This plays an important role in helping these animals cope with the viral challenges they face in nature.”
Multiple evolved solutions to fight viruses
This finding suggests that evolution has not settled on a single universal antiviral strategy. Instead, different animal groups may have independently developed different molecular systems to detect the virus and prevent its spread.
“Humans and sea anemones both need protection from viruses, but this study shows that evolution can orchestrate those defenses in fundamentally different ways,” Moran added.
This study also highlights the importance of looking beyond traditional laboratory animals. Ancient organisms such as sea anemones can preserve evolutionary innovations that would remain hidden if scientists focused only on humans, mice, and other commonly studied species.
As researchers continue to explore life’s astonishing diversity, discoveries like this reveal that evolution is repeatedly finding unexpected ways to solve some of biology’s most fundamental challenges.
