Bacteria collected from more than a mile below the surface of the Pacific Ocean may have just cleared one of the longest running assumptions of immunology out of the water.
The bacteria they are so alien to humans that our immune cells do not even record their existence, making them completely invisible to ours immune systems.
This goes completely against one of the classic tenets of immunology – that the human immune system evolved to be able to sense all the microbes so that it could catch on. the infectious ones.
“The idea was that the immune system is universal, it doesn’t matter if something was a threat or not, it got rid of it. But no one really really put pressure on it. that idea so far, “Jonathan Kagan, a psychologist at Boston Children ‘s Hospital and one of the study’ s leaders, told Live Science.
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To prove this, the researchers had to find bacteria that never seemed to communicate with mammalian immune systems. They chose a place deep in the middle of the Pacific Ocean, in the Phoenix Islands Defense Zone in Kiribati, 1650 miles southwest of Hawaii.
“It’s not just the deep ocean, but the deepest, oldest, most remote and protected part of the ocean,” study co-author Randi Rotjan, a Boston University marine ecologist, told Living Science. “It’s 4,000 meters [13,100 feet] deep; there are no resident mammals; and it’s in the equatorial area where there would not even be any whales for whale fall, ”said Rotjan, noting that whales tend to breed in one globe and feed in the other, so they would be just across the equator while migrating. “This was a great place to find bacteria completely different from the bacteria we work on land.”
Once there, researchers used a remote submarine to collect marine bacteria from water, sponge, starfish and sediment samples, before growing them to 117 cultivated species. After identifying the properties of their bacteria, the researchers injected 50 of the rays into mouse and human immune cells. To their surprise, they found that 80% of the microbes, mostly belonging to the genus Moritella, fled searching. The receptors on the mammalian bone marrow immune cells used in the study could not be seen.
“It was a big surprise,” Kagan said. “What you end up with is a picture of the immune system as being defined locally by the lice it lives near, and that the lice and their immunity have improved. If you your immune system to a different ecosystem, a lot of the lice there will be silent. “
For example, Kagan said, “it is possible that there is an invertebrate animal in the Minch that is blind to it. E. coli. “
To try to reduce which features of the marine bacteria made them invisible to our immune receptors, the team also exposed the mouse and human cells to just one specific part of the bacterial cell wall, called the lipopolysaccharide (LPS) . Mammalian immune systems are known to use this part of the bacterial cell wall to identify and fight known gram-negative bacteria. The researchers found that the receptors of the mammalian cells were blind to the LPS alone as well.
“The LPS molecules looked similar to what you would find in bacteria on land, but many of them were completely silent,” Kagan said. “This is because the lipid chains on the LPS were much longer than the ones we are familiar with, but we still don’t know why that means they can go unnoticed.”
Despite their sputum ability to avoid detection, the researchers said deep-sea bacteria pose no risk to humans from becoming infected.
“First, they didn’t come forward to suppress mammalian immune systems, so if there was any pathogenity it would be undetected,” Rotjan said. “The second reason is that the temperature, pressures and chemical environments inside our bodies are very unlikely to be as different as you would at the bottom of the ocean. These bacteria are not happy to more than a few minutes outside their normal range. “
Now that the researchers have laid the foundation for how these foreign bacteria interact with our immune systems, they plan to apply this knowledge to help developing better immunotherapeutics. They also hope to return to Kiribati to study the immune systems of the organisms that these bacteria have developed.
The researchers published their findings online on March 12 in the journal Psychology of science.
First published on Living Science.